Study On The Mechanical Property And Rock Burst Mechanism Of Hard Rock Under H-M Coupling Conditions

The rockburst often threats safety of deep tunnels in hard rock, making the underground engineering becoming unstable. Deep rock at the high pressure and seepage environment fields, its mechanical properties not only relate to the mineral composition and microstructure of the rock itself, but also to the environment in which its relevant, the mechanical properties of the rock under a single physical field can’t be used to study the rockburst problems of deep tunnel in hard rock. Laboratory mechanical test and numerical analysis has been the main tool in researching the rock mechanical properties and damage mechanism in a complex environment (such as high hydraulic pressure, high stress), therefore, in this test, MTS815Teststar-type program-controlled servo rigidity testing machine of U.S. production and Particle Follow Code be used to carry out Series of laboratory mechanical test and numerical test under H-M coupling condition of sandstone. On this basis, analysis the mechanical characteristic of sandstone under different humidity, hydraulic pressure, confining pressures and different stress path, and research micro and macro damage deformation and failure characteristics, AE energy, crack spread and the failure mechanism under H-M coupling, the main results are as follows:(1) In the uniaxial tests, with the increase of humidity, sandstone strength, modulus of elasticity were significantly reduced, poison’s ratio increases significantly, AE energy decreases, and crack distribution range from partial to whole, plastic deformation, damage fracture micro plastic deformation characteristics more and more obvious, this suggests that the humidity conditions lead to sandstone from brittle to plastic shift and reduce the possibility of rock burst.(2) In the triaxial test, with the increase of humidity, compressive strength, elastic modulus, AE energy, cohesion and internal friction angle significantly lower, and the poison’s ratio, plastic deformation were significantly increased. In unloading triaxial test, the brittle destruction features of the microscopic fracture morphology are less and the plastic deformation characteristics are more, all of this shows mat humidity led to the sandstone change from brittle to plastic, reduced the possibility of rock burst.(3) In triaxial tests, the influence to sandstone strength, elastic modulus, poison’s ratio, mechanical parameters are small under H-M coupling conditions, but the influences to the dynamic failure process of rocks are bigger. Hydraulic pressure accelerates fracture progress in rock, greatly reduced the lateral plastic deformation. The microscopic damage morphologies show brittle failure fracture are more and plastic deformation are abate. Under the action of H-M coupling, AE maximum instantaneous energy released of and cumulative energy also have been a sharp increase. It suggests that compare to the sandstone under saturated humidity condition, H-M coupling effects lead to sandstone from plasticity to brittleness and increase the possibility of rockburst.(4) With the increase of hydraulic pressure, effects of H-M coupling decreases macro damage angle, which show that tension fractures enhanced and shear damage reduced. It suggests that mechanics mechanism of rock burst from tension to shear under H-M coupling conditions.(5) Compared with conventional triaxial test, peak strength, peak strain, modulus of elasticity and other mechanical parameters of the unloading triaxial test change are small under H-M coupling conditions and volume strain increase and the sample destruction angle decreases, which show that tension fractures enhanced and shear damage reduced. It suggests that mechanics mechanism of rock burst from tension to shear under the effect of unloading. At the same time, the bigger initial design of confining pressure, the unloading effects are more obvious.(6) Based on analysis of PFC numerical test, the effects of H-M coupling has less influence to peak strength, peak strain, modulus of elasticity and other mechanics parameters, but accelerate the speed of samples’ crack extension and connected after the unstable failure stage. With the increase of hydraulic pressure, tension crack increased and shear crack reduced, and distribution are more concentrated, which indicates that tension fractures enhanced and shear damage reduced. It suggests that mechanics mechanism of rock burst from tension to shear under H-M coupling conditions.(7) Based on analysis of PFC numerical test:unloading effects in the numerical tests are more remarkable than the effects in the laboratory mechanical tests because unloading rate of the numerical test are faster than the rate of the laboratory mechanical tests. Unloading effects leads the peak strength, peak strain of the sample are decreased significantly, and inhibit the shear crack initiation, and stimulate the extension, penetration of tension crack, and make damage section more smooth, which is consistent with the laboratory mechanical test results and further evidence that mechanics mechanism of rock burst from tension to shear under H-M coupling conditions.(8) Based on analysis of PFC numerical test:the bigger initial confining pressure, the weaker of effect of H-M coupling, the stronger of the unloading effect, which are consistent to the results of laboratory mechanical tests.