Numerical Simulation Of Excavation Deformation Of Foundation Pit Over Existing Tunnels

The limited land resources and space resources in cities,the rapid development of subway tunnel construction,and the frequent occurrence of new foundation pits have made it increasingly common for new foundation pits to cross over existing tunnels.There will be various deformations during the excavation of the existing tunnel excavation.If these deformations exceed the relevant warning values,the normal construction of the foundation pit and the safety of the use of public facilities such as tunnels under the ground will be affected.It may even cause relevant foundation pit engineering accidents,so studying the issue has great theoretical and practical significance.In practical projects,the deformation caused by excavation has always been a difficult problem.It is complicated and varied,with many influencing factors,and it is very specific.Many scholars have conducted meticulous analysis on their own perspectives.This paper focuses on the deep and systematic research of the foundation pit that spans the existing tunnel in the city.The relevant model is built by numerical simulation software FLAC3 D to analyze the ground surface settlement around the foundation pit,the lateral deformation of the surrounding structure during the excavation of the foundation pit,The deformation of the bottom of the foundation pit and the deformation of the underlying tunnel uplift deformation.This article mainly studies through the following aspects:(1)Firstly,a two-dimensional analysis of the typical section of the foundation pit is performed.Through the establishment of more than 20 two-dimensional models,the following discussion focuses on different excavation depths,different depths of enclosing constructions,different types of enclosure structures,and different excavation methods.The law of change in the deformation,pointed out from the calculation results of the danger zone of the deformation of the foundation pit,to provide guidance for the actual project.(2)Set up several large and medium-sized three-dimensional model of foundation pits,taking into account the spatial effects during excavation of foundation pits,and discuss the parallel and orthogonal conditions of the above-mentioned foundation pits and the underlying tunnels,and the simultaneous existence of multiple tunnels underneath the pit.The possibility to analyze the deformation characteristics under these conditions;to improve the soil parameters in different areas of the foundation pit by increasing the soil parameters,and to discuss the reinforcement effects of the long-soil reinforcement scheme at the bottom of the pit and the soil reinforcement scheme on both sides of the tunnel.(3)Taking the example of a deep excavation of a station that spans an existing tunnel as a research background,after the reinforcing measures such as the reinforcement of the bottom of the pit and the supporting system of the sheet pile,etc.are taken,The space effect and time effect of deformation of deep excavation of newly constructed station under layered block excavation are studied.By plotting the three-dimensional deformation curve of the corresponding working conditions,the cloud deformation map of the excavated soil and the grid deformation map of the envelope structure and the tunnel lining are displayed to provide theoretical guidance for the related projects in the future.