Back Analysis And Stability Study Of Surrounding Rock Deformation Of Metro Shield Tunnel

In order to solve the problem of urban traffic congestion in China,the rail transit project has developed rapidly.The number and mileage of subways have been increasing.The surface settlement and collapse of tunnels have occurred.The speed of subway shield construction is also getting faster and faster,and its construction safety has attracted much attention.The monitoring and analysis and early warning of tunnel surrounding rock deformation and surface building settlement are particularly important.In this paper,taking multiple subway tunnel construction as an example,the finite element method is used to simulate the tunnel excavation process,which is affected by the parameter value,which leads to the accuracy reduction.The BP neural network and numerical simulation method are used to invert the mechanical parameters of the tunnel surrounding rock.Furthermore,the deformation law and stability influence factors of surrounding rock during shield construction are studied.The main research contents are as follows:1)According to the subway tunnel engineering situation and the shield construction method,a set of on-site shield construction monitoring schemes is established,and the changes of arch settlement and horizontal convergence displacement of monitoring points of different tunnel shield sections are monitored and analyzed.Combined with the on-site section shield construction section,a finite element model is established,and the influence law of the deformation of the tunnel surrounding rock during shield construction is numerically simulated.By changing the five physical parameter values of the relevant soil and orthogonal design,25 sets of model parameters were set up,and the corresponding 25 sets of arch settlement displacement and horizontal convergence values were obtained,which provided an experiment for BP neural network inversion model analysis.Data to verify the reliability of the inversion model.2)Combining the calculation results of finite element,the finite element-neural network inversion model is used to simulate the construction method of shield shield.The arch settlement and horizontal convergence value are used as input layer data,and the orthogonal parameters are used as output.The values in the layer are trained on the BP neural network model.The post-test difference method is used to test the trained BP neural network.When the posterior difference ratio C<0.35 and the small error occurrence probability P>1,it is concluded that the neural network prediction ability is excellent.Then the field monitoring data is input into the inversion model to obtain the corresponding physical parameter values,and the finite element software is used again to input the physical parameter values obtained by the inversion,thereby obtaining the inverted arch settlement displacement and the horizontal convergence value,and the measured values.A comparative analysis shows that the inversion results are reliable.This method is simulated by Ma Yin and Yue Bai interval,which shows that the method is applicable under different geological conditions.3)A combination of finite element method and strength reduction method is proposed to calculate the self-stability coefficient as a criterion for judging the stability of surrounding rock.The shear strength parameters are selected: cohesion force and internal friction angle.The strength reduction coefficient of tunnel surrounding rock at each section is calculated by strength reduction method,and the self-stability of surrounding rock is analyzed.The results show that the horse month interval is DK35+855 with a self-stability coefficient of 1.726 as the lower limit,and the partial section safety factor is less than the lower limit.Based on the Loganathan formula,the sensitivity analysis of surface settlement caused by grouting filling rate,support pressure ratio and eccentricity construction process is carried out.It is concluded that the excessive eccentric over-excavation has the greatest influence on the ground subsidence,followed by the grouting filling rate and the supporting pressure.The construction method of the most effective control of surface settlement is to control the shield attitude and grouting effect.A series of construction reinforcement measures and methods are proposed for the stability analysis of strength reduction method and the influence of construction technology on soil settlement.