Research On Optimization And Numerical Simulation Of Combined Support System For Deep Foundation Pit

This paper is based on the background of Nine Foundation Pit Project of Rongxin Yangzhong City in Taijiang District of Fuzhou City.Firstly,selecting four kinds of combined support system schemes through engineering definition and specification requirements.Secondly,using Yaahp software,it establishes a hierarchical structure model,carries out quantitative analysis of the foundation pit support system,and then chooses the optimal scheme.Thirdly,it uses Lizheng deep foundation pit software to check and support the optimal scheme,and then carries out structural design calculation and support.Finally,on the basis of the above,the MIDAS/GTS NX software is used to carry out the three-dimensional simulation of the project,and the reliability of the three-dimensional model and the rationality of the optimal scheme are verified by comparing with the actual monitoring data.The main research results are as follows:(1)Relying on the four combined support systems selected at the beginning of the project;using Yaahp software,four indexes and 14sub-indexes of the project are selected to establish the hierarchical structure model.Combining with expert scoring method and 1-9 scaling method,the weight of the four schemes is calculated by groupdecision-making in turn as follows: 0.2693,0.2739,0.2798 and 0.1770,thus the best support scheme is selected: SMW pile method and Steel support(0.2739).(2)Taking the 3-3 section with the most disadvantageous conditions as the research object,through the software of Lizheng deep foundation pit,the optimum scheme "SMW method pile and steel support" is checked to meet the safety and stability requirements of the project.Secondly,through numerical simulation,the steel support is optimized in detail,and it is concluded that the auxiliary support of the foundation pit can use profiled steel support instead of steel pipe support,thus effectively reducing the cost.(3)Using MIDAS/GTS NX software to carry out three-dimensional simulation research,the analysis shows that when SMW pile modeling,"equivalent diaphragm wall and insertion section steel" is compared with the traditional method "direct equivalent diaphragm wall",which can reduce SMW pile deformation by 5.6 mm and is closer to the measured data.(4)Through numerical analysis,it is concluded that the maximum displacement of deep soil is 23.3 mm,located near the excavation surface(5.44 m in soil depth).The maximum displacement of crown and beam is19.6 mm,located in the middle of the east side of the foundation pit.The maximum settlement of surrounding buildings is 11.2 mm,located at theKing’s Temple of Luowu Xian,and the maximum vertical displacement of columns is 7.2 mm,which is in a uplift state and located at the right side of the middle part of the foundation pit.Comparing the simulation results with the measured data,the error is within the controllable range,the maximum value does not exceed the early warning value,and the deformation trend in the construction process is roughly the same.The location of the maximum value points in the numerical simulation of each project is basically consistent with the actual monitoring maximum point.