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The evolution process of the surrounding rock failure mechanism is studied because of spalling and roof fall accidents at the top corner of longwall top coal caving faces affected by mining and the difficulty of moving the advanced end support. Methods are proposed to improve the stability of surrounding rocks at the top corner of the end including cutting at the top corner of the end, reinforcing the anchor cable, changing the stress distribution of surrounding rocks at the top corner of the end, and transferring the stress concentration area of surrounding rocks to the deeper rock. Field observations of the surrounding rocks at the top corner of the 15107 fully mechanized caving face show that the stress value of the surrounding rocks at the corner between the roof of the return airway and the coal wall of the working face is 28.9 MPa when the surrounding rocks are in a stable state without mining. The stress value of surrounding rocks at the top corner of the end is 32.3 MPa when it is affected by mining, which results in spalling and roof fall. The surrounding rocks are in a stable state when the maximum stress of the surrounding rocks at the top corner of the reinforced anchor cable’s back-end is 26.1 MPa. The results show that cutting of the surrounding rocks at the top corner of the end and the reinforcement of the anchor cable can avoid the spalling and roof fall when the top corner of the end is affected by mining and can ensure that the end support advances and working face moves forward.

The fracture characteristics and zoning model of overburden during longwall mining are the basis of coal mine disaster prevention. However, the existing theoretical model is inconsistent with the field measurement. In order to further research into the strata’s fracture characteristics and optimize the overburden’s zoning model, we used the elasticity and Winkler foundation theory to establish first fracture and periodic fracture mechanics models of clamped boundary supported by an elastic foundation with a key stratum as the research object. We analyzed the stress distribution characteristics and fracture evolution pattern of the mining-induced key stratum. We analyzed the zoning characteristics of mining-induced overburden and established the zoning model according to different fracture mechanisms. The results show that the key stratum formed a double “O-X” shaped interconnected fracture zone after the first fracture. The key stratum formed a double “C-K” shaped interconnected fracture zone after the periodic fracture. We divided the mining-induced overburden into three zones along the horizontal direction: the original rock zone, the inverted triangular compression-shear fracture zone, and the trapezoidal tensile fracture zone. The study revealed the mechanism of inverted step fracture in the separation zone, explained the fracture mechanism of the coal pillar support zone, and has significant theoretical value for the prevention and control of water disasters, gas outbursts, and strata movement.

The Gravity Recovery and Climate Experiment (GRACE) satellite mission provides measurements of Earth’s static and time-variable gravity fields with monthly resolution. In this study, changes of water storage in northwestern China were determined by GRACE monthly gravity field data obtained from 2003 to 2010. Comparisons of water storage change (WSC) simulated by a four-dimensional assimilation model (Noah) and observed by GRACE revealed similar patterns of change and a correlation coefficient of 0.71(P<0.05). Trend analysis indicated significant changes in the spatiotemporal variation of WSC in northwestern China during the 8-year study period, which were stronger in the east than in the west and more pronounced in the south than in the north. The most pronounced increase in water storage occurred in Gansu and Qinghai provinces, but, overall, water storage increased by 0.61 mm/a over northwestern China during the study period. Clear seasonal variations of WSC and precipitation were found, because glacial meltwater and precipitation are the main sources of water in the hydrosphere; meanwhile, the distributions of glaciers and permafrost also affect the spatial distribution of WSC.