Study On Surface Deformation Caused By Shallow Buried Pipe Jacking Construction In Electric Power

Pipe jacking construction has the advantages of small footprint,short construction period and low economic cost,and is widely used in pipeline laying projects.And pipeline excavation will inevitably cause road deformation and collapse hazards.This paper relies on the 110 k V Bijiang power transmission and transformation pipe jacking project in Shunde area of Foshan to investigate the surface deformation caused by the construction of shallow buried small diameter pipe jacking tunnels in saturated silty clay strata.The main work content and research results are as follows:(1)Read and study the relevant literature and books in the field of pipe jacking engineering,analyze the reasons for the construction of the pipe jacking tunnel,summarize the disturbance mechanism of stratum loss and soil reconsolidation,and obtain the space of the surface deformation disturbance zone and the lateral subsidence range.Effect and time variation of longitudinal deformation of soil.(2)Using ABAQUS finite element software,a three-dimensional tunnel model with a jacking distance of 18 m and a pipe diameter of 1.84 m was established.The results show that the vertical displacement of the soil cross section is consistent with the Peck settlement tank formula,and the horizontal displacement at the pipe axis is the largest,The soil moves away from the pipe and is extruded laterally,while the top and bottom of the vault move towards the pipe.In the axial direction,the soil formation loss near the tool tube nose has a negative axial displacement,while the front and subsequent tube sections of the tool tube have a positive axial displacement under the action of friction and positive thrust.The soil stress change curve presents an "M" shape,the soil stress on the side of the pipe increases,while the soil stress above and below the pipe decreases.The influence of different working conditions on the surface settlement was compared,and the value of grouting pressure was discussed.It was found that when the grouting pressure was 0.9?1.1 times the weight of the overlying soil,the soil layer disturbance was small.The stress of the soil above and below the pipeline is released,resulting in negative excess static pore water pressure,but the stress release of the soil at the top of the vault is smaller than that at the bottom of the vault,and the soil on the side of the pipe and in front of the tool pipe is subjected to grouting pressure and the support of the pipe body.A positive excess pore water pressure is produced.(3)Carry out the indoor thixotropic mud ratio and direct shear test,combined with the control variable method,to study the influence of each component content of the mud on the performance,and the optimal mix ratio is bentonite: CMC: soda ash: water = 8%:0.10 %: 0.05%: 91.85%,at the same time,the mud and undisturbed soil were mixed in different proportions,and the direct shear test was carried out with the C50 concrete slab,the drag reduction effect of the thixotropic mud was analyzed,and the 1.5: 1 mixing ratio of the mud and soil was obtained.The pipe wall friction The coefficient is 0.2247,and the friction coefficient between the undisturbed soil and the pipe wall is reduced by about 49.6%,and the drag reduction effect is good,which is in line with the actual engineering experience.At the same time,through the test of the model box made of acrylic glass plate,we have a qualitative understanding of the surface deformation law of pipe jacking construction.