Numerical Simulation Research On The Influence Of Deep Foundation Excavation Engineering Of Subway Station On Surrounding Environment Deformation

The deep foundation pit engineering of subway station is often located in areas where buildings and underground pipelines are distributed densely.It is of great significance to study the influence of deep foundation pit engineering of subway station on the surrounding environment deformation.This paper,which is based on the deep foundation pit engineering of a subway station in Nanjing,analyzed the impact on the deformation of surrounding environment by numerical simulation,and used ABAQUS software to put forward and optimize the deformation control scheme for the surrounding environment of the foundation pit.Based on the analysis of the monitoring data,the rationality of the numerical simulation results was verified.The main work of this paper is as follows:1.According to the results of numerical simulation,the influence rule of the foundation pit construction on the deformation of adjacent buildings and underground pipelines was explored.The results show that the building tends to incline towards the middle and inside of the foundation pit;attention should be paid to the buildings close to the foundation pit,whose settlement and inclination are obviously larger than other buildings;the deformation distribution curve of the underground pipeline along the length of the foundation pit is approximately U-shaped;for the shallow buried pipeline adjacent to the foundation pit,the buried depth and the distance to the foundation pit have no significant effect on its settlement;the settlement of the underground pipeline near the middle of the foundation pit should be mainly controlled,and the differential settlement of the underground pipeline near the foundation pit at both ends should be mainly controlled.2.Based on the design scheme of the supporting structure used by the engineering,the optimization design of the six inner supports was simulated considering different vertical arrangement,horizontal arrangement and section types.The results show that the downward movement of the sixth support increases the deformation of the surrounding environment;the arrangement of temporary inner support or increasing the cross-section size of the second inner support is beneficial to restrain the deformation of the surrounding environment.According to the above results,the optimization scheme of the supporting structure is determined: the section size of the second inner support is increased from Φ609mm×16mm to Φ800mm×16mm,and the temporary inner support is set 3.0m above the fourth inner support.3.A shallow foundation building adjacent to the foundation pit protected by isolation piles was numerically simulated,factors such as pile length,pile center distance,pile diameter,location and range of plane layout were considered.The results show that the longer the pile length,the smaller the center distance and the larger the pile diameter,the better the deformation control effect;the effect of deformation control can be improved by extending the isolation pile wall to the middle of the foundation pit;the closer the isolation pile wall is to the protected building,the better the deformation control effect is.According to the above results,the optimal layout scheme of isolation piles is determined: pile length,center distance and pile diameter are35 m,1600mm and 1000 mm respectively,the plane layout length is equal to the length of the protected object and extends 15 m to the middle of the foundation pit,and the layout position is3 m away from the protected building.4.According to the monitoring data of the project,the rationality of the numerical simulation results was verified,and the deformation of the surrounding environment of the foundation pit in practical engineering was analyzed.The results show that the numerical simulation results can reflect the main deformation characteristics of the foundation pit and the surrounding environment,and the numerical simulation results are basically consistent with the deformation rule reflected by the monitoring data;when the foundation pit has not been excavated to the bottom,large deformation has appeared in the surrounding environment of the foundation pit,taking deformation control measures for the surrounding environment is suggested.5.According to the results of numerical simulation,the proposed deformation control scheme for the surrounding environment of the project foundation pit was determined: take measures to optimize the supporting design scheme adopted in the project and set the isolation piles for the shallow foundation buildings and pipelines adjacent to the foundation pit.A shallow foundation building was taken as an example to simulate and verify the scheme,the results show that: the scheme determined can satisfy the requirement of deformation control for the protected buildings,and make the deformation of all kinds of pipelines in most protection areas of the isolation pile wall within the control values.