| In the process of underground engineering construction such as tunnel excavation and coal mining,the stress redistribution generated by excavation causes the germination,expansion and penetration of rock cracks,which can form waterconducting cracks and lead to geological disasters such as water inrush and sand collapse.The compressive shear permeability characteristics of single fractured rock mass have important theoretical and practical significance for evaluating the permeability of fractured rock mass and predicting water inflow.In this paper,a single through crack model that can form compressive shear failure deformation is designed.Cement mortar is used to make rock-like prefabricated crack specimens,and lateral constraint is realized through the pressure shear seepage test device.The pressure shear seepage test under different dip Angle,opening and osmotic pressure difference is carried out combined with the pressure stabilizer pump and axial loading device.The interaction between seepage flow and dip Angle,openness,vertical displacement,vertical load and lateral pressure is studied.The main research results are as follows:(1)Under the condition of bidirectional constraint,the compressor-shear displacement curve of single-fracture rock mass has a stage of compaction,elastic deformation,plastic deformation,strength failure,residual strength and stress re-rise,and its peak strength decreases with the increase of fracture opening.For the compressor-shear seepage test,the compressor-shear displacement curve is consistent with the curve without seepage.The peak strength and the vertical displacement corresponding to the residual stage decrease with the increase of the crack Angle and crack opening,and the osmotic pressure difference has little effect.(2)Under the condition of bidirectional constraint,normal pressure and horizontal pressure show a certain trend with the increase of axial load;For specimens with small opening(the crack opening can be closed when loaded with vertical displacement),the normal pressure changes with the change of axial load,which has the same trend.For specimens with large crack opening(the crack opening cannot be closed when loaded with vertical displacement),the normal pressure first changes with the change of vertical load,and when the stress rises again,the vertical load increases gradually,while the normal pressure remains stable.The parallel pressure remained relatively stable with the change of vertical load,and its value varied within 0.1～0.5 k N.(3)Under the condition of bidirectional constraint,the fracture opening of singlefractured rock mass decreases linearly with the increase of vertical shear displacement,and the slope of the curve increases with the increase of the fracture opening.The fracture opening is distributed along the fracture plane with thick at both ends and thin in the middle,and the difference is about 10% of the central opening of the fracture plane.For the crack specimens in the pressure-shear seepage test,Lomitier formula was used to calculate the actual opening during the pressure-shear loading process.The change rule of the crack opening was consistent with that of the compressive shear test without seepage flow.The slope of the curve of the crack opening with vertical displacement increased with the increase of the crack opening and the decrease of the crack Angle.(4)Under the condition of bidirectional constraint,the seepage flow of throughsingle fractured rock mass shows a first-order exponential growth law with the increase of crack opening,and a linear growth law with the decrease of crack dip Angle and the increase of osmotic pressure difference.In the process of axial loading,the seepage flow of the 60° crack and 75° crack decreases gradually,and the change rate increases with the decrease of the dip Angle.However,for the 90° crack specimen,the seepage flow increases with the failure of the specimen,and the rest process remains relatively stable.(5)Under the condition of bidirectional constraint,the seepage flow of crack specimens with 60° and 75° dip Angle decreases gradually with the increase of vertical displacement,and its variation rule is affected by the crack opening.When the opening is 0.5 mm,the seepage flow changes linearly with the vertical displacement.At 1 mm,the seepage rate fluctuates with the vertical displacement in a step shape.When the opening is 2 mm,the seepage flow remains stable with the change of vertical displacement before the failure of the specimen,and decreases linearly with the vertical displacement after the failure of the specimen.(6)Under the condition of bidirectional constraint,the variation law of seepage flow of crack specimens with 60° and 75° dip Angle is similar with the increase of vertical load.In the elastoplastic deformation stage and the residual stage,the seepage flow varies with the increase of vertical load in a first-order negative exponential pattern,and its rate of change increases with the increase of the opening and the decrease of the dip Angle.In the strength failure stage,the vertical load drops abruptly and the seepage flow remains relatively stable.The vertical load increases linearly and the seepage flow remains stable after the crack is closed(the stage of stress rise again). |
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