Stability Analysis Of Deep Excavation Based On Reliability Theory

With the advancement of urban construction and deep foundation pit engineering to the great depth,new forms of support continue to emerge.The double-row pile support method has become one of the important methods of foundation pit support because of its wide applicability and recognition under the complicated engineering conditions.Taking into account the current researches on the pit support are behind the status of engineering practice,the frequent accidents of deep foundation pit engineering,as well as the conservative support design,this paper focuses on the stability theory of deep foundation pit support and explores the relative verification methods.The main contents and analysis results are as follows:(1)The data of the project site are sorted out according to the survey results,and the parameters are classified according to the survey results.According to the statistical results,the distribution rules of each parameter are depicted.It is found that the cohesion,the internal friction angle and the weight of the soil are generally compounded with normal distribution.(2)The FLAC3 D numerical model of double-row pile support with deep foundation pit is established.According to the actual engineering condition,the boundary condition,initial condition and parameters of the model are determined,and the support pile is arranged rationally.The results show that the stability of the foundation pit can be finally reached after the excavation.After the foundation pit excavation,the trace and magnitude of main stress will change,and stress concentration occurs at the foot.The horizontal displacement of the top of the excavation surface is larger and the vertical displacement occurs at a certain distance from the slope.The row pile can improve the stress of the soil in the surrounding area and restrict the deformation of the soil.The support effect of the rear pile is larger than that of the front row pile.(3)According to the numerical results,the possible sliding surface of the soil after the foundation pit is determined,and the sliding surface curve is fitted,also the mathematical expression is determined.The formulas of stability calculating for the slope are given according to the method.(4)Based on the Monte-Carlo reliability method and the probability distribution of input parameters,the calculation model for failure probability of foundation pit is established and the corresponding calculation program is compiled.It is found that the probability density of a large number of calculated values obtained by the stability formula is generally obey the normal distribution.From the cumulative probability curve we can see that under this condition,the probability of soil stabilization is 98%,and the support satisfies the safety requirement.(5)Based on the influence of different parameters in different layers on the calculation results,it is found that the internal friction angle has the greatest influence on soil stability.The influence of parameters on the stability of different soils is different,and the influence of silty clay is greater than that of silty clay.The weight of soil has little effect on the calculation results.