Study On Reliability Analysis And Design Optimization Of Foundation Pit Support Structure

Because of the theory,environment and construction conditions of foundation pit engineering are very complex,there are a series of uncertainties in foundation pit engineering.However,these uncertainties have not been fully considered in the safety evaluation of foundation pit engineering and the design of supporting structure of foundation pit engineering at present.In this paper,the reliability analysis and optimization design of foundation pit are regarded as uncertain problems.The research is divided into three parts:(1)Reliability evaluation index is used to replace safety factor in safety evaluation of foundation pit engineering.In the analysis of the safety of foundation pit support system,uniform test and ACE nonparametric regression are used to establish an efficient response surface,then combined with Monte Carlo sampling,the reliability evaluation index of foundation pit support system,which based on deformation and stability is obtained.However,the reliability index does not take into account the correlation of soil mechanics parameters and the complexity of failure mode of foundation pit.So the copula theory is introduced to improve the method so as to make the reliability index of foundation pit support system more reliable.Finally,compare the improved method with the unimproved one in an engineering example.(2)The reliability evaluation index is taken as the constraint condition to optimize the design of foundation pit support structure.On the one hand,it is necessary to consider the possibility of choosing various parameters of foundation pit support as comprehensively as possible;on the other hand,it is necessary to improve computational efficiency,so the optimization process is divided into two steps.The first step is to optimize the layout of some components in order to ensure that the stress and deformation of the supporting structure are more reasonable;the second step is to optimize the design parameters of the main support,to choose an as economical as possible design which meets the reliability of foundation pit support structure.At last,the optimization method is applied to practical engineering,optimize the foundation pit support structure based on original design scheme(3)Based on the measured data of construction,the equivalent parameters of soil layer are inverted and the supporting structure of foundation pit is dynamically designed.Firstly,a constructed working condition is selected to form an efficient response surface by uniform test and non-parametric regression of ACE.Then generate a large number of samples in accordance with response surface,combining Monte Carlo sampling and Copula theory and back analysis the equivalent shear strength index of soil layer.At last,design the next working condition with the equivalent shear strength index of soil layer.The dynamic optimization method is applied to practical engineering and compared with the original design scheme.