Search Results (2)

The stability of the composite structures formed by coal pillar and roof rock is of great significance to safe production and sustainable development of coal mines. In order to explore the failure and instability mechanisms of coal–rock combinations (CRCs) with varying rock-to-coal height ratios, uniaxial compression tests of CRCs with varying rock-to-coal height ratios were performed via laboratory tests and numerical simulation of particle flow tests, and the mechanical response and failure mechanisms of CRC were comprehensively investigated with regard to their strength, failure characteristics, crack and energy evolution. The results show that the stress thresholds for the crack initiation, uniaxial compressive strength, and elastic modulus of CRCs rose with the decreasing coal-to-rock height ratio, and the fragmentation degree of the coal samples increased with rock-to-coal height ratio. The instability and failure of CRCs are the result of the interaction between the strength of sandstone and coal at the interface and the strength of sandstone and coal far from the interface region; in addition, they are influenced by the distribution range of microfractures during the loading process. The point effect and slip effect formed by coal failure cause sandstone split failure and shear failure, respectively. The number of cracks, macrocrack length, total input energy, elastic strain energy, and dissipated strain energy all reduce first and then increase as the coal thickness reduces. CRCs still have a certain load-bearing capacity in the post-peak stage, mainly due to their strong load-bearing skeleton structure and the friction between particles in the fracturing area, which can resist external forces. Full article

To investigate the effect of the pure coal/rock strength on the mechanical behavior, failure behavior, and energy evolution of coal-rock combined (CRC) specimens, an AG-X250 Shimadzu Precision Universal Test was used to conduct uniaxial compressive loading, uniaxial cyclic loading, and unloading compression experiments on pure coal, pure rock, and different CRC specimens. The results show that the uniaxial compressive strength, Young’s modulus, and peak strain of the CRC specimen mainly depend on the coal specimen instead of the rock strength. The major failure modes of CRC were the shearing fracture and axial splitting failure, and for the CRC specimen with the same hard rock, the CRC specimen severely failed due to axial splitting cracks. In addition, the released elastic energy U_e, dissipated energy U_d, and kinetic energy U_r increase with increasing rock mass/coal strength, and for CRC specimen with the same coal, the greater the difference in strength between the rock and coal is, the greater the kinetic energy is. Full article