Numerical Simulation on Uniaxial Compression Failure of A Roof Rock–Coal–Floor Rock Composite Sample with Coal Persistent Joint

Geological dynamic hazards during coal mining can be induced by the structural instability of a composite structure of roof rock, coal and floor rock layers, whereas the joint in coal plays a vital role in the corresponding structural instability. In this paper, the effects of coal persistent joint on the uniaxial compression failure of a roof rock–coal–floor rock composite sample were analyzed using PFC^2D software. The results show that with an increase of included angle \(\alpha\) between the loading direction and coal persistent joint plane, the uniaxial compressive stress (UCS) and peak strain of the composite sample decreased firstly and then increased. The change of elastic modulus was not obvious with \(\alpha\). The UCS and peak strain at \(\alpha\) of 45° were the smallest. Additionally, the coal bodies in composite samples were mainly destructed as a shear failure. The roof or floor rock presented a tensile failure or no damage. And four failure patterns were observed for composite samples after failure, i.e., inverted V-shaped shear failure in coal and tensile failure in roof or floor rock, M-shaped shear failure in coal and tensile failure in floor rock, shear failure along the joint plane in coal and tensile failure in roof and floor rocks, shear failure along partial joint plane without obvious damage for roof or floor rock.