Study On Deformation Of Deep Excavation For Subway Station Under Seepage And Stress Coupling

With the development of subway transportation,deep excavation engineering of station appears continuously.In water-rich and permeable strata,seepage of excavation dewatering will seriously affect the deformation of excavation of station,easily lead to seepage damage and destabilization of excavation.Therefore,it is of great significance to explore the deformation law of excavations under seepage to guide engineering practice.Based on the deep excavation of Shidaiyanguang Avenue Station in Changsha Metro Line 5,through actual monitoring,numerical simulation and other means,using the seepage-stress module of Midas software,this paper explores the deformation law of excavation under seepage and the influence of support parameters on excavation deformation.The main contents and research results of this paper are as follows:(1)By analyzing the measured data of surface settlement,horizontal displacement,axial force of steel support and groundwater level,it is found that the surface settlement is a groove curve that increases first and then decreases,and the horizontal displacement is a bellows curve with small two ends and large middle.The axial force of support increases first,then falls back and then tends to be stable.Groundwater level decreases continuously with dewatering and finally tends to be stable.(2)Midas seepage stress slope module is used to simulate the excavation,and the simulation results are compared with the measured results to verify the accuracy of the model and analyze the deformation law of excavation;The results of considering seepage and not considering seepage are compared.It is found that the surface settlement and horizontal displacement increase and the excavation uplift decreases after considering seepage;The results of dewatering deformation and the effects of dewatering depth and permeability coefficient on excavation deformation are analyzed.It is found that the surface settlement and horizontal displacement will increase with the increase of the two factors.(3)Aiming at the defect and water leakage of concrete structure,the defect leakage of retaining pile is simulated,and the influence of defects in different positions and sizes on the excavation is explored.It is found that the defects will change the flow path of water,increase the seepage speed and seepage flow,and change with the defects position.Increasing the size of defects unit will also increase the seepage flow and seepage speed,which is not conducive to the stability of excavation.(4)The influence of embedded depth,pile diameter,pile distance,support stiffness on the stability of excavation is explored by orthogonal test method.The results of 16 working conditions are analyzed by range analysis,variance analysis.It is concluded that the support stiffness,pile diameter and embedded depth have a significant impact on the surface settlement,and the embedded depth is the most sensitive;Support stiffness and pile diameter have significant effects on horizontal displacement,and pile diameter is the most sensitive;Pile diameter,embedded depth and pile spacing have significant effects on excavation uplift,and pile diameter is the most sensitive;The surface settlement and horizontal displacement caused by 1.1m pile diameter,1.2m pile spacing,twice the support stiffness coefficient and 5m embedded depth are the smallest.