An RMT-150B electrohydraulic servo testing system was used to perform uniaxial compression and uniaxial grading relaxation (creep) tests. The deformation, strength, and failure characteristics of the progressive failure process of coal samples under three loading modes were analyzed. The analysis results show that the prepeak stress-strain curve of the coal samples and the load relationships are not clear and that the whole compression process of coal still showed compression, elastic, yielding, and failure stages. The local stress drop characteristics during our relaxation creep grading tests showed no clear peak value and showed a yield curve with the shape of a conventional single plateau. The values of the mechanical parameters of axial compression were significantly higher than those obtained in the grade relaxation (creep) tests, which showed the mechanical parameters of coal samples with aging characteristics. In the relaxation (creep) tests, when the stress ratio was less than 70%, the relaxation (creep) characteristics of the sample were not clear. When the ratio of stress relaxation (creep) was more than 70% in the relaxation (creep) tests during displacement (stress) with a constant relaxation (creep) over the duration of the test, the evolution, development, and convergence of microcracks in the coal samples were observed. Relaxation (creep) stress was higher, failure duration was shorter, and the duration of failure was longer. For fully mechanized coal faces, increasing the support resistance and timely moving the support after coal cutting may prevent rib spalling accidents by reducing coal stress and exposure time in the front of the working face. Additionally, routine uniaxial compressive failures showed a simple form, having a clear tension-shear dual rupture surface. The staged relaxation creep failure testing of coal is more complex. The entire coal samples were divided into many thin-sheet debris via gradual collapse and shedding, and the number of cracks increased significantly, showing evident lateral expansion characteristics that are similar to the rib spalling characteristics in high coal mining working faces.

Based on simulated material scale modeling and numerical simulation, the protective seam mining method was conducted at one coal mine. After extracting the No.15 seam, the overlying strata movement and the deformation of the No.9-10 protected seam were studied. The experiment results show that it is feasible to destress the protected seams with large interburden thickness. When the face had advanced 200 m from the setup room, the No.9-10 seam was fully destressed, resulting in easy gas drainage in the destressed zone. Recommendations on mining sequence of multiple seams mining in the same coal areas were made.

Sliding structure refers to the process and result of rock deformation caused by the continuous downward sliding and cutting of the upper stratum under the influence of gravity. In the process of tectonic formation, the strata go through two times of sliding to the south and then sliding to the north after the over thrusting and overstretching, so that the strata of the overthrusting and underthrusting strata are opposite to the inclination of the overthrusting and underthrusting strata, forming the anticlinal tectonic zone. Nowadays, under the conventional geological mining conditions, the underwater mining technology and surface subsidence laws are quite mature, but the fracture zone and surface movement characteristics of the sliding structure and the antioverturning mining are still rarely studied. This paper analyzes the dam damage in the mining process and discusses the three-dimensional reconstruction of laser scanning and the acquisition method of settlement information. The three-dimensional laser scanning technology is compared with the traditional monitoring technology. The deformation characteristics of surface structures above 25091 working face are revealed. The 3D laser point cloud shows that the uneven sinking of the dam is obvious and is associated with the uneven damage of the dam mass. The actual observation at the site shows that the uneven settlement of the dam on the surface was noticeable during the 25091 working face retraction. The damage on the east side of the dam was more serious and was accompanied by the generation of cracks running east-west. The DEM model of part of the surface and dam above the 25091 working face was obtained by 3D laser scanning technology. The model was analyzed to obtain information on surface subsidence. The study reveals that the uneven subsidence condition of the dam is apparent, with the overall characteristics of large subsidence on the east side of the dam and small subsidence on the west side of the dam. The displacement of the maximum surface subsidence point reflects the special phenomenon of overburden fracture and surface movement under the influence of overburden reverse inclination.