Table of contents

Many ancient landslides have become active due to the impoundment of the Three Gorges Reservoir. Considering the Muyubao landslide in the Three Gorges Reservoir area as the research object, we analyzed the long-term deformation law since the impoundment of the reservoir and conducted centrifugal model tests of the landslide deformation process under different reservoir water fluctuation rates. The monitoring data analysis reveals that the deformation of the Muyubao landslide is mainly affected by the elevation of the reservoir water level and its rising and falling rate. A deformation greater than 30 mm mainly occurs at the water level of 165–175 m. A higher reservoir water rising rate promotes landslide deformation, with a monthly cumulative displacement of above 30 mm in the reservoir water rising stage. Further, a lower reservoir water decline rate can promote several landslide deformation events with monthly cumulative displacement greater than 30 mm. A Centrifugal model test demonstrates the Muyubao landslide deformation to the hydrodynamic buoyancy pressure of reservoir water. The head difference inside and outside the slope is minimal when the reservoir water rising and the falling rate is small, and the reservoir water buoyancy controls the deformation of landslides. However, the head difference inside and outside the slope increases with the reservoir water rise and fall rate, leading to increased hydrodynamic pressure, which weakens the landslide deformation in the reservoir water rising stage, and strengthens the deformation in the reservoir water-falling stage. The results provide a significant reference for landslide control and reservoir operation optimization in the Three Gorges Reservoir area.

The middle reach of Taohe River, in the south part of Gansu Province, China is severely threatened by debris flow hazard. Eryang River is an important branch of Taohe River. On May 10, 2012, many debris flows were triggered by extreme heavy rainfall (1% frequency), resulting in serious losses of human lives and properties. In order to recognize the hazard of debris flows in small watersheds, six key debris flow gullies in Eryang watershed, Lalonggou, Zhalonggou, Yizigou, Jiehagou, Lalugou, Paizuigou, were selected as the research area. The numerical simulation software FLO-2D was used to analyze the debris flow movement and accumulation characteristics of each debris flow gully under the actual '5.10' rainfall conditions, so as to reconstruct the '5.10' debris flow disaster scenario. Numerical simulation results show that the flow speed increased to the maximum after 15-30 minutes since the outburst. The flow lasted for about 3 hours. The speed in the moving section was very high, and decreased sharply at the gully-mouth, then deposits accumulated in the river valley. According to the satellite images and field investigations, the simulation results were compared with the actual situations. The comparison shows the simulation effect is good, the deposition area, the discharge process, and the main damage area were well-reconstructed by FLO-2D simulation. Then, the same method and parameters are used to simulate the accumulation range, depth and velocity of debris flows under the precipitation of 2 % and 0.2 % frequency (fifty and five hundred years rainfall, respectively), and then the risk zoning map is produced using the simulation data. The potentially threatened houses and properties were outlined. The threatened area is 37900m² and 60500m² under 2% and 0.2% rainfall frequencies. There are 22 houses in the highest hazard level. This provides direct reference to the local government to control the debris risk. This work also provides a practical approach for the debris flow hazard assessment.

The 2008 Wenchuan earthquake (Ms = 8.0) occurred in Sichuan, China, and triggered many landslides that were more concentrated near the epicenter. A watershed of Min River of length 80 km and an area of approximately 2100 km² was chosen in this study to assess the spatial distribution of the co-seismic landslides. Both the widely used indexes, including co-seismic landslides number (LN) and landslide concentration (LC), and two new indexes, slope pixel percentages (SPP) and landslide pixel percentages (LPP), are used to make correlation analysis with topographical factors. The SPP is defined as the pixel percentage of topographic factors related to the entire study area on pre-earthquake digital elevation model. The difference between the SPP and LPP is that the latter is only considered in the area where co-seismic landslides occur. The main results of this study are: (1) The distance from surface rupture (rf) leads to a better correlation with LC; (2) greater than one twice of the landslides that occur on the west side of the Min River line; (3) the distribution of the landslides in our study area shows a larger average distance to fault rupture comparing to the average value in the total Wenchuan earthquake; (4) the most remarkable correlation found is with the topographic aspects and the fault thrusting direction.

The flexural toppling and block toppling of rock slopes show different failure mechanisms due to the distinctions in lithology and structures. Two typical modes of toppling are quantitatively studied in this work using discrete element (DE) modeling, and the influence of key parameters on slope failure behaviors is discussed. Furthermore, the feasibility of this method in the stability analysis of toppling slopes is demonstrated through comparison, and the main points of numerical simulations for such slopes are proposed. Results of calibration analyses of a physical model test prove that the DE modeling achieves good simulation effects and reflects the gradual evolution of the internal stress of rocks during toppling failure. Modeling results also indicate that block toppling exhibits significant kinematic characteristics and that flexural toppling displays the structural features of superposed cantilever beams. Rock tensile strength substantially influences the stability of flexural toppling slopes; thus, it is necessary to reduce the value of tensile strength when conducting strengthened reduction analyses.

Vegetation is widely used to prevent landslides worldwide. However, rainstorm-induced landslides frequently occur on vegetation-covered slopes during the typhoon season in the southeastern coast of China. The results of a wind tunnel test reveal the effect of typhoon-induced loads on a slope through vegetation. Under a wind speed of 17m/s, the wind load can increase the sliding force by over 10%. Strong typhoon-induced loads cause the vegetation to exert a strong torque on the soil via roots, resulting in crack development. These cracks provide paths for rainwater infiltration and increase the soil permeability coefficient by over 10-fold when the typhoon passes. Therefore, special attention should be paid to the potential impacts of vegetation, especially large trees, on slope stability.

High-position landslides mainly occur in the upper part of the steep slope wherein the shear outlet is much higher than the toe of the slope. It often transforms into the rapid and long-runout debris flow, causing severe loss of life and property. This paper describes a high-position landslide that occurred on the right bank of the Heishui River in Songxin Town, Ningnan County, southwestern China, on June 28 and August 16, 2012, resulting in five deaths. Based on the field investigations, borehole drilling, in situ, and laboratory experiments, the initiation mechanism of the landslides are unraveled. Detailed crack surveys are conducted to identify the deformation tendency of this landslide in the future. The Baishuihe landslide originated on a 310 m-high hillslope, which provided a favorable free surface for the landslide occurrence. The Baishuihe landslide is located in the influence zone of the Zemuhe fault, and the active fault activities dramatically contribute to the fragmented stratigraphic structures and well-developed minor structures. The initiation of the June 28 landslide is considered a long-term creep under the inner and outer integrations, while the consequent bedding slope and persistent precipitation are the primary factors. The failure of the August 16 landslide is analyzed using the retrogressive slide in the source area of the first landslide. The sustaining deformation of the landslide is controlled via cracks on the surface of the main deformation zone and hydraulic influences induced by rainfall. The slip process follows creep deformation and can be aggravated under rainfall. Based on the crack distribution, the potential instability volume is calculated as 1.66 × 10⁴ m³ ∼ 54 × 10⁴ m³. The Baishuihe landslide provides a crucial case study for evaluating high-position landslide and zoning risk areas in mountainous areas.

Various regular discontinuity patterns are observed in rock masses and one of the common discontinuity patterns is hexagonal pattern, which is mostly observed in all extrusive volcanic rocks such as basalt, andesite, ryholite and welded tuffs as well as in some sedimentary rocks subjected to desiccation or freezing-thawing processes. In this study, the authors investigate the dynamic stability of rock slope consisting of hexagonal blocks through model tests on shaking table. Experiments indicated that toppling or sliding failures, which may be of active or passive modes occur. Critical acceleration levels can be estimated from the limit equilibrium method with the consideration of results of frictional properties and geometry of model slopes.

To realize the harmonious unification of safety and economy when designing slopes, we used geological analysis and performed a qualitative evaluation to investigate the controlling factors affecting slope stability. The finite element strength reduction method (SRM) and traditional limit equilibrium method were used to investigate the stability safety factor of a high and steep rock cutting slope in Northern Guangdong. The results showed that the influence of the structure surface on slope stability is determined by the combination of the structure surface, shape of the structure surface, filling between structure surfaces, penetration of the structure surface, and water content and sensitivity of the structure surface, the influence of only one factor on slope stability is limited. We analyzed the slope and design it optimally, the results showed after reinforcement of the second-level slope, the slope revealed an incompletely penetrated shallow slip zone and an evident deep potential slip zone. Compared to the reinforcement that was without an anchor cable, the safety factor increased when the potential slip zone moved down. Based on the SRM and traditional limit equilibrium method, the design scheme of this slope meets the safety requirements of permanent slopes, and the excavated stone can be used for roadbed filling. Thus, the optimized design scheme can coordinate safety and economic indicators. Moreover, the application of strong engineering measures to the joint development of slope in engineering practice is conservative and unreasonable. The design of these slopes can provide a reference for slope design and construction.

This paper presents the different contributions of two shear strength parameters to the factor of safety (FOS) value in limit equilibrium method (LEM)-based slice techniques. Many potential slip surfaces are designed and evaluated for their FOS values with respect to the slip depth in a homogeneous soil slope. This paper found that FOS values contributed only by internal cohesion decrease rapidly and inversely as the slip depth increases. However, FOS values contributed only by internal friction angle increase slowly and linearly as the slip depth increases. Because of the different contributions of cohesion and internal friction angle to slope stability, FOS values decrease and then increase with respect to the slip depth, allowing it to have a minimum value at an intermediate depth. This is the mechanical reason for the existence of a critical slip surface with a minimum FOS value in LEM-based slice techniques in slope stability assessment. Further evaluation of an actual slope shows that these findings are also valid to the presence of groundwater and soil inhomogeneity.

The road-construction and nature create rock slopes along the Anticlinal Folded Belt in the eastern part of the Chittagong hill tracts, the northern margin of Surma Basin, and some eastern parts of Sylhet, Bangladesh. The total number of death due to slope failure in these regions is 622 from 2000 to 2017. Shale outcrops occur in several parts of the hilly region where rock fragments are on the roads at the slope base, and slope failure is common in these regions. This research aimed to find out the mechanism of formation of the rock fragments and the slope failure at a shale slope by water immersion, slake durability, direct shear, and triaxial compression tests. The rock is very unstable in the presence of water and, wet and dry cycles where water is absorbed along with the clay layer and breaks along with the layer. The gradient of the slaking index is 20 SI%/cycle in the 1st, 2.5 SI%/cycle in the 2nd, and 1.17 SI%/cycle in the 3rd stage which reveals that the rock degrades immediately upon exposure to wet and dry cycle. The ten shale pieces before the durability test became more than 300 pieces after the test. From the image analysis, it reflects that the average area decreased by 98% with increased aspect ratio, circularity, and roundness. The strength decreased to around 75% by wetting having low cohesion and internal friction of 105 kPa and 24.2° respectively. Effective countermeasures for slope failure should be investigated.

The studies of mechanism and calculated model of the earth-fill dam and landslide dam have a significant impact on the prediction and risk assessment for dam failure. The present study selected the event of a multi-stage landslide dam failure in southwestern China as a case study. Based on a mathematic model that can consider the failure mechanism, the key parameter can be obtained by back analysis, the twice failure processes can be displayed as well. It indicates that the second landslide dam cannot break under natural conditions, i.e. the landslide dam failure needs manual intervention, which is consistent with the actual situation. Because the landslide would occur again in different cumulated volumes in the future, the dam failure is predicted using the same model. The result illustrates that the maximal flow comes up to 20,000-60,000 m³/s after the dam failure and the failure would occur in a short day. The analysis and prediction provide an improved insight into the landslide dam failure process and risk control.

Based on the nonlinear Mohr-Coulomb failure criterion, the upper bound method of limit analysis is used to investigate slope stability by introducing new strength parameters c_t and φ_t. It is assumed that the potential weak zone in the soil layer is a straight line, so the straight line fracture surface is used to study the non-reinforced soil and reinforced soil in this study, and the expression of the stability coefficient Ns of the non-reinforced soil slope is derived. In addition, the calculation equations of the safety factor F, the ultimate slope height H, and the ultimate slope height H of the reinforced soil slope are also derived. The CVX toolbox developed by Stanford University and a MATLAB program developed by the authors are used for illustrations, and good results are obtained. The relationship between the nonlinear parameter m and the limit slope height H, the included angle θ, the new strength parameter φ_t, the slope stability coefficient Ns, the relationship between the slope angle β and the safety factor F, and the relationship between different reinforcement tensile strength Kt and the limit slope height H are summarized.

Cracking is the principal mechanics of failure in engineering structures and geo-logical systems. Complex cracking patterns are observed in rock-like materials under compressive stresses. On the other hand, rainfall is one of the main triggering factors of landslides. Therefore, the rainfall induced landslides should be investigated by considering complex relationships between rainfall and rising groundwater table and related reduction of shear strength. In this paper, we present a new phase-field method for modeling the transition from diffuse damage to localized cracks. The damage variable is assumed to be driven by the deviatoric strain and positive (or dilatant) volumetric strain. This allows the description of tensile, shear and mixed cracks. The phase-field method is extended to partially saturated porous media by considering hydromechanical and phase-field coupling mechanisms. The proposed phase-field method is then applied to the analysis of rainfall-induced landslides in partially saturated conditions. The evolutions of pore water pressure, displacement and damage fields are predicted. Different failure mechanisms are discussed.

This study presents a catastrophic landslide that occurred on June 17, 2020, on the left bank of the Xiaojinchuan River in Danba County, Sichuan Province of China. This landslide was a large-scale reactivation of the Aniangzhai ancient landslide. The failure event blocked the Xiaojinchuan River, induced a landslide-outburst flood disaster chain, destroying a 6.6 km-long section of national road G350 and causing significant economic losses. Based on field investigations, unmanned aerial vehicle surveys, and geophysical prospecting, this study unravels the causing factors and reactivates the landslide mechanism. The results suggest that the topography and unconsolidated rock-soil mass are predisposing factors for reactivation. The hourly precipitation within three hours reached 61.80 mm and induced the Meilong debris flow. The debris flow rushed into the Xiaojinchuan River and converted it to flow along the foot of the Aniangzhai ancient landslide. The intense scouring of slope toe caused by the rise of river level is the inducing factor of the landslide. Based on the geometry and geomorphic parameters, the landslide can be divided into four areas: leading edge collapse area, middle bulging area, upstream cracking area, and downstream cracking area. The reactivated Aniangzhai landslide could be determined as a compound landslide involving incipient retrogressive failure and latter progressive slide. Several cracks had developed in the upper part of the slope due to the movement of the landslide, and the four areas of the reactivated landslide mass were still creeping. A detailed monitoring and mitigation measure should be paid to this reactivated deposit.

On July 23, 2019, a large-scale, high-position landslide was triggered by heavy rainfall at Pingdi Village, Jichang Town, Shuicheng County, Guizhou, China. Based on a field investigation, multi-temporal remote sensing images, and topographic maps, the elevation of the crown of the landslide and the front edge was approximately 1700 m and 1233 m, respectively. The height difference of the landslide was 467 m, and the horizontal distance was approximately 1332 m with a main sliding direction of NE20°. Its volume was up to 1.81 million m³. The landslide buried 21 houses, leading to the death of 51 people. The landslide first exited from the upper part of the steep slope in the Emeishan Formation with a basaltic lithology, which accumulated continuously at the back of a previous residual landslide and triggered the slope instability under the exit. The erosion volume due to the "overloading effect" was up to 1.44 million m³, and the landslide then transferred to a long-runout double-channeled debris flow. The landslide then converted to diffused flow and finally accumulated to the east side of the Jichang reservoir because the terrain was wide and the slope angle decreased gradually. Based on the above investigation, the entire movement process of the Jichang landslide was retrieved using dynamic numerical simulation technology. In contrast to the previous erosion model, the overloading erosion effect was proven, which added loads and drove the deposit below to move downward together.

