| The excavation of deep foundation pit is often used in dock,navigation lock and coal overturned room of port and other civil and hydraulic engineering infrastructure construction.Because of the complex geological conditions,groundwater conditions,the surrounding environment of the foundation pit,construction schedule and arrangement,construction technology and organization,and the choice of supporting structure form,the safety of deep foundation pit excavation will be affected.A little carelessness can cause a safety accident.At present,the number of foundation pit in China is the largest in the world.It has abundant on-site monitoring data and accumulated a lot of engineering experience.But every year there are also the most accidents in the world,causing a lot of huge and irreversible losses.Therefore,how to design a safe,reliable,economical and reasonable support structure and construction scheme without damage to the surrounding environment is particularly prominent.This paper is based on a deep foundation pit in a port in Tianjin.The deformation of foundation pit is monitored by inclinometer,total station and leveler,and the field monitoring data of the project are sorted out and analyzed.The dangerous situation that the displacement of slurry wall exceeds the alarm value is analyzed according to the field situation.The main reasons are found out and the measures to control the deformation are put forward.ABAQUS finite element method is used to simulate the process of layered dewatering excavation in the foundation pit.Modified Cambridge model for soil constitutive model.Three-dimensional solid pore pressure element,three-dimensional solid element and beam element are used to simulate soil,slurry wall and internal support respectively.Friction contact between wall and soil.The on-site monitoring data is compared with the digital-analog calculation data.The measured data is consistent with the simulated calculation data,which indicates that the model can correctly simulate the deformation of the foundation pit during the stratified precipitation excavation of the soft soil foundation pit.The numerical simulation results are analyzed,and the deformation of the soil inside and outside the pit and the deformation of the underground continuous wall are analyzed.The main conclusions of the paper are as follows:(1)Analysis of the monitoring data of the foundation pit deformation:With the increase of excavation depth,the rebound of the continuous wall top,the horizontal displacement,the deep horizontal displacement of the underground continuous wall,the surface settlement around the foundation pit,and the deep water displacement of the soil gradually increase.The deep horizontal displacement of the underground continuous wall is mostly arched(2)In the second step of excavation,the side displacement of the QC-7 measuring point exceeds the side displacement alarm value,and the main reason is found in combination with the situation analysis.According to the reasons and controlling the deformation caused by subsequent excavation,corresponding control measures have been formulated to effectively control the deformation of the underground continuous wall,which can provide valuable experience for similar dangerous situations in the future.(3)Analysis of the digital simulation data of the foundation pit deformation:Numerical simulation and on-site monitoring can effectively predict the deformation of foundation pit and timely take corresponding control measures for dangerous conditions,which can provide reference for similar soil foundation pit engineering.The lateral displacement of the underground continuous wall along the depth direction is roughly arcuate.The displacement value increases with the increase of the excavation depth.There are three main settlement areas on the surface of the foundation pit,and the settlement forms are all groove-shaped;the soil uplift at the bottom of the foundation pit The uplift occurs,and its shape is roughly "centered,small around". |
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