Research On Parameter Optimization Design Of Deep Foundation Pit Supporting Structure Of Utility Tunnel In Water-rich Stratum

In recent years,with the acceleration of urban development,more and more cities have built urban utility tunnels due to the shortage of construction land.However,there are more and more safety accidents caused by improper construction and optimization.Therefore,in order to improve the engineering efficiency under the premise of ensuring the stability of foundation pit,it is necessary to further study the deep foundation pit supporting system of utility tunnel.Based on a deep foundation pit project of utility tunnel in water-rich strata,this paper analyzes the monitoring results,explains the reasons for the difference between the numerical simulation results and the actual construction,and proves that the simulation accuracy meets the requirements.The influence of different supporting structure parameters on the stability of foundation pit is analyzed,and the optimal supporting structure combination is selected by orthogonal test.The main research work and results of the paper are as follows:(1)Summarize the deformation forms of foundation pit,Numerical simulation according to practical engineering,And according to the actual results show that the model is accurate,With the increase of the depth of the foundation pit of the pipe gallery,the displacement of the retaining structure increases,and its deformation law presents the form of’bulging’,and the settlement around the pit also increases.(2)The influence of different supporting structure parameters on the stability of foundation pit is analyzed by establishing the finite element model of different supporting structure parameters.Among them,changing the form of composite pile diameter has the most significant effect on the deformation of foundation pit.When the form of composite pile diameter is changed from 0.65 m pile diameter with H500×200 steel to 1 m pile diameter with H850×300,the maximum horizontal displacement of pile body is reduced by about 25.60%,and the maximum surface settlement is reduced by about 7.18%.(3)Taking horizontal displacement of pile as index,orthogonal test is established by selecting influencing factors and levels.The influence degree of each factor on the consideration index is as follows:composite pile diameter>steel layout>internal support spacing>pile depth.(4)Combined with the orthogonal test results and comprehensive engineering efficiency and deformation control effect,the optimal combination scheme is:pile depth of 16m,composite pile diameter of 0.85m with steel H700×300,steel layout for close insert,internal support spacing of 4m.Compared with the original scheme,the maximum horizontal displacement of the pile body is reduced by 8.89%,the maximum surface settlement is reduced by about 4.36%,and the optimized single pile saves 1.33 m~3 of cement soil.