In the construction and operation of tunnel engineering in high intensity areas, the slope at a tunnel's entrance and exit section has become a section prone to problems because of seismic load and tunnel excavation disturbance. To study the dynamic response characteristics of rock slopes at the tunnel entrance and exit section, considering the strong earthquake area in western China as the research area, a three-dimensional finite element (FE) model was established and the FE modal analysis of the slope at the tunnel entrance and exit section was conducted. The dynamic response characteristics of the slope body were investigated based on a frequency domain by analyzing the natural frequencies and corresponding vibration modes of different models. The results show that the tunnel excavation affects the slope's dynamic response characteristics and natural frequency but has little effect on its vibration mode. The natural frequency ratio of slopes without and with a tunnel is 1.1:1.35 as a whole, under the same conditions. The slope gradient has a considerable effect on the natural frequency of the slope at the tunnel entrance and exit section. The natural frequency of the slope gradually increases with the gradient, and the changing trend is more obvious with an increase in the vibration mode order. The low-order vibration mode of the slope at the entrance of the tunnel is relatively simple, primarily demonstrating bending and torsional deformation. The vibration mode of the slopes with and without a tunnel is the same when the slope gradient is the same. The vibration modes of the two tunnel slope models with different gradients are also the same. This study investigated the dynamic response characteristics of the slope and tunnel structure based on the analysis of the inherent characteristics of the slopes at the tunnel entrance and exit section, which can provide a reference for the seismic design of the tunnel entrance section.

This study presents a toppling-deformed slope located at the entrance of the Tonghua 1# tunnel of Wenchuan-Maerkang highway in southwestern Sichuan, China. The characteristics, zonation, and failure mechanism of this toppling-deformed shape were explored based on field investigations, geological mapping, and numerical simulation. The results suggested that the prerequisites for toppling deformation were the typical rock structure and special lithologic composition. The studied slope can be zoned into three areas: falling area, strongly toppling-deformed area, and slightly toppling-deformed area. Numerical modeling based on the discrete element method indicated that strongly toppling-deformed area exhibits the largest displacement on the bottom, with a total displacement of 5.74 cm in the natural scenario, 9.07 cm in rainfall scenario, and 1.44 m in earthquake scenario. The slope is unstable and damaged under earthquake conditions. The slope's failure mode can be summarized as follows: the earthquake caused the slope toe to collapse→the retrogressive deformation occurred→the slope surface collapsed and the sliding surface gradually penetrated→the deformed slope accelerated deformation→the deformed slope caused the overall failure.". The results also showed that this toppling slope has not yet advanced to the later stages of progressivity failure and is currently limited to collapsing at shallow levels. This study can provide an insight into toppling-deformed slope failure in the construction areas associated with the combination of seismic activities.

This project is located on the gentle slope of the third-level terrace in the upper reaches of the Dadu River. Because of the deep ice water accumulation layer and the inclusion of a large number of pebbles and silt lenses, studying the failure mechanism of the slope of the deep heterogeneous pebble accumulation body is critical. The cohesive force and internal friction angle are nonsynchronously reduced through the software program by comparing the slope equivalent to the plastic strain area calculated by nonsynchronous reduction step conditions with the stress and strain data monitored on site. Simultaneously, the displacement and load data of the sample during the staged loading process, were calculated in detail. The results proved that during the predetermined load application process, the pebbles are gradually shifted, and the silt lens interspersed between the pebbles is quickly destroyed. The friction angle between the pebbles provides the shear strength, further verifying the rationality of the nonsynchronous dual-strength reduction method. Compared with the general synchronous reduction method, analyzing the slope stability is more reasonable. Simultaneously, the double strength reduction method provides a solution to calculate the slope stability, and can be used for similar slope projects in the future.

One of the main failure modes of rock slope is the instability of the key block formed by cutting combination of structural planes. In view of the block stability and control problem caused by the combination of structural planes in the high and steep rock slope in Southwest China, the key block theory method and on-site monitoring method are used to study the stability of the key block after the excavation of the slope, the optimization of the design parameters of anchor cable support, and the deformation characteristics and change laws of the slope with the construction process are analyzed. The research results show that the large block formed by the discontinuity layer and layer fracture of the slope reaches 26000 m³, sliding along the structural plane on both sides, with low safety factor. The safety monitoring data show that the block is stable after the reinforcement with anchor cable.

At present, research on the spatial variability of soil parameters mostly considers isotropy and transverse anisotropy correlation structures; by comparison, little research on other general correlation structures is available. To address this issue, the present study generates a general rotated anisotropy correlation structure random field considering stratum rotation by using random field theory and the matrix decomposition method. FLAC3D and strength reduction theory are used to analyze the influence of the rotation angle of the correlation structure and the angle between the principal axes of the correlation structure on slope reliability. Thereafter, the influences of the coefficient of variation (COV) and shear strength cross-correlation on slope reliability are revealed. Results show that slope stability first increases and then decreases with increasing rotation angle of the correlation spindle. Slope stability is related to the rotation angle of the correlation spindles. In the two-parameter random field of shear strength, slopes in which the dip direction of the strata is against the dip direction of the slope demonstrate higher reliability than slopes in which the dip direction of the strata is along the dip direction of the slope. This effect is more obvious when the COV is small. Compared with the slope reliability analysis results obtained when considering the cross-correlation of shear strength parameters, the results obtained when cross-correlation is ignored demonstrate underestimation of the probability of failure.

A forest fire can affect most soil properties, lead to severe erosion responses, and sometimes even catastrophic consequence: post-fire debris flows. Five years after a forest fire occurred on June 1^st, 2014, in the Ren'eyong basin located in the central part of the Hengduan Mountains, the burned area was still being affected by the post-fire debris flows and flash floods. Therefore, assessing the extent of soil properties recovery is very important for predicting the development impact of wildfire-induced geological hazards. We tested the selected soil properties: soil moisture content (SMC), dry density, total soil porosity, soil organic matter content (SOM), saturated hydraulic conductivity, soil sorptivity (S), and soil water repellency (SWR) by in situ and laboratory experiments at two depths: 0∼2 cm and 2∼5cm beneath the soil surface in the low severity (LS) fire, medium severity (MS) fire, high severity (HS) fire areas, and adjacent unburned areas (as a control, C), respectively. The water drop penetration time (WDPT) test results showed that the SWR disappeared. The ANOVA analysis results indicated that, for the topsoil (0∼2 cm), most of the selected soil properties had a significant variance except for the S; only SMC and SOM showed a significant change for the deeper soil. The LS fire had negligible effects on these soil parameters at both depths. However, for the topsoil, the MS and HS fire effects were significant for most of these soil properties. The MANOVA analysis and paired t-test results indicated that the fire severity effects on the soil properties were significant, and the variance of fire severity effects was not constant at both depths. The Principal Component Analysis (PCA) further confirmed that the HS and MS fires had significant impacts on the soil properties, and the effects of the LS fire were negligible. These results demonstrated that the medium-term effects of the high and moderate severity wildfires on the selected soil properties of the topsoil were significant. The partially recovered soil properties forebode an intense slope erosion or even a further catastrophic consequence.

Dangerous rock refers to an unstable rock block that is cut by weak structural planes and gradually separates from the slope, and at present, it is challenging to effectively identify the separation degree of dangerous rock and accurately warn of its sudden failure. In this paper, a microelectromechanical system (MEMS) acceleration sensor is used in combination with the calculation principle of the included angle of the space vector to establish an integrated monitoring method of the microtilt angle and strong vibration acceleration (SVA). Through long-term field monitoring, the tilt angle and the SVA information of the whole collapse process are obtained. The analysis results show that (1) the tilt-time curve of dangerous rock is of the step-type, and the continuous and rapid increase of the tilt rate is a deformation precursor characteristic of a collapse; (2) in the absence of strong vibration source disturbance, the SVA is an early identification parameter for dangerous and stable rock, and the abnormal increase of triggering frequency of the SVA is the vibration precursor characteristic of a collapse; (3) three warning modes of dangerous rock based on the tilt rate and the SVA are obtained, i.e., stable mode, perturbation mode and alarm mode. This study provides an important early warning indicator for rock collapse.

In the construction of hydropower projects in southwestern China, the powerhouse, diversion tunnel, tailrace tunnel, access tunnel, and other structures are often located underground in cavern groups. The high slopes of the outlets of these large cavern groups are often characterized by steep terrain, high elevation, and frequent rockfalls, which seriously threaten the safety of construction and operation personnel. Therefore, it is urgent to carry out research on protection technology for dangerous rockfalls on underground excavation outlet slopes. In this paper, Uncrewed Aerial Vehicle (UAV) survey technology is applied. First, large-scale three-dimensional (3D) terrain data is collected by a UAV, then a Digital Orthophoto Map (DOM) and Digital Elevation Model (DEM) of the slope are obtained, and a 3D visualization is constructed. Meanwhile, an orthophoto image for detailed UAV route planning is generated. Second, according to the 3D visualization, a preliminary judgment of potentially dangerous rockfall areas is made by the engineers, and the UAV track planning for these areas is carried out. Third, refined low-altitude aerial photography is carried out on the dangerous areas according to the results of the UAV trajectory planning, and high-precision pictures are obtained. Based on the rock joints, fissures, and configurations displayed in these pictures, the areas with the most likely rockfall risks are further determined. Finally, 3D rockfall simulation software is used for rockfall simulation analysis. Comparing the rockfall interception rates and the distribution probability of rockfalls in each area under different protective net schemes, the final protective net plan is determined. The research results are applied to the design of a dangerous rockfall protection scheme on a natural slope at the outlet of a large underground hydropower station on the Dadu River, which provide a scientific basis for the setting of the protective net. The researches results can be used as reference for similar projects and provide a new idea for the design of dangerous rockfall protection measures on high slope tunnel outlets.

Based on the working process and technical requirements of geological hazard survey in China, a geological hazard field survey data acquisition system was developed based on online technology. The system, capable of presenting remote sensing images or topographic maps with a scale of 1:50,000 or higher accuracy and providing accurate positioning based on GPS and Beidou system, can satisfy the requirements of geological hazard field data collection. The system provides numerous functions, including data download, survey route navigation, online form filling, graph drawing, photo recording, and data synchronism. The development of the proposed system will provide rapid, accurate, and convenient data collection and information search for geological hazard field survey. The proposed system has been widely applied in practice and has significantly improved the working accuracy and efficiency of geological hazard field survey.

Landslide early warning is a systematic project involving multidisciplinary integration, i.e. geology, mechanics, engineering, monitoring technology, and information technology. When conducting landslide studies, due to the limitation of failure theory of geological body, landslide warning system is purely based on monitoring data nowadays, so it is difficult to integrate interdisciplinary techniques. A trigger condition based prediction theory and disaster stage judgment approach are introduced, with which the landslide time prediction is converted to the disaster stage judgment. The definition and significance of fracture degree is presented, by which the disaster stage judgment is convert to inner fracture state analysis. At last, the numerical-simulation-based landslide warning system is discussed in detail. This system contains four parts, namely parameter acquisition part, disaster kernel analysis system, current state back analysis part, and landslide reliability evaluation part, respectively. In the first part, the essential parameters and its acquisition method is presented, and then the necessity and advantages of dimensional analysis is discussed. In the second part, the new numerical method named continuous discontinuous element method (CDEM) is introduced, and main features, i.e. Lagrange equation, strain strength distribution criteria, element crack strategy, and indented point & indented edge contact model is introduced. In third part, the inverse analysis method of current parameters of geological body based on monitoring data and numerical simulation is discussed. In the fourth part, the reliability evaluation steps are presented in detail. Finally, the sliding occurrence probability of Liangshuijing landslide in Chongqing, China is discussed, which demonstrated to show the precision and rationality of the proposed landslide warning system.

Because of the typical geological environment and climate conditions, the number of debris flow geological disasters in low mountain red bed area is small, and most of them have high concealment. Identifying and monitoring debris flow under this kind of special disaster pregnant background has a certain significance for the prevention and control of geological disasters. Taking Wenjiagou debris flow in Danjing street, Eastern New District of Chengdu as an example, this paper uses InSAR technology and optical remote sensing technology to identify and monitor Wenjiagou debris flow by multi-period, multi-source and multi-means method. Combined with the geological environment conditions of red bed area, this paper comprehensively analyzes the causes and development characteristics of Wenjiagou debris flow. Research shows:1) The debris flow in Wenjiagou is very hidden. The source of landslide in the early stage can be detected by using InSAR technology, which has certain deformation characteristics. 2) Using multi- period optical remote sensing images, the partial slope deformation can be identified in the study area, and the debris flow can be effectively identified in the early stage. 3) The provenance of Wenjiagou debris flow is mainly controlled by geological structure and stratum lithology. Finally, combined with the results of remote sensing interpretation and ground survey, the paper puts forward the targeted prevention and control suggestions of "Stable material source + Combination of blocking and drainage + Ecological restoration" for Wenjiagou debris flow, which has a certain guiding role for the development and planning of the Eastern New District of Chengdu.

It is difficult to monitor the change of rock stability effectively and warn of the damage of rocks by using external deformation indicators. The article analyzed the change of the cantilevered rock's natural frequency during its stability decline and proved that the rock's natural frequency can reflect the rock's stability. The article analyzed the motion characteristics of cantilevered rocks and gave the calculation method of the natural frequency of cantilevered rocks. Using the formula, the natural frequency value within each stage of the rock can be calculated, and the critical natural frequency value before rock damage can be determined. Based on the theoretical equations' calculation results, the monitoring of dynamic changes in cantilevered rocks' stability and early warning of rock collapse can be accomplished using vibration sensors.

The determination of the maximum safe-slope angle with a planned slope height is a critical issue in slope design and construction. In this study, to overcome the drawbacks of the rule of thumb and trial-and-error methods, the optimization of slope angle is treated as a root-finding problem. The kinematical element method (KEM) within a rigorous theoretical framework is used to solve this problem using the modified false-position method. The critical noncircular-failure surface and the associated minimum factor of safety are located using the KEM. A rock slope with planar failure is given for demonstrating the validity of this method. The result shows that the maximum safe-slope angle obtained using the KEM is consistent with the analytical solution. The method proposed in this study has a satisfactory convergence speed. In addition, a bench-shape fill slope in an iron and steel base is used as a case study. The maximum safe-bench face angle of the fill slope, under self-weight condition, is 41.43°, and it decreased by 17% due to seismic loading. Finally, the effect of the slope height on the maximum safe-slope angle is analyzed, and strong correlations that display an exponential function are found. The critical failure surface associated with the maximum safe-slope angle becomes deeper as the slope height increases.

