The impact of blast vibration on the site response

In civil engineering, one of the main problems is the stability of structures. Blast vibrations can be one of several elements influencing the stability of these structures. In order to prevent any effects on the structures, the maximum suggested values of the peak particle velocity and frequency from the blast are generally determined using the existing appropriate government rules and industry standards as reference. In this paper, the effect of these vibration on the site response has been investigated. Parameters such as peak ground acceleration, Pseudo spectral acceleration and maximum stress and strain has been compared for two different soil models. The results indicate that the soft soil has a significant impact and amplifies the input parameters considerably.


Introduction
Explosive materials, which have been used for different purposes since ancient times, have started to be used in the construction sector over time, apart from military and defense purposes.Explosive materials, which cause great damage when used for military and defense purposes, have been found worth using in rock excavations when used for the right purposes.With the developing technology, drilling equipment has developed.explosive materials started to be mass produced and became affordable.Thus, excavation has made by drilling and blasting method started to be used on a large scale and even became widespread.In large-scale construction projects (Tunnels, airports, dams, high standard highways, etc.) where mechanized excavation (earthmoving works) is not feasible, it has been preferred because it is advantageous in terms of time and cost [1].The ability to disable primary crushers and target mass displacement is also an ultimate engineering ideal.The planning and execution phases of this type of project with drill-blasting are of a different dimension compared to other excavation methods.It usually consists of drilling of holes, charging and blasting, loading, transportation, crushing-grinding [2].Before starting these operations, which we call blasting excavation, the geological characteristics of the site, the energy required for excavation, the amount of production and the required time are calculated.Then, planning is made and a list of equipment supply list is made in accordance with the required number and purpose.During the working period, blasting records are kept and working methods are continuously examined and improved if necessary.These drilling-blasting activities, which are methods of soil loosening or direct excavation, have become widely used because they are more advantageous in terms of cost and time compared to conventional methods such as mechanized excavation (earthmoving works), which are limited by the material-mass properties of soils and the technology of use.Today, 1304 (2024) 012005 IOP Publishing doi:10.1088/1757-899X/1304/1/012005 2 drilling and blasting is used in areas such as foundation excavations and tunneling activities.It is applied together with the control of environmental factors.

Effect of Environmental Factors
There are four different disadvantages of bastings which are rock particles throwing around, dust emission, ground shaking and noise.These negativities of blasting activities, which have started to be carried out in urban areas in parallel with population growth and urbanization, cause environmental problems.Explosive excavation is inevitable in activities such as tunnels, subways, foundation excavations, dams, etc.The increase in the size and capacity of these activities also affects the amount of explosive material.For this reason, since they are often close to settlements, ground shaking and noise cause environmental problems.Considering the safety of life and property and psychological problems, it should be taken into account that such problems should be prevented or kept below the danger limits during blasting.The most important feature expected from a good blasting is to be safe in terms of environmental impacts.Standards have been established in most countries for environmental problems arising from blasting excavations.However, complaints about ground shaking and the noise have not been prevented [3].
When the explosive placed in a hole is detonated, it releases a huge amount of energy through pressure (up to 50 GPa) and temperature (up to 5000 K). 20-30% of this energy is used for fragmentation and displacement of the rock mass, while the remaining energy is used for impacts such as ground shaking, noise, excessive fracturing and back cracks [3].In other words, a very small fraction of the energy released by blasting is absorbed for fragmentation and translation.The damped energy spreads as seismic waves from the blasting source and causes negative environmental impacts.Blasting-induced ground shaking generates transient (short-term) and irregular ground motion.The velocity of motion in soil particles starts from zero, reaches its highest value and gradually dampens.The most important issue in ground shaking investigations is the maximum particle velocity.Because as the highest velocity value increases, the shaking intensity of the structure will also increase.In places close to the blasting zone, the characteristics and nature of ground shaking are affected by blast design, hole layout, explosive quantity, firing interval and firing direction.In short, particle velocity is an important damage indicator.Away from the blasting zone, the characteristics and nature of ground shaking are influenced by the characteristics of the rock or soil environment.The frequency and terrain coefficients of ground shaking are also important factors in determining whether or not damage occurs [4].

