To achieve green and efficient mining of deeply buried thick coal seams under thin bedrock, this study takes the Zhaogu No.2 Mine as the engineering background and employs theoretical analysis, laboratory experiments, and field measurements. The technologies and equipment, technical difficulties and corresponding solutions, and economic benefit indicators under multi-slicing mining, large-cutting-height mining, and top-coal caving mining are compared. An adaptability evaluation model for mining methods is established based on economic and mining-technical indicators. A surface subsidence prediction method for extra-thick alluvium is proposed. Results show that top-coal caving mining exhibits the highest adaptability, followed by large-cutting-height mining and multi-slicing mining shows the weakest adaptability. The dynamic load method established based on the instability characteristics of the overburden caving arch can be used to guide the selection of hydraulic supports. Grouting-based modification and reinforcement at the bottom of the alluvium can enhance the integrity and water-resisting capacity of the thin bedrock-alluvium interface, promoting the formation of the towering roof beam structure, and weakening the concentrated transfer of thick alluvium load to the supports in the working face. The established surface subsidence prediction model reveals the mechanical mechanism of a surface subsidence exceeding 1.0. This study provides references for mining method selection, strata control, and subsidence mitigation in deeply buried thick coal seams under thin bedrock.

To investigate the shear strength evolution of soil-rock material in waste dump induced by freezing and thawing cycle (FTC), the shear tests are conducted by a self-developed direct shear apparatus, and the effect of FTCs on the shear strength degradation curve of soil-rock material is obtained. Furthermore, the inner microstructure of soil-rock material induced by FTC is analyzed by computer topography (CT)scanning testing.Finally, the stability of waste dump after and before freezing and thawing is compared. The results show that the shear and displacement curves of soil-rock material present strain softening during low normal loading pressure. However, the shear and displacement curve development trend changes from strain softening to strain hardening, and the shear dilatancy happens during loading process. As the FTCs increase, the strain hardening behavior becomes more obvious and the shear dilatancy effect is weakened. In addition, both the cohesion and friction angles decrease as the FTCs increase. When the number of FTC increases to 15, the decrement of cohesion and friction angle is 18.45 % and 9.42 %, respectively. The reason is mainly attributed to the dislocation and regroup of fine rock particles induced by freezing crack.The change in porosity of soil-rock material mainly happens within the initial 5 freezing and thawing cycles. The safety coefficient decrement of waste dump is approximately 7.6 % as the FTCs increase from 0 to 15. The results can provide guidance for waste dump in cold regions.

With the adjustment of China's energy structure, decentralized coal mining has been transformed into refined, centralized and precise mining, which greatly reduces the number of coal mines in China.And a large number of coal mines with exhausted resources and backward production capacity are facing closure or abandonment.This transformation will confront China, at present and for a long time in the future, with a "post-mining" era similar to that in Germany.From the development trend of the transformation of China's energy structure and the macro strategy of coal resource development, there is no possibility to re-develop those coal mines that have been closed or will be closed.The closed mines not only cause environmental problems such as water and air pollution, but also social and economic problems such as difficulty in relocating employees and disposing fixed assets.Therefore, in view of the problems after the mining area is closed or abandoned, the treatment plans for post mining and the sustainable development strategy of resources in post mining industrial zone in Germany are referenced in this paper.Compared with the treatment schemes of closed mining areas in China, the concept that the utilization of resources after the closure of mining areas should be included in the top-level design of the whole mine development, and the idea of comprehensive utilization of coal underground space, mine water and other resources are proposed.Although various forms of abandoned mine utilization schemes have been put forward at home and abroad, the overall utilization rate is not high.It is still necessary to further explore the basic theories and methods of resource utilization in closed mining areas, as well as the corresponding education and technical personnel training measures to meet the development of these areas.

The waste dump of Tibet Jiama Copper Mine, which has a steep and soft base, is taken as the engineering background to reveal the failure mode and mechanism with assistance of similarity simulation principle.Using a method combining bottom friction test and numerical simulation.The deformation evolution of the waste dump is obtained by the contactless displacement monitoring system.The experimental results show that: ①The deformation and instability of the soft steep base dump can be divided into three stages: unloading deformation at the slope toe, vertical tensile crack penetration and tensile crack propagation.②The soft soil layer at the base is compressed and the soft soil layer at the slope toe is subjected to shearing.The slope toe is the trigger zone for slipping deformation and instability.③The potential slip surface passes through the soft soil layer to form an approximate circular arc slip surface.The instability failure of the soft-steep base dump mainly presents the modes of settlement, cracking and slippage.