In the coal-rock system

the interlayer weak zone between coal and rock layers is the primary area of fracture distribution. These fractures penetrate the coal and rock layers

seriously impacting the mechanical properties and engineering stability of the coal-rock system. To investigate the impact of penetrating fractures on the mechanical properties of the coal-rock system

axial loading tests were conducted on prefabricated coal-rock composite bodies with five different fracture lengths and angles. The findings indicate that: 1) As the fracture length increases

the compressive strength

elastic modulus

peak energy

and impact energy index decrease linearly. Regarding the fracture angle

the compressive strength

elastic modulus

peak energy

and impact energy index initially decrease and then increase. 2) The destructive acoustic emission tests of the samples exhibit three stages: a quiet period

an active period

and an intense period

respectively. With increasing fracture length

the cumulative energy of acoustic emission initially increases and then decreases. Similarly

with increasing fracture angle

both peak energy and cumulative energy of acoustic emission first increase and then decrease. 3) The length and angle of fracture have a certain influence on the wing crack

secondary inclined crack

secondary coplanar crack

oblique crack

secondary derivative crack

wing crack derivative crack

far field crack and spalling phenomenon. 4) As fracture length increases

the cohesion and internal friction gradually decrease

while an increase in fracture angle leads to a decrease followed by an increase in cohesion and internal friction. 5) The Drucker-Prager strength criterion considering fracture length and angle was developed

and rationality verification indicated a sample error within a reasonable range of 1.367% to 5.055%. 6) Based on the dissipative structure theory

the study analyzed the mechanism of instability failure in the coal-rock combined body. The failure process of the combined body involved four main stages: quasi-steady state

metastable state

instability

and establishment of a new steady state. An energy migration model for the fractured coal-rock combined body was developed

and the energy migration pattern during the instability and failure of the fractured coal-rock combined body was analyzed. The ends of the fracture were identified as the primary areas of energy accumulation. Destruction of the coal component’s fracture end led to the migration of energy towards the fracture end of the rock component

resulting in the release of energy through rock component destruction or deformation. These research findings offer valuable insights for investigating the mechanical characteristics of deep coal and rock

as well as understanding the mechanisms behind dynamic coal and rock disasters.