Experimental And Theorectical Studies Of Rock Fracture Seepage Considering The Three-dimensional Morphology Characterization

With the rapid development of China’s economy and society,more and more large-scale water conservancy projects are being put into construction,and the bedrock and dam abutment of the dam will withstand greater physical pressure and infiltration pressure.In the excavation of water-rich rock mass,the rock is subjected to a three-dimensional stress state before excavation.After excavation,the stress state of the rock is changed,resulting in changes in the mechanical properties of the rock mass.Due to the influence of excavation,there are excavation disturbance zones in the rock mass,which contain many micro-cracks and macro-cracks.In the water-rich area,these cracks will provide a channel for the internal seepage of the rock under the action of infiltration pressure.Cause landslides,collapses and other hazards.Many scholars at home and abroad have found that under the action of high stress and seepage pressure,the law of seepage inside the ruptured rock mass after the peak is inconsistent with Darcy’s law,and its seepage phenomenon exhibits nonlinear seepage characteristics.To describe the seepage process inside the rock mass behind the peak,there will be a large deviation from the real situation,which is very unfavorable for guiding the seepage stability of the fractured rock mass in the actual project.Therefore,this paper adopts a self-developed temperature-stress-seepage multi-field coupled rock test system to analyze the change of physical and mechanical properties of rock during compression,and on this basis,the post-peak fractured rock under different confining pressures is studied inside.The evolution law of water flow velocity and seepage pressure gradient is to provide a basis for the analysis of the physical mechanism of rock fracture seepage through the three-dimensional optical scanning of the fracture surface of the rock specimen after seepage.The research content and research results of this article are mainly reflected in the following aspects:(1)The triaxial compression test of granite and metamorphic slate was carried out.The results show that the stress-strain curve of the rock shows four different stages during the stress loading process,namely:the first stage is when the external force on the rock is small,The micro-cracks existing inside the rock will be gradually squeezed and closed;the second stage is that the rock begins to deform linearly as the stress gradually increases,and the cracks in the rock begin to develop and expand;the third stage is that the stress increases continuously The rock begins to deform nonlinearly,the cracks in the rock increase significantly,and the interconnection eventually leads to the penetration of the rock cracks;the final stage is when the rock reaches the ultimate compressive strength,the stress is concentrated in the local deformation area,and the cracks extend through.In the end,the specimen slips and slips,and the rock breaks down,losing its stability.According to the development trend and change speed of the stress-strain curve during the loading process,the change process inside the rock at each stage is summarized.The test results show that the peak compressive strength of granite is greater than that of metamorphic slate,indicating that granite is stronger than metamorphic slate,and it is not prone to deformation and damage under high stress.(2)Study the evolution law of the seepage phenomenon inside the rock along with the gradient of the seepage pressure under a certain confining pressure state of the cracked rock after the peak.The results show that the post-peak seepage phenomenon in the rock gradually changes from a linear seepage to a non-linear seepage process as the osmotic pressure gradient increases,indicating that as the osmotic pressure gradient increases,Darcy’s law has changed and is no longer applicable.Therefore,by using the Forchheimer equation to quantitatively describe the relationship between seepage flow and seepage pressure gradient,the seepage process is divided into two stages of Darcy flow and nonlinear seepage flow,and the nonlinear factor E is introduced,and most of the actual rock engineering projects define E=0.1 is used as the boundary point between linear flow and nonlinear flow,so as to solve the threshold and Reynolds number of critical Darcy flow.In order to quantify the energy change during the seepage process of rock fissures,the relative loss of momentum-Eulerian number is introduced to describe.The Euler number has a tendency to decrease rapidly and then gradually stabilize.(3)The three-dimensional structured light scanner was used to measure the surface of rock fractures of granite and metamorphic slate,and the roughness and undulation characteristics of rock fractures were studied using joint roughness coefficient JRC and morphological statistical parameters.The results show that from the macroscopic characteristics,the overall undulation of granite is large,but the microstructure is smooth;on the contrary,the general undulation trend of the metamorphic slate fissure surface is slow,but the microstructure is rough..In fact,one of the main factors affecting the undulation and roughness characteristics of the fracture surface of granite and metamorphic slate is its lithological characteristics.Due to the different mineral composition,geological origin,physical and mechanical properties of the rock,different types of rock failure surfaces the difference in roughness.(4)The three-dimensional geometric model of rock fractures is digitally reconstructed based on the three-dimensional scanning results of the fracture surface,and numerical simulations under different conditions are carried out.The results show that,whether it is granite or metamorphic slate,the closer to the crack wall,the smaller the flow velocity of the water flow.The faster the flow velocity at the greater the roughness of the rock crack,the smoother the roughness,the more the flow Yu stable.The flow velocity in granite is obviously smaller than that in metamorphic slate.The location of the water flow inlet is the most unstable,and the physical properties of the rock change the most at this junction.Therefore,at the water flow inlet,the fluctuations in the velocity,pressure and vortex size of the fissure water flow are more obvious.The pressure of the fissure water flow is gradually reduced by the rough consumption with the wall surface.The pressure gradient changes faster where the undulation is greater,and the smoother the fissure roughness,the smaller the pressure gradient change.The fissure water flow easily passes through the place where the undulation is large,and the vortex phenomenon is easily formed,which causes the pressure gradient to decrease rapidly,and in the smoother area,the vortex is not easy to form.