Stability evaluation of reservoir slope is a key issue affecting the safe operation of water conservancy projects, especially the new unexpected slope deformable bodies caused by changes in the hydrodynamic environment during the reservoir operation. The present study investigated the slope stability evaluation based on geomechanical parameters back-analysis and monitoring data of the left bank deformed slope of Guandi reservoir in China, of which the soil mechanical parameters result of laboratory test do not match the actual operating. In order to accurately evaluate the stability of this slope under the complex external environment, the deformation characteristics and instability mode of the slope were analysed based on the systematic study of the relationship between monitoring data and reservoir water level as well as rainfall. The failure mode of deformed slope was proposed, and the geomechanical parameters were obtained through back-analysis according to monitoring data of slope deformation. Based on the back-analysis results, the detailed analysis of the slope stability was studied, and the stability sensitivity analysis of the deformed slope under the sudden drop of the reservoir water level was carried out combining with the reservoir dispatch requirements. The results show that the slope stability using the back-analysis parameters are objective and reasonable. The research results could provide scientific references for stability evaluation of similar slopes.

The soil-water characteristic curve (SWCC) is the constitutive relationship curve of soil suction and water content, which has important engineering significance for studying the soil strength, permeability coefficient and volume change of unsaturated soils. Considering the experimental measurement of the SWCC is time-consuming, many empirical methods have been suggested to estimate the SWCC. This paper proposed a machine learning algorithm to predict SWCC from limited sets of soil properties. By predicting the parameters of the Fredlund and Xing model (which is called FX model), the most probable SWCC can be obtained. Since SWCC can't be accurately determined, the residual probability distribution functions of parameters of FX model are also derived in this paper. Finally, this paper predicted the 90% confidence interval of the SWCC. The result shows that the machine learning algorithm has high accuracy and generalization ability. The suggested method provides a practical means to estimate the SWCC and the variability of it, so that the error associated with the prediction model can be explicitly considered.

Emeishan basalts are widely distributed in Southwest China, where several large-scale sliding disasters occurred in recent years. At about 5:00 am on July 2, 2017, a high-elevation basalt landslide occurred on the slope of Dongbiangou in Nantang Village, Nantian Township, Leibo County, Sichuan Province, forming a deposit with a volume of about 563.0 × 10⁴m³ and burying houses, roads, and farmland. On the basis of a large number of geological surveys and engineering geological investigations on the disaster site, the formation mechanism and process were revealed by means of remote sensing satellite, unmanned aerial vehicle (UAV) aerial shot, and synthetic aperture radar on the ground, among other technical means. The results show that the weathered and broken basaltic rock mass and argillitization zone are the internal landslide causes, while the saturated water loading and infiltration softening caused by continuous rainfall and the disturbance of highway cutting slope are the external causes. The in-depth study of the formation mechanism and formation process of the Nantang landslide shows that the weathered and fragmented basalt slope should pay attention to interception and drainage measures and support measures during the construction and prevention process, to reduce the influence of water and human excavation on slope stability.

Slope failures are always frequent and important issues in surface mining, where a single calamity can disarrange mining schemes and endanger workers' lives. Simultaneously, the design and verification of "landslide early warning systems" in open-pit mines is a pivotal tool for mitigating risks. Notwithstanding, a prevalent model for heralding slope impending failures has not been available yet. The purpose of this article is to present a novel approach based on mean standard deviation (MSD) coupling weighted Markov chain (WMC) model to evaluate and perform the evolution that can detect onset-of-acceleration of landslides analysis procedure based on the indicator of real-time ground-based radar low-frequency measurements (e.g. displacement rate). The proposed method has been applied and tested in a open-pit coal mine situated in Inner Mongolia, China. An explanatory example of back analysis of a 4-month continuous surface monitoring dataset were regarded as a random process, and a binary classifier (i.e. steady-state and unsteady-state) was constructed based on the characteristics of mean standard deviation (MSD). Afterwards, properties of none aftereffect and bouncing allocation on the efficiency of Markov chains are studied. In order to modify and optimize the model, three indexes are integrated to verify the accuracy of the model and proof the predicting results: (1) precaution sensitiveness; (2) proper rate; (3) consensus rate. The consequences show that when the size of training samples was 20 days, the early warning accuracy reached 93%. When the model was performed seven days before the landslide occurrence, the true positive rate of the model was 84%, thus indicating the early warning for the landslide was timely. The integration of the proposed model and on-site monitoring data provides a useful tool for early warning of landslide displacement rates, and opens new perspectives on predicting slope instabilities.

Waste dump landslides caused by the excavation of the base of the waste dump slope were simulated, and the guided wave technique was applied for waste dump stability monitoring. The influence of inner diameter and wall thickness of waveguides on guided wave attenuation is analyzed. The variation characteristics of the ring down count (RDC) rate and the trend of b value during landslide are discussed, which provides a theoretical basis for the guided wave monitoring and early warning for the stability of waste dumps. The results show that: (1) The guided wave signal attenuation is related to the frequency and the wall thickness, while the inner diameter has little effect. In the range of 0∼170 kHz, the signal attenuation increases with the frequency. In the range of 170∼512 kHz, the higher the frequency and the thicker the wall, the greater the signal attenuation is. (2) Guided wave RDC rate and video monitoring can reflect the whole process of landslide. The RDC rate curves have three prominent data peaks, which implies three landslide accidents. The video monitoring can respond to the whole process of changes in the scene in real-time. The change of parameter curve is more intuitive than the field picture. (3) The b value fluctuates significantly during the instability of the waste dump. At the early stage of the waste dump landslide, low-amplitude guided wave events are the majority, and the b value is at a high level. When a landslide occurs, the high amplitude events caused by friction and collision between gravel and waveguide increase rapidly, and the b value drops to the minimum value rapidly. When the waste dump is readjusted to the equilibrium state, the b value shows an upward trend. There is an obvious turning point in the b value curve before waste dump failure, which can be used as the precursor of landslide.

Exploring more effective landslide susceptibility assessment methods play an important role in mitigating landslide effects. This paper aims to compare the performance of different popular ensemble learning models that combined with GIS system to assess coseismic landslide susceptibility in the 2017.8.8 Jiuzhaigou earthquake area. Eight influencing factors (slope, elevation, aspect, relief altitude, lithology, peak ground acceleration, distance to river, distance to fault) were considered to construct a spatial database after the Pearson correlation analysis. The 4834 landslides from inventory data are randomly divided into 70% train samples, and 30% validate samples. We construct the random forest (RF), gradient-boosting decision tree (GBDT), and adaptive boosting (AdaBoost), which all three models use decision tree model as basic unit, and utilize the receiver operating characteristic (ROC) curve, area under curve (AUC) values, Kappa value to validate the performance of three ensemble models. The results indicate that the AdaBoost model achieved the best performance (AUC= 94.4%, Kappa=0.766), outperforming the GBDT (AUC=92.5%, Kappa=0.720), RF (AUC= 93.6%, Kappa=0.756) focused on the validation data. This study can provide an insight into evaluating coseismic landslide susceptibility with high accuracy.

The limestone of the South China Lower Permian Qixia & Maokou Group usually features high purity, high strength, and poor weathering, while the limestone of the Qixia & Maokou Group at margin of the Chuan-Dian Paleouplife of southeast China is characterized by obvious strength weakening. The weakening of limestone strength leads not only to excessive errors in the estimation of useful material reserves in the limestone quarry, but also increases the engineering slope support cost in the limestone distribution area on the eastern margin of the Kangdian Paleouplife. In order to ascertain the cause mechanism of the strength weakening of the limestone in the stockyard, we take the stockyard in the dry valley as an anatomical point. The strength weakening of limestone is comprehensively analyzed by means of drilling, large-section excavation, site investigation, sampling, and physical mechanics tests. The main findings are as follows: (1) The limestone area of the Qixia & Maokou Formation near the Kangdian Paleouplife generally contains terrigenous fine-grained materials and mud iron; (2) The weakened rock masses are divided into two types of weakening: deep dissolution type and deep strong weathering type. The uniaxial compressive strength of the deep weakened rock mass is only 2.5-25 MPa, which is 70%-90% lower than that of the fresh rock mass. Compared with the natural state, the compressive strength of the saturated rock mass is reduced by 60%-90%. The deep weakened rock mass has the characteristics of weakened strength and is softened by water; and (3) The dissolution type rock mass is weakened as a result of the dissolution of the high-level exposed broken spring along the east-west fracture zone; the formation mechanism of the strong weathering rock mass weakening is that under the conditions of tectonic shear, terrigenous muddy interlayer and dry-heating condition. The buried depth of groundwater is large, the hydrodynamic force is weak, and the coupling of water and rock under long-term infiltration environments makes the limestone body softened and argilized in situ, leading to a significant decrease in the strength of the rock mass.

In order to analyze the impact of the near-fault pulse ground motions on the slope, the method of seismic vulnerability analysis based on IDA is introduced into the stability evaluation. Taking the slope reinforced by stabilizing piles as an example, a typical analysis model is established. The seismic performance is divided into four stages: basically intact, partial damage, severe damage and overall instability. A large number of calculations are used to compare the instability probability of slopes with near-fault and far-field ground motions. The results show that: 1) The calculation model which combines the Newmark and the limit analysis method can reflect the difference between the near-fault and the far-field ground motions. 2) The IM-DM curve with indexs of PGA and displacement has a better fitting effect. The vulnerability analysis based on IDA can be used to evaluate the slope failure risk under seismic loads. 3) The IDA curve shows a monotonous increasing trend. When the seismic intensity is lower(GPA=0∼0.5), there is no obvious difference between the vulnerability curves of the near-fault and far-field. As the intensity increases(GPA=0.5∼1.2), the failure probability of near-fault is significantly higher than the far-field. Meanwhile, the failure mode changed from the partial failure to the complete failure. It is clear that near-fault ground motions have the characteristics of large energy and strong impact, which are more likely to cause slope instability. If the impact of the near-field earthquake is ignored, the disaster may be underestimated.

Waste dump stability has long been a major concern in open-pit mine production. This paper describes the landslide morphology in detail, based on a summary of the geological conditions of the Dagushan Waste Dump. The modified Mohr–Coulomb strength criterion, which is more suitable for the deformation and failure behavior of waste materials, was adopted based on the limit equilibrium theory to study waste dump stability under complex working conditions such as dumping, vibration, and basement softening, as well as the parameter sensitivity of the main influencing factors. The test results revealed that: (1) the safety factor of the Dagushan Waste Dump first decreased from 1.343 to 1.238 when the waste dump increased from +150 m to +201 m. Thereafter, it decreased from 1.238 to 1.129 because of the weakened basement of silty clay. Afterward, it decreased from 1.129 to 1.029 because of the toe excavation of the waste dump. Finally, the mechanical vibration at the slope toe made the safety factor of the waste dump change periodically every 6 s. The lowest safety factor of the waste dump under mechanical vibration was 0.747, which can eventually result in landslides. (2) The dump stability was moderately sensitive to the third-grade slope angle, basement cohesion, and mechanical vibration strength; however, it was highly sensitive to the third-grade slope height, basement friction angle, basement moisture content, and first-grade slope excavation angle. The dump stability decreased with an increase in the third-grade slope height and angle, basement moisture content, first-grade slope excavation angle, and mechanical vibration strength. The dump stability increased as the basement friction angle and basement cohesion increased. (3) Slope reshaping is proposed as a remedial measure because it was discovered to be effective in maintaining slope stability. These results can be used as a reference point for further dump stability studies.

As the occurrence of earthquakes is highly uncertain, the permanent displacement of a slope during a given exposure time is also uncertain. Probabilistic analysis can be used to assess the effect of uncertainty in the ground motions on the permanent displacement. However, the number of ground motions to be considered in a probabilistic assessment of permanent displacement of a slope is still not clearly defined. In this paper, a numerical study is conducted to investigate the effect of number of ground motions on the variability of fragility curves and the hazard curve of the permanent displacement. It is found that for the slope study in this paper, the median fragility curve and hazard curve are not sensitive to the number of ground motions. The width of the confidence interval of the fragility curve can be reduced by half when the number of ground motions is increased by four times. It can be learned from the COV of the hazard curve of permanent displacement that the determination of the number of ground motion records should be based on a concerned critical permanent displacement.

In this study, a machine learning method, i.e., random forest (RF) model, was employed to assess post-fire debris flow (PFDF) susceptibility after the Xichang forest fire occurred on 30 March, 2020. First, we conducted a tracking survey in the rainy season, on-site tests, and remote sensing image interpretation and obtained 10 impacting factors, i.e., the basin area, relief ratio, basin shape coefficient, percentage of area with a slope greater than 50%, proportion of moderate or high severity burned areas, distribution of gravel in the basin, vegetation types and distribution in the basin, early cumulative erosion after fire, peak rainfall in a 1-h interval, and peak rainfall in a 24-h interval, after their correlation test to build a spatial database. Subsequently, a total of 181 PFDF events in the database were randomly divided into training (70%) and validation (30%) samples. Thereafter, the RF model was used to acquire the susceptibility of PFDF in the study area. Finally, receiver operating characteristic (ROC) curve, area under curve (AUC) value, sensitivity, specificity, and accuracy were utilized to validate the predictive performance of the model. Results show that the RF model has good predictive ability with AUC of 93.4%, sensitivity of 88.3%, specificity of 99.3%, and accuracy of 97.8%. This study provides a scientific basis for PFDF disaster prevention and risk management in Xichang City and its surrounding areas.

According to the investigation on the distribution of surface geological hazards in Maoping Mine, Yunnan Province, the stability calculation and discrete element numerical simulation of Meitanyakou landslide were carried out. The result shows that under the action of earthquake and rainfall, the Meitanyaku landslide has a chain disaster mode of high source start-up, acceleration slippage on the steep slope, gentle slope debris flow scattering and accumulation, and block rolling and throwing. Based on this, the reinforcement and treatment scheme in the landslide source area was formulated: the surface soil and vegetation in the gentle slope area were used to block the landslide, the passive protective net was installed at the bottom, and the reinforcement and treatment facilities were monitored. Meanwhile, a complete set of advanced and reliable slope online monitoring and early warning systems was established. After treatment, there was no unstable landslide, and the slope and its engineering structures in the monitoring area were stable, which shows that the chain disaster mode of landslide geological disaster and the complementary scheme of prevention and control countermeasures are effective.

Landslide susceptibility is an important activity in landslide hazard assessment. With the advancement of artificial intelligence, the machine learning algorithm is applied in the landslide susceptibility assessment, has recently gained immense attention due to the advantages of obtaining the insights of landslide events and conditioning parameters based on data mining, which is important when tackling the challenge of mapping landslide prone areas in regional scale due to the complex nonlinear correlations among landslides and parameters and uncertainties associated during parameters reclassification. Therefore, the machine learning algorithm has become a standard approach for modeling landslide susceptibility over large regions. In this study, the random forest method is applied to produce the China national landslide susceptibility mapping based on the national landslide database containing more than 300 thousand landslide events. Thirty different categories of conditioning parameters related to the development, triggering, and potentially vulnerable elements of the landslide were collected using a scale of approximately 1:1,000,000. Through the data mining process, lithology, faults, topography, soil erosion, precipitation, and human activities were found to be the top six important contribution factors to landslide susceptibility. The mapping results show the areas of four degrees of susceptibility from high to low are 101, 191, 337, and 331 thousand square kilometers, respectively. The receiver operating curve (ROC) and area under curve (AUC) value was calculated to 0.81, indicating that results are well satisfying and could guide landslide mitigation on the national level.

