The Method Of Determining The Limit Displacement Of Surrounding Rocks Stability For Deep Soft-rock Tunnel Based On The Catastrophe Theory

With the development of underground space projects continue to develop deep,the large deformation and stability of soft rock under deep buried condition becomes a difficult technical difficulty,therefore,it is of extremely great engineering significance to study the imit displacement of surrounding rocks stability for deep-buried soft rock tunnels.Referring to the "Code for Design of Highway Tunnels(JTGD70-2004)" to select surrounding rock test parameters and tunnel section forms,and conduct uniform test design on the physical and mechanical parameters of surrounding rock and tunnel support parameters.A constitutive model that can clearly and comprehensively reflect the elastic-viscoelastic-viscoplasticity CVISC model in soft rock rheology is selected as the constitutive model for FLAC3D numerical simulation of deep-buried soft rock tunnel excavation,then analyzed the displacement and stress of the surrounding rock after the completion of the excavation in the deep-buried soft rock tunnel.The cusp catastrophe model is constructed based on the volumetric variation sequence of the yield zone in each excavation step monitoring section obtained from the numerical simulation results,and the mutation eigenvalues ? are solved,then through the change of the catastrophe eigenvalue of the excavation step,the ultimate displacement value of the surrounding rock instability of the deep-buried soft rock tunnel is obtained,and the training sample is constructed by using the uniform test design parameters and the volumetric catastrophe theory of the plastic zone to obtain the limit displacement value,taking the ultimate displacement of surrounding rocks as the dependent variable and the physico-mechanical parameters of surrounding rock and tunnel supporting parameters as independent variables,mathematical prediction model for building subsidence displacement and ultimate horizontal convergence displacement of surrounding rock of deep-buried soft rock tunnel by using multiple linear regression algorithm;Using evolutionary support vector regression algorithm(SVR for short),the mathematical prediction model for the deep dome subsidence displacement and ultimate horizontal convergence displacement of deep-buried soft rock tunnel surrounding rock was established respectively,and the accuracy of the mathematical model was verified,it will provides certain reference experience and relevant theoretical guidance for the design and construction of deep-buried soft rock.The paper made innovative achievements are as follows:(1)In this paper,the theory of volumetric catastrophe in plastic zone is put forward,based on the three-dimensional numerical simulation of viscoelastic plastics in the construction of deep-buried soft rock tunnel,a method for determining the stability limit displacement of surrounding rock in the construction of deep-buried soft rock tunnels is proposed.(2)In this paper,an evolutionary support vector regression(SVR)algorithm was introduced,through sample training,an SVR intelligent model was established between the stable ultimate displacement of rock mass and the rock physical and mechanical parameters and engineering geological conditions.Based on the SVR theory,an equation for the calculation of the stability limit displacement of surrounding rock in the construction of deep-buried soft rock tunnels is proposed.