To solve the problems in blasting roof-cutting related to pressure-relief entry retaining mining, a liquid directional roof-cutting technology is proposed in this article. To verify the adaptability of liquid directional roof-cutting technology in the practice of pressure-relief entry retaining mining, a lab cutting test was performed. The effects of the four main cutting parameters (type of abrasive, pump station pressure, speed of cutting head, nozzle diameter) on cutting capacity were examined through the test, and the optimal cutting parameters that meet the design requirements were ultimately identified. Based on the above test parameters, field engineering test equipment was developed. The results of a hole mouth cutting test and single-hole unilateral cutting test show that the liquid directional roof-cutting technology can be used to complete field cutting work, and the cutting depth and directional function can meet the design requirements. However, some new problems were found in the field application. For example, in the process of multihole bilateral cutting, the rock mass between four holes cannot form a cut-through face. However, these problems can be addressed by increasing the cutting capacity and optimizing the seam direction. In summary, the design idea of conducting roof directional cutting by using liquid directional cutting technology is viable, and the proposed technology is expected to replace blasting work in several engineering applications requiring pressure relief, such as impact pressure control and coal and gas outburst control.

Non-coal pillar mining with roadway formed automatically (RFANM) is a new mining approach, which demonstrates revolutionary significance because it does not require making roadway before mining and coal pillar retaining. In order to explore the stability of the surrounding rock structure in RFANM, the deformation of the surrounding rock was theoretically analyzed and simulated based on three different fracture positions of the main roof. It was concluded that reasonable control of temporary support strength in roadway is of great importance to control the deformation of the entry. The deformation process of surrounding rock under different fracture positions in RFANM was simulated by using the Universal Discrete Element Code (UDEC). The results of the numerical simulation showed that the main roof was fractured at the solid coal side or gob side; the deformation of the roadway was small. The fracture condition of the main roof at the gob side required a higher effect of roof slitting or temporary support from the roadway. Through drilling and peeping at the retained roadway, it was judged that the main roof was broken inside the coal wall. Field monitoring results revealed that the deformation of the roadway can be effectively controlled.

Although the hydraulic fracturing treatment can improve the conductivity of shale reservoirs, the low recovery rate of the fracturing fluid may cause potential environmental and production issues. For an accurate investigation of these issues, an appropriate model of the water imbibition in shales is required. However, the hydraulic parameters related to water imbibition in shales are hard to be measured due to their tiny pores. In this study, an effective method is proposed to estimate the water imbibition volume. The nuclear magnetic resonance method is applied to obtain the related parameters including the capillary curve, the intrinsic and relative permeability of the shale, which can significantly cut down the time and cost needed to get these data. This model is validated by water imbibition experiments. In addition, we compare two empirical equations used to calculate intrinsic permeability in the NMR method and calibrate the corresponding parameter a for shale, which is poorly investigated in literature. Finally, we suggest that the capillary force dominates the early stage of water imbibition process in unsaturated shales, and the late period may be influenced more by other mechanisms such as the osmosis and the surface hydration.