The Kahalo Jinsha River Super Large Bridge of the Sichuan Riverside Expressway spans the deep canyon of the Jinsha River and is situated in a high-intensity, complex, and dangerous mountainous area. Long-term deformation and stability of the gravity anchor slope are the main controlling factors affecting bridge safety. The maximum slope height formed by the excavation of the gravity anchor foundation pit on the Sichuan Bank of the Kahalo Jinsha River Bridge is 110m, and the anchorage area is located on the Q3h thick accumulation with a thickness of more than 170 m. First, the important soil mechanical parameters, such as shear strength, deformation modulus and bearing capacity eigenvalues of rock and soil were obtained by conducting field shear tests, deformation tests, and load tests. On this basis, the pseudo-static method was used to simulate the seismic conditions, and a three-dimensional numerical analysis and calculations of the potential instability range of the high slope of the gravity anchor foundation pit excavation were conducted. The results reveal that the slope of the super-deep foundation pit with a huge thick mixed accumulation layer will deform and become unstable under the influence of an earthquake, with a maximum deformation of about 20 m in the slope body. A two-level earthquake prevention and disaster-reduction target for the bridge foundation pit and slope engineering protection is proposed based on the two-level seismic fortification requirements of super-long-span suspension bridges. An active reinforcement scheme of excavation pre-reinforcement, step-by-step excavation, and zoning protection is designed and proposed based on this target and the deformation and stability analysis results of the field test and three-dimensional numerical calculation.

Anti-slide pile has been one of the most used preventive measures for the landslide treatment in the recent years. The pile spacing has a significant impact on the arching effect which develops due to the relative compressibility of soil relative to the anti-slide piles. To reveal the interaction mechanism of pile and soil, the soil stress behind the anti-slide piles was studied based on the stress analysis of a semi-infinite plate. The influencing factors, such as time, pile spacing, and pile number were considered for the soil arching effect determination. A new method for determining the maximum pile spacing was presented, based on the Mohr-Coulomb failure criterion and the ultimate equilibrium method. The stress nephogram behind the anti-slide piles was obtained, and different distributions of soil arches, including the hyperbolic arch, extended shoulder arch, inverted bell arch, and circular arch were observed to be influenced by both the pile width and spacing. For the same pile width, the additional stress of soil decreases with the increase in the pile spacing. However, for the same pile spacing, a less apparent soil arching effect was observed when the pile width was smaller. This work can provide a simple solution for determining the soil stress and maximum pile spacing for the anti-slide pile design.

Debris flow carries a large amount of sediment into the main river quickly, which causes river-blocking or diversion and leads to considerable losses in alpine regions. The research on the deposition characteristics of debris flow at the confluence with the mainstream channel is significant to understanding the riverbed evolution. However, the deposition mechanisms and morphology of debris flow at the confluence with the mainstream channel are not clear. This paper analyzes 80 debris flow cases at the Minjiang basin confluence in the Wenchuan earthquake area according to this phenomenon. It is found that the frequency of debris flows increases sharply after the earthquake. Moreover, the debris flow has the characteristics of sudden and mass occurrence. The deposition morphology of debris flow is also discussed with satellite images. Compared with the surface debris flow, the depositional fan at the confluence is mainly diffused along the flow direction of the main river and often presents an asymmetric broom shape because of the erosion of the main river. The relationship between the possibility of river-blocking and the properties of debris flows is also discussed. Results reveal that the river-blocking is closely related to the discharge and topography of the confluence. Furthermore, debris flow with high discharge (>200 m³/s), large density (>1.8 t/m³), and high velocity (>10 m³/s) easily trigger river-blocking. On this basis, a dimensionless parameter representing the characteristics of debris flow and mainstream hydrodynamic conditions is established, which can be used to measure the characteristics of regional river-blocking. Thus, the discriminant formula of the runout distance and the deposition morphology of debris flows are obtained. This paper studies the interaction between mainstream and debris flow and provides scientific methods for preventing and treating debris flow.

Overpressuring from generation of CO₂ gas caused by thermal decomposition of basal carbonates can raise pore-fluid pressure and reduce friction during landsliding. We used thermogravimetry and dilatometry to determine the evidence of raised pore-fluid pressure from carbonate thermal decomposition at the base of the 2009 Jiweishan landslide. Results from thermal expansion experiments showed that the rock undergoes expansion and thermal fracture. At a heating rate of 20°C/min, the coefficient of linear thermal expansion increased sharply at 807.3 °C and reached a maximum of 36.6×10⁻⁶ °C ⁻¹ at 827.3 °C. DTG data show that the temperature of the maximum thermal decomposition rate of calcite is 852.5°C. The evidence showed that CO₂ gas can produce great pressure during the rapid sliding process of Jiweishan landslide, and it is conducive to reduce the effective normal load. In addition, thermal fracture may be a explanation for the ultra-low friction during the rapid sliding by reducing the strength of the rock at the sliding surface and making it more easily entrained.

To better understand biogeochemical processes associated with the dynamics of soil organic matter (SOM), the δ¹³C and δ¹⁵N values were analyzed in the SOM of limestone soil (developed on limestone) and sandstone soil (developed on sandstone), as well as in dominant plant species and litter samples collected on the studied soil profiles in karst areas of Southwest China. In general, the content of soil organic carbon (SOC) and soil organic nitrogen (SON) is highest in the surface soil layer and decreases downward in both types of soil profiles. In addition, the content of SOM (including both SOC and SON) in the limestone is much higher than in sandstone soil. The higher pH values, as well as the content of calcium, magnesium, and clay minerals, are probably the reasons for the higher SOM content in the limestone soil compared to the sandstone soil.

In the SOM of the upper layers of yellow sandstone and limestone soil δ¹³C values range from 2.6‰ to 6.3‰ and δ¹⁵N values from 5.1‰ to 8.1‰, which is larger than in litters. Yellow sandstone soils have smaller differences between δ¹³C and δ¹⁵N values of SOM from litter and topsoil than the limestone soil. The δ¹³C and δ¹⁵N values of SOM increase with depth in yellow sandstone soil profiles, but not in the limestone soil profiles. An increase in the values of δ¹³C and δ¹⁵N with a decrease in the SOM content in the yellow sandstone soil significantly substantiates the decomposition of SOM, which causes higher values of δ¹³C and δ¹⁵N values in the deeper soil horizons. By contrast, the limestone soil has complex depth profiles of δ¹³C and δ15N, which can be mainly attributed to land-use changes and organic and mineral interactions between soil accumulations.

A double porosity finite element model (FEM) is used to analyse the stability of a wellbore during carbon dioxide (CO₂) injection in a carbon capture and storage (CCS) scheme. Elastoplastic deformation and continuous damage effects were considered. Attention was given to the pore and fissure pressures of the rock surrounding the wellbore as these can create stresses which can lead to potential fracturing. The size of the wellbore was also discussed as well as the studied depth and the different injection pressures of CO₂.

The influence of unloading of overloaded prestressed anchor cables in underground caverns on overall stability is discussed in this paper, including the theoretical background on the reinforcement effect of anchor cables, and quantitative estimates from numerical modeling of the influences of anchor cable force unloading on rock mass deformation and forces in the other adjacent support systems. The numerical model shows the same results as the recording during the site unloading test: unloading the force of overloaded anchors by about 50-150 tonnes has limited influence on rock deformation, stress adjustment, the depth of the plastic zone in the rock mass, and the forces on the adjacent rock bolts and anchors. From the perspective of the overall stability of the underground caverns, unloading the force of the overloaded anchors can be another solution in addition to replacing the overloaded anchors with new ones to meet the requirements of the design standard.

Considering the wide distribution range of deposits, the complicated geological conditions, and the potential detriment to slope stability during the caving period, underground goaf and slope stability is a critical concern in the Yangla copper mine. In this paper, goaf and slope stability is studied by implementing empirical analysis and numerical simulations with an equivalent continuum model. An overall understanding of underground goaf stability is obtained by the Laubscher graph method, and an approach composed of the geological modeling technology GoCAD and the specialized meshing tool Griddle is proposed to manage the geological database and prepare the numerical model for stability analysis with FLAC^3D. The Hoek–Brown constitutive model is introduced to simulate the complicated mechanical behavior of rock mass in the process of mining, i.e., the brittleness and confinement effect of rock mass. The key orebodies KT2 and KT5 develop in reverse inclination from slope surface to the inner slope with a maximum depth of 900 m, which means the rock mass bears a high stress induced by mining. The mechanical parameters are calibrated carefully by performing mining simulations that are consistent with the field instability phenomenon and measurement results. In particular, rock-mass behavior is predicted by sensitivity modeling in consideration of the goaf span, mining sequence, and material filling, the aim of which is to optimize the mining design to maintain slope stability during the third mining phase. The calculation results indicate that large deformations at the roof of the goaf and pillar are a critical problem in the Yangla copper mine as they are detrimental to slope stability. Moreover, many goafs collapse during the second and third phases of underground mining, which is also detrimental to slope stability, and the span of the goaf with a deep buried depth needs to be adjusted from 36 to 24 m in the third mining phase. The slope is stable in the second mining phase, but, in the third phase, it enters the large-scale instability state due to the destruction of the rock-mass structure near the slope surface by underground caving. Accordingly, goafs with the potential for collapse should be filled with high-strength materials to maintain slope stability.

In this paper we present a case history in which tunneling heavily impacted onto a karst system. This paper deal with a hydraulic tunnel under pressure crossing a mountain ridge constituted by calcareous and gypsum units, karstfied in recent geological time. The tunnel was driven right above the water table, and above the base level of karstification, in the transfer zone. During time, the concrete lining suffered deterioration mainly due to cavitation processes that led to pierce the lin-ing and the water flowing from the tunnel into the surrounding rock-mass. The water pressure into the tunnel changes daily, according to the needs, from 400 to 600 kPa. That led to inflowing water into the karstfied rock-mass creating a bub-ble of water infilling the karst system tubes and conduits above the tunnel for a highness of 40 m to 60 m and asymmetric shaped to the lower end of the moun-tain ridge and its sides. Therefore, many springs at higher level of the natural wa-ter table were activated and the base water flow in the karst emerging springs largely improved. When for the execution of the remedial works the tunnel was empty a surplus of water flow of about 6 Mm3 was recorded, all this water was drained from the water bubble created into the karst system. Once the tunnel had been cladded by a steel tube and the water flow reopened no more water losses occurred.

In the construction of hydropower station in high mountains and canyons of southwest China, it is common to encounter deposit slopes of scattered collapse and debris flow. The deposit is formed by multi-phase and multi-genesis. Their material composition is dominated by crushed and lumpy rock and soil, and their structure is relatively dense. In natural conditions, the failure mode is mostly small-scale collapse, which has little influence on the project. With the construction of hydropower station, some deposits will be partially or completely submerged after reservoir impoundment. In reservoir impoundment condition, the stability of the deposit body decreases, and the local instability of the deposit body may cause the overall instability of the bank slope, resulting in surges and thereby endangering the safety of the dam and residents nearby.

In this paper, a typical reservoir bank of a hydropower station in western China is taken as an example. The seepage characteristics and stability of the deposit body are calculated by using Geostudio series software. On this basis, the three-dimensional numerical simulation of the deformation of the deposit body is carried out by using FLAC-3D software. Through the comparison and analysis of the calculation results, the stability, deformation development trend and failure mode of the deposit body are summarized. It can provide reference for the comprehensive determination, monitoring arrangement and treatment of the similar deposit body.

Wellbore instability (WI) is a challenge in the drilling process, which often causes complex accidents. Measures should be taken to prevent WI in low-strength formation. It is crucial in wellbore engineering to ensure wellbore stability. In fact, WI was solved with large sources of lost time and trouble cost. However, at present, the mechanism of the instability of the shale borehole wall is unclear. To study the shale WI in Wushi Oilfield, the rock mechanics parameters of rocks were tested according to the actual situation of the oilfield. Experimental results were helpful to determine parameters for numerical simulation. A mechanical–chemical coupling model of shale wellbore was established. The numerical simulation results indicated that there was stress concentration around the wellbore wall. The effects of rock elastic modulus, cohesive force, deviation angle, azimuth, drilling fluid density, and hydration time on the stability of the shale borehole were analyzed. The numerical simulation results could provide a reference for on-site drilling optimization.

Affected by faults of different scales, there is a big difference between the local stress and regional stress in the crust. The Xianglushan tunnel of Central Yunnan Water Diversion Project is located in the Sichuan-Yunnan block with violent tectonic activity, and the tunnel passes through complex strata and fault development areas. Due to the limitations of testing methods, the measured stress data in Xianglushan tunnel project are mainly distributed in the relatively intact rock mass, so it is difficult to reflect the stress characteristics in the fault-affected area. Therefore, based on the tectonic geological data of Xianglushan tunnel, this article explores the construction method of multi-scale 3D geological model of fault development area. The corresponding information processing mechanism is established to realize the interactive interpretation, supplement and correction of fault data, and then gradually approach the actual situation of the geological body in the modeling process. According to the modeling method, a generalized large-scale model and a refined sub-model were established separately for the whole Xianglushan tunnel project area and the Longpan-Qiaohou fault affected area. At the same time, combined with the stress test data of Xianglushan tunnel, the first-stage stress field inversion calculation of large scale model is carried out based on multiple regression analysis method. The macroscopic stress field distribution characteristics of the strata and fault zones along the tunnel are preliminarily explored. From the first-stage inversion result, the displacement boundary conditions of the sub-model can be obtained by interpolation in the displacement field, which is applied to sub-model for the secondary elastic-plastic iterative calculation. Finally, the construction of the refined sub-model and the secondary elastic-plastic iterative calculation not only optimize the detail features of the initial stress field obtained by the first-stage inversion analysis, but also reveal the disturbance law of the complex strata and the Longpan-Jiaohou fault on the initial stress state, which has a high guiding significance for the construction and support of tunnel engineering.

Halahatang oilfield in Tarim Basin is a typical ultra deep fractured vuggy carbonate reservoir, which is the main production area of crude oil in Tarim Basin. The wellbore instability is serious in Triassic and lower strata (the borehole enlargement rate is 22% - 31%). Due to the complex rock characteristics, the drilling cycle for single well is long (124 days on average), and it is difficult to speed up. Based on the log interpretation curves, the calculation methods of pore pressure, collapse pressure and fracture pressure profiles established, and the spatial distribution characteristics of three pressures in this area were analysed; The rock drillability, rock hardness, compressive strength and abrasiveness of the roller bit and PDC bit single well measured by laboratory tests. Based on the statistical regression method, the relationship between the above drilling rock mechanical parameters and logging acoustic time difference and the formation drillability profile single were studied. The research results guide the drilling design optimization and operation of 15 wells in Ha 8 and Ha 12 blocks, The average drilling cycle is reduced by 21% (from 124 days to 98 days), and the hole enlargement rate is reduced from 24% to less than 10%.

Rock failure is one of the major concerns of drilling operation, especially in the formation with narrow drilling window, which may lead to several technical issues and even endanger the operation safety, such as wellbore collapse, stuck pipe, formation breakdown, lost circulation, etc. A new technology is proposed in this paper to prevent rock failure and maintain wellbore stability through controlling the annular pressure profile.

A new managed pressure drilling equipment named pressure control drilling system (PCDS) is developed which combines the constant bottom hole pressure technique and micro-flux control technique to quickly create overbalanced, near-balanced and underbalanced wellbore condition in the whole process of drilling operation. Based on the proposed MPD equipment, a novel technology is developed to maintain the annular pressure within the range of formation fracture pressure and formation collapse pressure, ensuring the formation rock to be neither shear failure nor tensile failure. Hydraulic calculation is performed before and during the drilling operation to predict the pressure profiles inside and outside the drill pipe, frictional pressure and equivalent circulating density, providing reference to the maintenance of wellbore stability. Real-time monitoring of multiple parameters such as properties of drilling fluid, bottom hole pressure and circulating flow rate as well as logging data is conducted to detect any minor change of down hole circulating system, minimizing the potential of wellbore collapse and formation breakdown.