Damage Classification
Blasting damage criteria developed by different researchers working on blasting in the world are still applied today.These researches have been analysed under two main headings: Identification, measurement and parameter analysis of blasting-induced vibration and noise; appropriate blasting design by determining damage criteria for various structures and matching these criteria with postblasting parameters.Due to the variation of the criteria in different countries, a unified table has been prepared as a source for reference and evaluation in applications.Some of these parameters are the damage criteria of the US Bureau of Mines (USBM) [5] and the German DIN 4150 Standarts [6].The damage classification scheme established by the USBM is given in Table 1.In order to prevent blasts in mines, quarries and similar activity areas from damaging the surrounding structures, the vibration level to be measured on the ground, except for the nearest structure, cannot exceed the values given in Table 2. Measurements are made in three directions and the highest of these is taken.Vibrations are measured as peak values in 1/3 octave bands [7].
Table 2.The highest permissible values of the ground vibrations that will be created outside the closest structure of vibrations to be caused by blast in mines and quarries and similar areas in Turkey [7] Structural Type The highest rate of vibration on the base of building (mm/s)

Equivalent Linear Method (EQLM)
The Equivalent linear analysis, based on the SHAKE program, is a practical type of analysis developed to accurately model soil behavior under dynamic loads.Shear modulus and damping ratio are used as iterative parameters.Thus, an equivalent linear site -response analysis is performed which shows the dynamic properties of the soil [8].Equivalent linear analysis, which reflects the nonlinear behavior of the soil, was developed in 1972 by Schnabel et al. to capture the inelastic response of the soil [9].Huang et al in 2001 showed that equivalent linear analysis gives higher maximum acceleration values than linear analysis [10].The reason for this is that the calculations can be performed at higher frequencies [11].Equivalent linear analysis method is among the most widely used methods for analyzing site response under dynamic loads [12].The major disadvantage of equivalent linear analysis is that the results become too biased in the face of increasing strains.In soft or liquefaction-prone soils, there are significant differences between the results of transient nonlinear analysis and equivalent linear analysis [13].Therefore, equivalent linear site-response analysis is not used at high strain levels.In case of high strain levels, it is recommended to perform nonlinear site-response analysis to obtain more accurate results [14].
Unit weight (γ), shear wave velocity (Vs), damping ratio (D) and seismic loading are the input parameters used in the equivalent linear analysis.For each soil layer, the shear modulus (G) and damping ratio (D) are calculated based on the shear strain [15].There are also nonlinear soil parameters that are usually described by the shear modulus reduction (G/Gmax -γ) and damping ratio (D -γ) curves.These soil parameters can be calculated by laboratory tests with undisturbed specimens.The limit of γ max is recommended to be 1% for the equivalent linear method to be useful in a limited shear stress range [16,17].The equivalent linear analysis method models the nonlinear and hysteretic stress-strain behavior of soil layers under cyclic loading.Where, the shear modulus is the secant shear modulus (Gsec).

𝐺𝑠𝑒𝑐 = 𝜏𝑐 𝛾𝑐
(1) In the equation, τc is the shear stress and γc is the shear strain amplitude.In other words, the secant shear modulus varies depending on the strain amplitude.The equivalent linear damping ratio (D) is the damping ratio that shows the hysteretic behavior of the soil layer in a single stress-strain cycle without repeated loading [17].Also, in this type of analysis, the representative values for the damping ratio (D) and the secant shear modulus (Gsec) are varied until they are consistent with the strain level in the soil [9].

Identification of blasting-induced ground motion in time domain
Ground motions and noises measured in three dimensions during the blasting operations were recorded by the device.Vibration meter devices can record at 5 millisecond (0.0005 second) intervals for the desired duration.In these studies, which are generally recorded in the range of 2-4 seconds, the device measures particle velocity.The output of the device consists of four columns.The first three columns show the ground motion while the fourth column shows the noise (dB).The value with the highest particle velocity among the values measured in three dimensions is the maximum particle velocity (PPV).The data obtained as a result of the measurements are taken from the devices and transferred to the computer.Acceleration records were started by creating time history from the programs specific to each brand of device.The maximum particle velocity values selected were chosen to be suitable for "structures such as houses, bricks and concrete" and "industrial structures", which are determined by the limit values of the regulation prepared by the Ministry of Environment, Urbanization and Climate Change of the Republic of Turkey [7].In this standard, concrete buildings and industrial buildings are categorized based on their functions: Concrete structures are located in cities and industrial buildings are supposed to have only industrial functions.

