Study On The Seepage Regularity Of Rough Rock Mass Fractures Under The Hydraulic Mechanical Coupling

Geological tectonic movements and engineering excavation disturbances affect the stress state of the original rock,change the mechanical properties of the rock,and induce the expansion and penetration of micro-cracks in the rock mass.The existence of these pores and fractures provides space for fluid storage and fluid migration channel.The seepage problem of fractured rock mass involves the safety and stability of major projects such as coal mine water inrush,water conservancy and hydropower,and nuclear waste disposal.The change of the stress field will affect the change of the seepage characteristics in the fracture.The research on the seepage law of fractured rock under complex hydraulic coupling conditions has always been an urgent scientific problem to be solved in engineering fields such as hydrogeology and rock mechanics.Aiming at the seepage characteristics of a single fracture in rock mass under stress,this paper adopts the research method combining laboratory test,theoretical analysis and numerical simulation to study the seepage law of matched and unmatched single fracture under different confining pressure and roughness conditions,and discusses the nonlinearity of fluid flow in fissures,the change of hydraulic aperture and the loss coefficient along the way are studied,and the influence of roughness and fissure opening on the seepage of fractured rock mass is studied through numerical simulation.These research results provide some references for better understanding of seepage in fractured rock mass.The main findings are as follows:① Through the independent modification of the rock fracture seepage comprehensive experimental system,the single fracture seepage experiment of matching sandstone and granite under different confining pressures was carried out.It is found that the pressure gradient ▽P and the volume flow Q in the fractures of sandstone and granite are matched,and it is in accordance with Darcy’s law;the increase of confining pressure does not change the linear mechanism of the flow state,but will cause the pressure gradient ▽P and volume flow Q.The slope gradually increases,and the flow resistance of the fluid increases.The hydraulic aperture of sandstone and granite decreases continuously with the increase of confining pressure,but the decreasing rate becomes slower.In the same range of confining pressure variation,the change of hydraulic opening of granite is more significant than that of sandstone.② The unmatched sandstone fracture seepage test shows that the increase of pressure gradient ▽P does not lead to a linear increase in volume flow Q,which proves that there is a nonlinear relationship between pressure gradient ▽P and volume flow Q.The Forchherier equation can describe this kind of nonlinear flow well.The regression fitting linear term coefficient a and nonlinear term coefficient b both increase with the increase of confining pressure,and the magnitude of the increase of the nonlinear coefficient b is greater than that of the linear coefficient a.The apparent hydraulic conductivity Ta decreases with the increase of Reynolds number.Under the same flow conditions,the pressure drop consumed by the nonlinear part of the Forchherier equation will increase with the decrease of permeability,and the increase of the pressure gradient ▽P will lead to the continuous increase of the nonlinear factor E.③The effects of roughness and fracture aperture on fluid flow characteristics were studied based on numerical simulation methods.As the aperture of the fracture decreases,the nonlinearity between the pressure gradient VP and the volume flow Q becomes more obvious;when the roughness and inlet velocity are constant,with the increase of the aperture of the fracture,the flow rate in the fracture surface also increases continuously.When the fracture aperture and inlet velocity are constant,with the increase of roughness,the pressure gradient flowing through both sides of the fracture surface increases continuously,resulting in a slow increase in volume flow.With the increase of roughness,the equivalent hydraulic aperture of rock fissures will decrease,the critical Reynolds number Rec will decrease,and the non-Darcy coefficient β will increase.