The proposed technology has been applied in several onshore and offshore wells with a great success. Generally, a relatively low density of drilling fluid is used to cooperate the application of this new technology, due to its advantage of fast response to down hole conditions, minimizing the possibility of formation breakdown and formation damage as well as enhancing the rate of penetration. The easily collapsed formation is successfully drilled through with the assistance of the proposed technology by maintaining the annular pressure profile to be constant as pre-designed and eliminating the pressure fluctuations. Several incidences of early phase lost circulation are detected in time, and the annular pressure would be modified, avoiding the failure of the borehole wall rock, therefore prevent the serious losses.

On the basis of specific MPD equipment, this new technology gives drilling engineers a fast and effective way to ensure the borehole wall stability, thus eliminate the potential of multiple technical issues due to shear and tensile failure of borehole wall rock. Application of this technology could significantly improve the operation efficiency and enhance the economic benefits of drilling operation.

The main treatment of the Wanzhou drawdown area in the Three Gorges Reservoir involving landslide and reservoir bank treatment is conductedA comprehensive treatment of Wanzhou drawdown area in Three Gorges Reservoir involving landslide and reservoir bank treatment is conducted. The slope cutting improves the stability of landslides in conditions of periodic water level fluctuation, and when excavated gravel is used as the filler for reservoir bank treatment, it satisfies the ecological requirements of earthwork balance. Two kinds of landslide gravel collected for treatment were subjected to a series of tests, including particle analysis, heavy compaction, and a large-scale triaxial compress, and the engineering utilization control conditions and mechanical properties were obtained. The results show that the coarse particles content of landslide gravel is high, while the viscous is a little strong. Completed relations of water content ω and dry density ρ_d are obtained by heavy compaction tests, and for K = 0.93, internal friction angles (ϕ) obtained by consolidated drained (CD) and consolidated undrained (CU) triaxial test are 21.9°∼22.4° and 18.2°∼19.1° respectively.

The Shunbei oil and gas field is located in the low uplift of Shuntuoguole, which is affected by the multistage tectonic movement of the basin. There are several strike-slip fault systems that have developed from north to south, and the geological characteristics of the reservoir are controlled by different combination of fault zones. A large cavernous fracture system is developed in the main fault zone. The stress inversion calculation and analysis methods are established for various types of faults. The three-dimensional stress field distribution in the study area was obtained through numerical simulation. The magnitude and direction of the stress field were analyzed at different depths and locations in different types of faults, including at the tip, in the middle, adjacent to the fault, and in the intersection to determine the magnitude and spatial distribution behavior of the stress field in the multi-fault area around the well. On the basis of the stress field simulation, the distribution of some natural fractures is preliminarily explained according to the statistical fracture distribution behavior, and a hydraulic fracturing process simulation is performed to reveal the distribution and influence range generated by hydraulic fracturing, which provides guidance for subsequent hydraulic fracturing scheme designs.

Deep carbonate reservoir heterogeneity is serious, fault and fracture development, geology characteristic upper and lower horizontal well is uncertainty. The fracturing design scheme applicability is not strong based on the well logging data of guide well or adjoining well. Therefore, it is necessary to combine the engineering geology, construction technology and the optimized design of the scheme organically to solve the above problems. Based on the interpretation model of logging data, this paper discusses the prediction method of rock mechanics parameters combined with logging and seismic data. The plane distribution law of shear wave and rock density was obtained by the seismic inversion algorithm, and the plane law obtained by 3D seismic inversion was used as the prediction constraint conditions to carry out 3D geological modeling for the rock mechanics parameter field in SHB block, and on this basis, the local in-situ stress field simulation was figured out. According to the established geomechanical model, the section was cut along the direction of the horizontal well bore, and important information such as reservoir development status and geomechanical parameter distribution of the upper and lower sections of the horizontal well bore were analysed. A full three-dimensional model of asymmetric fractures was established. The research work in this paper is of great significance to improve the success rate of stage fracturing of ultra-deep horizontal well and the economic development of single well.

With the gradual development of oil and gas exploration, deep and ultra-deep shale gas has become the main block for shale gas reserve growth and production addition in China. Deep and ultra-deep shale gas is characterized by deep burial depth, high pore pressure and formation fracture pressure, so the production and transformation means in the later stage are more complicated. Deep shale gas cementing puts forward higher requirements on cement slurry system, especially the mechanical properties and long-term sealing ability of cement sheath under high temperature and pressure conditions. This paper studies the cement slurry system which can meet the requirements of staged fracturing and long-term sealing. Through the physical simulation device, the mechanical property analysis and evaluation method of cement sheath under staged fracturing condition is developed. By interphase filling technology, a new type of elastic material is developed. Meanwhile, nano-emulsion filling technology is used to realize void filling and reduce porosity of cement stone and micro-ring gap. Finally, a high-strength flexible cement slurry system for deep and ultra-deep shale gas well cementing is constructed, with a temperature resistance of 200°C, elastic modulus of cement stone less than 6GPa and compressive strength ≥25MPa/48h. It can meet the requirements of 120MPa and 25 cyclic loading staged fracturing. This cement slurry system has been widely applied in shale gas areas, and the durability and sealing ability of cement sheath have been significantly improved, which can meet the needs of large-scale staged fracturing and ensure the efficient development of deep and ultra-deep shale gas wells.

There are multiple sets of vertical salt faults in some blocks of the Keshen area of the Tarim Basin. The formation of the pressure system is complicated and vertical wells cannot meet safe drilling requirements. Using highly deviated wells to avoid faults is an effective means to ensure safe drilling. Simultaneously, it can also increase the drainage area to increase well production. There is a series of engineering problems faced in the implementation of highly deviated wells in the salt and gypsum layer, such as trajectory optimization and directional drilling, well structure design, stress checks of bending casings, and running casings in the deviated section. The engineering geology multidisciplinary integration concept is used to carry out the design of a drilling and completion plan for thick salt–gypsum and highly deviated wells. Through the successful initial drilling of Keshen 1002 in the Tarim Oilfield 600,000 m³/day of natural gas production was obtained. The drilling and completion technology has completely freed up the development of the Keshen 10 reservoir and provided reliable engineering technical support for the development of similar gas reservoirs.

Limestone, igneous rock and dolomite are widely distributed in ultra-deep wells in Tarim Basin. Hard brittle rocks show different mechanical properties under high stress conditions in ultra-deep wells. Traditional wellbore stability theory states that the greater the rock strength the more stable the wellbore. The actual drilling in Tarim oilfield (more than 7000 m true vertical depth) shows that in the same section of hard dolomite and mudstone formation, there are more dolomite enlargement and block falling during drilling, while the caliper of mudstone formation is regular. The unloading mechanical experiment of hard brittle rock shows that the deformation and failure characteristics of rock during unloading are different from those during loading. In the process of unloading confining pressure, the axial stress and confining pressure decrease linearly with the increase of strain, and the unloading modulus increases with the increase of the decreasing rate of confining pressure. The smaller the unloading rate of confining pressure, the more obvious the axial plastic flow becomes. The failure of unloading rock occurs mainly due to its brittleness. By comparing the failure degree under different stress paths, the unloading confining pressure before peak is greater than that after peak, and the unloading confining pressure after peak is greater than that of the loading test. Most of the unloading cracks are tensile cracks, but there are shear cracks in the sample, and tensile flakes on the surface of the sample after unloading confining pressure. Within the experimental range (unloading rate), there may be an unloading rate that causes the most severe damage to the rock sample, that is, with the increase of the rate of penetration (ROP), the degree of rock damage caused by stress unloading does not increase monotonously, and there may be a certain ROP that causes the greatest damage to the wellbore. Large unloading will aggravate the damage evolution and failure of tight brittle rock. For the safe drilling of such rock formation, the drilling rate and drilling fluid density should be optimized based on complete understanding of the geo-mechanical environment to minimize the damage and instability of surrounding rock caused by drilling unloading.

In order to effectively prevent the occurrence of sand production during the gas well production, rock mechanics tests were carried out for a deep tight sandstone gas reservoir in Bashijiqike Formation of the Keshen blockk, and the logging prediction models of mechanics parameters were established. At the same time, considering the effect of reservoir pressure and stimulation measures, based on the analysis of stress state of borehole wall and using M-C criterion, the calculation model of the critical production pressure of gas well was established to achieve the purpose of guiding production and improving the gas well production. The results show that the relationship between rock mechanic parameters with acoustic wave and volume density of the Bashijiqike Formation reservoir was studied, and the response mechanism of rock mechanics parameters was revealed, thus the logging calculation model of rock mechanics parameters was established. Based on the drilled fracturing and logging data, the multi-parameter prediction method of the formation pore pressure and the in-situ stress calculation model were established. The critical production pressure has also been significantly reduced, and the risk of sand production in gas wells increased significantly. After water immersion and acid fracturing, the compressive and elastic modulus of the rock samples decreased obviously, and the maximum decrease of the critical production pressure of the reservoirs in the study area reached 9 MPa. In order to ensure the safe production, it is necessary to supplement formation energy or take more effective sand control measures in the study area. The research results can provide guiding significance for gas well production allocation in this area.

Different from the long-term and low-speed depletion of conventional gas fields or monotonous gas injection in carbon dioxide geological sequestration, the engineering background of multi-cycle intensive injection and production of underground gas storage (UGS) makes the dynamic sealing capacity and stability of the trap cap and pipe string under alternating load become the key problem that cannot be ignored. Firstly, the basic mechanical parameters of sandy mudstone and G-grade oil well cement were determined by conventional uniaxial tests, then, different upper load levels and alternating times were set to carry out alternating mechanical tests for sandy mudstone and G-grade oil well cement stone. The deformation, failure and stress-strain curve characteristics of the two types of rocks were analyzed, and the variation laws of the strength and elastic modulus with the upper stress and the alternating times of the two types of rocks were obtained: The strength of cement stone decreases, while that of sandy mudstone increases with the increase of upper limit stress and alternating times, and the reasons for the different laws of the two types of rocks were further analyzed. Then, after undergoing different alternating times with different upper load levels, the dynamic breakout pressure tests of two types of rocks were carried out by the step-by-step method. The results show that the breakthrough pressure of the two types of rocks decreased gradually and significantly with the increase of the alternating times. The dynamic evolution prediction model of the breakthrough pressure with the alternating times was established. And because the breakthrough pressure of the cement stone in the nondestructive state exceeds the measuring range of the equipment, the initial breakthrough pressure of the cement rock was also predicted by the prediction model of the breakthrough pressure. All of these results above can be significant reference value for the sealing evaluation of gas storage site selection and the real-time monitoring after it is put into operation.

Shunbei area is located in the belt structural of the northern margin of the shuntuogole low uplift. The proven oil reserves of the adjacent blocks are 142.93 million tons, which has the potential of exploration and development. In the igneous strata of Shunbei block, there are many complicated conditions, such as wellbore collapse, stucking pipe and so on, which seriously restrict the exploration and development speed and benefit of the block. In order to solve this problem, firstly, the composition, microstructure, mechanical properties and other parameters of igneous rock intrusion in Shunbei block are determined through laboratory experiments. The experimental results show that the igneous rock intrusion in Shunbei block does not contain expansive clay minerals, has weak hydration ability, and has developed micro fractures. Thirdly, the wellbore stability model considering fractures is established, and the influencing factors of wellbore instability are analyzed by combining the mechanical properties of igneous rocks, porosity and permeability characteristics, and in-situ stress state. The results show that the micro fractures and weak surfaces have a controlling effect on wellbore stability. The longer the immersion time is, the deeper the drilling fluid invasion depth is, and the higher the wellbore collapse pressure is. Finally, according to the microstructure and physicochemical properties of igneous intrusions, the main points of drilling fluid technology are determined, that is, the anti sloughing drilling fluid technology is mainly strong plugging. In this paper, through the analysis of the rock characteristics of igneous rocks and the main controlling factors of wellbore instability mechanism in Shunbei block by using the method of mechano-chemical synthesis, the clear main controlling factors of wellbore stability are of positive significance for ensuring the safe well construction, shortening the drilling cycle, reducing the drilling cost and improving the development efficiency in Shunbei block.

Tectonic fractures can be important reserving space and the main contributor to permeability in ultra-deep reservoirs of Kuqa Depression. In this study, a workflow based on geomechanical method is presented. Firstly, a 3D heterogeneous mechanical field is constructed by core-logging-seismic data; then the finite element in-situ stress simulation is carried out, which is established using heterogeneous mechanical parameters instead of uniform parameters. Based on strain energy theory and energy conservation principle, the relationship between tectonic fracture parameters and in-situ stress field is established by a suitable rock fracture criterion for ultra-deep tight sandstone. Characteristics of tectonic fractures are predicted and revealed by the above stress field simulation and the established relationship between stress and tectonic fracture parameters. The results show that the maximum horizontal principal stress (S_H) orientation is generally N-S-trending in Bozi-1 gas reservoir. The present-day in-situ stress magnitudes are generally high with the minimum horizontal principal stress (S_h) is about 110∼160MPa, and the stress difference is over 35MPa. The characteristics of present-day in-situ stress largely vary among different structural styles. The in-situ stress magnitude and burial depth generally indicates a linear relationship. The in-situ stress gradient is stratified with burial depth and is consistent with fold stress stratification. Controlled by the effect of fold bending and protection of salt layer, the development of tectonic fracture in pop-up structures is better with larger fracture aperture and higher permeability, and fracture strikes are generally consistent with the SH orientation. Tectonic fractures in imbricated structures indicate great heterogeneity because of the development of faults and folds, and the rebuilding effect (permeability reduction) under the present-day in-situ stress field. Optimization of favourable zone for in-situ stress and tectonic fracture is of practical effects during well drilling and completion works.

ShunBei 1 block is located in the northwest of Shuntuoguole low uplift in the north of Tarim Basin, with a block area of 4453km². The reservoirs are mainly distributed in the Middle Ordovician carbonate rocks, and the burial depth is generally more than 7500m. A large number of strike-slip fault zones are developed in ShunBei #1 block, which results in low drilling rate, difficult drilling and poor formation drillability. In this paper, through rock drillability experiment and acoustic test experiment, the experimental analysis of the core of the study block is carried out, and the fitting relation formula of drillability level value is determined by comparing a variety of fitting methods. Based on the calculation model of drillability class value, this paper calculates the drillability class value of Well X in No. V fault zone of ShunBei #1 block, and establishes the drillability profile of Well X. Through the analysis of the drillability profile and drilling conditions, it is believed that with the increase of formation depth, the drillability class value of formation increases, and the drillability of formation becomes worse. Because the fluctuation of the strata drillability class value in the fault zone is small, but the strata drillability class value is large. The drillability class value of induced fracture zone strata changes dramatically, showing obvious sawtooth shape, but in general, the value of drillability class value is consistent with that of conventional strata. The strata drillability level of sliding crushing zone increases obviously, but its fluctuation is small. In addition, the drillability of the strata under different fault types is compared. It is concluded that the drillability class value of the strata controlled by the compression fault zone and the strata controlled by the translation and pull-apart fault zone fluctuates very little, but the drillability class value of the strata controlled by the compression fault zone is larger, and the formation drilling difficulty is greater, and the drillability is worse.

