Field research on supersized rectangle pipe-jacked tunnels beneath a navigable river in the urban area

With technological progress in recent years, supersized rectangular jacked pipe tunnels have been increasingly used for developing urban road-crossing nodes, owing to their convenient construction and economic benefits. However, owing to the weak waterproofing performance of the joint, jacked supersized rectangular pipes have been employed beneath a navigable river. This study used on-site monitoring data of an underground expressway with supersized rectangular jacked pipe tunnels in Shanghai. Additionally, we analyzed the deformation of the ground surface and embankment and the mutual influence of jacked adjacent pipes. The results revealed the following. 1) the over-excavation of the jacked pipe causes partial surface subsidence. The jacking parameters were adjusted through feedback to control the surface deformation. 2) The spatial deformation of the old embankment were stabilized, suggesting the successful realization of micro-disturbance jacking construction. 3) The secondary disturbance of the soil due to post-construction causes a slight sinking and tilting trend of the former jacked tunnel.


Introduction
The traditional open-cut method has gradually been replaced by non-excavation technology owing to the influence of urban aesthetics and the interruption of ground traffic.The rectangular pipe jacking method (RPJM), a trenchless construction technology, significantly aids in guaranteeing traffic smoothness and maintaining an urban style.The rectangular pipe jacking technology was first successfully applied in the 1970s to cross the Tokyo subway passages in Japan.This technology has undergone rapid development in China despite its relatively late introduction in the country.With the increase need for developing and utilizing underground spaces in urban areas, rectangular pipe jacking technology has been widely employed in diverse applications, such as urban underground pedestrian crossing tunnels [1], entrance tunnels of subway stations D], municipal underground roads and railways [4][5][6], and utility tunnels [7][8][9].Rectangular jacked pipe tunnels often feature large cross section to satisfy the demands of expressways and large traffic volumes.For example, the width of a pipe used for a project in Zhengzhou exceeded 10 m [1], while in Jiaxing, it astonishingly reached 14.8 m [10].
Pipe-jacked tunnels typically employ an "F-shaped" pipe-socket joint.The waterproofing performance of the joint depends on the extrusion force between the steel plate and rubber ring [11], which is well-suited for circular tunnels.However, significant differences are observed in the stress states between rectangular and circular tunnels.The waterproofing performance of the joint degrades 1333 (2024) 012018 IOP Publishing doi:10.1088/1755-1315/1333/1/012018 2 as the size of the rectangular section increases.Therefore, in some cases, the jacking method for supersized rectangular pipes has been adopted beneath a navigable river [12].
This study analyzed the deformation of the ground surface and embankment and the mutual influence of adjacent jacked pipe construction, using on-site monitoring data of an underground expressway with supersized rectangular jacked pipe tunnels in Shanghai.

Project Overview
The Zhuowen Road Tunnel, extending from Zhangheng Road in the north and to Zhongke Road in the south, is located at the heart of the Zhangjiang Central District in Shanghai (figure 1).The tunnel has a total length of 800 m, with four lanes in both directions.2.1.Background RPJM was employed for constructing two parallel tunnels beneath the Chuangyang River.The launch and reception shafts were placed on both sides of the river, as shown in figure 2. Each tunnel had a length of 106.2 m and was separated by a net distance of 5.6 m.Two tunnels were built using a jacking machine, and the western line (WL) was prioritized for construction.
The cross-section of the tunnels measured 10.06 m, 5.26 m, and 0.7 m in width, height, and thickness, respectively, (figure 3), adhering to the construction clearance standards.Otherwise, a single pipe had a length of 1.5 m.

Soil characteristics
As shown in figure 4, the depth of the tunnels changes significantly.The overburdened soil of the tunnels in the land section exceeds 11m, while the shallowest cover in the underwater section was less than 6m.Table 1 presents important properties of the soil layers.Furthermore, the stable groundwater level in this area was +2.12-+4.32m, whereas the water level of Chuangyang River was +2.50-+2.80 m.Table 1.Properties of the relevant soil layers.

Monitoring plan
Figure 5 shows a schematic of the monitoring points fixed on the surface and old embankment.We obtained 63 points to monitor surface subsidence and the prefix DB was used to represent a point.These points were divided into nine sections along the jacking direction: five on the north bank of the Chuangyang River and four on the south bank.The jacking construction must cross beneath the old embankments on both sides of the river, which were built long ago using gravel and bricks.To determine the effect of jacking, 12 points, identified using the prefix GZW, were arranged on both sides of the embankments, as shown in figure 5.The deformation data were recorded in three directions for all points.The X-, Y-, and Z-directions were oriented along the axis of the tunnels, perpendicular to the axis of the tunnels, and vertical direction, respectively.The net distance between the two tunnels was less than the horizontal width of the section, and the tunnel construction has a mutual influence.Therefore, deformation-monitoring sections were set up in the WL, with four points in each section, as shown in figure 6.The points were placed after every five pipes.

