Design Optimization Of The Secant Pile Wall At Lanzhou Subway

At present, the secant pile wall system has been used widely in the southeast coastal areas in China but rarely used in the northwest China due to the special geological conditions. This thesis select the foundation pit retaining engineering at Lanzhou subway station as case study to investigate the performance of the secant pile wall.In this thesis, the finite element software ABAQUS is used to establish a finite element model equivalent to secant pile wall to simulate pile displacement and bending moment under the different working conditions of foundation excavation. By comparison with field monitoring date, the feasibility of the model is verified. Based on numerical simulation results, this thesis analyzes the effect of pile section size, concrete pile strength and ratio of embedded depth of piles on the pile displacement and bending moment of the retaining structure in Lanzhou subway foundation pit. And some suggestions are given for reference to optimizing the design of secant pile wall.The research conclusions can be drawn are as followings:(1) The design of the secant pile wall system in Lanzhou subway foundation is reasonable, which can achieve desired safety.(2) Generally, the secant degree between adjacent piles has little effects on pile displacement and bending moment. Considering the factors of safety, the secant degree of secant pile wall in Lanzhou subway foundation is advised to be selected as 200 mm.(3) Pile section size of secant pile wall has a great influence on pile displacement and bending moment. Comprehensively considering other factors such as safety, economy and so on, the pile section size of secant pile wall in Lanzhou subway foundation is advised to be choosed as 1000 mm.(4) Strength of plain concrete piles of secant pile wall has a little influence on pile displacement and bending moment. After comparison, the strength of plain concrete piles of secant pile wall is advised as C15.(5) The ratio of embedded depth of piles under the bottom of the pit of secant pile wall has a great influence on pile displacement and bending moment. After considering other factors, the ratio of embedded depth of piles of secant pile wall is advised as 0.5.