Study On Numerical Simulation Of Permeability Characteristics And Seepage Flow In Fractured Rock Masses

Fractured rock mass is composed of rock blocks and discontinuities,it does not belong to the continuum,while as the hydro-mechanical problem of rock mass is analyzed in practice,rock mass is always regarded as equivalent continuum by using the theory of equivalent continuum theory.The permeability of rock blocks in rock mass is very low compared with fractures,and the permeability of rock blocks can be neglected.Actually,the seepage problem of rock mass is fracture network seepage,It is assumed that the seepage in the fracture obeys Darcy's law,the equivalent continuum model uses flow equivalent principle,the flow in the fracture is equivalent to the rock mass,which is regarded as continuum with anisotropic symmetric permeability tensor.?1?Based on detailed analysis for the random distribution laws for every single geometrical property for rock fracture,and the assumptions of fracture network model,the computational programs have been coded for two-dimensional random fracture network model by using Monte-Carlo to simulate the fracture network model of rock mass.?2?The equivalent continuous medium model is used to study the seepage characteristics of fractured rock mass.The two key parameters are the representative elementary volume?REV?and permeability tensor.Through the calculation of permeability coefficient of different scale and direction,principal permeability values are calculated by referencing permeability ellipse method,and then determine the permeability tensor.Based on constants and tensor properties,the representative elementary volume?REV?is further determined.?3?The distribution of fractures with different geometric features in the fractured rock mass makes the permeability characteristics of rock mass have an objective anisotropy in space.In this paper,the influence of geometric features?density,trace and occurrence?on the permeability tensor of rock mass and the representative elementary volume?REV?are studied.The study found that,with the increase of the crack density,the representative elementary volume?REV?becames smaller;with the increase of intersection angle,the representative elementary volume?REV?decreases first and then increases;with the increase of trace,the representative elementary volume?REV?decreases gradually,when the track up to a certain size,it has no effects on REV.?4?Take the case of Jinping-I hydropower station,the fracture network model is established based on the statistical parameters and distribution of fractured in studied domain.Numerical simulation of RFPA^2D-Flow is applied to calculate the equivalent permeability coefficient of different size in different directions of fractured rock masses,in order to obtain the representative elementary volume?REV?and permeability tensor.The permeability tensor and principal value of permeability are further modified based on the water pressure test results.The results after correction and initial data are of the same order of magnitude,which further shows the reliability of the simulation method.?5?Permeability tensor and principal value of rock mass for Jinping-I hydropower station are determined.To determine the permeability zoning of fractured rock mass,the evolution law of seepage field in the rising process of reservoir water level is studied considering geostress and rising rate of reservoir water level.Obviously,considering geostress or slow storage conditions,the seepage field changes slowly,especially the flow rate of discontinuity surface decreases,but it is still the advantages of seepage path,need to focus on seepage control.?6?The influence of pore water pressure on permeability,rock strength and crack propagation is studied based on RFPA^2D-Flow.Under the water pressure,the strength of rock is obviously reduced,and the crack propagation is also greatly affected.