Decheng Ge

Based on the mechanical characteristics of hard rock strata subjected to vertically non-uniform loading conditions in mountainous regions, gullies, and similar areas, this study investigates the fracture and failure patterns of hard rock strata under such conditions. A stepped rubber cushion loading method was employed to continuously apply distributed loads across the entire upper surface of the sandstone plates. Experiments were conducted to examine the fracture failure behavior of the sandstone plates under central vertically non-uniform loading with lateral clamping constraints. The displacement, stress, strain, and electromagnetic radiation characteristics of the sandstone plates were analyzed. The research results indicate the following: (1) The stepped rubber cushion loading method successfully achieves vertically non-uniform loading on the sandstone specimens. The vertical displacement of the sandstone plates increases with the number of stepped cushion layers. The average stress proportions in the thin, medium, and thick regions are 5.0%, 61.5%, and 100%, respectively. (2) Under vertically non-uniform loading, the fracture process of hard rock strata undergoes three stages: tensile failure, shear fissure development, and shear dislocation. During the tensile failure stage, a brief, stable-hinged micro-structure exists within the rock block. The entire process dynamically alternates between structural failure and the formation of temporary stable structures, accompanied by repeated fluctuations in stress states between decrease and recovery. Upon entering the shear fissure development stage, the frequency of stress fluctuations decreases, indicating a trend towards concentrated failure and instability. In the shear dislocation stage, shear fissures connect, resulting in the maximum stress drop throughout the entire failure process. (3) Under vertically non-uniform loading, tensile-shear fracture of hard rock strata occurs on the side experiencing greater vertical load. Correspondingly, in on-site engineering conditions within mountainous terrains, areas with increased vertical stress may be more prone to roof tensile-shear fracturing, thereby inducing mining tremors. These results may provide preliminary guidance for controlling rock bursts and mining tremors in mines in mountainous and gully areas, although further validation is required.

This study investigates the asymmetric evolution of overburden deformation and fracture during unilateral roof cutting in a deep pillarless longwall panel. The No. 31120 working face at Suncun Coal Mine was used as the prototype for a 1:40 physical similarity model. Fracture observations, digital image correlation fields, subsidence profiles, and paired vertical-stress histories were analyzed throughout support advancement, sustained support, and support withdrawal. The maximum-subsidence region and dominant fracture boundary shifted toward the non-cutting side, whereas the cutting side developed smaller caved blocks and a shorter retained roof span. A longer cantilever-like roof segment formed on the non-cutting side and a shorter segment formed on the cutting side, accompanied by contrasting loading and unloading responses at corresponding roof levels. The combined observations show that unilateral roof cutting redirects roof fracturing and load transfer and provide an experimental basis for evaluating retained roof span, separation, and support demand near a gob-side roadway.

The mining of extra-thick coal seams is prone to triggering mine earthquake, which causes damage to surface buildings and severely restricts the sustainable development of coal mines. This study constructs a spatial structural model of hard rock tearing-type fracture at the 61,607 working face in Longwanggou Coal Mine. Through analytical modeling of stress-energy characteristics during fracture propagation, we quantitatively estimate the vibrational energy partitioning within rock mass discontinuities and evaluate the maximum potential magnitude (ML) of mine earthquake. Critical kinematic parameters, including peak ground acceleration (PGA) and particle velocity (PGV), are extracted to systematically evaluate vibration-induced damage to surface structures, with data sourced from seismic waveforms. The results indicate that the maximum magnitude estimated by the calculation model for hard rock tearing-type mine earthquake is in close agreement with on-site monitoring results, exhibiting a deviation of approximately 14%. The peak values of the acceleration response spectrum for seismic signals are concentrated in the 0.1–0.5 s range, where the bottom frames of buildings with natural vibration periods close to this interval are affected to a certain extent but exhibit lower vibration intensity than that induced by natural earthquakes. The attenuation of mine earthquake vibrations adheres to a power-law exponential pattern, with PGA decaying to an extremely low level at kilometer-scale distances. Additionally, the velocity response of mine dormitories meets relevant safety standards, collectively indicating that mine earthquake exerts essentially no substantial impact on the structural integrity of surface buildings.

