Numerical Experimental Study On Failure Process Of Rock With Fracture Under Load

In the process of underground engineering construction,micro-cracks in rock will affect the stability of rock mass engineering,so it is of great theoretical significance to study the failure characteristics of fractured rock mass.At present,there are many research achievements about rock with single fracture,but few researches on the failure behavior of rock with cross fracture under static and impact loads.In this paper,RFPA numerical simulation software is used to carry out numerical simulation tests on rock with fractures under different loads,focusing on the mechanical properties,failure process,energy evolution and acoustic emission characteristics of rock with orthogonal fractures.The main conclusions are as follows:(1)In order to determine the numerical model parameters and verify their rationality,static uniaxial compression laboratory tests and numerical tests were carried out on intact and single-fracture sandstone.The test results show that the stress-strain curves of numerical tests and laboratory tests have good consistency,and the failure modes are similar.(2)The static mechanical properties and energy evolution law of rock with orthogonal cross fractures were obtained through the static uniaxial compression numerical simulation test.It was found that the compressive strength and elastic modulus of rock showed a parabolic trend of first increasing and then decreasing with the increase of the inclination Angle of the main fracture.The peak strength of the sample decreases with the increase of the length of the secondary crack.The energy evolution process can be divided into three stages:elastic,plastic and post-failure.The energy storage limit increases first and then decreases parabola with the increase of the inclination angle of the primary fracture,and decreases exponentially with the increase of the length of the secondary fracture.The dissipated strain energy at the stress peak is linearly correlated with the uniaxial compressive strength.The variation of inclination angle and length of primary crack changes the failure mode of the specimen.(3)The dynamic load numerical simulation test was carried out on the rock with orthogonal cross fracture.The test results show that the rock with orthogonal fracture is mainly tensile failure under stress wave.The failure pattern of the specimen is similar to that of the static failure with the increase of stress wave length.The increase of peak strength will increase the damage degree of sample.Both the dip angle of the primary crack and the length of the secondary crack will lead to the change of the fracture propagation mode.With the increase of the inclination angle of the main fracture,the attenuation of stress wave decreases first and then increases.The longer the length of the secondary crack,the more obvious the stress wave attenuation.(4)Combined with the acoustic emission signals in the failure process of specimens,the acoustic emission characteristic curves of orthogonal fractured rock under static load are in good agreement with the full stress-strain curve,and the acoustic emission signals reach the maximum value at the stress peak point.The maximum cumulative acoustic emission count increases first and then decreases with the increase of the inclination angle of the main fracture,and decreases with the increase of the length of the secondary fracture.The acoustic emission characteristics of samples under dynamic load show two peak values.At the first peak value,the cumulative AE number of samples changes in a "V" shape with the increase of the inclination Angle of the main fracture,and increases with the increase of the length of the secondary fracture.The second peak value appears under the action of reflected wave,and the cumulative AE count of samples with different inclination angles of the main fissure changes in an inverted "V" shape.When the main fissure is fixed,the cumulative AE count of samples decreases with the increase of the secondary fissure.