The resistance transfer coefficient of supports plays an important role in support selection in coal mines, which is the main factor in support crushing accidents. Based on the key layer theory, the formula for calculating the resistance transfer coefficient of supports under the load of a loose layer was deduced. The analysis of four working faces with thick loose layers and the corresponding mining pressure data were used to deduce the load transfer coefficients of the thick loose layers and ultimately illustrate the relationship between thick loose layers and different influencing factors. By using microseismic technology to monitor the process of roof failure in a thin bedrock working face with a thick loose layer during mining, the roof failure characteristics of a large-mining-height working face under the load of a thick loose layer were further verified. The results show that a thicker loose layer and thinner bedrock caused more of the load to transfer to the working face, the roof microseismic events were mainly concentrated in the range of 60 m to 75 m above the coal seam, and the most active events occurred during the square stage (the length of the working face’s goaf is equal to its width). The height of the water-conducting fracture zone was analyzed by microseismic data and then verified with theoretical calculations.

In parts of North China Plain, there are several aquifers in the thick alluvium over the coal seam, which overlays a large amount of coal resources. Roof water inrush accident occurred during coal mining often caused by multiple reasons. Based on the case of roof water inrush in Zhaogu Mining Area, by hydrologic supplementary exploration of the north flank, the stratum data were obtained; combined with previous geological drilling data of the mine, the structural characteristics of five main aquifers and five main aquicludes in the alluvium of the north flank were classified. By pumping test of the No. 1 and the No. 2 supplementary exploration drill holes, the water richness of the 5th aquifer of north flank is identified as medium level. Three thin layers of gravel aquifer beneath the 5th aquifer were found in No. 1 drill hole, and the water richness of the lowest thin gravel (2.95 m thickness) was identified as medium by the followed pumping test, which reveals an important factor leading to the insufficient size of the safety pillar. The leakage self-closed aperture test on the sand soil of the 5th aquiclude clarifies that in case of fracture connection, it cannot resist water and sand crushing under high water pressure of the 5th aquifer. Based on the mechanism of high-pressure water on the working face supports, the calculation method of support resistance under high water pressure alluvial layer is put forward, and the main reason of roof support failure and water inrush is the insufficient support resistance, which leads to abnormal height caving. The methods of experiment and calculation are clarified for preventing water and sand inrush accident of working faces with the similar mining background.

In Jiaozuo mining area of North China coal field, there are multiple strong water-richness aquifers close to the coal seam. In order to prevent floor water inrush accident, it is need to be reinforced by floor grouting before mining. According to the changes of the mechanics and hydrogeological properties of the floor key rock strata after floor grouting, the coal seam floor is divided into ‘two zones’ of ‘water conduction fracture zone’ and ‘mechanical strength damage zone’. The composite water control model of ‘floor structure stability water control key layer’ and ‘floor damage infiltration water control key layer’ is established after grouting reinforcement of upper hard rock aquifer. Microseismic(MS) technology is used to analyse the characteristics of ‘two zones’ and the water control capability of ‘dual key layers’ in fault regions and no-fault regions respectively of experimental working face. It is revealed that the L8 limestone plays the role of mechanical barrier key layer after grouting. The change of elastic modulus of rock mass before and after grouting is measured by borehole ultrasonic method, which result shows that the elastic modulus of different rock mass increases by 40–852% respectively after grouting. By using the formula method, FLAC3D numerical simulation and field measurement, it is found that the failure depth of the floor after grouting is reduced by 51% compared with that without grouting. Seven influencing factors for floor water control ‘dual key layer’ are proposed, which are quantified by AHP (Analytic Hierarchy Process) method. A scheme of ‘dual key layer’ water control capability evaluation is formed by AHP method and influencing factors evaluation method. It is revealed that fault activation and fault with water-filling are the main factors that affect the failure of water control capability of ‘dual key layer’ and floor water inrush. The results of the research are consistent with the water inrush of the experimental working face, which will contribute to the early warning, prevention and evaluation of floor water inrush in mines with the same hydrogeological conditions.