The development of deep shale gas reservoirs has become economically and commercially viable through novel horizontal well completion and multistage hydraulic fracturing technologies in recent years. In the Sichuan Basin, the deep Longmaxi shale is a major target formation that has attracted increasing interest. Shale is generally characterized as a sedimentary rock with fine grains, high clay, and organic content, low permeability and porosity, and high heterogeneity and anisotropy. Geomechanical characterization of these organic-rich rocks usually includes an estimation of the elastic modulus, strength properties, hysteresis behavior, and creep deformation. Understanding and characterizing the viscoelastic behaviors of shale is essential because they affect the elastic and fracture properties of rock and cause a series of drilling problems related to the wellbore stability, such as borehole shrinkage, pipe sticking, and casing collapse. The viscoelastic behavior of specimens retrieved from a deep well in the Sichuan Basin was examined using nanoindentation creep tests. Nanoindentation is a technique based on a hard tip, which is pressed into the surface of a sample. The advantage of this test is the use of a small sample volume, such as drilling cuttings or fragments, which are obtained easily during drilling. The results indicated that the creep modulus parallel to bedding and normal to bedding is similar, while the creep modulus of drilling cuttings is the lowest. A linear relationship was both observed between the creep modulus and hardness, Young's modulus for deep Longmaxi shale. The Burgers creep model showed good agreement with the experimental data. The creep behavior of Longmaxi shale exhibited anisotropy, and the effect of drilling fluids could aggravate the creep displacement. These results have elucidated the creep properties in engineering problems of shale gas formation, drilling, and stimulation.

In the past decade, the extraction of shale gas has become economically feasible due to innovations in horizontal drilling and multistage hydraulic fracturing. This has led to increased interest in deeper understanding of the mechanical properties of shale rocks. Currently, the deep Longmaxi shale with a burial depth of more than 3500 m has been receiving increasing interest in the Sichuan Basin. The first task of large scale development of these reservoirs is to understand the mechanical properties of deep shale rocks. Usually, these properties, such as the Young's elastic modulus E, hardness H, fracture toughness K_IC and other parameters are commonly obtained from laboratory tests with core plugs and logging data interpretations. However, these methods have their own limitations. In recent years, the nanoindentation test has been widely used to predict mechanical properties of shale and other rocks. The advantage of this test is the small sample volume required, which means that drilling cuttings or fragments, which are easily obtained during drilling, can be used. In this study, the nanoindentation method is adopted for the accurate measurement of K_IC, which is of vital importance for the better understanding of the drilling-induced tensile fractures and for the design of hydraulic fracturing. The specimens retrieved from a deep well in the Sichuan Basin are examined using nanoindentation tests to obtain K_IC. The results show that K_IC is strongly dependent on mineralogy and is anisotropic. Usually, K_IC values measured parallel to the bedding planes are generally higher than the corresponding values measured normal to the bedding planes. The obtained fracture toughness can be used to predict the fracability and brittleness of shale, which have instructional significance for drilling and hydraulic fracturing.

In recent years, the deep shale gas reservoirs has been a major shale gas target in Sichuan Basin. Usually, the burial depth of this target formation is more than 3500m, which is receiving increasing interests to get industrial natural gas. The deep shale gas reservoirs, characterized by fine-grained nature and low matrix permeability as the common shale, require good understanding of geomechanical properties to optimize drilling and fracturing strategies. Meanwhile, the shale reservoirs are anisotropic and inhomogeneous, exhibiting a nonlinear feature under stress loading. However, very limited studies are devoted to characterization of the mechanical properties of deep shale, as opposed to other shale formations. Due to an increasing demand for fundamental properties of this formation to meet the needs of development of this deep shale gas, a comprehensive characterization studies is needed. One of the most important investigation is to obtain the mechanical properties based on an integration of unconfined/triaxial compression tests and creep tests. In this study, the time-dependent, elastic, hysteresis, and strength properties of deep shale specimens, retrieved from a deep well in Sichuan Basin, are evaluating by performing a series of triaxial creep experiments. With respect to mineral composition, the shale cores are found to be organic-rich. The response of these shale specimens are found to be influenced by the planes of weakness and the presence of micro-cracks. The results of creep experiments show that shale tends to significantly creep under the applied stress. The time-dependent axial strain increase linearly with differential stress. And the Power-Law creep model can be used to describe the time-dependent behaviour of shale well. Moreover, the existence of bedding planes results in the creep anisotropy of shale. It is observed that the overall time-dependent axial strain normal to bedding is higher than the parallel to bedding. But the axial strain at 45° angle with respect to the bedding plane is highest. These research results are of great significance for safe and fast drilling in deep shale gas reservoirs. Also, it can be used to guide hydraulic fracturing.

The fracture propagation length and propagation angle can be calculated quickly using the fracture propagation analytical model. But for fractured-vuggy carbonate reservoirs, the addition of a discontinuous medium in the analytical model makes it difficult to obtain accurate results via calculation. In this paper, an analytical solution model for fracture propagation in carbonate reservoirs is established. On the premise of ensuring calculation accuracy, the discontinuous displacement algorithm is used to introduce the fracture and hole characteristics into the calculation. The model comprehensively considers the interference of in-situ stress, fracture tip stress, and stress field of fractures and holes on fracture propagation. The calculation accuracy of the model in a fractured-vuggy carbonate reservoir is verified by a true triaxial fracturing physical simulation experiment. The model can be used for subsequent research on the fracture propagation law of carbonate reservoirs containing discontinuous bodies, such as fractures and caves.

Hydraulic fracturing has become an important stimulation method for unconventional oil/gas reservoirs to achieve industrial capacity. Fracability evaluation has become one of the most important step during the reservoir characterization and fracturing job design, which is beneficial for identifying the best candidate fracturing zone. In this paper, we provide a detailed review of the existing fracability evaluation methods. The evolution of the fracability evaluation method from the single-factor method, i.e. the brittleness method, to the multi-factor methods which incorporate brittleness, fracture toughness, in-situ stress as well as natural fracture parameters has been summarized. For the brittleness methods, different definitions of brittleness have been summarized and compared. For the multi-factor fracability evaluation methods, particular emphasis has been paid on illustrating how the factors were selected and incorporated into different fracability evaluation methods and possible field evidences validating the effectiveness of different fracability evaluation methods. In addition, the emerging 3D fracability evaluation attempts based on 3D seismic data and geomechanical analysis, which may serve as a guidance for finding the so-called engineering sweet spots, have been introduced in details. Finally, possible future work to improve the effectiveness of fracability evaluation is discussed.

Fracability evaluation of unconventional oil/gas reservoirs has become a general practice during the hydraulic fracturing job design to identify the best candidate pay zone. The brittleness of the reservoir rock was first used to characterize the capability of the reservoir rock to form a complex fracture network. Later, other factors like fracture toughness, in-situ stress, and natural fracture parameters were introduced in combination with brittleness to more comprehensively describe the fracability of the reservoir. However, most of the existing fracability evaluation has been performed for single wells. In contrast, the three-dimensional distribution of fracability within reservoirs was less pursued, though it might be beneficial for guiding the well placement.

This study developed an integrated multi-scale fracability evaluation method for tight sandstone reservoirs based on three-dimensional geomechanical analysis. Factors like brittleness, fracture toughness, in-situ stress contrast that influence the hydraulic fracture initiation and propagation at different scales were first identified and analyzed. Then methods of deriving these quantities from well logs and three-dimensional seismic data were summarized. Finally, an integrated index incorporating these quantities was defined to differentiate the so-called engineering sweet-spot zones favorable for stimulation. A typical application of this method is the integrated multi-scale fracability evaluation method applied to a tight sandstone reservoir located in China's south sea oil field, which demonstrated the effectiveness of the method. In addition, some implications for improving fracturing operations of tight sandstone reservoirs have been provided.

H underground gas storage (H-UGS), located in the junction of the southern margin of the Junggar Basin and the eastern part of the northern Tianshan Mountains, is one of the large natural gas storage in China. It is of significance to study the deep rock stresses in H-UGS for fault slip tendency, safe storage of energy and other research. Most of the regional stress information in H-UGS data from in-suit measurements lacks deep in-suit stress data in this region. This research proposes a hybrid constrain stress magnitudes present in deep rock masses. First, the fault friction strength, an essential parameter of lateral pressure coefficient polygon, is established by the stress accumulation index method and apparent friction strength evaluation method. Second, we inverse the stress factor R from the focal mechanism solutions in this area, and the lateral pressure coefficient polygon is qualified quadratic to narrow down the range of results by this parameter. Finally, the complete stress profile of H-UGS is obtained by using the simple transition relationship between lateral pressure coefficient and in-situ stress. The result shows that the principal compressive stress of the H-UGS region is determined by the N22°E, the maximum lateral pressure coefficient K_max (or S_H) at three depths (3.0km, 6.5km, and 12.0km ) are 1.2 (80.22 MPa), 1.22 (202.72 MPa), 1.28 (421.34 MPa) respectively, and the minimum lateral pressure coefficient K_min (or S_h) are 0.87 (58.21 MPa), 0.86 (142.12 MPa), 0.86 (282.61 MPa) respectively. The result is primarily consistent with in-situ measurement from the depth of 3.0km to 3.7km. The maximum horizontal principal stress and the minimum coincidence ratio are 54% and 69%. The result of estimating deep rock stresses established in this research provides sufficient regional stress field data in H-UGS.

The traditional prediction method of wellbore instability in fractured formation cannot effectively solve the problem of surrounding rock collapse in ultra-deep fractured reservoir. This paper focuses on the coupling effect of complex geological conditions such as high stress, high temperature, fractured formation and drilling fluid. It establishes the induced stress field expression based on the heat exchange effect between drilling fluid and wellbore surrounding rock, and synthesizes the superposition effect of temperature and fracture. The strength failure criterion of wellbore surrounding rock in fractured formation is optimized, and the mechanical model of wellbore instability in fractured reservoir is established based on mechanical-thermal-chemical coupling model. The results show that as drilling fluid density increases, the stability of wellbore surrounding rock in ultra-deep fractured reservoir initially increases and then decreases. In other words, excessive drilling fluid density will aggravate wellbore collapse. In addition, the decrease in the temperature of the surrounding rock of the wellbore caused by the circulation of drilling fluid also leads to the increment in the degree of wellbore collapse. Based on these findings, reasonable drilling fluid density and properties can be optimized, and the instability problem of an ultra-deep fractured reservoir in Northwest China can be alleviated.

Accurate prediction of lost circulation fracture width and lost circulation pressure is the basis for preventing lost circulation and curing the losses. They are controlled by many factors, such as in-situ stress, wellbore fluctuating pressure, rock properties, natural fractures, and so on. Researchers have put forward a variety of calculation models of lost circulation pressure for fractured formations; however, in the field practice, it is still mainly based on the minimum horizontal principal stress. The lost circulation of fractured formation seriously jeopardizes the safety and progress of drilling and production. At present, the success rate of curing the losses is low, one of the important reasons is that the fracture width cannot be accurately predicted. It is difficult to determine the wellbore strengthening method and particle size of the lost circulation materials due to unknown fracture width. Various prediction models of fracture width are used to calculate the fracture width of the loss layer, and the influence of the factors such as the loss time, drilling fluid properties (viscosity and yield value), and the angle between the fracture and the wellbore on the calculated fracture width is studied. For the lost circulation pressure, the acceptable loss rate in the drilling process is given. On the premise of the calculated fracture width, the lost circulation pressure under the acceptable loss rate is determined. The results show that the values of fracture width and lost circulation pressure predicted by the three methods are close to each other, and the prediction results of the three methods can be averaged in the field application to provide reference for the following work. The fracture width is sensitive to drilling fluid viscosity, bottom hole pressure, and other parameters, so the value of these parameters should be accurately measured in the field to reduce the uncertainty. The results also show that the larger the angle between fracture and wellbore, the more serious the lost circulation will be.

The relationship between coal permeability and temperature under 200 °C was studied using a coal-heating experiment, and the mechanism of coal permeability increase was analyzed using X-ray diffraction analysis and electron microscope scanning. The results show that coal rock's permeability could be increased from 0.5 to 15 md after heat treating. These mechanisms may be explained as follows. First, the desorption of methane molecules and the dehydration of gelatinous microcomponents in the matrix, which shrinks the coal matrix. Second, dehydration of coal rock and volatile coal, which will flow out and form new pores. Third, coal rock encounters inhomogeneous deformation under thermal stress, producing a small crack, unevenly. Fourth, coal rock generates hydrocarbon gases after oxidation, forming tiny cracks and reducing the degree of coal rock compaction. Finally, the study proposes a new mode of coalbed methane (CBM) exploitation to enhance CBM recovery by injecting thermal CO₂. The above studies may be used to exploit CBM reservoirs with low permeability.

As a tight conglomerate reservoir, the Baikouquan formation reservoir in the Mahu depression is vital heterogeneous. The development model of unconventional oil and gas fields such as shale gas is copied in the early development process. Advanced horizontal wells and volumetric fracturing technologies are adopted, with high development costs and low economic benefits. During the development of tight conglomerate reservoirs, there are typical problems such as underdeveloped natural fractures, complex fracture formation mechanisms during fracturing, and serious interlayer channeling in fractured wells. Practical results show that the adequate characterization of in-situ stress distribution plays a decisive role in the scientific and efficient development of tight conglomerate reservoirs. To accurately characterize the three-dimensional in-situ stress distribution law of conglomerate reservoirs, the paper selects the Mahu 131 demonstration well area. The mechanical parameters of the demonstration area are finely described through a series of core tests, well-drilled logging data, and seismic inversion data. As a result, the spatial distribution of essential parameters of the demonstration area has been established, such as the three-dimensional elastic modulus attribute volume and the three-dimensional Poisson's ratio attribute volume. Further, an advanced finite element simulator and large-scale parallel computing technology establish the test area's high-precision three-dimensional stress field model. Based on enormous fracturing data, microseismic data, and production data, quality control and correction of the three-dimensional stress field model are carried out. The results show that the established geomechanical model accurately reflects the direction, magnitude, and heterogeneity of the in-situ stress in the demonstration area. Through the three-dimensional minimum in-situ stress distribution, the three-dimensional horizontal stress difference distribution, the lithology characteristics of conglomerate, rock mechanical properties, and other factors in the test area, it is believed that the difference in interlayer stress is the main reason for the interlayer channeling of fracturing. According to the established high-precision in-situ stress model and the rational fracturing construction process, it can actively strengthen or weaken the instantaneous and local stress field and pressure field, from near field to far-field, and promote the expansion of hydraulic fractures in the desired manner.

Sichuan Changning block is rich in shale gas resources reservoirs, but the lost circulation problem is prominent during the horizontal drilling process of deep shale gas wells, which seriously restricts the exploration and development of deep shale gas resources in the Changning Block. Aiming at the problem of lost circulation in the drilling process of deep shale gas in Changning well area, the difference of the vertical and horizontal distribution of lost circulation is clarified by comparing the information of deep shale lost circulation in this block. Based on single well logging data and 3D seismic interpretation, the 3D distribution model of shale gas formation fracture, in-situ stress and formation pressure was established. The response relationships among fracture development, in-situ stress distribution, formation pressure and lost circulation in shale formations were studied, and the lost circulation mechanism and main influencing factors of deep shale gas formations in the Changning well area were clarified. The results of the study show that deep shale lost circulations in the Changning well block is prominent and widely distributed longitudinally and horizontally with unclear regularity, and that regional fracture development, in situ stress field and formation pressure have obvious effects on well leaks. The distribution of fractures, in-situ stress field and formation pressure in Changning block have a significant and highly responsive effect on lost circulation. The results of this paper reveal the complex mechanism of deep shale lost circulation in the Changning block and the main influencing factors, and provide a certain scientific basis for prevention and treatment of deep shale reservoir leakage in Changning block.

