Purpose: The purpose of this paper is to obtain the mechanical behavior and damage mechanism of the coal and rock near the stope under the stress state and stress paths of the surrounding rock with the dynamic mining. Design/methodology/approach: Through the three-axial compression test and the uniaxial compression test by meso experiment device, the mechanical behavior and fracture evolution process of coal and rock were studied, and the acoustic emission (AE) characteristics under uniaxial compression of the coal and rock were contrasted. Findings: Under the three-axial compression, the strength of coal and rock enhance significantly by confining pressure. The volume of outburst coal shows obvious stages: compression is followed by expansion. The coal first appear to undergo compaction under vertical stress due to volume decrease, but with the development of micro- and macro-cracks, the specimens appeared to expand; under the uniaxial compression, through the comparison of stress–strain relationship and the crack propagation process, stress drop and fracture of coal have obvious correlation. The destruction of coal was gradual due to the slow and steady accumulation of internal damage. Due to the influence of the end effect, the specimens show the “conjugate double shear failure”. The failure process of the coal and rock and the characteristics of the AEs have a corresponding relationship: the failure causes a large number of AE events. Before the events peak, there was an initial stage, calm growth stage and explosive growth stage. There were some differences between the rock and coal in the characteristics of the AE. Originality/value: These research studies are conducted to provide guidance on the basis of mine disaster prevention and control.

Fully mechanized caving mining in extrathick coal seams is currently the most efficient mining method. To figure out the mining‐induced stress in extrathick coal seams which is significantly different from the normal ones is essential for mining safety. This research is based on the No. 3106 working face of Lu‐Zi‐Gou coal mine in China, which extracts extrathick coal seams by using the comprehensive mechanized top‐coal caving method. According to the elastoplastic theory, a multiforce superposition mining‐induced stress model is constructed in this research. In this model, the mining‐induced stress is generated by the side coal seam of the stope, including the load formed by the broken roof blocks in the caving zone, the unbroken rock layers in the side of the goaf, and the rock layers in the bending zone. To verify the model, electromagnetic wave CT detection and borehole endoscopy are used to test the coal’s electromagnetic wave attenuation and internal joints. The results indicate that the mining of extrathick coal seams forms internal and external stress fields in the side coal seams of the stope. As the depth increases, the mining‐induced stress first increases and then decreases within the two areas. According to the above conclusions, the width of coal pillars and the location of roadways between adjacent working faces can be reasonably determined.

Preexisting fracture network (PFN) is ubiquitous in natural rock mass and is one of the key factors affecting the mechanical properties of rock mass. This research employed a combined approach of theoretical analysis and finite element numerical simulation to investigate the mechanical behavior of PFN-containing rock mass. Based on the sliding crack model and fracture mechanics theory, the initiation mechanism of closed and open cracks driven by compressive and shear stress was theoretically analyzed. Rock mass models with different inclination angles (β) of PFN were built in Fast Lagrangian Analysis of Continua in 3 Dimensions. The complete stressstrain curves of rock mass and the secondary crack propagation were obtained. Results indicated that the increase of β reduced the strength and elastic modulus of rock mass. When β is less than 45, this influence is more prominent. Based on the load-bearing capacity of PFN-containing rock mass, the stressstrain curves can be classified into two types: type I curve has multipeak and is strain-softening in the postpeak stage when β is 15, 30, 45, 60, and 90; type II curve is unimodal and with brittle failure when β is 60 and 75. Secondary crack propagation can be classified into four main types: type I is the coplanar crack, type II is the wing crack around PFN, type III is the near-field wing crack, and type IV is the macroscopic shear crack.