Considering the current situation that it's difficult to quantify the discrimination of rockburst hazard, an analytical solution for the softening zone energy of surrounding rock under rockburst in a circular roadway is obtained theoretically based on the elastoplastic softening model of a circular roadway. The critical softening zone energy, critical softening zone radius, critical roadway shrinkage displacement, and critical roadway shrinkage rate are determined. An energy extreme value discrimination method of softening zone for bursting hazard is proposed. The critical softening zone energy is taken as the evaluation basis of the bursting liability of the coal seam where the roadway (a full coal roadway) is located. The uniform energy index, which is the ratio of the external disturbance energy of the surrounding rock softening zone to the critical softening zone energy, is used as the evaluation basis for bursting hazards. Theoretical analysis shows that the smaller the critical softening zone energy of the roadway surrounding rock is, the stronger the bursting liability of the coal seam is, and the greater the uniform bursting hazard index is, the stronger the bursting hazard of the roadway. Subsequently, based on the critical softening zone energy and the uniform energy index, a classification standard of bursting liability and an evaluation method of bursting hazard are proposed. The reliability of the softening zone energy extremum criterion, the bursting liability classification standard, and the bursting hazard evaluation method was verified through indoor and field tests. The energy extreme value discrimination method of softening zone for bursting hazard considers the internal and external factors of roadway rockburst comprehensively and can judge the rockburst risk through field real-time observation, which is a more scientific and reasonable method to predict the risk of roadway rockburst. The research work has important theoretical guiding significance for the prevention and control of roadway rockbursts.

The conventional fracture in shale hydraulic fracturing belongs to the type-I fracture, and the size of the fracture process zone (FPZ) is an important index to measure the fracability of rock mass. This index is also one of the feasible entry points to study the complexity of the fracture network. In order to visually observe the type-I FPZ at the tip of shale fractures, and to study the relationship between the mechanical properties, the shape and size of the FPZ, and the bedding structure, Notched Semi-Circular Bend (NSCB) tests were conducted with three typical fracture direction-bedding orientations (splitter, arrester, divider). The digital image correlation (DIC) method was used to realize the intuitive observation of the real fracture process and the FPZ near the fracture tip. The test found that the FPZ of shale is narrow and long as a whole and is “flame-like”. The height-to-length ratio of the FPZ at the fracture tip determines whether bending and deflection happen between the new fracture and the prefabricated cracks when the fracture occurs. Most of the specimens often appear in the FPZ with a beaded high shear strain zone before the fracture, which is caused by the oblique communication of micro-cracks in the FPZ before the fracture. The appearance of a beaded zone of high shear strain indicates that macroscopic fracture is imminent. The research results can be used for the design of disaster early warning and prevention programs.

Due to the discrete and non-homogeneous of similar materials and the inability to realize large-size and original scale modeling, it is difficult to restore the structure and stress state of underground coal and rock mass in similar simulation tests. To solve this problem, a lightweight and suitable for large-scale modeling similar material, rock-like porous material has been developed. The quasi-static uniaxial compression experiment was carried out by using the large tonnage multi-module electronic control test system. And the influencing factors of controllable mechanical behavior of rock-like porous materials were studied. The results showed that, under uniaxial compression conditions, the material stress–strain curve exhibits three phases: elastic stage, failure stage, and platform stage. The uniaxial compressive strength, elasticity modulus, stress drop, and softening modulus of rock-like porous materials basically increase with the increase of density. The stress after peak strength changes from a slow decrease to a “stepped” or even “cliff like” downward trend. Polypropylene fibers have the effect of enhancing the uniaxial compressive strength, elasticity modulus, stress drop, softening modulus, shear deformation, and residual strength stability of rock-like porous materials. The rock-like porous material has a critical loading velocity, and it increases with density. At the critical loading velocity, the material shows obvious shear failure, and the shear inclination angle is the largest, and so is the uniaxial compressive strength. Through the experimental research, the influence laws of density, polypropylene fiber, and loading velocity on the failure mode, mechanical parameters, and mechanical behavior of the material are clarified, and the quantitative relationship between density and each mechanical parameter is obtained. The research is helpful to realize the accurate control of mechanical behavior of rock-like porous materials and further inverts the deformation and failure mechanism of underground coal and rock structures through indoor similar simulation tests.