The characterization of the mechanical parameters of rock mass is a basic problem in the field of rock mechanics, and it is also an important basis for surrounding rock classification, stability analysis, and support design in underground engineering. Based on the engineering background of pressure relief drilling in Guotun Coal Mine, this paper carries out an engineering test while drilling. The numerical simulation method is used to explore the influence of different lithology rocks, different control conditions, and different confining pressure conditions on the parameters while drilling and to study the variation in drilling time, drilling depth, drilling rate, and revolution speed. The results show that under the same control conditions, the drilling rate of coal, mudstone, sandy mudstone, and siltstone are in the order of coal > mudstone > sandy mudstone > siltstone. For similar rock specimens, when the thrust is fixed, the drilling rate increases with the increase in the revolution speed, and when the revolution speed is fixed, the drilling rate increases with the increase in the thrust. When the rock specimen is in different confining pressure states, the drilling rate decreases with the increase in confining pressure, and the torque increases with the increase in confining pressure. This study provides a scientific basis for the realization of in situ rapid and effective measurement technology for the rock mechanical parameters of coal and rock mass, which is helpful for improving the measurement accuracy and efficiency and promoting the safe and efficient mining of coal mines.

Fractures and voids are widely distributed in slope rock masses. These defects promote crack initiation and propagation, ultimately leading to rock mass failure. Investigating their damage evolution mechanisms and strength characteristics is of significant importance for slope hazard prevention. A numerical simulation study of Brazilian splitting tests on disk samples containing prefabricated holes and fractures was conducted using the Finite Element Method with Cohesive Zone Modeling (FEM-CZM) in ABAQUS by embedding zero-thickness cohesive elements within the finite element model. This 2021 study analyzed the effects of fracture angle and length on tensile strength and crack propagation characteristics. The results revealed that when the fracture angle is small, cracks initiate near the fracture and propagate and intersect radially as the load increases, ultimately leading to specimen failure, with the crack coalescence pattern exhibiting local closure. As the fracture angle increases, the initiation location of the crack shifts. With an increase in fracture length, the crack initiation position may transfer to other parts of the fracture or near the hole, and longer fractures may result in more complex coalescence patterns and local closure phenomena. During the tensile and stable failure stages, the load–displacement curves of samples with different fracture angles and lengths exhibit similar trends. However, the fracture angle has a notable impact on the curve during the shear failure stage, while the fracture length significantly affects the peak value of the curve. Furthermore, as displacement increases, the proportion of tensile failure undergoes a process of rapid decline, slow rise, and then rapid decline again before stabilizing, with the fracture angle having a significant influence on the proportion of tensile failure. Lastly, as the fracture angle and length increase, the number of damaged cohesive elements shows an upward trend. This study provides novel perspectives on the tensile behavior of fractured rock masses through the FEM-CZM approach, contributing to a fundamental understanding of the strength characteristics and crack initiation mechanism of rocks under tensile loading conditions.

With the development of faults in many coalfields, many large faults will form a relatively independent area, forming regional tectonic stress concentration. Under the influence of mining, it is easy to induce fault activation, produce mine tremor, and then induce rock burst. Through field investigation, theoretical analysis, numerical simulation, and engineering verification, the overburden movement model of No. 3504 working face square and fault activation in Liangbaosi Coal Mine was established. The stress variation and energy release law of working face advance and fault area were analyzed, and the mechanism of rock burst under the coupling action of working face square and regional tectonic stress was revealed. The results show that the regional stress adjustment and fault activation are caused by the large‐scale overall movement of overburden during the working face square, and there is a peak value of elastic energy release during the fault activation, which is easy to produce large energy mine earthquake. The energy level of the daily maximum energy event is higher than that of the initial mining stage in the square period, and the location of on‐site large energy microseismic event is basically consistent with the predicted fault strike. The study provides a theoretical basis for the prevention and control of rock burst during the working face square under the condition of regional tectonic stress.