To better understand the physical and mechanical behavior of weakly cemented rock with different moisture contents for the success of water-preserved mining, this paper presents the systematic tri-axial compression tests on three typical rock samples (i.e., mudstone, sandstone, and sandy mudstone) sampled from Ili mining area, where the environmental requirements for water conservation are significantly strict. Both the influences of moisture content and confining pressure on the failure mode and the stress-strain behavior of weakly cemented rock have been discussed and compared with each other. Test results showed that: (1) compared to sandstone and sandy mudstone, both the peak stress and residual stress of the weakly cemented mudstone are much more sensitive to confining pressure and moisture content. In detail, the peak stress is very relevant to moisture content, whereas, the residual stress is more sensitive to the confining pressure, (2) with the increase of moisture content, both the yield and ductility of weakly cemented mudstone have been significantly enhanced. However, a similar experimental observation has been found for sandstone and sandy mudstone, and (3) the microstructure and the mineral component are believed to be the two main factors leading to the scatter in terms of the stress-strain behavior for different weakly cemented rocks. Experimental results and discussions presented in this paper can provide the guideline for further research on the application of water-preserved mining in other coal mines with a similar geological condition.

Rocks are natural heterogeneous materials. It is common for a rock to have several kinds of minerals, which will have a significant effect on its mechanical behavior. The purpose of the numerical simulation study in this paper is to explore the effects of minerals on the crack patterns and mechanical properties of rocks. First, the corresponding calculation model is established by using the discrete element method (DEM), whereby the mechanical parameters of the blocks and joints in the Tyson polygon procedure are fitted with the rock properties obtained in the laboratory. Then, various combination models of different mineral sizes and ratios are established to study the effects of mineral size, position, and ratio on the fracture distribution and mechanical properties of rock samples. The results indicate that with increased circle size of the center mineral and the mineral ratio, the elastic modulus and uniaxial compression strength (UCS) of the model gradually increase. The drop degree of post-peak stress decreases, and the integrity and bearing capacity increase. It is found that there is a quartic polynomial relationship between elastic modulus and mineral circle radius, with R² ≥ 0.94. The minerals located in the crack propagation path will effectively block the crack and change the propagation direction. When the mineral position is close to the model boundaries, especially the lateral boundaries, it has a significant influence on the crack initiation position, causing crack initiation to occur at the upper boundary of the mineral circle and propagate to the middle of the model. With increased mineral percentage and small-size mineral circle proportion, the depth of extension of the crack from boundary to center is reduced, the crack has wide development in the boundary area, the number of central cracks in the rock specimen decreases, and the degree of fragmentation decreases.

An analysis of the causes behind coal bursts in Xinzhou Kiln Mine showed that they are primarily induced by the following factors: left-out pillars, hard coal seams and/or roofs, stress concentration due to complex geological structures, and stress distribution characteristics of the primary rock. This study found that hydraulic cutting not only reduced and transferred the stress concentration region inside the coal seam, but also weakened the burst tendency of the coal-rock mass, thus reducing the possibility of coal burst occurrences in a fundamental way. By taking Face No. 8937 in Xinzhou Kiln Mine as the test object, a coal burst prevention test was performed using hydraulic cutting. In combination with theoretical analysis and numerical simulation, the mechanism of hydraulic cutting for preventing coal burst was discussed, and reasonable cutting parameters were established. Onsite monitoring results indicated that after hydraulic cutting, the coal-rock mass was no longer intact, the stress inside was released and its water content was increased, which weakened its burst tendency. The cutting slot were deformed and fractured and the boreholes closed, which transferred the stress concentration region inside the coal seam to a deeper area and to the two ribs. After cutting, the number of coal burst occurrences and impact energy thereof significantly dropped; convergence of the roadway at the cutting area showed an obvious increase over that at non-cutting areas. Furthermore, displacement of the roof and floor increased by 78.9% and that of the two ribs increased by 47.4% after cutting, which made the coal-rock mass unable to gather high stress. In conclusion, hydraulic cutting merits further consideration and application, as it can effectively prevent coal burst occurrences and safeguard mining activities.