Research on strength and failure mechanism of deep coal-rock combination bodies of different inclined angles

Experimental and numerical simulation researches on the strength property and failure mechanism of different inclined angles coal-rock combination bodies have been carried out.The macro-failure mechanism of coal-rock combination bodies has been obtained.And the effect of the interface between coal and rock has also been analyzed in detail.The uniaxial experimental results indicate that the failure strength of coal-rock combination bodies decreases slowly at first and then rapidly with the increasing of combination inclined angle.For the same inclined angle for coal-rock combination bodies,the whole failure strength increases with the increasing of the confining pressure.In addition,the smaller the combination inclined angle,the smaller the increasing rate of the failure strength;the bigger the combination inclined angle,the bigger the increasing rate of the failure strength.Therefore,the effect of the confining pressure on the large inclined angle of the coal-rock combination body is obvious.The cohesion and internal friction angle of coal-rock combination bodies have also been obtained through the triaxial experiments.The cohesion of combination bodies decreases with the increasing of the inclined angle.However,there are no clearly relationship between the internal friction angle and the inclined angle.The extended finite element method(XFEM) has been applied to simulate the failure of different inclined angles combination bodies.The simulation results from inclined angle 0° to 60°,of which the interval 5° indicate that external force work,yield stress and elastic strain energy decease with the increasing of the inclined angles.However,when the inclined angles are more than 45-50°,the external force work and the yield stress will change inversely with the elastic strain energy.This is an important symbol of failure mechanism changing from shear failure to slip failure mechanism for the coal-rock combined bodies.