Study On The Stability Of Tunnel's Surrounding Rock Based On Three Catastrophic Models

Due to tunnel's construction,the former state of surrounding rock is broken.There exists stress redistribution in stratum,leading to the decrease of rock's strength and stability.It is easier to cause the engineering disasters such as instability of surrounding rock,collapse and water inrush.And these accidents can also bring adverse influence to tunnel construction and operation.Therefore,it is always an important research project in academia about accurately analyzing mechanical mechanism of unstable failure in surrounding rock due to the variation of stress,deformation and environment conditions,and grasping the effective instability criterion.Based on catastrophe theory,this paper researches on the unstable mechanism of surrounding rock with different failure forms.Through theoretical analysis,three catastrophic models of chamber-surrounding rock system are established with general equation.The formulas of potential function,balance equation and bifurcation set are obtained respectively in the failure pattern of tension,shear and tension-shear.And the acquired approaches of parameters including control variations,rigidity ratio and judging criterions are given.When the system occurs to catastrophe,the relationships between related parameters are studied.On the basis of abovementioned results,the correctness of theoretical deductions in this paper are verified by comparing the expressions of rigidity ratio and control variations with other relevant references.And the plastic radius of chamber are deduced with a classical constitutive equation.By adopting finite difference software FLAC^3D,The excavation process of Lanzhou Metro's tunnel is stimulated and analyzed.And the variation rules of displacement and plastic regions in metro's tunnel are displayed during excavating.Based on the contours of plastic regions and displacement values,the formulas of surrounding rock's potential function are obtained by linear regression in key measuring points of different sections.According to the instability criterions of catastrophic models,the stability states of surrounding rock are judged in stepped excavations.And the numerical analysis and theoretical results are compared.The study results indicate that the systematic instability of chamber-surrounding rock system is controlled by the internal variations and all kinds of external factors are only the triggering factors for the instability of system.