Stability Analysis Of Deep Foundation Pit Excavation Based On A Subway Station In Jinan

In recent years,the process of urbanization is accelerating,in order to solve the contradiction between the urban population explosion and the high tension of urban land,Jinan has accelerated the construction of underground space project.The construction of these projects makes the Foundation Pits Engineering has characteristics of large scale,deep excavation,small site,complex supporting and environment.The stratum deformation,support deformation and internal force are interrelated in the foundation pit deformation.However,there are still problems in the current design concept of Foundation Pits Engineering,such as basing on internal force control and neglecting deformation control,being too conservative,and pursuing economical which lead to design mistakes.In addition,the reliability of simulation and technology of complex support system is not verified in the numerical simulation method.Therefor the research on the establishment of the model,the simulation and optimization of the supporting structure and the stability excavation carried out through theoretical analysis,numerical simulation and on-site monitoring.the research results are as follows.(1)Establish the model of foundation pit excavation and support analysis accurately and reasonably.In terms of parameter selection,equivalent modulus and weighted average method are adopted respectively to determine the elastic modulus of pile and friction coefficient between pile and soil.In terms of support simulation,solid element is adopted for pile,and beam element is adopted for soil nailing wall and cross-brace.However the pile and the soil nailing wall should be equal stiffness converted to continuous wall and "plate structure" in the three-dimensional model.In terms of contact setting,embedded contact is adopted for soil nail-soil,friction contact is adopted for pile side-soil,pile bottom-soil and support-pile adopt tie constraint.Simulation results show that this setup is reasonable.(2)The deformation law in the process of foundation pit excavation and support is analyzed through the simulation of four kinds of models of 2-dimension and 3-dimension without and with support.In terms of deformation,the results show that the excavation without support has a large plastic deformation.Meanwhile,with the support excavation,thehorizontal deformation of the support structure changes from "cantilever type" to "parabolic type" and then to "combined type with M".The ground surface settlement is "groove type".The basement uplift shows elastic uplift.In terms of model,the simulation results show that the two-dimensional model is easy to operate and fast to solve,but the three-dimensional model is more realistic and the spatial effect is significant.(3)The research and simulation results are applied to the design and construction of Huayang road station of Jinan metro line M1.In terms of construction,the feasibility of the model is verified by comparing the data,meanwhile the on-site construction can be guided by the research with on-site monitoring.In terms of design,the values of on-site monitoring and simulated are far less than the control values,which indicates that the design is too conservative.Therefore,the supporting structure can be optimized appropriately by the parameters of pile diameter and reinforcement ratio,so as to save materials and construction period.