Damage Rupture Process Of Layered Rock And Excavation Damage Zone Evaluation Of Tunnel Under Multi Field Coupling

Aiming at the large deformation phenomenon of grating frame distortion,dome shotcrete cracking and bottom drum under the effect of multi – field coupling in layered rock tunnel,comprehensive application of lab test,numerical simulation,theoretical analysis,physical simulation and field testing and other methods,and supplemented by SEM and CT scanning and other microscopic test means,the damage characteristics of layered hydro-shale and layered composite rock mass,the supporting mechanism of tunnel support structure and the calculation and detection method of tunnel excavation damage area have been studied.According to the test results,a coupling model of seepage-stress-damage(HMD)was built.This model studies true triaxial numerical computation of stratified pore-like holes under multi-field coupling(HMD)and support structure,and analyzes the damage evolution rule.The numerical calculation model was applied to the calculation of excavation area(EDZ),and the results of numerical simulation were verified by three-dimensional ultrasonic imaging of geological radar and rock mass.The results show that the numerical application model is effective in field application.The main results achieved are as follows:(1)Strength parameters and seepage characteristics of the layered rock mass are closely related to their bedding angle and moisture content.The water content has a linear relationship with the damage of its strength parameters.That is,the higher the water content is,the strength profile is more likely to decline linearly.And the influence of bedding on its strength characteristics is relatively complex.In general,the compressive strength and tensile strength decrease before rising with the increase of the bedding angle.The internal mechanism of the above-mentioned changes was obtained by analyzing the microstructure of shale with different water content.Namely,the internal mineral particles at the face of the shale bedding swell up with water,resulting in the production of expansion force.This expansion force makes the internal structure of the shale become loose and broken,micro-cracks gradually increased and widened,and the macro performance of the secondary cracks increased.The adhesion between the mineral particles are also reduced so that the shale strength decreases and its deformation is intensified under the influence of the water.(2)Based on the microstructure method,the microstructural tensor can be introduced to reflect the distribution of particles and microcracks in the material.The anisotropy parameters of the rock are defined by the tensor,and the anisotropic parameters are introduced into the Drucker-Prager yield criterion,which can take account of inherent anisotropy of the rock.The damage variable of shale is deduced by Weibull distribution stochastic statistical function,and the damage constitutive model is established according to the improved Drucker-Prager yield criterion.According to the characteristics of rock penetration,the permeability evolution equation is established by percolation theory.Finally,based on the classical Biot pore elasticity theory,the seepage-stress-damage coupling(HMD)model is established by introducing the damage tensor.(3)In order to analyze the mechanism of the supporting structure and supporting characteristics in the layered and weak rock tunnel,the mechanics and deformation characteristics of the rock anchored by ordinary thread bolts and steel tubes were firstly studied through the indoor physical simulation test method of the uniaxial compression test.And the supporting mechanism of the anchor to the layered rock was obtained.Then,the bending behavior of grille and I-beam was studied by three-point bending test of steel arch-concrete composite beam,and the failure process of steel arch-concrete composite beam under load was analyzed.Finally,the support characteristics of the common drug bolts,steel pipes,grids and I-beam in layered rock and silty clay were analyzed by stress test of anchor force,surrounding rock pressure and steel arch.On the basis of the understanding of the mechanism of supporting structure in the tests,the strength,deformation characteristics and crack propagation rule were studied by uniaxial compression test and CT scanning in the lab.The true triaxial test of rock under seepage-stress-damage coupling was carried out by using 3DEC numerical simulation method.And the damage evolution process and the distribution characteristics of fractured flow were analyzed.(4)By means of numerical simulation(3DEC)and geophysical prospecting method,the damage zone of layered surrounding rock excavation in tunnel(EDZ)was calculated and detected,and the two are in good agreement.This indicates that the established 3DEC model can be used to analyze the engineering problems under the seepage-stress-damage coupling(HMD)in the field,and the simulation results can be used to guide the tunnel design and construction.