Study On Damage Of Rock Mass In Excavated Disturbance Zone Considering Fluid - Solid Coupling

Considering both unsymmetrical pressure and percolation effects on surrounding rock, a damage variable was applied to evaluate the safety and stability of rock in excavation disturbed zone.Based on the previous studies, it summarized the reason for formation and distribution of the initial geo-stress as well as its importance in tunnel engineering. According to the practical situation in construct site, the reasons of unsymmetrical pressure effects in tunnel are analyzed and then it gave two calculation methods used in tunnel designing. According to a set of simple numerical simulations, the importance of balancing the geo-stress was verified and some methods to achieve balancing the geo-stress in finite element software ABAQUS/CAE are introduced in detail.After considering the influence of percolation and the previous researches, a new form of single-phase flow continuity equation based on Darcy’s Law was derived by introducing rock coefficient of compressibility Cf and liquid elastic coefficient of compressibility CL; Then, stress equilibrium equation of the deformation field was derived through virtual work principle and effective stress of porous media principle. By means of introducing pore water pressure on the time derivative as the same variable, it could be coupled the percolation and stress equation finally.Based on ABAQUS/CAE. multiple groups of numerical simulation experiment have be taken on tunnel with unsymmetrical pressure and symmetrical pressure in considering percolation effects and without considering fluid-structure coupling respectively. The main results of these numerical simulations which conclude surface displacement, mechanical characters of the concrete lining and the plastic range of the disturbed surrounding rock were compared to determine the impacts of fluid and unsymmetrical pressure on the mechanical properties of rock.Based on continuum damage mechanics theory, a further scalar damage variable that associated with plastic strain was put forward according to the previous elastic-plastic damage model, and then applied it into Mohr-Coulomb yield criterion. In consideration of fluid-solid coupling effect and referring the previous researches on rock’s permeability evolution in the process of damaging, a theoretical elastic-plastic model of rock damage with the corresponding finite element numerical model was established.Taking the new Guanjiao tunnel of Qinghai-Tibet Railway as data sources and using subroutine USDFLD written by fortran language, damage variable can be defined and coupled with the plastic strain through ABAQUS/CAE platform. Finally, a numerical simulation of the tunnel with unsymmetrical pressure effects and influences of percolation had been taken. According to the simulation results, the damage evolution of surrounding rock in excavation disturbed zone had been obtained from the variation of stress, pore pressure etc. in tunneling process. Compared with the traditional method using plastic distribution only, the damage variable evaluation on surrounding rock is more superior and rational.