A thorough understanding of mining-induced overburden deformation characteristics and the associated stress redistributions are essential to effectively manage complex safety and environmental issues that arise from underground mining. This is particular for mining in deep environments. This paper presents a numerical modelling study on a kilometer-deep longwall coal mine where a thick sandstone aquifer is situated approximately 200 m above the working seam. The mine adopts a special mine layout with narrow and wide pillars between longwalls and areas to manage water inrush and coal burst risks. The modelling results show that overburden deformation stops at a certain height, above which the displacement profile over multiple longwall panels become nearly flat. Increasing panel width and extraction height lead to a greater extent of the fractured zone and a larger magnitude of surface subsidence. An extraction height of more than 7 m may breach the thick aquifer. Stress concentration on the wide pillar can undergo up to 5 times increase in the in-situ stress, posing high risks of coal burst. Adjusting mining parameters such as panel width and extraction height can facilitate an effective strategy to minimize water inrush and coal burst risks in such a mining condition.

Mining‐induced voids are the main circulation pathways for underground fluids such as water and coalbed methane. The collapse of these voids transmits to the ground surface, resulting in subsidence and building collapse. Accordingly, effective and feasible solutions are needed to control surface subsidence. In this study, a novel technique of void filling in the short‐wall caving zone was proposed to better control surface subsidence in thin coal seam mining. The width of the working face plays a key role in the proposed technique. A maximum surface subsidence value was predicted using numerical simulation and physical simulation experiments with different working face widths. The results indicate that the appropriate working face width should be less than 50 m for the studied coal mine. In this example, the surface subsidence coefficient was less than the standard value for initial damage to rural structures. Both advancing speed and productivity of the working face were achieved using the proposed technique because the filling and mining processes were conducted simultaneously on different faces. The results suggest that surface subsidence during thin coal seam mining could be controlled using the proposed technique. This technique can also help mitigate mining‐induced water inrush and gas leakage disasters by filling voids.

Understanding how mining-induced strata movement, fractures, bed separation, and ground subsidence evolve is an area of great importance for the underground coal mining industry, particularly for disaster control and sustainable mining. Based on the rules of mining-induced strata movement and stress evolution, accumulative dilatation of mining-induced unloading rock mass is first proposed in this paper. Triaxial unloading tests and theoretical calculation were used to investigate the influence of elastic dilatation of mining-induced unloading rock mass on the development of bed separation in the context of district No. 102 where a layer of super-thick igneous sill exists in the Haizi colliery. It is shown that the elastic dilatation coefficient of mining-induced unloading hard rocks and coal were 0.9~1.0‰ and 2.63‰ respectively under the axial load of 16 MPa, which increased to 1.30~1.59‰ and 4.88‰ when the axial load was 32 MPa. After successively excavating working faces No. 1022 and No. 1024, the elastic dilatation of unloading rock mass was 157.9 mm, which represented approximately 6.3% of the mining height, indicating the elastic dilatation of mining-induced unloading rock mass has a moderate influence on the development of bed separation. Drill hole detection results after grouting, showed that only 0.33 m of the total grouting filling thickness (1.67 m) was located in the fracture zone and bending zone, which verified the result from previous drill hole detection that only small bed separation developed beneath the igneous sill. Therefore, it was concluded that the influences of elastic dilatation of mining-induced unloading rock mass and bulking of caved rock mass jointly contributed to the small bed separation space beneath the igneous sill. Since the accurate calculation of the unloading dilatation of rock mass is the fundamental basis for quantitative calculation of bed separation and surface subsidence, this paper is expected to be a meaningful beginning point and could provide a useful reference for future, related research.

When there are multiple key strata in the overburden of a deep coal seam and the surface subsidence coefficient after mining is small, this indicates that the overlying key strata fail to break completely after mining. On this occasion, stress is easily concentrated in the working face, which in turn leads to the occurrence of dynamic disasters such as rock bursts. This study adopted a comprehensive analysis method of field monitoring and numerical simulations to explore the influence of the key stratum on the evolution law of mining-induced stress in the working face. A distributed optical fiber sensor (DOFS) and a surface subsidence GNSS monitoring system were arranged inside and at the mouth of the ground observation borehole, respectively. According to the monitoring results of strain obtained from the DOFS, the height of the broken stratum inside the overlying strata was obtained and according to the monitoring results of surface subsidence, the surface subsidence coefficient was proven to be less than 0.1, indicating that the high key stratum is not broken completely, but enters a state of bending subsidence instead. In order to reveal the influence of the key stratum on the mining-induced stress of the working face, two 3DEC numerical models with and without the key stratum were established for a comparative analysis. As the numerical simulation results show, when there are multiple key strata in the overburden, the stress influence range and the stress concentration coefficient of the coal seam after mining are relatively large. The study revealed the working mechanism of rock burst accidents after large-scale mining and predicted the potential area with a rock burst risk after mining of the working face, which was verified by field investigations. The research results are of great guiding significance for the identification of the working mechanism of rock bursts in deep mining condition and for their prevention and control.

There is a layer of the unconsolidated confined aquifer (UCA) made of non-cemented sand and grit on the bed of Quaternary thick topsoil in many coal mines in east and north China. Existing on the bedrock of coal measures, it poses a serious threat to coal mine safety. Worse, it caused many supports crushing and water inrush disasters (SCWIDs) and resulted in significant economic losses. Aiming at the above problems, this paper adopts a simulation experiment, field measurement, engineering detection, and theoretical analysis to conduct the research. The research reveals the overburden’s destructive rules during mining under UCA. The results indicate that UCA plays an important role in the process of load transfer due to its mobility and replenishment in time. When mining close to the aquifer, the load transfer of aquifer leads to overburden breaking entirely and sliding instability of the bond-beam structure, then, the water flowing fractured zone develops rapidly and connects the aquifer, which is the fundamental reason for SCWID under the UCA. Based on the mechanism of SCWID, a prediction method of support crushing and water inrush hazard zones was put forward. Artificial pre-split blasting based on the location of a key stratum was applied to prevent SCWID. The proposed methods have been used in 7₁31 working face and safe mining was achieved.

Longwall pier-column backfilling is a partial backfilling technique initially designed in thin coal seam mines. With the increase of mining intensity, the mining height and width of the backfilling working face will also increase. It is necessary to analyze how changes in working face dimensions influence the control effect of overburden subsidence in pier-column backfilling. In this study, a mining model with a combination of 25 conditions (five different mining heights (1~3 m) × five different mining widths (80~240 m)) was designed using a FLAC3D (Vision 5.0) numerical simulation. The simulation was used to analyze the control effect of overburden subsidence with varying mining heights and widths. In addition, according to the field working face conditions, two physical similarity models were performed to explore the overburden subsidence law in pier-column backfilling with different mining heights and widths. It was observed from the above study that mining heights and widths will have a different influence on the overburden subsidence in longwall pier-column backfilling. The result of this study provides strong theoretical support for evaluating the control effect of overburden subsidence in longwall pier-column backfilling.