Research On Optimal Design Of Deep Foundation Pit Support Scheme For Large Subway Stations

With the development of urban construction,more and more urban subway tunnel projects pass through underground space,and large subway stations not only encounter the conventional foundation pit support problems,but also involve the joint problems with shield tunnels.In this paper,based on the large-scale foundation pit project of Changzhou Rail Transit Line 1,the selection of the foundation pit support scheme is determined based on the optimization analysis of the evaluation index system.Through numerical analysis,the stress characteristics and deformation laws of different support structures are analyzed,and the suitable support structure parameter range is put forward.In deep well precipitation,the calculated result is larger than the actual result when calculating the water inflow by the traditional Qiubuyi theoretical formula.This paper considers the multi-well system theory to optimize the precipitation scheme of large subway stations;In this paper,the soil reinforcement at the end of shield at the joint between station and subway line is studied.The main contents are as follows:(1)according to the characteristics of foundation pit engineering,hydrogeology and environmental conditions,the evaluation index system and weight set are established around four first-level evaluation indexes of technology,construction period,cost,construction quality and safety and 14 second-level evaluation indexes of engineering geological conditions,and it is concluded that the best support method of the proposed site is: the first area adopts the "pile anchor" support method;Row piles+internal support are adopted in Area 2.(2)With the help of finite element numerical simulation software,the foundation pit excavation model is established,and the horizontal displacement and bending moment of supporting structures in different sections are analyzed.By changing the parameter values of influencing factors(pile length,pile diameter and cross-section size of inner support),the internal force and deformation law of supporting structure under different parameter values are analyzed,and the suitable parameter range of supporting structure is put forward.(3)According to the equivalent beam method,the depth of the supporting structure and the overall stability of the foundation pit are calculated.The horizontal displacement,bending moment,pile depth,foundation pit stability and uplift resistance of the retaining structure are calculated or checked by Tianhan software.(4)Expounding the principle of mutual interference between well groups,determining hydrogeological parameters by comprehensive comparison of pumping test and conventional methods,considering mutual interference between well groups,optimizing the precipitation scheme,and the optimized scheme is consistent with the actual operation results.(5)It is analyzed that the reinforcement of shield starting and reaching ends should meet the requirements of geometric size criterion,shear strength and soilstability after reinforcement.