A Study On Roughness Characterization Of Rock Mass Discontinuities And Shear Mechanical Behavior Under Confining Pressure

The rock mass is a discrete medium composed of a continuous medium of intact rock blocks and discontinuities with discontinuous features.The intact rock masses need to interact through the discontinuities with discontinuous features.In addition to the fact that discontinuities make the physical and mechanical properties of the rock mass have the characteristics of anisotropy,discontinuity,and inhomogeneity,it should be noted that the discontinuities destroy the integrity of the rock mass and determine the potential failure mode of the rock mass.For the common discontinuity of unfilled open type or filled with weak medium in rock mass engineering,its tensile strength is relatively small,and it is generally considered that the discontinuity does not have the ability to withstand the tensile load.Under the action of compressive shear load,there have been many shear failure disasters along the rock mass discontinuities,which brought huge engineering renovation costs.The stability of rock mass depends largely on the shear strength of the discontinuity in the mechanical environment of the three-dimensional stress state.The shear strength of the discontinuity in the mechanical environment of the three-dimensional stress state is the key mechanics index for the evaluation of rock mass stability and disaster prevention.The essence of the existing discontinuity shear strength estimation model is"how to evaluate the shear strength of the discontinuity according to the roughness",that is,it mainly reflects the influence of the mechanical properties of the discontinuity and the two internal factors of the roughness on the shear strength.Shear strength estimation models are mostly based on direct shear tests on discontinuities.However,the discontinuity of deep rock mass is in a mechanical environment of three-dimensional stress state which is different from the direct shear test.This mechanical environment will cause the peak shear strength of the discontinuity,the dilatancy-closure characteristics of the discontinuity,and the shear mechanical behavior of the gap width.The changes,different from the direct shear mechanical behavior,will cause the discontinuity shear strength estimation model,the rock mass stability evaluation method and the disaster prevention countermeasures established around the discontinuity direct shear mechanical behavior to be probably unsuitable for this geological situation.Therefore,it is urgent to carry out research on the shear mechanics characteristics of the discontinuity in the mechanical environment of the confining pressure effect,reveal the correlation mechanism between the surface roughness and the triaxial shear strength of the discontinuity,and then provide a theoretical basis for the evaluation of the stability of engineering rock mass discontinuity and the formulation of disaster prevention countermeasures.To this end,this paper takes the confining pressure effect rock mass discontinuity roughness characterization and its correlation mechanism with the shear mechanical behavior as the theme,and comprehensively uses theoretical analysis,experimental research and particle flow simulation analysis to carry out the confining pressure effect rock mass discontinuity shear strength test method,comprehensive parameters of rock mass discontinuity roughness evaluation,rock mass discontinuity roughness characterization,confining pressure effect rock mass discontinuity shear mechanical behavior,and particle flow analysis research of confining pressure effect rock mass discontinuity shear mechanical behavior.The main conclusions are as follows:1)In order to consider size effect,anisotropy characteristics of rock mass discontinuity surface roughness and the point spacing effect at the same time,the ratio of the average undulation amplitude of the discontinuity and the horizontal projection length is used to reflect the undulation amplitude and size effect characteristics of the discontinuity.The average value R_vh of the ratio of the vertical projection length to the horizontal projection length of the discontinuity in the tangential direction reflects the anisotropic characteristics of the roughness of the rock mass discontinuity.Different point spacing is used to discrete the Barton standard discontinuity contour line to establish different point spacing roughness evaluation formula that reflects the effect of point spacing on the surface roughness of the discontinuity.And,the rock discontinuity roughness evaluation index was proposed based on the above,by which the evaluation formula of discontinuity roughness of different point spacing was established.2)Based on the confining pressure effect structural surface shear strength test and structural surface roughness characterization,the research on the correlation mechanism between structural surface roughness and shear strength was carried out.A confining pressure effect structural surface shear strength model was established by fully considering the fact that the influence of structural surface roughness on shear strength will be weakened by the increase of normal stress σ_n caused by lateral pressure,and the increase of σ_n as well as the decrease of tensile strength σ_t.3)Based on the particle group contact discrimination method on both sides of the discontinuity,a particle flow simulation program for the confining pressure effect discontinuity shear test is formulated.The simulation results are basically consistent with the results of triaxial shear physical tests,which proves that this method can effectively simulate and reproduce the shear mechanical behavior of rock mass discontinuities and physical test results,and has a good applicability to further explain and verify the triaxial shear mechanical behavior of discontinuities.