Research On Secondary Support Of A Deep Foundation Pit In Chengdu

At present,there is a remarkable characteristic in the social development of China: the process of urbanization is speeding up,the urban population is rising,and the population density is increasing day by day.This feature represents the rapid development of China’s economy,but it also brings some challenges: urban land resources need to be more fully utilized.This demand makes the current deep foundation pit engineering more and more complex,which also leads to a lot of foundation pit secondary support or reinforcement support because of various problems.This paper is based on the foundation pit support engineering of "territory · global financial center" in Chengdu.The design change occurred during the excavation of the foundation pit.Because the original supporting structure of the foundation pit has been completed and excavated to the bottom of the original design pit,a new pile is redesigned for the part without the original supporting pile,and the excavation is continued after the secondary support for the existing part of the original supporting pile.In the case of cantilever pile,two methods are adopted for the secondary support,i.e.driving anchor cable on the original pile,adding soil nailing wall below the bottom of the original pile,and directly splicing the new pile in the middle of the original pile.This paper uses the Rational deep foundation pit software.to design and calculate the foundation pit,uses Midas GTS NX software to carry out the overall three-dimensional numerical simulation of the foundation pit,and compares the simulation calculation results with the actual monitoring results.After the above research process,the main research contents and achievements of this paper can be summarized as follows:(1)Collect and sort out the foundation pit data of this project,analyze and summarize.The monitoring data,production design calculation results and numerical simulation results are compared to determine whether the design calculation and numerical modeling are reasonable.(2)The foundation pit of the project is designed and calculated.Firstly,the parameters are selected and determined.Then,the calculation methods of two kinds of secondary support methods,i.e.adding anchor cable and soil nailing wall to the original cantilever pile,and directly splicing new pile in the middle of the original cantilever pile,are explained,and the design calculation is carried out by using the Rational deep foundation pit software.Finally,the design and calculation results are compared,and the two secondary support methods are preliminarily analyzed.(3)The Midas GTS NX software is used for numerical simulation.After introducing the parameters of foundation pit modeling,Midas software is used to model the foundation pit,and the numerical simulation results are compared with the actual monitoring results to determine whether the calculation method used in the design calculation is appropriate,and finally determine the feasibility and effect of the two secondary support methods.(4)In this paper,the secondary support method of pile extension is deeply studied,and multiple models are established by using Midas GTS NX software to simulate the effect of different pile extension positions on the effect of butt pile and the influence of the distance between new and old row piles on the effect of butt pile.The displacement under different conditions and the stress of connecting beam between new and old piles are analyzed.