Numerical Simulation And Analysis Of Deformation Characteristics Of Rock And Soil Mass During Excavation Of Subway Foundation Pit On River Terraces

River terrace is one of the common geomorphic units in urban geological environment.The construction of underground railway in this geomorphic unit needs to deal with geotechnical engineering problems caused by groundwater,neighboring structures and temporary loads.In the study of deformation characteristics of rock and soil mass in the excavation of metro foundation pit at present,in view of the complex environmental impacts such as geological structure,water environment and the distribution of surrounding loads,the regularities obtained by means of multistrata,quasi-dynamic groundwater and simplification of neighboring loads are discussed.These laws still fail to reflect the quantification effect of anisotropy in plane,binary structure in depth and groundwater level variation in river terraces in engineering activities.The article relies on the first phase of the earth bridge entrance and exit section of Changsha Metro Line 5.Based on theoretical analysis and field test and monitoring.The deformation characteristics of rock and soil in open excavation of Subway Foundation Pit under river terrace conditions are analyzed by numerical simulation.The research results provide technical support for the construction process optimization and site safety assessment relying on the project,and also provide theoretical reference for the foundation pit design of similar projects.The research contents and conclusions are as follows.1.Aiming at the complex stress-strain problem of rock and soil mass in river terrace environment,a numerical analysis model under river terrace environment is established.Based on this model,the deformation characteristics of rock and soil mass in foundation pit excavation under river terrace condition are analyzed.The difference of deformation between longitudinal and transverse terrace rock and soil mass is compared,and the variation law of stress-strain in foundation pit excavation site in longitudinal and transverse direction is obtained.2.Based on the theory of fluid-structure interaction,the numerical simulation of fluid-structure interaction in river terrace environment is realized by using finite element computing program and field pumping test.This paper analysis and compares the difference of rock and soil deformation in excavation of foundation pit in three states of water level change(high,low and normal),and reveals the law of rock and soil deformation in foundation pit construction under different water levels in river terrace environment.3.Combined with field monitoring data and numerical simulation results,the influence of stratum structure and composition,groundwater level,temporary load and neighboring structures on the deformation of rock and soil mass in the excavation of long and narrow foundation pit is considered.The combination of the most unfavorable factors in the construction process is put forward,which provides a reliable evaluation and prediction for the safety construction of later projects.