Mechanical And Hydraulic Characteristic Of Single Fissure Rock Under The Action Of Water-rock Coupling

Friction sliding characteristics of rock are related to seismic dynamics and rock mass stability in engineering.Fracture is the weak plane in rock mass,and sliding along the fracture plane is the main movement form after rock fracture,and it is also the inducement of a variety of geological disasters.At the same time,there is a large amount of groundwater in the crust,and there is a complex water-rock coupling between the crust and the rock,which changes the structure of rock fracture plane and affects the mechanical and hydraulic properties of the fracture in the process of rock friction and sliding.Through the VS test(velocity step test)and the SHS test(slide-hold-slide test),the polishing marble and sandstone under the environment of different water-rock coupling friction strength,speed,dependence,permeability and mechanical and hydraulic characteristics,such as time dependence and contrast analysis of fracture surface microstructure changes before and after the test.The test results show that:(1)The friction strength of sandstone reaches its maximum when it is dry and increases with the increase of seepage velocity,and the permeability coefficient also increases with the increase of seepage velocity.After the test,a large number of granular wear objects remain on the fracture surface,and the "micro-convex body" on the fracture surface decreases with the increase of seepage velocity.Water lubrication reduces the friction strength of sandstone,and weakens the structural strength,leading to a large number of "micro-convex body" fractures,resulting in rolling friction and reducing the friction strength.The abrasive particles play a major role in controlling the friction strength.(2)The frictional strength of marble reaches its maximum when it is dry and decreases with the increase of seepage velocity,while the permeability coefficient increases with the increase of seepage velocity.After the test,there is a small amount of powdery wear on the dry fracture surface,the "micro-convex body" on the fracture surface decreases with the increase of seepage velocity,and the number and area of "pits" increase with the increase of seepage velocity.Water lubrication reduces the frictional strength of marbles,and weakens the structural strength,which leads to a large number of dissolution of surface minerals,dissolution after shedding or erosion after shedding.The fracture surface morphology plays a major role in controlling the frictional strength.(3)The friction force of sandstone and marble increases with the increase of confining pressure,while the friction coefficient and permeability coefficient decrease with the increase of confining pressure.The increase of confining pressure leads to the intensification of water-rock coupling,and a large number of "micro-convex bodies" are reduced.At the same time,with the increase of confining pressure,the fracture closes,the equivalent hydraulic opening of the fracture surface decreases,and the permeability coefficient decreases accordingly.(4)Both sandstone and marble show velocity strengthening,and the permeability coefficient decreases and tends to be stable with the extension of test time.In this paper,the confining pressure and seepage velocity have no obvious effect on the velocity dependence of rock.(5)In SHS test,the decreasing amount of friction strength of sandstone and marble in the control stage and the healing amount of friction strength at the moment of re-sliding are time-dependent.The absolute value of the decrease of sandstone friction strength decreases with the increase of fracture surface wetness,confining pressure or seepage velocity,while the healing value of friction strength increases with the decrease of fracture surface wetness,confining pressure or seepage velocity.The absolute value of the decrease of friction strength of marble decreases with the increase of fracture surface wetness,confining pressure or seepage velocity,while the healing value of friction strength decreases with the increase of fracture surface wetness,confining pressure or seepage velocity.The two are different with the variation of microstructure of fracture surface.