China is rich in shale oil resources. With the continuous breakthrough of exploitation technology, shale oil has become an important strategic oil resource in China. As it turns out, Multi-cluster fracturing technology of horizontal well is an efficient method to produce shale oil. However, most of the research on the initiation and propagation of fractures in shale reservoirs is based on numerical simulation. In this paper, through the improved true triaxial hydraulic fracturing physical simulation system, the rock multi-cluster fracturing physical simulation experiment, obtain the fracturing process parameters, and analyze the mechanism of fracture generation. The numerical model of fracture is established to analyze the interfracture interference phenomenon and optimize the segmenting and clustering problem. The results showed that: The larger the fracturing fluid viscosity is within a certain range, the smaller the probability of fracturing fluid leakage is, and the more conducive to the formation of fractures; Cluster spacing has a great influence on fracture propagation. Compared with double clusters, three clusters of fractures are more conducive to forming effective fractures. This paper comprehensively considers the multi-field coupling effect in the fracturing process, deeply understands the mechanical parameters of natural fractures, improves the understanding of the regularity of mechanical parameters of natural fractures under the multi-field coupling effect of fluid-solid-temperature, and provides further guidance for the optimization design of fracturing parameters.

China has abundant deep shale gas resources, but the complex problem of wellbore collapse in horizontal well drilling is prominent. Aiming at the problem of wellbore collapse in deep brittle shale, deep shale's mechanical loading simulation experiment scheme under a complex wellbore alternating mechanical environment was carried out. Triaxial mechanical tests of shale under different confining pressures are carried out in this paper. The stress-strain and acoustic characteristics of shale under different confining pressures during loading are analyzed, and rock's stress-strain and dynamic acoustic response mechanisms are discussed. The mechanical constitutive relationship, plastic brittle mechanical properties, and anisotropic characteristics of deep brittle shale under a complex mechanical environment of the wellbore are studied. The collapse failure law of deep brittle shale wellbore is also analyzed. The results show that the deep brittle shale has high mechanical strength, is highly brittle, and developed bedding fractures. Under the condition of low confining pressure, the stress-strain curve of shale before fracture is mainly elastic deformation, and the plastic mechanical damage is not obvious. With the increase of confining pressure, shale's compressive strength and elastic modulus increase, and its plastic damage gradually become apparent. In the process of triaxial loading, the change of acoustic wave velocity increases first and then decreases. With the increase of confining pressure, the peak stress point becomes smaller and smaller, revealing the plastic failure characteristics of rock under high confining pressure. The brittle features of shale under low confining pressure are obvious. The fracture morphology of rock after stress is mainly the splitting tensile fracture, and the number and size of cracks are significant. Under high confining pressure, shale exhibits plastic failure, and plastic damage characteristics are evident in the process of rock sample failure. Rock sample failure is mainly manifested as single shear failure or conjugate shear failure with tensile fracture. The experimental results show that the failure mode of brittle shale under a complex wellbore mechanical environment is mainly tensile splitting and shear coupling failure. The research results of this paper have particular guiding significance for the study of wellbore stability during drilling in the deep brittle shale formation.

Cuttings re-injection is an effective method to solve the accumulation of solid waste such as oil-based cuttings in offshore oil and gas fields, which has the advantages of low cost, high efficiency, and environmental safety. But, the slurry leakage events occur frequently due to the poor understanding of the fracture initiation and extension of cuttings re-injection in existing studies. This paper develops a rock cuttings intermittent re-injection simulator based on the open-source hydraulic fracturing software Pyfrac. The impact of different construction and formation parameters on the propagation of induced fractures was investigated through numerical simulations. The simulation results show that Young's modulus, Poisson's ratio and the magnitude of in-situ stress have less influence on the final scope of the fractures. The difference in-situ stress between the re-injection layer and the compartment, the viscosity of the re-injection fluid and the re-injection interval time have significant impacts on the length and height of the fracture. Therefore, in the actual construction process, the liquid viscosity and interval time can be adjusted to obtain the different scopes of induced fractures.

The tight sandstone reservoir of Shaximiao Formation of Middle Jurassic in Qiulin block of central Sichuan Basin, with a burial depth about 2200 to 2300 m, is characterized by undeveloped natural fractures. It is difficult to form complex fracture network during the implementation of traditional volume fracturing technology, affecting the benefit of tight sandstone gas development. A series of true triaxial hydraulic fracturing tests were conducted on the sandstone outcrop (dimensions: 300 mm × 300 mm × 300 mm), collected from this block, to investigate the initiation and propagation law of hydraulic fracture in tight sandstone reservoir under different conditions. Experimental results indicate that the peak value disturbance and increasing stress shadow in the back section of the pump pressure curve of staged multi-cluster fracturing in horizontal wells of sandstone reservoir will dominate the fracture morphology. The small interval leads to the increase in dynamic hydrostatic pressure on the fracture wall and increase in the deflection angle and degree of multi-cluster fractures, and it is easy to form crosscut fractures. The symmetrical middle segment perforation cluster inhibits the initiation and expansion of fractures, and the fractures will extend perpendicular to the maximum horizontal in situ stress direction and gradually approach the fractures on both sides and finally stop expanding. High-viscosity fracturing fluid is easy to form high hydrostatic pressure in the perforated section, reducing the difficulty of fracture initiation. The angle between the borehole and the minimum horizontal in situ stress ( σ h) will affect the propagation direction of hydraulic fractures. When the angle is large, the propagation direction of fractures is easily affected by the natural weak surface and induced stress field, resulting in fracture diversion. This study has mastered the initiation and propagation mechanism of artificial hydraulic fractures in tight sandstone reservoir, established the optimization chart of fracturing parameters in sandstone reservoir, and has certain guiding significance for the establishment of on-site fine optimization fracturing scheme design.

Large amounts of oil and gas resources are stored in carbonate rocks, and fracturing is an important technology to exploit carbonate reservoirs, The communication between artificial fractures and natural fractures is very important for the fracturing effect of carbonate reservoirs, The effect evaluation after fracturing lacks quantitative description. Therefore, it is necessary to study the fracturing effect evaluation of carbonate reservoirs. This paper analyzes the pressure curve obtained in true triaxial fracturing experiment. The communication with natural fracture and vugs in the process of fracture propagation is explored. Finally, the pressure curve characteristics of artificial fracture communicating with natural fracture cavity under different modes are obtained, and the communication between artificial fracture and natural fracture is identified.

There are abundant oil and gas resources in carbonate reservoirs of Tarim Basin, and more than 90% come from fractured-caved carbonate. These fractured-caved reservoirs are formed by the superposition of large fracture zone and karstification. The fractured-caved bodies generally appear in strips along the fracture zone and are distributed irregularly in vertical and horizontal directions. In addition, the ultra-deep burial (6500-7500m) leads to strong heterogeneity of the reservoirs. This paper presents using horizontal wells to cross the fractured-caved bodies is an effective means to improve the economic profit of oil and gas field development. Based on geomechanical study, the development mechanism of high-quality fractured-caved bodies can be determined, the contradiction between multiple fractured-caved bodies and safe drilling can be solved, and the reservoir stimulation plan can be optimized. The study can provide quantitative data basis for well trajectory optimization, prediction of drilling safety window, determination of maximum build-up slope in deviated section, how to use one well to cross multiple fractured-caved bodies and optimization of reservoir stimulation program. The results show that the ultra-deep carbonate reservoirs are affected by four factors: faults, fractures, irregular karst and in-situ stress, resulting in strong heterogeneity and anisotropy of reservoir. Therefore, the probability of high-quality fractured-caved bodies encountered by well trajectory drilling in different directions and depths is different, and the stability of wellbore in different directions and deviation is also different. When the drilling trajectory crossed the fault zone, it experienced a large range of in-situ stress, so the stimulation effect varied greatly in different well sections. The geomechanical study of ultra-deep carbonate reservoirs shows that the strike of the fault is similar to the present in-situ stress, and it is easier to develop high-quality fractured-caved bodies in relatively weak stress environment. Through the study of the relationship between fracture system and in-situ stress, it provides a method to optimize the well trajectory in consideration of both high-quality reservoir and drilling engineering safety.

On the basis of optimizing the best well trajectory, it can predict the safe drilling window more accurately, guide drilling through multiple fractured-caved bodies as much as possible, and implement reservoir stimulation effectively, laid a foundation for high-quality and high-yield drilling. So far, three carbonate reservoir oilfields' 3D stress modelling have been completed and applied to well placement, drilling and development. The average oil production per well exceeds 300 tons under 6mm nozzle conditions.

China has abundant coalbed methane (CBM) reserves, but the production of single well is rather low. The Ultra-short Radius Radial System (URRS) technique can drill multiple radial branch holes with hydraulic jetting to effectively improve the production of single well. The high-pressure jet nozzle plays an important role in URRS technique and the structure of nozzle directly affects the efficiency of radial drilling. This paper adopts the experimental study on breaking coal rock efficiency of the self-rotating multi-orifice nozzle with different structures. The uniaxial compressive strength, tensile strength and shear strength of experimental rock samples were tested and calculated. Using natural coal and briquette rock, number of experiments under submerged conditions were carried out. The effects of nozzle pressure, jetting distance, jetting time and jetting direction on rock breaking effect were studied. The experimental results show that natural coal rock has strong anisotropy and demonstrate the coal rock breaking efficiency of the self-rotating multi-orifice nozzle. The key findings are expected to provide theoretical and technical support for development of CBM reserves by using the URRS technique.

A reliable estimation of unplanned dilution is one of the most vital parameters in open stopping mining methods as unplanned dilution and sloughing can lead to an increase of the cost production and most importantly to safety concerns. Owing to this importance, several predictive models to estimate unplanned dilution and stope overbreak have been proposed. However, some of these existing models do not provide any physical meaning of the underlying dilution problem. To overcome this limitation, a fuzzy inference system (FIS) is proposed. In this paper, a new design tool capable of assessing unplanned dilution in a reliable manner is developed. The methodology relies on a fuzzy inference system (FIS) as many epistemic uncertainties that are associated with unplanned dilution are not systematically accounted for in existing methods. To this end, a dilution database from Ridder-Sokolny mine in Kazakhstan has been compiled. It consists of unplanned dilution cases and includes stope geometry, rock mass characteristics and stope reconciliation data. Subsequently, knowledge-based FIS was implemented. Overall, the results of the FIS show good classification performance (84% of accuracy). In comparison to the dilution graph developed based on traditional method, the FIS results show better performance. Hence, it was concluded that the proposed FIS could be an alternative tool for empirical open stope design.

Rock burst caused by mining-induced tremors is a dynamic disaster in mines that can cause great damage. Based on the mining-induced tremor that occurred at the MKQ Coal

Mine, Inner Mongolia Autonomous Region, China, on March 3, 2018, the present paper studies the mechanism of mining-induced tremor occurrence using theoretical analysis, numerical simulation, and focal mechanism. The study found four inferior strata and a primary key stratum in the overlying strata on LW3102, and discovered that upon breaking the key stratum movement releases a large amount of energy thereby causing the mining-induced tremor. When the internal stress of the coal pillar in the air-return way of LW3102 reaches 72.77 MPa, the static load stress concentration appears in the coal body near the air-return way, thereby facilitating easy coal body instability due to the overlay of the dynamic load, which in turn produces the rock burst. Based on the analysis of the moment tensor theory, this study finds the ratio of the moment tensor double couple part (MDC) of the strong mining-induced tremor focal to be 8.91%, indicating that the tensile fracture appears in overlying strata on LW3102, and a large amount of energy is released, thereby inducing the mining-induced tremor. The rock burst of the working face is controlled by applying control measures.

With the deepening of underground excavation, rockburst has become a serious geological disaster, which will always cause casualties, machine damage and delay of construction schedule. Therefore, many scholars at home and abroad have carried out researches on rockburst. Because the mechanism of rockburst is complex, and there is no unified understanding of its generation mechanism at present, thus it is hard to predict the rockburst happen or not and the intensity to guide for the underground engineering construction. Support Vector Machine (SVM) was used to classify the rockburst. Some main factors of rockburst, such as the maximum tangential stress σ_θ, the compressive rock strength σ_c, the tensile strength σ_t, the stress coefficient T_s, the brittleness coefficient of rock B, and the elastic energy index W_et were selected in the analysis. The factors were divided into two combinations: index I and II. SVM model and criterion were acquired through 36 training samples. Another 10 testing samples were used to evaluate the model. As a consequence, the evaluated results agree well with the measured record. No matter the training samples or the testing samples, the misjudgement ratio using the combination index I is smaller than that using the combination index II. It is suggested that using SVM model and the index I can classify the rockburst grade very well.

In view of the problem of rockburst in over-kilometer shaft, based on 220 rockburst cases at home and abroad, combined with forward and backward cloud generator to determine the each rockburst proneness evaluation index belongs to the certainty and reasonable numerical characteristics of each rockburst level. Indexes weight are determined by using the improved CRITIC method. An improved multidimensional normal cloud-critic rockburst proneness evaluation model is proposed. Compared with the evaluation results of the entropy weight method-cloud model and the cloud model for rockburst proneness based on the index distance and the uncertainty measure, which verifies the effectiveness of the model. At the same time, the magnitude of σ_θ/σ_c is obtained plays a dominant role in the occurrence degree of rockburst. Based on this, taking elastic strain energy, average energy release rate and plastic zone volume as evaluation indexes, the rockburst prevention and control countermeasures with reducing σ_θ/σ_c and energy release rate as the core are put forward: optimizing bore speed, implementing stress release holes on palm surface and bolt-shotcrete support. Optimizing bore speed can reduce the average energy release rate of surrounding rock; Uniform arrangement of stress release holes around the palm surface can effectively reduce the stress concentration behind the palm surface, and form a large low-pressure crushing zone around it. By bolt-shotcrete support, the energy release rate of surrounding rock of shaft wall can be reduced. The above three methods are jointly implemented to effectively prevent and control rockburst. The research results can provide an effective basis for identification of rockburst hazard area and establishment of prevention and control measures in deep engineering.

After coal mining into the deep, pressure bump and outburst coexist, which are mutual inducers and compounds that increase the mining risk and control difficulty. The hazard evaluation of compound dynamic disaster before mining can predict the dangerous area and take preventive measures to reduce casualties and property losses. This paper establishes a mechanical model of "stress surrounding rock gas support," taking into account the stress environment of coal body, impact tendency of coal body, gas pressure, roadway structure, and support stress. Taking, for example, 22220 working face of a mine, according to the history of composite dynamic disaster in the same level coal seam, the composite dynamic disaster evaluation grade is divided. The minimum critical stress index of composite dynamic disaster is taken as the medium risk evaluation standard, while the maximum is taken as the strong risk evaluation standard. The critical stress index of each area of the working face is calculated, and the risk grade is divided. The results show that the strong dangerous area of working face is mainly located in the open cut and the distance between the track transport and the open cut is 20∼250 m, and the medium dangerous area is mainly located in the air return roadway 40∼250 m. Compared with the comprehensive index method, the critical stress index method can predict the relationship between support strength, gas concentration after drainage, and composite dynamic disaster. Moreover, the evaluation results tend to be quantitative and conservative.

