The development of cracks in mining is the scientific basis for the safety and environmental exploitation of shallow multiple-seam. According to the “thickness of coal seam, interactive distance, and buried depth,” four mining coal mines are selected in Shen Fu-Dong Sheng coalfield (SFDSC). To research the mining conditions of shallow coal seam under different base-load ratio mining conditions and different working faces by the physics simulation and in-sit measurement, the key roof caves are sketched by different colors. This study shows that the typical shallow coal seams in the thin overlying bedrock and thick loose sand layer (LSL) as well as the development of the setup entry cracks (SEC) is dominated by LSL arch damage. The surface cracks are almost directly above the setup entry. The flat seam mining and the SEC development is dominated by parabolic type. The surface cracks are located inside the setup entry. With the mining height increased typically in a shallow coal seam, the rate of crack development and the extent of damaged area increased significantly. The SEC and boundary cracks are fixed. The dynamic periodic cracks (DPC) show the ability of the strata to self-repair. During the multiple-seam mining, the above three kinds of cracks have the phenomenon of activation and development. Through the reasonable coal pillar distance arrangement, the development of boundary cracks can be effectively controlled and the relatively uniform surface settlement and crack closure can be achieved. The purpose of reducing damage mining can also be achieved. Furthermore, it provides scientific support for the green mining in the shallow coal seam.

In order to explore the rational coal pillar malposition distance (CPMD) based on coupling control of stress field, displacement field and fracture field (three-field) in shallow buried closely spaced multi-seam (SBCSM-S) mining, and realize coupling control of underground concentrated stress and ground surface fractures, taking the No. 1–2 and No. 2–2 coal seams mining in the northward east area of Ningtiaota coal mine as background, through physical simulation and theoretical analysis, the three-field evolution in SBCSM-S mining was analysed, the effect of different CPMD on coal pillar concentrated stress, ground surface subsidence and fractures development was revealed, and the rational CPMD based on coupling control of three-field was put forward. The results show that the concentrated fractures and concentrated stress are due to the strata’s uneven subsidence by coal pillars. Rational arrangement of CPMD can avoid the superposition of vertical stress caused by upper and lower coal pillars and reduce the development of ground fractures and uneven subsidence. Two theoretical models were established: one was based on the control of a concentrated stress field, the other on the control of the displacement and fracture fields. These results will be applied in a follow-up arrangement at the Ningtiaota coal mine, and can provide a new way for safe and green mining in SBCSM-S.

The overburden movement of the large mining height working face of shallow buried thin bedrock (SBTB) is a complex engineering problem with “time-space-intension”, which is of great significance to realize efficient and safe mining in the northern Shaanxi mining area. Based on the research object of No. 22201 working face in Zhangjiamao Coal Mine, the roof structure characteristics of large mining height working face in SBTB are researched by field drilling measurement, laboratory test, physical and numerical simulation. The results show that: (1) Based on the measured data of the drillholes, it is concluded that under the mining conditions of SBTB with large mining height, the roof movement is ahead of the weighting of the working face, and the working resistance has a significant time effect. The advanced movement distance is about 20 m, which can be used as an early warning index of the weighting. The lag movement distance in the roof with horizon of 30 m is two periodic weighting intervals, which are about 26 m. (2) The first weighting interval of the working face is 32 m. The roof first break has obvious step sinking phenomenon, and the measured surface appears at a position 45 m away from the transport slot. It is statistically concluded that the periodic weighting interval is 9.5~16.5 m, the average weighting interval is 13 m, which is equivalent to the periodic dynamic crack spacing of the surface. (3) The results of field measurement and physical simulation show that the breaking angle of the roof of the No. 22201 large mining height is about 66°, and the periodic stepping distance of the T-junction suspension area is 6~8m. Along the strike of the working face, the roof breaking is mainly arc arched. The research results ensure the safe and green mining of shallow coal seam.

