In order to study the physical and mechanical properties of sandstone under high-temperature water-cooling cycling conditions, an RMT-150B electrohydraulic servo rock testing system and a DS-5 acoustic emission detection and analysis system were used to conduct uniaxial compression acoustic emission tests on sandstone after high-temperature water-cooling cycles. The deformation, strength, and acoustic emission characteristics of sandstone were analyzed under different temperatures and cycle times. The results show that the high-temperature water-cooling effect caused changes in the physical properties of sandstone. The volumetric expansion rate of the rock samples first decreased, then increased in temperature, and the strength first increased, then decreased, whereas the number of cycles had less of an impact on the physical properties. At 200 °C, with increased cycle number, the elastic modulus increased by 20.1%, and the compressive strength increased from 63.9 MPa to 71.46 MPa. At 300–600 °C, the elastic modulus and compressive strength of sandstone gradually decreased with increases in the temperature and cycle number, with reductions of 6.04%, 7.24%, 28.7%, 35.57%, 17.6%, 18.2%, 20.4%, and 60.5%, respectively. With increased temperature and cycle times, the acoustic emission ringing counts increased, ringing counts and cumulative energy appeared earlier, the rock samples entered elastic deformation earlier, the yield stage length increased, and the samples showed a tendency to transition from brittle to ductile damage.

Research on the deformation characteristics and failure modes of buried pipelines under local suspension conditions caused by groundwater loss in coal mining subsidence areas is conducive to grasping the failure evolution law of pipelines and providing technical support for the precise maintenance of gathering and transportation projects and the coordinated mining of gas and coal resources. First, a test system for monitoring the deformation of pipelines under loading was designed, which mainly includes pipeline load application devices, end fixing and stress monitoring devices, pipeline end brackets, and stress–strain monitoring devices. Then, a typical geological hazard faced by oil and gas pipelines in the gas–coal overlap area—local suspension—was used as the engineering background to simulate the field conditions of a 48 mm diameter gas pipeline with a localized uniform load. At the same time, deformation, top–bottom strain, end forces, and damage patterns of the pipeline were monitored and analyzed. The results show that the strain at the top and bottom of the pipeline increased as the load increased. In this case, the top was under pressure, and the bottom was under tension, and the conditions at the top and bottom were opposite.. For the same load, the strain tended to increase gradually from the end to the middle of the pipeline, and at the top, it increased significantly more than at the bottom. The tensile force carried by the end of the pipeline increased as the applied load increased, and the two were positively correlated by a quadratic function. The overall deformation of the pipeline evolved from a flat-bottom shape to a funnel and then to a triangular shape as the uniform load increased. In addition, plastic damage occurred when the pipeline deformed into a triangular shape. The results of the investigation clarify for the first time the mathematical relationship between local loads and ultimate forces on pipelines and analyze the evolution of pipeline failure, providing a reference for pipeline field maintenance. Based on this, the maximum deformation of and the most vulnerable position in natural gas pipelines passing through a mining subsidence area can be preliminarily judged, and then the corresponding remedial and protection measures can be taken, which has a certain guiding role for the protection of natural gas pipelines.

Taking Yujialiang Coal Mine as the engineering background, aiming at the actual demand of 5-2 coal seam mining and 4-4 coal seam upward mining, the temporal evolution and spatial distribution characteristics of overburden failure height after 5-2 coal seam mining are systematically investigated by using multi-source field detection technology such as ground drilling, logging, and borehole peeping, combined with a numerical simulation method. The field detection results show that after the 5-2 coal seam is mined, the development height of the water-conducting fracture zone (WCFZ) is 116.25–129.92 m, and the height of the caving zone is 9.32–21.56 m. The 4-4 coal seam is located within the fracture zone, 15.99–22.88 m above the caving zone. The strength of the 4-4 coal seam and its surrounding rock affected by mining is reduced, with a more significant decrease in the middle of the goaf. The numerical simulation further reveals the law of overburden movement and deformation. After the 5-2 coal seam mining, the maximum subsidence of the 4-4 coal seam floor reaches 4.57 m, and there is stress concentration above the remaining coal pillars. The maximum vertical stress after mining all three working faces (52,204, 52,205, 52,206) is 4.10 MPa, and the stress environment above the goaf is better. The results show that the average distance between the 4-4 coal seam and 5-2 coal seam is about 39.45 m, and the upward mining is feasible, but the stability of the rock strata in the fracture zone should be paid more attention to. Based on the movement law of overlying strata and the characteristics of stress distribution, it is suggested that the mining gateway of the 4-4 coal seam should be arranged in the middle of the remaining coal pillar of the 5-2 coal seam or the corresponding area in the middle of the goaf so as to ensure the stability of the roadway surrounding the rock during mining. The research results provide a reliable theoretical basis and technical support for the upward mining design of the 4-4 coal seam in Yujialiang Coal Mine and have important reference value for the upward mining projects of coal mines under similar conditions.

In order to study the acoustic emission characteristics of sandstone under the action of the high temperature-water cooling cycle, the RMT-150B electro-hydraulic servo rock test system and the DS-5 acoustic emission detection and analysis system were used to conduct a single analysis of the sandstone after the high temperature-water cooling cycle. Experimental study on acoustic emission characteristics under axial compression, analyzing the deformation, strength and acoustic emission characteristics of sandstone under different temperatures and cycles. The results of the study show that the high temperature-water cooling action causes changes in the physical properties of the sandstone. The expansion rate of the rock sample decreases first and then increases when the temperature rises, and the strength first increases and then decreases. The number of cycles has little effect on the physical properties of the rock sample; sandstone acoustic emission ringing count increases with the increase of temperature and cycle times, acoustic emission activities become more frequent with the loading process; with the increase of cycle times and temperature, acoustic emission ringing counts and accumulative acoustic emission energy appear earlier The rock sample enters the elastic deformation stage ahead of schedule, the yielding period increases, and the rock sample presents a trend of transition from brittle failure to ductile failure; the ringing count and cumulative energy increase with the increase in temperature and cycle times, and the high-energy ringing count and cumulative energy increase. The simultaneous sharp increase of the rock sample is the harbinger of the failure and instability of the rock sample.