Seepage Test And Fluid-solid Coupling Mechanism Analysis Of Heterogeneous Single Fractured Rock Mass

The rock mass is a complex natural geological body composed of different scale joint fractures, composed of intact rock and jointed fracture. When there is groundwater flow in fractured rock mass, ground stress field and seepage field of underground will influence each other.Ground stress field and seepage field of underground coupling effect seriously affect the permeability characteristics of rock mass and the engineering stability. Coupling study of stress field and seepage field in fractured rock mass is mainly based on the fluid-solid coupling of single fracture. It is necessary to study fluid-solid coupling of multi-fractured rock mass from single fracture study. Although the above work has made a series of innovative achievements in the seepage of fractured rock mass,the understanding of the seepage characteristics of the fracture surface in the contact zone of different nature strata is not comprehensive, and the existing theory of fracture penetration cannot be applied to the contact zone of different stratum in the actual engineering or provide a reliable theoretical basis and accurate calculation method for calculating the permeability coefficient of fracture surface.The variation law of permeability coefficient of single fractured rock with fracture water pressure, confining pressure and lithology on both sides of fracture is analyzed by the seepage tests of single fractured fine sandstone, single fractured coarse sandstone and single fractured coarse-fine sandstone composite rock mass to solve the above problems in this paper. And then based on the fracture-rock displacement model under the three-dimensional stress condition, the calculation model and formula of the permeability coefficient of fractured rock considering the fracture water pressure, the confining pressure and the rock block with different properties on both sides of the fracture is deduced. The correctness and applicability of the new formula for calculating the permeability coefficient of fractured rock are also verified by the seepage test. The following main conclusions are drawn from the research:(1) During the test, the change law of the permeability coefficient of the heterogeneous rock single composite fractured rock is the same as the permeability coefficient of the same rock block, which increases linearly with the increase of the fracture water pressure and decrease exponentially with the increase of the net confining pressure.(2) The confining pressure causes the closure of the fracture, which leads to the decrease of the permeability coefficient; The fracture water pressure makes the fracture expand and increase the permeability coefficient of the fracture, which is a key factor that cannot be ignored to influences the initial fracture width and initial permeability coefficient at the beginning of the single fracture. Therefore, it is not appropriate to calculate the fissure permeability coefficient by using the net confining pressure obtained by confining pressure minus the fissure water pressure,the influence of fracture water pressure on the permeability coefficient of fracture should be considered.(3) The permeability of the fractured rock mass is significantly affected by the lithology on both sides of the fractured surface. Under the same fracture water pressure and confining pressure coupling, the fracture permeability coefficients of single fractured coarse sandstone,composite single fracture rock mass and single fracture fine sandstone are different. Among them, the permeability coefficients of the single fracture coarse stone is the largest, the composite single fracture rock mass is larger, and the single fracture fine sandstone is the smallest.(4) On the basis of the displacement model of fracture and rock under three-dimensional stress condition, a calculation model and formula for permeability calculating are obtained with the effect of fracture water pressure , confining pressure and lithology on both sides of fracture. Correctness and applicability of the formula for permeability calculating have also been verified by the permeability tests. The new formula can provide a reliable theoretical basis and a relatively accurate calculation method for the calculation of the permeability coefficient of the fractured surface in the contact area of different strata in practical engineering.