Study On Ultimate Displacement Of Surrounding Rock Supporting Structure In Highway Mountain Tunnel

China has a vast territory and complex terrain conditions.The surroundings rock supporting environment is very complicated due to the large mountainous area.When mountain tunnel is excavated,the stress mechanism and deformation mechanism between tunnel structure and surrounding rock are difficult to predict.If there is no timely support,surrounding rock structure will appear large deformation and even collapse phenomenon.In view of this phenomenon,this thesis took the ultimate displacement as the criterion of tunnel stability,and deeply studied the ultimate displacement value of tunnel surrounding rock initial support.The determination of ultimate displacement was of great significance to the safety of tunnel construction.Based on the Mohr-Coulomb strength theory,this thesis used ABAQUS software to calculate the displacement values of IV surrounding rock at different burial depths,different construction stages and different monitoring points.The order of sensitivity of surrounding rock parameters to arch displacement values was obtained by grey correlation analysis method.Rock mechanical parameters with higher sensitivity were as random variables of the orthogonal test,and the simulated displacement values of rock mechanics parameters were the dependent variables.Design-Expert 8.0.6 software was used for interactive analysis of each variable.The displacement function and limit equilibrium equation of the arch roof,arch waist and arch foot were deduced by referring to the R-S structure model.The main conclusions are as follows:(1)The geological strength index(GSI)quantitative value table was constructed by introducing the rock integrity coefficient(K_V),rock structure grade(SR),wave velocity ratio(K’_V)and structural surface grade(SCR).By using multiple geological characteristic parameters to constrain GSI value,the subjectivity of GSI value has been reduced and the precision of rock mechanics parameter has been improved.(2)The sensitivity of mechanical parameters of rock mass to vault displacement was ranked by grey correlation analysis.The sensitivity order of mechanical parameters of rock mass to vault displacement is γ、c、v、φ、E.All mechanical parameters of rock mass have the same sensitivity order to displacement at different monitoring points.(3)According to the principle of orthogonal test design,a displacement function of IV surrounding rock of highway mountain tunnel under 100m has been proposed based on displacement analysis.Based on the R-S model of structural function,the equilibrium equation of limit displacement at different monitoring points under 100m depth of IV level surrounding rock has been established.