Reliability Analysis For Pile-anchor Retaining Structure Stability Of Deep Foundation Pit In Loess Area

The pile-anchor support structure is widely used in the deep foundation pit support project in the loess area.Its design uses the safety factor method based on limit equilibrium for structural analysis and check calculation.The safety factor method uses fixed values to check the design parameters and design conditions,and cannot reflect the randomness and variability of actual rock and soil parameters.Although the value determined by the safety factor method represents the safety index,it cannot reflect the reliability of the safety factor itself.Therefore,the quanti-fication of the stability and safety of the pile-anchor supporting structure cannot be reflected by the fixed-value safety factor method.The reliability design of foundation pit engineering can express the correlation,variability,uncertainty,distribution status and other factors of soil pa-rameters in a probabilistic way and its impact on structural safety.Regarding the stability design of foundation pit engineering,the reliability index has clear meaning.This article is based on the foundation pit project of the multi-functional pavilion in the west area of Weinan city center.Through the analysis of the project main structure and other project information,the engineering geology,hydrological conditions,surrounding environment,economic factors and previous engineering experience of the foundation pit site are integrated Choose a suitable foundation pit support plan.First,the equivalent beam method is used for the preliminary design of the pile-anchor support,and then the final support plan is designed and checked using the rationalized deep foundation pit software,and the overall stability reliability program for the foundation pit is compiled by MATLAB Performance analysis,and finally use the finite element software ABAQUS to numerically simulate the excavation and support of the foundation pit,analyze the displacement of the foundation pit and the supporting pile,the stress of the anchor cable and the plastic deformation of the soil.The main research contents are as follows:(1)Combined with engineering examples,the equivalent beam method was used for the preliminary design of the pile-anchor supporting structure.The embedded depth of the support-ing pile was 15.5m,and the elastic fulcrum method was used to analyze and verify the pile-anchor supporting structure to meet the requirements of the specification.At the same time,the verification results of the overall stability of the foundation pit and the stability of the foundation pit against uplift show that the design meets the requirements.(2)Compile the reliability program of the overall stability of the pile-anchor supporting foundation pit based on MATLAB language,evaluate and analyze the influence of the variability of the friction angle and cohesive force in the soil on the reliability of the supporting scheme,and obtain the failure of the foundation pit The probability is 0.361%,and the reliability index is 2.69.The reliability calculation program compiled by MATLAB is intuitive and clear,and has certain guiding significance for the reliability evaluation of similar projects.(3)The general finite element software ABAQUS is used to numerically simulate the excavation and supporting process of the foundation pit,and to monitor the soil,supporting piles and anchor cables,and conclude that the foundation pit supporting scheme is reasonable.At the same time,the analysis of the variability of the friction angle and cohesive force in the soil has a great influence on the distribution of the plasticity of the foundation pit soil and the size of the equivalent plastic strain.