Stability Analysis And Optimization Design Of Deep Foundation Pit Supporting Structure In Expansive Soil Area

With the rapid development of urban rail transit and tall building projects,deep foundation pit projects appear constantly.It is extremely important to ensure the safety and stability for deep foundation pit is directly related to people's lives and properties.In particular,it may cause great potential safety hazard to the foundation pit project when the expansive soil condition is encountered.Affected by rainfall and other external environment,the soil around the foundation pit absorbs water and then expands.This process forms horizontal expansion force on the foundation pit support structure and reduces the safety and stability.This study took the deep foundation pit project of Sichuan Road station in Hefei metro line 5 as the research background.First of all,A large number data through field foundation pit monitoring was obtained.The change law of in each working condition during foundation pit excavation was analyzed,and the influence of expansive force on foundation pit support structure was judged preliminarily.Then,ANSYS and Midas GTS/NX finite element software were used to simulate the excavation process,and the simulated values of pile deformation and supporting internal force were obtained with and without expansive force.Finally,The simulated data was compared with the field monitoring data to get the conclusion that the presence of expansive force affect the stability of foundation pit supporting structure.At the same time,the deformation values of piles with different lengths,diameters and spacing of piles were calculated by Lizheng deep foundation pit software,and the design parameters of the supporting structure that have the greatest influence on the deformation of piles are obtained after analysis and comparison.This study can provide certain reference for the design and optimization of foundation pit support structure in the future.The relevant conclusions are as follows:(1)in the design of deep foundation pit support structure in expansive soil area,the influence of expansive force should be considered.The expansive force loading model is established according to the humidity field,and the value of expansive force is 30%of the standard value of indoor experiment;(2)when using lizheng deep foundation pit software to design and calculate the foundation pit support structure,the equivalent method of loading triangular load on the ground and at a certain depth is adopted to load the expansive force;(3)through the lizheng deep foundation pit software,the deformation of three supporting structure design parameters,namely,pile length,pile diameter and pile spacing,are calculated respectively,so as to analyze the effect of changing pile diameter on the deformation of the supporting pile body.