Dynamic Inversion For Deformation Parameters Of Tunnel Surrounding Rock Based On Damage Deterioration Effect

In recent years,the phenomenon of instability and failure of tunnel surrounding rock often occurs,the fundamental reason is the inaccurate judgment of rock parameters around the tunnel and the unclear deterioration law.At present,many scholars have conducted back analysis research on the initial deformation parameters of surrounding rock based on the actual monitored displacement values in engineering.However,these methods do not consider the deterioration and reduction of some surrounding rock parameters.Therefore,it is an important research direction of displacement back analysis to inverse the dynamic change process of surrounding rock deformation parameters,and it has certain reference significance for studying the whole damage evolution law of surrounding rock.Based on the engineering background of Xingzishan Tunnel,this paper studies the vertical settlement and horizontal deformation of the large deformation section of the tunnel respectively.Based on the sensitivity analysis of various parameters and the comparison of displacement back analysis methods,a dynamic displacement back analysis method considering the damage and deterioration effect of surrounding rock is proposed and verified.Finally,the change process of surrounding rock deformation parameters and the influence range of excavation disturbance are further discussed.The main conclusions and achievements are as follows:（1）Through sensitivity analysis of different related parameters affecting the deformation of surrounding rock,the results show that the parameter with the greatest influence on the vertical deformation of surrounding rock is elastic modulus E;The parameter with the greatest influence on the horizontal deformation is the internal friction angleφ,followed by the lateral pressure coefficient K₀ and the elastic modulus E.（2）By comparing the two methods of displacement back analysis,it is found that the optimal solution of each parameter can be obtained better by using BP neural network.（3）Considering the damage and deterioration effect of surrounding rock,the fitting equation of the deterioration law of vertical elastic modulus E_y of surrounding rock is established by dynamic displacement back analysis,and the vertical deformation of surrounding rock in subsequent sections is predicted.（4）Based on the horizontal deformation of surrounding rock,the back analysis of two-parameter dynamic displacement is carried out,and the deterioration law equation of the horizontal elastic modulus E_x of surrounding rock is fitted.It is found that the damage and deterioration of carbonaceous slate also has the characteristics of anisotropy.For tunnel engineering of this kind of rock mass,the horizontal geostress is always greater than the vertical geostress.