Study On Stability Of Deep Foundation Pit In An Open Excavation Section Of Guangzhou Metro

In recent years,with the development of our country’s economy and society and the improvement of urbanization,the rapid development of urban rail transit construction has sprung up a large number of deep foundation pit projects and frequent construction safety accidents,which bring serious hazards to people’s life and property safety.In the analysis of the safety and stability of deep foundation pit engineering,site monitoring and finite element numerical analysis are the most commonly used means,which can effectively reflect the change trend and law in the construction process of foundation pit engineering,so as to realize the information construction of deep foundation pit,and formulate the corresponding engineering and technical measures to ensure the stability of engineering and structures.Based on the excavation of deep foundation pit in the open section of Xiangling Station ～Zhonggang Station of Guangzhou Metro Line 21,this paper analyzes and studies the deformation law and stability of the deep foundation pit project by using the method of combining field monitoring and numerical simulation,and determines the main factors affecting the stability of the deep foundation pit project,and draws the following main conclusions:(1)The calculation methods of surface settlement and supporting structure deformation caused by foundation pit construction are summarized,and the influencing factors of foundation pit stability are summarized;(2)The deformation of continuous wall,surface settlement,axial force of supporting structure and horizontal displacement of wall top are monitored on site.The results show that the deformation of the diaphragm wall on the north side of the foundation pit is a combination of "bow" shape and "reverse kick" shape,while that on the south side is a "bow" shape,and the maximum horizontal displacement of the diaphragm wall on the south side is greater than that on the north side.The surface settlement outside the pit is "groove-shaped",and the maximum surface settlement is 6m(0.38H)away from the edge of the foundation pit,and the surface settlement on the north side of the foundation pit is larger than that on the south side.The maximum axial force of the foundation pit supporting structure is 1557.30 KN,and the maximum horizontal displacement of the wall top is 18.5mm,both of which are less than the allowable value of the engineering,indicating that the supporting structure can ensure the stability of the foundation pit;(3)The finite element numerical model was established to study the variation rules of the displacement and surface settlement of the foundation pit supporting structure under different excavation and supporting processes,and the results were compared with the field monitoring results.The results show that the development trend,maximum value and location of deformation obtained by numerical simulation are basically consistent with the field monitoring results;(4)The influence of different seepage conditions and supporting structure parameters on the stability of foundation pit is studied.The results show that the maximum horizontal displacement,maximum surface settlement and maximum basement uplift of diaphragm wall decrease by 37%,26% and 27% respectively when seepage is not considered.When the depth of the continuous wall and the stiffness of the supporting structure are less than 21.7m and1.0MPa,respectively,the influence of the value on the foundation pit deformation is obvious,but when the depth of the continuous wall and the stiffness of the supporting structure are greater than 21.7m and 1.0MPa,the influence on the change of the foundation pit gradually decreases.