Study On Fracture Evolution Mechanism And Numerical Simulation Of Fractured Rock Mass Under Freeze-thaw And Load

Frost heaving pressure is the fundamental reason for the freeze-thaw failure of fractured rock mass in cold regions.The freeze-thaw failure of fractured rock mass with water content causes the loss of rock strength and causes a series of engineering problems.Among them,frost heaving pressure and frost heaving crack propagation are the key factors to determine the degree of freeze-thaw deterioration of fractured rock mass.Therefore,the common saturated fractured rock mass in cold region is taken as the research object,and the crack frost heaving pressure test,crack frost heaving fracture process monitoring and uniaxial compression test of fractured rock mass after freeze-thaw cycle are carried out.Through indoor test,the evolution law of crack frost heaving pressure,frost heaving crack propagation characteristics and the strength loss law of fractured rock mass caused by frost heaving crack are obtained.Then,the whole process of fractured rock mass under freeze-thaw and load is simulated and analyzed by using particle flow numerical simulation technology,and the evolution mechanism of fractured rock mass under freeze-thaw and load is revealed.Based on this study,the main conclusions are as follows:(1)The evolution process of frost heaving pressure of non-penetrating fracture samples includes incubation stage,explosion stage,falling to steady stage,melting rising stage and dissipation stage.The peak value of the frost heaving pressure at the freezing stage,the stability value and the peak value of frost heaving pressure in the melting stage are negatively correlated with the length of the fracture,positively correlated with the width of the fracture,positively correlated with the depth of the fracture,and negatively correlated with the length-width ratio of the fracture.(2)The frost heaving fracture modes of single fractured rock mass can be divided into two types: coplanar propagation crack and horizontal propagation crack.The frost heaving crack starts from the crack tip and propagates along the coplanar direction of the crack.At the same time,an approximately horizontal crack will appear in the middle of the crack and gradually extend to the side and back of the sample,forming through frost heaving crack.(3)The frost heaving fracture modes of double fractured rock mass can be divided into three types: coplanar propagation crack,deflection propagation crack and horizontal propagation crack.Except for Y-45° and L-90° specimens,the frost heaving crack first propagates along the coplanar direction of the crack and then deflects to another crack or to another crack when only crack angle changes or bridge angle is small;when bridge angle is large,the frost heaving crack mainly propagates along the coplanar direction and deflects slightly to the horizontal direction;finally,the crack extends to the side and back of the specimen,forming through frost heaving crack.(4)The actual engineering rock mass freezing and thawing conditions mainly include uniform freezing and thawing of exposed fractured rock mass and unidirectional freezing and thawing along the direction of fracture opening.The results show that the fracture mode of unfrozen and uniform freeze-thaw fracture specimens is relatively consistent,and the strength variation law is roughly the same.The unidirectional freezethaw fracture specimen is greatly affected by freeze-thaw,and the frost heaving crack is obvious.The shear failure mainly occurs along the frost heaving crack path,resulting in a significant decrease in the strength,especially for the specimen with crack angle or bridge angle close to the fracture angle.(5)Based on PFC numerical simulation technology,the frost heaving cracking process of fractured rock mass and the loading cracking process of elliptical single and double fracture specimens before and after freeze-thaw are systematically simulated.The simulation results show that the crack frost heaving fracture mode is tensile failure,and the unidirectional freeze-thaw fracture specimen is mainly shear failure along the frost heaving crack path.The numerical simulation results are in good agreement with the experimental results,which indicates that the particle discrete element method can reproduce the experimental process to a certain extent.