The formation of coalesced fractures critically alters the mechanical properties of the surrounding virgin material, significantly changing the stress distribution and deformation behavior of the rock mass. However, understanding the generation mechanism and accurate prediction of rock fracture growth remain challenging in many engineering projects. Despite, wide range of conventional approaches including field investigations, laboratory-scale tests, and numerical modeling, the complex geological conditions hinder their accurate determination. This study introduces a new robust and cost-effective holistic geophysical approach to determine fractures propagation and predict failure in coal-rock masses at laboratory scale applicable across scales. The proposed approach combines rock mechanics and Acoustic Emission (AE) testing systems to make useful correlation between AE source parameters and deformation kinetics. This correlation analyzes the spatiotemporal distribution of AE events to elucidate the evolution of fracture patterns in coal-rock specimens from a complex mining project. Results showed dense and complex fracturing networks within coal specimens due to higher density, compaction, and mechanical strength compared to rock samples. This is indicated by peak acoustic events at 80%–100% load versus minimal events at 0–15% load. Simulated fracture patterns closely matched observed acoustic events, identifying key lineaments (macro-cracks) representing the transition from microcracks to macro-fractures. The convergence of these lineaments indicated intensely deformed zones prone to failure, consistent with previous field investigations. Acoustic parameters describing critical damage revealed an inverse relationship between stress and AE event magnitude. At roughly 70% σ _max, a dramatic fall is seen in acoustic parameters indicated the shift from small-scale to large-scale microfractures, ultimately leading to catastrophic failure of the samples. Furthermore, Single Link Cluster (SLC) analysis demonstrated strong correlation among AE events, spatial correlation length (ξ) and information entropy (H). Both increased significantly at the onset of loading and fluctuated in proximity to ultimate failure. Using the micro-crack density criterion and 3D-crack growth theory, changes in above parameters verified the cracks transformation process. These findings showed that, the proposed approach compared with the conventional approaches, can improve disaster control and management plans, predict critical failures, and save lives in global mining projects when applied to field-scale studies.

The steeply inclined and extremely thick coal seams (SIETCS) under the condition of gob filling frequently suffer from the occurrence of rockbursts. Figuring out the mechanisms of rockbursts under this condition for taking targeted measures to mitigate rockburst hazards in SIETCS is of great significance. Using the typical SIETCS with an average dip angle of 87° at Wudong Coal Mine (WCM) as a case study, a mechanical model and elastic deformation energy (EDE) function of a “steeply inclined suspended roof structure” was developed, and the influence factors were analyzed by theoretical analysis. Simultaneously, the rockburst risk assessment was carried out based on the theory of a rockburst start-up. The pressure relief measures are optimized by comparing the pressure relief effects of three kinds of destress blasting schemes. The results indicate that the damage characteristics of rockburst are mainly floor heave, the sidewall’s inward deformation and roof subsidence. The damage degree of headentry on the roof side is more severe than that of tailentry, and the resultant impacts showed the directionality from the roof side to the coal side. The steeply inclined and suspended roof breakage is one of the main causes for the occurrence of rockbursts. The EDE of the roof increases with an increasing dip angle of the coal seam from 0° to 72.6° and then decreases as the dip angle increases. Furthermore, that increase is accompanied by the decrease of the lateral pressure coefficient and the supporting force coefficient. The EDE stored in the roof is sufficient to cause roof breakage and induce rockburst after the complete roof exceeds a certain length. The mechanism of rockburst in SIETCS for fully mechanized top-coal caving mining under gob filling conditions was proposed, i.e., “high compressive stress concentration plus breakage of the suspended roof-induced stress” rockburst, and this is further verified by ground destruction, microseismic (MS) monitoring and numerical modeling. The results also indicate that alternate deep and shallow hole-blasting modes are more suitable for pressure relief in SIETCS.

Early warning of a potential rockburst risk and its area of occurrence helps to take effective and targeted measures to mitigate rockburst hazards. This study investigates the microseismic (MS) spatial-temporal precursory characteristic parameters in a typical steeply inclined and extremely thick coal seam (SIETCS) with high rockburst risk and proposes three spatial/temporal quantification parameters and a spatial-temporal early warning method. Analysis results of temporal parameters show that the sharp-rise-sharp-drop variation in total daily energy and event count can be regarded as a precursor for high energy tremor. The appearance of peak values of both energy deviation (≥20) and event count deviation (≥1) can be regarded as precursors that indicate imminent rockburst danger. A laboratory acoustic emission (AE) experiment reveals that precursor characteristics obtained from the study can be feasibly used to warn the rockburst risk. The spatial evolution laws of spatial parameters show that the high energy density index of MS (EDIM), velocity, velocity anomaly regions correlate well with stress concentration and rockburst risk areas. The field application verifies that the temporal-spatial early warning method can identify the potential rockburst risk in a temporal sequence and rockburst risk areas during the temporal early warning period.

This study focuses on steeply inclined and extremely thick coal seams (SIETCS) characterized by immense thickness, a steep inclination of coal seams (87°), and high horizontal stress. The geological conditions and mining technology associated with SIETCS differ significantly from those of generally inclined coal seams, resulting in notable variations in roadway stress distributions. On SIETCS have predominantly examined the impact of rock layers flanking coal seams on rock bursts, with limited emphasis on SIETCS roadways. This study employs comprehensive methods, integrating numerical simulations, theoretical analyses, and field detections to investigate the stress distribution of SIETCS and the mechanisms of rock burst-induced vertical damage, subsequently validated in situ. The vertical stress in SIETCS is minimal, while horizontal stress is concentrated, leading to the formation of layered crack structures (LCS) that distribute above and below the roadways. Additionally, elastic energy significantly concentrates within the LCS. Axial dynamic compressive stress and vertical dynamic tensile stress along the LCS diminish its stability, readily triggering failure. During the LCS failure process, the stored energy is released, converting into kinetic energy required for coal body ejection after reaching the minimum energy for failure and dissipative energy, ultimately leading to rock burst-induced vertical damage in roadways. On-site detection and analysis within SIETCS, along with historical rock burst data, confirm the existence of LCS and its role in inducing vertical rock burst damage. This research establishes essential foundations for preventing rock bursts within SIETCS.