Research On Inversion Of Rheological Parametersan Of Surrounding Rock Of A Deep-buried Soft Rock Tunnel And Its Long-term Stability

With the continuous development of my country’s economy and the rapid advancement of the Western Development,the construction scale and scope of underground projects（especially tunnel projects）have continued to expand,and a large number of soft rock tunnels have appeared,and most of these tunnels have"large,long and deep buried"And many other features.However,soft rock has a significant rheological effect.Under the action of high ground stress,it will continue to deform over time,causing the pressure on the tunnel lining structure to continue to increase,which brings great challenges to the design of the tunnel lining structure and seriously threatens the tunnel.Safety and stability during operation.This article is based on a highway tunnel in Chongqing,and the analysis is carried out by theoretical analysis,field monitoring and measurement,and numerical simulation.The deep-buried soft rock section of the tunnel is selected as the research object.Based on on-site monitoring and measurement and numerical simulation methods,the BP neural network is used to establish the creep parameter inversion model;The long-term stability during operation has been systematically studied,and the main research contents are as follows:（1）Based on the theory of rheological mechanics,the characteristics and applicable conditions of various element combination models are introduced in detail.According to the type of tunnel surrounding rock and combined with the characteristics of measured displacement changes on site,the Burgers creep model is selected to consider the attenuation creep characteristics of soft rock.（2）Three different types of functions are used to perform regression analysis for the actual measured data of the tunnel site,and the best fitting function of the measured data of the vault settlement and the measured data of horizontal convergence is obtained.Based on the above fitting results,the changes in the tunnel surrounding rock deformation during the excavation process are evaluated and the final deformation value is predicted.（3）Use BP neural network to establish a displacement back analysis model,and calculate the creep parameters and lateral pressure coefficientλof the Burgers model through on-site measured displacements.Comparing and analyzing the calculated displacement and the field measurement results,the error between the two is relatively small,which verifies the reliability of the inversion parameters.（4）FLAC^3D finite difference software was used to establish a creep stratum-structure three-dimensional model,and the influence of surrounding rock creep effect on the long-term stability of the tunnel was analyzed.The origin software was used to fit the empirical formula of the lining safety factor over time to predict the tunnel The safe use life of the product is about 55 years.The results show that the lining safety factor of the tunnel decreases continuously due to the creep of the surrounding rock during the operation,but it basically meets the requirements of the long-term stability of the tunnel lining structure.（5）Based on the established three-dimensional numerical model,the long-term deformation and stress of the tunnel structure under different supporting opportunities of the second lining are analyzed,and the reasonable supporting time of the second lining of deep-buried soft rock tunnels is discussed;the lining thickness is determined based on the reasonable supporting time of the second lining Research and analysis of the change rule of the minimum principal stress extreme value of the lining under different thickness conditions,the calculation results show that the lining thickness between 0.45 and 0.50m is reasonable.