Inversion Of Mechanical Parameters Of Surrounding Rock And Stability Analysis Of Subway Tunnel

For Nanhua Section Project of Line 2 with Dalian subway,the rock level includes IV and VI grade rock,which need blasting construction.The geological conditions of VI surrounding rock section are very complex with local cave and fracture rock,so the blasting construction has a particularly large impact on underground pipelines and the construction of both sides of the China North Road.It is very easy to cause landslides in virtue of difficulty for distinguishing the karst cave and controlling the settlement deformation and plus the blasting construction of the large structure section with the civil air defense section and single cross section in the construction process.In order to obtain mechanical parameters of surrounding rock accurately,improve the stability of tunnel and reduce the risk of tunnel construction,a back analysis method of displacement based on the priority table and neural network is applied to obtain accurate mechanical parameters of surrounding rock and stability analysis of subway tunnel using numerical analysis and safety assessment techniques is carried out relying on the Nanhua Section Project of Dalian subway for the paper.The main research contents are as follows:(1)Used the Real-time Process Algorithm of priority table to determine mechanical parameters of surrounding rock mass for inversion,the orthogonal test design was used to find the optimized combination of back analysis parameters,the forward modeling was put to use to acquire the sample for training and for test.BP neural network optimized by hybrid genetic algorithm was used to find nonlinear mapping relationship between the inversion parameters and deformation of surrounding rock,deformation information of surrounding rock from the engineering field was taken as input samples,the mechanical parameters of surrounding rock were inversed and the sensitivity of the parameters was checked.(2)In the light of numerical simulation of five construction schemes for Dalian subway,the stability of subway tunnel under the support of advanced small pipe,system mortar anchor and perfusion of cement mortar behind initial support and so on was studied respectively.(3)According to analysis of the monitoring and numerical simulation data in the subway tunnel construction process,assessment index system of stability of subway tunnel was established,assessment level was divided and converted to triangular fuzzy numbers and the nonlinear mapping relationship between comprehensive index data and assessment level was found with BP neural network optimized by hybrid genetic algorithm.Results show that mechanical parameters of surrounding rock acquired by the back analysis method of displacement can reflect the overall state of the surrounding rock layer better;results of numerical analysis can provide technical guidance for the design pefection and construction control of the subway tunnel with small spacing;the established assessment model of stability of subway tunnel is strong consistent with actual situation.This study has been used in Nanhua Section Project of Dalian subway construction successfully and achieved good results.