Optimization Research On Supporting Structure Of Deep Strip Foundation Pit With Internal Bracing

By processing and analysis of monitoring data that is from Harbin subway station pit construction site, this article discovers that measured displacement and surface subsidence are smaller than the original design. So it concludes that support structure design is conservative. As the excessively safe design will result in economic waste, it is necessary to optimize supporting structure. Optimization design of excavation support system is generally divided into two levels, namely program optimization, detail optimization. This article optimizes the detail under the premise of known support program.The process of the deep pit section excavation and support is plane simulated and analyzed using large geotechnical finite element software PL AXIS. And horizontal displacement of the deep pit supporting structure is analyzed using HS model. As the reliability of finite element simulation results largely depends on the soil constitutive model and calculation parameters, so firstly it obtains a set of calculation parameters of controlling deformation through displacement inverse analysis.On the basis of the original design, it changes the brace number, brace vertical layout, support pre-stress, pile diameter and pile spacing etc under the premise of the same construction procedure. By studying influence of these parameters on deformation and bending moment of the pit, it draws the design variables that are required by the optimization program.Through optimization analysis of support structure parameter of Internal-shoring strip of deep pit based on genetic algorithm in MATLAB and writing optimization program using MATLAB language, then applying to the YANCHANG pit and using equivalent beam method to calculate, a mathematical optimization model is proposed with Minimum Cost as the objective function. By studying the constraints that each design variable needs to meet and making the objective function minimum under the premise of meeting constraints, optimal design program is obtained. Comparison optimization scheme with the original scheme can be seen that the optimization program can reduce construction costs, so optimization of the pit is very necessary.The results shows that soil mechanics Parameters are optimized by displacement back analysis; optimization variables are the rows and situation of braces, the pile diameter and space between piles with finite-element method; detail optimization is realized with genetic arithmetic, it optimize the internal structure and achieve the lowest cost.