Investigation on whole failure nonlinear model for deep coal-rock combined bodies

Coal is a kind of complex geological body with a large number of cracks and pores.In the coal-rock combined bodies,rocks are the hard part and coal and its internal cracks,pores and the interface between coal and rock are put together to be the soft parts.According to the engineering strain and natural strain,a nonlinear theoretical model has been built to characterize the coal-rock combined bodies.This nonlinear theoretical model generally matches well with the uniaxial compression testing data.Then parameters are discussed by the simplified model and finding that,a is approximately equal to 1,b and c are the parameters that associated with size,elastic modulus of coal.Parameter b extends gradually in the nonlinear phase and the incremental rate basically remains unchanged.Parameter c also goes up increasingly in the nonlinear phase.The incremental rate decreases with a gradual overlap trend in the linear phase when the axial load increases.