Because of the problem of gangue discharge and surface subsidence during coal mining, the current research on underground filling mainly focuses on the paste filling, solid filling, and grouting filling of the overburden separation layer after scaffolding. We proposed the technology of fluidization gangue grouting for filling the collapse area based on our previous research. The prediction method of residual space in the collapse area and the diffusion law of gangue fluidization filling slurry are two essential points for successfully implementing the technology and maximizing the use of goaf for gangue backfilling and reducing overburden settlement. To further explore the remaining space distribution law of the collapsed goaf in thick seam fully mechanized top coal caving mining and the effect of coal gangue fluidization filling, the caving goaf of the 3307 fully mechanized top coal caving face in Sangshuping No. 2 coal mine in the Weibei mining area was detected by the transient electromagnetic method. We studied the distribution law of the measured abnormal area in the caving goaf, which reflects the distribution law of the remaining space from one aspect. The coefficient of the remaining space was calculated to be 19.5%. Then, we applied COMSOL simulation software. The diffusion law of coal gangue fluidized slurry in the caving goaf was simulated and analyzed. It shows that the most obvious diffusion direction of the coal gangue slurry is the trend of the gradual expansion of the “cavity pore” multi-type residual space, indicating that with the increase in the diffusion distance, the diffusion resistance gradually increases, and the slurry morphology gradually presents the “claw” form. According to the space theory and fractal dimension theory, the prediction method of the remaining space in the caving goaf is given, and the design basis of the filling drilling parameters is determined. Finally, the field-filling test was carried out. The results show that the high- and low-level fluidized filling in the caving goaf can safely and efficiently handle the gangue in the mine, and the residual space characteristics and slurry diffusion law in the caving goaf are consistent with the above. The research results provide theoretical support for the fluidization filling technology of coal gangue in thick seam fully mechanized top coal caving areas.

The fully mechanized mining with large mining height is the main method for high yield and efficient coal mining in China. The key stratum structure (KSS) is the basis of revealing the mechanism of roof weighting and determination of support working resistance of the longwall face with large mining height (LFLMH) in the shallow coal seam. The height of the caving zone at LFLMH is large, the thick immediate roof forms the “short cantilever beam” structure commonly, and the hinge layer of the overlying key stratum will move upward to the higher position. The “high position oblique step voussoir beam” structure of single‐key stratum (SKS) and “oblique step voussoir beam and voussoir beam” structure of double‐key stratum (DKS) in the shallow coal seam were proposed with physical simulation and Universal Distinct Element Code (UDEC). The analysis of the KSS and numerical simulation reveals the mechanism of strong roof weighting at the SKS longwall face and large‐small alternate periodic weighting at the DKS longwall. It is concluded that the large static load caused by the “equivalent immediate roof (EIR)” is the basic load, and the instability load of the KSS is the additional dynamic load of support. Besides, the calculation methods of the reasonable support working resistance at LFLMH were obtained and verified with engineering applications.

The dynamic load effect of supports is mainly caused by the movement of the roof structure and the load transfer of overburden. In view of the practice issue that the phenomenon of strong ground pressure is easy to happen, when the working face of the lower coal seam passes the inclined coal pillar in shallow buried closely multiple-seam, it will lead to supprot damaged. This paper takes the mining of over-inclined coal pillars in the 22410 working face of the Bulianta Coal Mine as the background, based on the research method combining the field measurement, physical simulation experiment, and numerical calculation, the evolution law of the front abutment pressure (FAP) and roof weighting in mining under the inclined coal pillar is analyzed, and the mechanism of the stress transfer of the inclined coal pillar and the dynamic load of the support is revealed. The research shows that the concentrated stress of the coal pillar is jointly borne by the front coal wall of the working face and the interburden structure above the support. The vertical stress transmitted from the coal pillar to the floor acts on the key blocks of the interburden of the lower coal seam, which causes strong pressure and dynamic load effect, such as roof structure cut-off. The periodic breaking of the key stratum of the interburden leads to the development height and range of the cracks increasing stepwise. The partition characteristics of the mutual transformation of the interburden stress, the FAP, and the working resistance (WR) by passing the coal pillar stage are revealed, which is divided into three stages and four regions. With the working face passing through the inclined coal pillar, the influence area of the concentrated stress of the coal pillar is reduced, and the peak stress of the coal pillar is gradually transferred to the outside of the coal pillar. When the working face is 5 m away from the coal pillar, the peak of FAP and WR reaches the maximum values, the roof is cutting along the peak stress line, and the working face has a strong weighting phenomenon. The research results are consistent with the field measurement results, providing a reference for the mining of working faces under similar conditions.