Study On The Anti-heave Stability Calculation Of Foundation Pit Excavation In Deep And Thick Silt Layer Area

In the Pearl River Delta region,due to the influence of river alluvium for a long time,there are a lot of silt and soft soil,and the geological conditions show the characteristics of low shear strength of soil,high porosity ratio,large compressibility and serious influence by groundwater,etc.basal upheave has become one of the most common forms of destruction.Therefore,in the deep soft soil area,especially in the deep silt area,it is of great significance to study the upheave destruction of the pit bottom.In the deep silt area,when the design software of Lizheng deep foundation pit is used to design the foundation pit,it is a common problem that the anti-heave stability calculation can't meet the requirements,but after these schemes have been proved and implemented by experts,the foundation pit has not appeared instability or upheaval destruction.In view of the common problems,this paper makes a thorough study,and puts forward a comprehensive design method of "Lizheng deep foundation pit" + "MIDAS/GTS finite element numerical analysis",then analyzes the factors that influence the basal upheave of foundation pit in the deep silt area,at last,the prevention and control measures of basal upheave destruction are put forward.The main contents of this paper are as follows:(1)The research section of the engineering case is calculated by using the design software of Lizheng deep foundation pit,which verifies the irrationality of the calculation of the stability against upheave at the bottom of the pit in the present code,and points out that it is necessary to check the stability of the cantilever retaining structure against the upheave at the bottom of the pit in the deep soft soil area where the geological conditions are especially poor and the strength is especially low;(2)In order to prove the feasibility of the comprehensive design method of "Lizheng deep foundation pit" + "MIDAS/GTS finite element numerical analysis",and provideguidance and reference for the engineering that meets similar problems,the appropriate constitutive model is selected to simulate the engineering case profile in this paper by MIDAS/GTS finite element method,and it is compared with the actual monitoring data;(3)This paper analyzes the factors influencing the pit bottom upheave in deep silt area,and probes into the influence law of supporting structure pile diameter,embedded depth,inner support position,number and the width,depth and strength of the passive zone on the pit bottom upheave;(4)Finally,the corresponding prevention and control measures are put forward to ensure that the basal upheave destruction will not occur at the bottom of the pit in the deep silt area.