Coupling Theory Of Seepage-Damage-Fracture In Fractured Rock Masses And Its Application

The mechanical properties of fractured rock masses in the seepage field and mechanism of water-rock interaction have become one of front direction concerned with rock mechanics field.The exist and change of seepage field is one of important reasons for the instability of rock masses engineering,even leads to large-scale geological disasters.With aggravating the branch cracks seeding,propagation and coalescence,seepage pressure in fractures leads to progressive failure of rock engineering.In the macro level,this process is also the process that seepage lead to the damage of rock mass strength,on the other hand,the change of rock mass stress field and the damage propagation of rock fractures cause the change of seepage properties and accordingly change seepage field distribution.Coupling effect of damage evolution of rock mass stress and seepage can be called coupling of seepage-damage-fracture in fractured rock masses.Coupling theory of seepage-damage-fracture in fractured rock masses has a good prospect of engineering application in the field of hydropower engineering,mining engineering slope engineering and tunnel engineering.The studied title is come from National Science Foundation Project (grant number:50774093):Coupling theory of rheology-damage -fracture in fractured rock masses and application under water-rock interaction.Using fracture and damage mechanism theory,the paper has researched the fracture mechanic property of fractured rock masses,and damage deformation of fractured rock masses under the action of seepage-stress.The paper has systematic studied seepage-damage-fracture coupling mechanism with the method of experimental study, theoretical analysis and numerical simulation,the research has focused on the subject of transformation effect of micro-macro analysis structure of fractured rock masses and macroscopic damage mechanical response of fractured rock masses under the action of seepage pressure.Around coupling theory of seepage-damage-fracture in fractured rock masses and application,the paper has carried out the research work involving several aspects as follows:(1)Study the rules of compression shear fracture of rock cracks,the wing cracks propagation and the rock bridge coalescence.The.wing cracks model subjected to compression-shear stress under the action of seepage-stress has been established firstly and the FEM numerical validation is aslo demonstrated.The damage fracture mechanics model and the fracture failure criterion of rock multi-crack body has been established.theoretically,the crack propagation subjected to rock mass hydraulic fracture has been revealed.(2)The macro-mechanical experiments on regular cracks body in rock-like materials and the test on rock fracture toughness have been made.Using white cement as the similar materials,the rock-like specimens in which the cracks were arranged in different echelon design through pre-installed steel slice were produced,the research on the models of fracture propagation and coalescence,as well as the law of strength variation with the cracks collocation and crack numbers under uniaxial loading were summarized systematically.The fracture toughness of multi-series rock specimens were measured by using the double torsional method,The results showed that there was a linear relation between rock fracture toughness and young modulus.(3)Using micromechanics theory,the paper has studied the laws of damage deformation of fractured rock masses subjected to the action of seepage-stress.Synthetically considering initial damage and damage evolution of rock mass,the constitutive model of seepage-damage-fracture coupling in fractured rock masses and permeability tensor evolution equation have been established,the meso-damage mechanics calculation program WFRD^2D for the stress-strain behavior of water-bearing fractured rock masses at the pre-peak has been developed.(4)From the aspect of rocks structure mechanics.based on the fluid-solid coupling model of fine pore-fissure rock media,the dual mida model for seepage-damage-fracture coupling in fractured rock masses has been put forworded.The coupling effect of seepage field on damage field not only is embodied by the fact that hydraulic gradient acts on stress calculation unit as body force or face force,but also the fact that the seepage pressure weakens element stiffness matrix.The coupling effect of damage field on seepage field is embodied by the fact that the permeability coefficients of the rocks and fractures depend on the stress,the wing cracks length.In coupling model,the discrete hydromechanical model is used to simulate fracture seepage,the equivalent-continuum model of seepage is used to simulate fracture network seepage in rock masses.(5)Finite element program DSDFC.FOR for the dual mida model for seepage-damage-fracture coupling in fractured rock masses has been developed,the 3D jointed elements are used to simulate discrete jointed rock mass during the stress analysis of discontinuities and 2D isoparametric elements are used to simulate discontinuities during seepage analysis of discontinuities,So the different media can exchange water,and water head,displacement of nodes which are in the interface between two models are equal.(6)Baesd on FLAC^3D existing computation modules,the programs of seepage-damage-fracture coupling(extended FLAC^3D model) in fractured rock masses has been developed.The developed calculation program has powerful numerical calculation function,including damage mechanics calculation module,seepage calculation module and double-field coupled calculation module.(7) The theory of seepage-damage-fracture coupling was applied to the fractured rock bank slope during the rising of water level in reservoir and unlined pressure tunnels.The laws of the distribution of the seepage field and damage field evolution in the fractured rock bank slope are obtained during the impoundment process of the reservoir.A preliminary study on deformation of bank slope during the rising of water level in reservoir also is made.Coupling Analysis holds that deformation of bank slope is due to the interaction of increment seepage force and increment uplift force.For the fractured bank slope with the hight relative elevation of water storage,the increase of seepage pressure in fractures lead to damage zone growth with starting-crack and fracture propagation occuring.High seepage pressure leads to damage zone growth in unfavorable fault zone and even transfixion may be the important reasons which result in bank slope instability.the paper also has studied the hydraulic splitting state,the distribution of the seepage field and the inner water leaking in unlined pressure tunnels.The hydraulic splitting safety factor of pressure tunnel under inclined ground is proposed firstly.The hydraulic splitting safety factor is in high correlation with geometric characteristics and mechanical characteristics of rock cracks and rock fracture toughness.(8) Industrial experiment on pressure water injection into coal to fracturing and weakening top coal and numerical study of the progress of coal seam water infusion were developed.Industrial experiment of pressure water injection into coal on the working face 4309 of fully mechanized sublevel caving mining in Lu'an Wangzhuang Mine were developed.The plan of weakening top coal by using water pre-infusion were put forward.The implementation of weakening top coal by using water pre-infusion made the coal face recovery impove 17%,dust concentration decrease 56%,production increase 45%,increased economical benefits of enterprise.The theory of seepage-damage-fracture coupling was applied to pressure water injection into coal,the laws of the coal seam water infusion course,coal mass deformation and damage field evolution in coal rock have systematic studyied form the aspects of seepage mechanics and rock mechanics.The mechanical principle in pressure water injection into coal to fracturing and weakening top coal lies in fracture damage evolution of fissure structure of coal rock subjected to high seepage pressure.