Data Analysis And Numerical Simulation Of Deep Foundation Pit Safety Monitoring

The research on the deformation law of deep foundation pit is an important topic in the construction process,which is of great significance to the safe construction of deep foundation pit engineering.This paper introduces the common types of supporting structures and the calculation theory of deep foundation pit.Based on the background of a deep foundation pit project in the Pearl River Delta water resources allocation project,a reasonable foundation pit monitoring scheme is formulated.Through theoretical analysis and field monitoring data,the fluid structure coupling simulation of deep foundation pit excavation process is carried out by using the finite element numerical simulation analysis software,The results show that the deformation law of the foundation pit under the two conditions of actual monitoring and numerical simulation is relatively consistent.The main research results are as follows:(1)The theoretical calculation results show that the ground settlement caused by foundation pit excavation and dewatering is less than the actual ground settlement,and both the theoretical calculation value and the measured value exceed the alarm value.It is suggested that the ground settlement alarm value should be adjusted considering the geological conditions of foundation pit,surrounding environment and construction conditions.(2)Through theoretical calculation and analysis,it is found that part of the seepage water of the foundation pit mainly enters into the foundation pit through the surrounding seepage of the rock under the diaphragm wall.It is predicted that other foundation pits of the project may have water gushing at the bottom of the foundation pit.The influence radius of precipitation is about 3 times of the excavation depth of foundation pit,which is beyond the design settlement monitoring range.The influence of precipitation on the surface settlement around the foundation pit is much greater than that of excavation.The surface settlement caused by excavation is within 100 m from the edge of foundation pit,and the surface settlement beyond100 m is mainly caused by precipitation.(3)With the increase of excavation depth of foundation pit,the horizontal displacement of diaphragm wall increases gradually,and the maximum horizontal displacement position of diaphragm wall moves downward.The deformation shape is "bulge belly" distribution,which is large in the middle and small at both ends.The maximum position is near the excavation surface.During the excavation of foundation pit,the exposed time of diaphragm wall should be reduced as far as possible.With the increase of the distance from the foundation pit,the surface settlement around the foundation pit first increases and then decreases.The maximum settlement is 24 m away from the edge of the foundation pit,and the maximum value is240.61 mm.In the early stage of foundation pit excavation,the soil settlement rate is small,but in the late stage of foundation pit excavation,the soil settlement rate gradually increases,and the surface settlement mainly occurs in the deep soil excavation stage.(4)Considering the fluid structure interaction of foundation pit excavation,the parameters of soil compressibility modulus are adjusted by using the finite element numerical simulation software.The results show that the simulated value of 1-fold compressibility modulus is better than the actual value,and the simulated value of 2-fold compressibility modulus is better than the theoretical value.The whole process of foundation pit excavation is simulated,and the simulation results are compared with the field monitoring data.The simulation results of diaphragm wall horizontal displacement and surface settlement around the foundation pit are smaller than the measured values,but the overall trend is consistent.(5)The influence of the stiffness,elastic modulus and embedded depth of diaphragm wall on the deformation of foundation pit is studied.The horizontal displacement of diaphragm wall decreases with the increase of stiffness.When the stiffness continues to increase to a certain extent,the control effect on the deformation of diaphragm wall decreases obviously,and the stiffness of diaphragm wall can control the deformation of diaphragm wall within a certain range.The increase of elastic modulus has a certain control effect on the horizontal displacement of diaphragm wall.With the increase of the embedded depth of diaphragm wall,the surface settlement around the foundation pit decreases gradually,but the reduction degree is smaller and smaller.