Properties of soils used in the study
In this study, two soil profiles were defined, one using the drilling data obtained from the field and one using the equation.The soil profiles were subjected to blasting data records.These blasting data were selected according to Environmental Noise Control Regulation of Republic of Turkey, Ministry of Environment, Urbanization and Climate Change.Under standard conditions for "durable structures such as houses, bricks and concrete" which has around 1-10 Hz limit value blasting data is rc1, 10-50 Hz limit value blasting data is rc2 and 50-100 Hz limit value blasting data is rc3.Again, according to these standards for industrial buildings, which has around 1-10 Hz limit value blasting data is i1, 10-50 Hz limit value blasting data is i2 and 50-100 Hz limit value blasting data is i3.The behavior analysis of soils under these dynamic loadings was modeled with DeepSoil v7.0.The DeepSoil program used for this study is based on the principle of one-dimensional soil behavior analysis.DeepSoil program, first developed in 1998, is capable of both frequency and time domain analysis and equivalent linear and nonlinear analysis [8].A total of 12 equivalent linear analyses were performed using 6 different blasting data.
A total of 2 soil models were used in the study.In the soil models used, the unit volume weight γ=24.0 kN/m 3 [19] was selected for the bedrock, the shear wave velocity was defined as 900 m/s and the damping ratio was defined as 5 in the soil models formed with rock.Soil 1 comprises a two-layer soil and soil 2 has 13 layers and has been defined as Vs= 120×(1+d) 0.32 .d shows the depth in this formula.Soil 1 is adopted from a Multichannel Analysis of Surface Waves (MASW) [20].The soil 2 has been adopted from Dehghanian and Yılmaz [21].The parameters determined for the soils are given in table 3. One-dimensional dynamic field behavior analyses were defined by dividing the soils into sub-layers rather than single layers due to the detailed representation of the shear wave velocity variation while creating the soil models defined in Deepsoil v7.0, a C++ based one-dimensional seismic hazard analysis program.

Analyses
Deepsoil program soil profiles exhibit different behavior under static and dynamic loading.Soil profiles subjected to dynamic loading show stress-strain behavior.Dynamic loadings that generate shear stresses and shear deformations affect the soil behavior.The resulting deformations cause nonlinear behavior and the soil behavior supporting the foundations of the structure can affect the structural damage that may occur.When performing field response analyses, stiffness and damping ratio reduction curves as well as shear wave velocity values are used as dynamic soil parameters in equivalent linear analyses.For rocky and sandy soils, Seed and Idriss [22] developed attenuation curves.These attenuation curves were prepared for 3 different cases according to relative densities.These are; "Lower Limit" curves for relative frequency values lower than 30%, "Mean Limit" curves for values between 30% -60% and 6 "Upper Limit" curves for values higher than 60%.For clayey soils, Vucetic and Dobry [23] have prepared the attenuation curves.These attenuation curves depend on the plasticity index.

PGA
Figure 1 shows the variation of Peak Ground Acceleration (PGA) with respect to the depth for soil model 1 and 2 respectively for concrete and industrial buildings.It can be seen that PGA is maximum at the surface.As the depth and the stiffness of the soil increases, the Peak acceleration decreases.In soil model 2, a soft layer has been embedded between two stiff layers.It can be seen that the PGA shows a sudden increase in 15 m depth.The trend is similar for both building types.

Max Stress and strain
Figure 3 shows the distribution of maximum stress with respect to depth.Figure 4 demonstrate the variation of maximum strain with respect to depth as well.It can be concluded that in both figures, the maximum of the parameters occurs at the surface and the values decrease with the increase in depth.For soil 2 there is a sudden increase at 15 m depth in which a soft layer is located between two stiffer layers.

Conclusions
Based on the results of the site response analysis, it is evident that the soft layer, affects the natural frequency of the blast waves.It was shown that, while maintaining all other characteristics, the natural frequency of the blast wave progressively switches to substantially lower frequencies as the Vs decreases.Natural frequencies tended to be lower for more vertical slopes as opposed to greater for flatter slopes.Another significant finding was that the maximum strain and stress are affected considerably by the soil layer specifications.The amplification results show a high amplification ratio specially at low frequencies.The behaviour differs for industrial and concrete structures due to the variation of the highest rate of vibration on the base of building as it is indicated in table 2.

Figure 1 .Figure 2 .
Figure 1.(a) PGA at limit values for durable structures such as houses, brick and concrete on Soil 1, (b) PGA at limit values for durable structures such as houses, brick and concrete on Soil 2, (c) PGA at limit values for industrial structures on Soil 1, (d) PGA at limit values for industrial structures on Soil 2

Figure 3 .9Figure 4 .
Figure 3. (a) Maximum Stress at limit values for durable structures such as houses, brick and concrete on Soil 1, (b) Maximum Stress at limit values for durable structures such as houses, brick and concrete on Soil 2, (c) Maximum Stress at limit values for industrial structures on Soil 1, (d) Maximum Stress at limit values for industrial structures on Soil 2

Table 1 .
[5]age Classification[5] brick falls in chimneys, decrease in loading capability1.2.1.Environmental Noise Control Regulation of Republic of Turkey, Ministry of Environment, Urbanization and Climate ChangeTurkey has a regulation with reference values such as USBM damage criteria and German DIN 4150 standard under the title of "Environmental Vibration Assessment", the principles regarding the control of environmental vibration caused by various vibration sources are given: