Existing studies on roof cutting and pressure relief mainly focus on their process parameters and engineering applications. However, they are limited in their whole-process coordinated evaluation on the appropriateness, controllability and sustainability of pressure relief, resulting in failure to timely identify insufficient or excessive pressure relief. This study therefore proposes a multi-source coordinated evaluation framework incorporating pre-cutting baseline identification, dynamic feedback during roof cutting, post-cutting effect verification and long-term stability tracking to enhance the effect evaluation of roof cutting and pressure relief. It characterizes the pressure-relief effect from point-scale stress, regional fracturing, stress redistribution and continuous deformation by summarizing the evaluation indicators of the drilling cutting method, microseismic monitoring, stress monitoring, and distributed fiber-optic monitoring. Results indicate that, instead of adopting site-independent absolute thresholds, the effect evaluation of roof cutting and pressure relief should take into account the relative changes of areas with and without, before and after roof cutting and the consistency of multi-source monitoring in spatial location, temporal evolution, and variation trends. The research findings can provide valuable reference for the study and engineering practice of roof cutting and pressure relief technology in deep coal mines.

In order to study the bearing capacity and acoustic emission characteristics of gangue aggregate, a hydraulic servo rock mechanics test system was used to conduct a confining compression test, with an acoustic emission system to collect acoustic emission information of crushed gangue aggregate. Considering the particle size distribution characteristics and stress state of broken gangue in caving zone, the stress-strain relationship, acoustic emission energy, particle size gradation and fractal dimension of gangue aggregate processes were analyzed with comparison between normal distribution and average grading under different axial stress loadings. The results show that the stress-strain curve of gangue aggregate is an exponential function relationship, but the normal distribution gangue aggregate changes significantly during the compaction process. Compared with the average gradation, the normal distribution gangue aggregate first occurs large-scale crushing phenomenon, and the frequency is higher, the distribution is more uniform, but the highest acoustic emission energy is less than the average gradation. The relationship between fractal dimension and loading stress is logarithmic function. The growth rate of fractal dimension of normal distribution gangue aggregate is higher than that of average gradation, and has a larger span interval.

To achieve carbon peaking and carbon neutrality, China has deepened its energy revolution with the largest renewable energy power generation capacity in the world.In face of the unstable power supply of large-scale renewable energy, a new power system has been proposed and constantly upgraded, which promoted the construction and development of pumped storage power station.Under terrain constraints and the ecological red line, the site selection of traditional pumped storage power station is a hard nut to crack.At the same time, a large number of closed/abandoned mines and resource exhausted cities emerged in the process of coal capacity reduction.This study gave a detailed overview of the status quo of pumped storage power station in China, and analyzed the environmental benefits of the combination of closed/abandoned mines and pumped storage, such as water resource pressure relief and greenhouse gas emission reduction.Based on the different modes of closed/abandoned mine pumped storage power stations, this study analyzed the application potential of closed/abandoned mine pumped storage.Finally, this paper proposed the development strategy of China's abandoned mine pumped storage, and the prospects of closed/abandoned mine+energy storage in multiple industries.

Based on the engineering background that rock masses of underground reservoirs in mines are frequently disturbed by cyclic loads such as mine earthquake and mining stress, uniaxial compression and cyclic loading tests for sandstones with different water contents were carried out in laboratory. The crack propagation and failure laws of sandstones with different water contents were revealed by digital speckle technique. Based on scanning electron microscopic (SEM) analysis, the micro deterioration mechanism of sandstones with different water contents under cyclic loading was obtained. The test results show that the peak strength of sandstone decreases gradually with the increase of water content under both uniaxial compression and cyclic loading conditions. The peak axial strain variation of dry sandstone experiences four stages of initial deformation, constant velocity deformation, accelerated deformation, and instability failure, and that of the water-bearing sandstone experiences three stages of initial deformation, constant velocity deformation, and instability failure. With the increase of water content, the peak axial strain in the corresponding stage gradually decreases. It is verified by the deformation rate analysis method that water has no effect on the deformation memory characteristics of sandstone. Under uniaxial cyclic loading condition, the failure mode of sandstone gradually transits from tension−splitting failure at dryness to tension−shear mixed failure, and presents a single shear failure at saturation. SEM results show that with the increase of water content, the fracture structure plane gradually transits from smooth structure, round structure, and sheet structure to completely broken structure. With the increase of water content, the absolute damage parameter increases, which reflects the positive correlation of water−rock coupling damage, and the cumulative damage parameter larger at the same cycle accumulates faster.