Data discussion
4.1.Surface subsidence Figure 7 shows the cumulative settlements of DB3-3, DB3-6, and DB3-8 during the construction of the WL, and figure 8 shows the surface deformations sustained by these points when the jacking machine passed the monitoring section of DB3 (from APR 23 rd to APR 29 th ).As can be observed from figures 7 and 8, all curves exhibit the same variation characteristics.The closer a point is to the excavation surface, the more pronouncedly its deformation fluctuates.The maximum deformation of DB3-6, right above WL is, −16 mm, which is observed when the tunnel face passes the point.Subsequently, the deformation remains stable at −10 mm.
This accounts for the abrupt reduction in soil strength observed when the jacking machine exits the reinforcement area.However, the construction parameters were not adjusted in time.Moreover, the mud was not replenished over time in the over-excavated area.Surface deformation was successfully stabilized by adjusting the parameters and increasing amount of the grout.According to the experience of preliminary construction, the surface settlement due to the subsequent construction was effectively reduced.Figure 9 shows the cumulative settlement from DB6-3 to DB6-6 during the construction of the EL.Overall, the curves tend to be straight, and the cumulative deformation was less than 2 mm.

Deformation of the old embankment
Figures 10 and 11 show the vertical deformations of the north and south old embankments, respectively, when the jacking machine passed the embankments during the construction of WL.The curve behavior depicted in figure 10 are essentially the same as those shown in figure 7.However, owing to grouting, the deformations increase when the tunnel face exits the embankment.
According to the experience of the preliminary construction, the vertical deformations of the old embankments in the south was effectively reduced.The cumulative settlement of each point shown in figure 11 was less than 2 mm, indicating the successful realization of micro-disturbance jacking construction.Figure 11.Vertical deformation of GZW2-5-10 Figures 12 and 13 show the spatial variation of the points GZW1-5 and GZW2-5, respectively, when the jacking machine passed the old embankments during the construction of EL.As can be observed, the two points exhibit minimal deformations in all three directions.Further, the deformations are controlled within 2 mm.Nevertheless, the deformations in the X-and Y-directions are slightly higher than that in the Z-direction.Moreover, the deformation in the X-direction is uniform and consistent with the jacking direction, possibly influenced by the earth pressure at the tunnel face.By contrast, the deformation in the Y-direction is random, potentially owing to the structural form of the embankments.Figure 13.Spatial variation of GZW2-5 (Tunnel face on AUG 21th is 3m in front of old north embankments; Tunnel face on AUG 24 th is just beneath old north embankments; Tunnel face on AUG 27th is 3m behind old north embankments).The above data analysis revealed that jacking construction had a particular effect on old embankments.However, micro-disturbance jacking construction was realized when optimum construction parameters were employed.

Influence between pipes
Table 2 presents the deformation of the 1#, 36#, and 71# pipes in WL observed when the construction of the EL was completed (the number of pipes is shown in figure 2).Evidently, pipes 1# and 71# are not affected by the connection between the shafts and pipes.In comparison, pipe 36# undergoes

Conclusions
The following conclusions were drawn from the study.1) Improper construction parameters, over-excavation, and insufficient grouting cause surface subsidence to a certain extent.The closer a point is to the excavation surface, the more acutely its deformation fluctuates.
2) According to the experience of preliminary construction, surface deformation can be effectively reduced by adjusting the parameters and grouting the pipes with the optimum amount of mud.
3) Data analysis revealed that jacking construction strongly affected old embankments.However, micro-disturbance jacking construction was realized when optimum construction parameters were employed.
4) Although the mud around the WL was solidified and the tunnel deformation stabilized before the construction of EL, the construction of EL through pipe-jacking caused a secondary disturbance to the existing pipe-jacked tunnel, with pronounced effect on middle pipes, which had weak constraints.This caused the pipes to sink and approach the EL.

Figure 5 .
Figure 5. Diagram of monitoring points fixed on the surface and the old embankments (Unit: m).The net distance between the two tunnels was less than the horizontal width of the section, and the tunnel construction has a mutual influence.Therefore, deformation-monitoring sections were set up in the WL, with four points in each section, as shown in figure6.The points were placed after every five pipes.

Figure 6 .
Figure 6.Diagram of monitoring points in WL.

Figure 7 .
Figure 7. Surface deformation of DB3-3, DB3-6, and DB3-8 during the construction of WL. (Tunnel face on APR 23 rd is 4 m in front of DB3; Tunnel face on APR 27 th is just beneath DB3; Tunnel face on APR 29 th is 5 m behind DB3).

Figure 9 .
Figure 9. Surface deformation from DB6-3 to DB6-6 during the construction of EL. (Tunnel face on AUG 24 th is 6m in front of DB6; Tunnel face on AUG 26 th is just beneath DB6; Tunnel face on AUG 28 th is 6m behind DB6).

Figure 12 .
Figure 12.Spatial variation of GZW1-5 (Tunnel face on AUG 5 th is 3m in front of old north embankments; Tunnel face on AUG 8 th is just beneath old north embankments; Tunnel face on AUG 10 th is 3m behind old north embankments).

Table 2 .
considerably larger deformations, which results in its sinking and approaching the EL.Before the construction of EL, the mud around WL had been solidified and the tunnel deformation stabilized.The results presented in table 2 indicate that the pipe-jacking construction of EL caused secondary disturbance to the existing pipe-jacked tunnel, significantly affecting the pipes in the middle, which had weak constraints.Deformation of 1#, 36#, and 71# pipes of WL when construction of EL is completed.