Uniaxial compression tests and acoustic emission (AE) monitoring on shale specimens with horizontal bedding planes and perpendicular bedding planes after subjection to high temperatures (25°C, 100°C, 150°C and 200°C) were performed to investigate the effect of high-temperature environment on shale in rock engineering. Results show that specimens in the two bedding directions experienced severe rockburst failure, and the increasing temperature made rockburst failure more intense. The rockburst phenomena for all the specimens were similar and consistent, including spalling, particle ejection and block collapse. Temperature had no significant effect on the failure mode of specimens with perpendicular bedding planes, while specimens with horizontal bedding planes turned to splitting with the increasing temperature. Fractal dimension of fragmentation increased with the increasing temperature, and that for specimens with perpendicular bedding planes increased much more than that for specimens with horizontal bedding planes. Before the peak, the cumulative AE counts can be divided into three stages by stress level of 40% and 80%.

A part of the elastic strain energy stored in Class II rock will be converted into kinetic energy, which results in rock ejection after the peak stress. This part of the strain energy is the intrinsic potential energy for strainburst. Therefore, the strainburst proneness of the rock can be quantitatively estimated by the intrinsic burst energy density or the corresponding intrinsic ejection velocity. This study aims to validate the idea of using the intrinsic ejection velocity as a strainburst proneness index by laboratory true triaxial compression tests. In the study, servo-controlled uniaxial compression tests were conducted on six types of rock. The intrinsic burst energy density of these rocks was determined based on the stress–strain curves of the rocks obtained under uniaxial compression. The strainburst proneness of the rocks was then assessed. The same types of rock were then carried out single-free-face true triaxial compression testing to examine the rationality of the evaluation result.

In view of the complex geological environment of deep buried tunnel, the great harm of rock burst, and the serious hidden danger to the underground engineering construction and the safety of the workers, it is necessary to adopt an effective method to reasonably predict the rock burst, so as to carry out the rock burst disaster warning. Based on the strength-stress ratio method, the possibility of rockburst in the deep-buried tunnel of Pingliang-Mianyang National Expressway is predicted in this paper. At the same time, the FLAC3D numerical simulation software was used to build a numerical model to simulate the excavation process of the deep buried tunnel, so as to analyze the stress state of the surrounding rock of the deep buried tunnel, and the ratio of the maximum principal stress σ₁ of the surrounding rock obtained from the simulation calculation to the uniaxial compressive strength R_c of the rock in the excavation process. According to the ratio, the possibility level of rockburst at different length sections along the deep buried tunnel is divided, analyzed and predicted, and compared with the actual situation of rockburst in the field, the results show that the location of rockburst and the rockburst level of the corresponding length are basically the same. This discriminant method can provide reference and relevant reference for rockburst prediction of similar engineering.

In underground mines, rockburst can cause significant damages to underground excavations and equipment, which impacts negatively mine safety and productivity. Hence, the establishment of model capable of predicting the rockburst damage in a reliable manner is essential. Despite the existence of the extensive number of predictive models for rockburst, a reliable prediction of rockburst damage potential is challenging. One of the main difficulties to predict rockburst with existing models is their inability to account for missing or incomplete data, which is commonly encountered in practice. To overcome this issue, in this paper, a Bayesian network (BN) approach is employed to develop a short-term prediction model for rockburst on the basis of mine seismicity monitoring data. A rockburst database consisting of 254 case histories was compiled. The input parameters include the stress conditions, ground support capacity, excavation span, effect of geological structure, peak particle velocity, and the output defined as the rockburst damage scale (RDS) index. The Tree Augmented Naïve Bayes classifier structure was implemented. The proposed BN was tested using 5-fold cross-validation. The practical use of the BN was illustrated as well. Overall, the BN results indicated acceptable prediction accuracies ranging from 70 to 78%. It was concluded that BN could represent a reliable predictor to control excavation damages due to mine seismicity, especially when incomplete data prevail.

The fracture mode under compressive shear loading is the research focus of rock fracture mechanics. In this paper, rock-like material with cracks was used to investigate its fracture mode. The physical and mechanical parameters of gypsum with specific paste-to-water ratio and curing time were measured by uniaxial compression test, and then, the shear box tests with loading angles of 0°, 15°, 30°, 45°, 60°, and 70° were carried out on gypsum specimens with initial double edge cut cracks. Finally, the strain field was monitored by the DIC method to analyze and summarize the phenomenon of crack initiation and propagation, and to analyze the fracture mode under shear box loading. The results show that the failure process of gypsum under uniaxial loading is a tensile split failure, and the fracture propagates through the entire specimen. Under the shear box loading, when the loading angle is less than 30°, the crack propagation presents a splitting tensile failure mode, that is, the crack propagation belongs to Mode I. When the loading angle is greater than 60°, the crack propagation shows shear failure mode after loading, that is, the crack propagation belongs to Mode II. While, when the loading angle is 45°, both the above two conditions exist, and the specimen presents both wing crack and secondary crack, in other words, the failure mode of the specimen is a superposition of shear fracture and tensile fracture. The research results can improve the understanding of the crack propagation mechanism of rock-like materials.

In situ stress has an important influence on the failure of rock in coal mines, but how to well utilize the test result of in situ stress to guide the engineering is still unclear. The stress to induce coal bursts was analyzed in this study. Based on the test principle of hydraulic fracturing, a quick-test device used in boreholes with an aperture of 31mm was developed to measure the in situ stress. An inversion software was programmed based on the multiple linear regression method to obtain the stress field. Lastly, three engineering cases were presented to introduce the application of the new technique, combining the in situ stress test and stress field inversion. The results show that the new method introduced in this paper is applicable for the evaluation of bursting risk, layout optimization of pre-mining, and mechanism analysis of coal bursts. It has a great significance for the safety of coal mines.

Rockburst is characterised by the wide occurrence areas and the long delayed time at a pumped storage power station in Heilongjiang province of China. For the study, a new method is proposed to identify the induced rockburst based on the combination of microseismic (MS) and electromagnetic radiation (EMR) monitoring methods. EMR monitoring method is introduced to make up for the shortcomings of the monitoring blind area caused by the propagation path of wave velocity during MS monitoring and a beneficial attempt is carried out for the comprehensive application of the two methods to monitor the rockburst. Firstly, a MS monitoring system is established around the underground powerhouse to recognize the propagation of micro-fracture during the deep excavation, while the typical five parameters including the frequency of the microseismic events, the total energy of daily events, energy index (EI), cumulative apparent volume (CAV) and microseismic signal b-value are analyzed to reveal the temporal and spatial evolution law of microseismic events. Secondly, an EMR monitoring system is also established near the MS events clusting area to study the characteristics of EMR produced from the fractured rock mass. The temporal and spatial variation of the two parameters including electromagnetic radiation intensity and pulse number are also analyzed and the distribution of higher values are compared with the geological structure. Finally, the correlation of electromagnetic signals, microseismic signals and local stress is studied based on theories of geophysics, electromagnetism and rock mechanics, and some credible results are obtained. Here are the following resluts: (1) The microseismic events are characterized by spatial clustering, and the joint action of the excavation disturbance and the weak structure body of the surrounding rock mass are the main factors for rockburst. The trend of sharp decrease of energy index and sudden increase of cumulative apparent volume generally indicates the occurrence of rockburst or macro-fracture. The magnitude of b value indicates that the rockburst failure type in the project belongs to fracture-slip rockburst. (2) The sudden change of electromagnetic radiation intensity in the fault fracture zone of the underground powerhouse can be used as the precursor information of rockburst or large-scale rupture events.(3) The micro-fracture activities revealed by EMR and MS methods are consistent in spatial distribution. The distribution of the peak values of electromagnetic radiation pulse number are basically consistent with the direction of the apparent stress migration disturbed by the field construction situation. So we can infer that it will play an important role to improve the accuracy of rockburst prediction based on the analysis of the multi-source singals.

Rockburst is a common dynamic disaster in underground engineering under high ground stress. A large number of rockburst examples show that there is a strong correlation between the instability failure of slab cracking surrounding rock and rockburst during the excavation process of hard and brittle surrounding rock. Seven cracks were made in a 150 mm × 150 mm × 35 mm granite cube sample, the lengths of cracks were reduced from the free face to the inside according to a certain proportion. The granite is cut to form a slab-like structure with the same thickness, and the slap cracking sample model was made. The uniaxial compression test was carried out on the cracking samples. Combined with the numerical simulation results, the crack initiation, propagation characteristics and failure process of the cracked rock samples were analyzed, and the relationship between the instability of the slab cracking surrounding rock and rockburst was revealed. The results show that the cracking of surrounding rock plate is easy to induce sudden rockburst disaster, but it also provides the possibility for monitoring and early warning of rockburst disaster. With the increase of the distance between surrounding rock and the excavation face, the failure mode of slab crack structure becomes complex and the degree of failure increases gradually. It is found that there are three types of failure mechanism in the process of slab rockburst formation. The rock slab on the sample that is a certain distance from the excavation frontage is the first to rupture. The failure of the rock slab far away from the excavation free face is relatively rapid, and its fracture mechanism is more complex, with the largest degree of damage, resulting in a large number of rock blocks and cuttings. The slabs close to the excavation face are mainly bent and broken, forming large blocks or slab-like blocks. Once the rock slab is bent and broken at the face of excavation, the slab-like rock block formed at the face of excavation and the inside of surrounding rock will pop out at a high speed instantly, resulting in a rockburst disaster. The results reveal the process of rockburst of slab cracking hard rock structure under high stress condition, which can provide a scientific basis for the prevention and control of rockburst.

In the present study, based on the geological information of the Yima Coalfield in Henan Province, People's Republic of China, a numerical model composed of five mines with F16 large thrust fault and extremely thick conglomerate is constructed. Next, a self-developed parallel program, i.e. CASRock, is applied to simulate the mining process in different mines and investigate the associate mechanical behavior. The evolution of displacement, stress and plastic strain of rock mass under different mining conditions of the mine group in the Yima Coalfield are thoroughly demonstrated. The results reflect the interactions in mechanical behaviors between neighboring mines. These interactions are strengthened due to the existence of the overlying extremely thick conglomerate and F16 large fault. The stress transfer via the large geological body in large-scale goaf is the main reason for the high stress concentration of the adjacent working faces.

The first impounding process in the foundation pit of an arch dam will lead to stress redistribution, and the working state of the dam needs to be reanalyzed. Taking the Wudongde Arch Dam under construction in China as the engineering background, ABAQUS finite element analysis software simulates the dam stress distribution and transverse seam opening of Wudongde Dam under four different impounding elevations. According to stress distribution and the opening degree of transverse seams, the optimal impounding elevation with the most negligible influence on the joint grouting process is determined. The simulation results indicate that the pressure generated by impounding will increase the dam deformation to the downstream river and banks. The maximum compressive stress of the upstream dam heel and the maximum tensile stress of the left and right arch abutments would decrease to some extent after impounding. The transverse seams have a tight compression tendency after impounding, and this tendency increases as the water level rises. According to the simulation results, the working performance of the dam is the best when the elevation difference between the impounding elevation and the joint grouting elevation is 36 m. Timely impounding is beneficial to the stress state of the dam and joint grouting process during the construction period.

Considering the difficulties encountered during the evaluation of the pile-soil interface parameters for the offshore wind power project, direct shear test, soil-structure interface shear test and the numerical analyses were carried out. Through these the pile-soil interface characteristics and influencing factors were revealed. Based on the direct shear test and soil-structure interface shear test results, the strength of the soil-structure interface was found to be less than that of the internal strength of the soil, most stress-displacement curves of the interface shear test presented strain softening, where the interface strength decreased after reaching the peak value to a stable residual strength. On the contrary, strain softening was unlikely to be discovered directly on the shear test. The material impacts and roughness on the soil-structure interface and the shear strength was found when a reduction factor was introduced to quantify the shear strength of the soil-structure interface, with a range of 0.53∼0.83. Combined with numerical analysis, stress concentration is generated at both the edge and the center of the shearing surface. The shear stress and shear displacement decreased gradually from edge to center of the shearing surface, and the shear displacement was strongly related to the size of the shear fracture.

The innovative excavation based EGS (EGS-E) scheme uses mining techniques to form deep underground access for creating artificial heat reservoir with multi-level fracture networks using excavation, blasting, and caving. The two-level heat transfer mechanism of distributed artificial heat reservoir has a dominant influence on the performance of excavation based Enhanced Geothermal System(EGS-E). However, due to the large-scale field testing and laboratory physical experiment are not yet realistic, the process of natural convection heat transfer within the surrounding rock enhanced permeability and water filled zones hasn't been effectively studied. The simulation software COMSOL Multiphysics was used to numerically simulate the natural convection heat transfer within the enhanced stimulated surrounding rock around a single straight roadway with its circular opening, which should be an elemental unit for mining heat in deep underground engineering structure. The simulation results demonstrated that the temperature difference inside the surrounding rock of a roadway causes the density of working fluid to vary. Driven by buoyancy, the natural convection of working fluid occurs in the surrounding rock. It enhances the heat transfer inside hot dry rock, and its efficiency is significantly more remarkable than that of the conduction through hot dry rock itself, which can improve the efficiency of heat recovery with regards to EGS-E. Due to the low solid heat conduction efficiency of the surrounding dry hot rock, adjusting the speed of the water flow inside the pipe can effectively control the temperature of the water outlet to improve the heat collection life of the system.

Shallow geothermal energy has received extensive attention as renewable energy for sustainable development in the last few decades. Thermal conductivity, usually estimated in-situ by thermal response test (TRT), is a key parameter for evaluating shallow geothermal energy resources and designing boreholes heat exchanges. However, it is still challenging to collect accurate data about strata thermal conductivity. With the application of copper mesh heated optical cable, actively heated fiber (CMCH), optics based thermal response test (ATRT) offers the possibility of fast and accurate in-situ estimation of thermal conductivity. However, the heat transfer process of ATRT is different from the traditional TRT and there is no standardized ATRT method yet. In this study, the influences of heating duration, heating power and recover time were studied using a physical model box. The results indicate that: (1) A more accurate calculated thermal conductivity requires a longer heating duration, considering the costs and errors, the heating duration is recommended to be in the range of 90∼400 minutes. (2) The heating power has no significant effect on the calculated thermal conductivity but 15∼40 W·m⁻¹ is recommended considering the measurement accuracy of DTS equipment. (3) If ATRT was interrupted, there should be a recover time longer than 24 hours before the following ATRT to avoid the interference of the previous test.

The abundant CBM in fractured soft and low-permeability coal is expected to be exploited by indirect fracturing coal technology. However, this technique often fails because the coal-rock interface hinders the hydraulic fractures (HFs) propagation. This article focuses on the root cause of the above phenomenon, that is, the mechanical properties of coal. Its ductile fracture-seepage relationship was deduced by the Park-Paulino-Roesler potential energy function and combining with Forchheimer equation. The elastoplastic damage-seepage relationship of coal matrix can be derived by combining damage mechanics, plastic mechanics and seepage experimental results. The numerical simulation results showed that the mechanism of the coal-rock interface hindering the HFs propagation lied in the large amount of hydraulic energy dissipation caused by ductile fracture of discontinuities and plastic damage of the coal matrix, which results in the proportion of elastic energy contributing to HFs propagation as low as 2% of hydraulic energy. However, this ratio will increase to 18%∼30% as interface friction, stress difference and injection rate increase, especially the distance between horizontal well and interface decrease. This finding is of great significance for the CBM extraction in the fractured soft and low-permeability coal through indirect fracturing coal technology.