Study On The Pressure Seepage Evolution Characteristics And Hydraulic Mechanism Of Fractured Rock Mass

In the process of water disaster in underground engineering,the water seepage caused by the fracture of the rock mass is relatively high.Under the condition of high pressure and high water pressure,the seepage pressure will not only change the internal stress state of rock mass,weakening the mechanical strength,but also have a strong destructive effect on the structure of fractured rock mass.The fracture network of rock mass expands,and the seepage resistance decreases continuously,which finally forms the low resistance seepage channel and causes the water inrush and other disasters.Through theoretical analysis,laboratory simulation test and field measurement,the structure evolution of seepage control effect and its mechanism of hydraulic pressure are studied and discussed in detail,and the following results are obtained:(1)The permeability evolution characteristics of soft rock and hard rock during the whole stress-strain process and the difference of permeability corresponding to different deformation stages are analyzed and compared by means of servo penetration test.The permeability and deformation degree have close relevance.The permeability appears an obvious change with the formation and expansion of fracture network.There are obvious differences between the permeability and the correlation degree between the brittle hard rock and the plastic soft rock.Based on the experimental results,the relational model between permeability and stress before peak strength is established,and the formula is also established.(2)The permeability evolution characteristics of fractured rock mass under the action of high pressure are studied through the in-situ high pressure permeability test of rock mass with different structures.Based on the fitting analysis of experimental data of seepage pressure,seepage water and inlet and outlet water pressure,the initial seepage pressure and maximum seepage pressure of rock mass are presented.Meanwhile,the maximum seepage pressure can be used as a parameter to measure the reducing infiltration capability of fractured rock mass.Based on the above,the relationship between permeability coefficient and seepage pressure is established,which reveals the law of crack propagation and its relationship with permeability under high seepage pressure.(3)Based on the identification technology of acoustic emission information for rock fracture process,the correlation between permeability and crack propagation of rock mass is analyzed from the theoretical point of view.The research shows that the destructive effect of seepage pressure on the fractured rock is mainly divided into two modes:the squeezing failure and the splitting failure.The acoustic emission parameters prevents the segmented characteristics with the stress increasing and exists catastrophe point under the action of water pressure and stress in the process of crack propagation.In this paper,the yield coefficient of rock fracture(the ratio of the time corresponding to the catastrophe point to total rupture time)is defined and used to define the critical information of rock fracture,which well explains the characteristics of the evolution of rock deformation and the hydraulic mechanism.(4)The seepage characteristics of fractured rock mass are studied by means of laboratory model tests.The test results show that,the penetrating fracture channels generally show high seepage resistance under seepage condition,and the fissure network seepage is turbulent flow.Seepage pressure and channel are two key factors that influence the evolution of fractured rock mass.On the one hand,the relationship between seepage velocity and hydraulic gradient of fractured rock mass is power function or quadratic function.The seepage velocity decreases with the increase of the channel width under definite seepage pressure.On the other hand,the seepage pressure decreases with the increase of distance during the fracture network seepage process,which means that the reduction of seepage pressure is related to the increase of seepage resistance.For a certain fracture permeability condition,the hydraulic gradient along the seepage path shows a negative exponential decay.(5)Physical response characteristics of groundwater and high viscosity chemical grout are compared during seepage process in fractures based on model test method.Seepage velocity of groundwater can be quantitatively determined according to the variation of natural electric field along the path of water seepage.The location of the seepage flow of the grout and the filling effect on the fracture space can be determined according to the rising of the excitation current and the variation of the apparent resistivity along the seepage path of chemical grout medium.The experimental results of the permeability of them are compared and analyzed in this paper,reveals that the structural control effect of rock fracture on groundwater seepage.