Compression Failure Characteristics And Fracture Evolution Of Coal And Rock Mass With Different Interface Angles

Some mining areas in China have gradually entered the stage of deep mining.In the complex stress environment of deep high stress and engineering disturbance coupling,the force and deformation failure characteristics of coal seam roof and floor strata change obviously when the dip Angle changes.It is a key scientific problem to be solved urgently in the engineering practice to master the mechanical response characteristics when the dip Angle of rock interface changes.Based on this,the research on failure mechanism of coal-rock assemblages with different interface angles has important engineering reference significance for the prevention and control of disasters caused by high stress in deep mining.In this thesis,the mechanical properties and crack propagation mechanism of coal and rock mass under different stress loading environments and interface angles are revealed by means of laboratory experiments and numerical simulation,and the mechanical response characteristics of equivalent coal and rock mass with different interface angles at multiple scales are explored by numerical simulation.The compressive strength and elastic modulus of coal and rock mass decrease by nearly 70% with the interface Angle from 0° to 60°,and the strength under cyclic loading is lower than that under uniaxial compression.Interface dip Angle and cyclic stress loading both weaken the mechanical properties of coal and rock mass.The increase of interface dip Angle and cyclic stress loading both reduce the pre-peak total energy and elastic strain energy of coal-rock mass,both of which weaken the energy storage limit of coal-rock mass.The AE count and energy characteristics of coal and rock composite structure are consistent with its stress-strain characteristics.The AE signals with high amplitude and high frequency are mostly distributed at the peak stress point of the sample,and small amplitude AE signals increase abruptly at the peak point of each cyclic load during cyclic loading.Based on fracture discrimination,the instability of coal-rock composite structure is mainly caused by tensile failure.When the interface dip Angle is 45° and60°,the failure mode gradually transitions to shear failure.Based on acoustic emission location,it is revealed that the typical characteristics of fractures are mostly developed in coal,and the fractures are offset to the interface dip Angle.The instability and failure of coal-rock mass is basically induced by the instability of coal mass.A coal and rock composite model with random cracks and different interface angles is constructed.It is found that with the increase of the size of the model,its mechanical properties change to elastic-plastic,and its peak strength and elastic modulus gradually decrease and stabilize to a certain value,which reflects the size effect of the model.The REV of coal and rock mass with different interface angles was determined by the REV characterization method,and it was found that the mechanical strength of the REV coal and rock mass weakened with the increase of the interface Angle.Through MATLAB image recognition,it is clear that the coal fissure expands faster than the rock mass in the composite body,and the coal fissure through is the root cause of the macroscopic failure of the coal and rock mass,and the fissure expands along the interface dip Angle until through.There are 46 figures,12 tables and 96 references in this thesis.