Effects of Water-Soaking Height on the Deformation and Failure of Coal in Uniaxial Compression

The stability of water-preventing coal pillar plays an important role in preventing gob water inrush. The gob side of the water-preventing coal pillar is soaked in a certain height of mine water. Different soaking heights may affect the stability of coal pillars. Few studies have been conducted on the properties of coals with different water-soaking heights. We carried out uniaxial compressive tests on coal specimens with different water-soaking heights to gain a better understanding of different water-soaking-height-induced weakening characteristics of coal. Results show that: (1) The water content of coal specimens increases with the soaking height. Water significantly weakens the strength of coal specimens. However, the extent of strength weakening of the coal specimen does not increase with the increase of the soaked height. The strength of the fully soaked coal specimen is lowest among all groups of coal specimens. The strength of the three groups of partially soaked coal specimens is between the fully soaked coal specimens and the coal specimens without being soaked in the water. In the three groups of partially soaked coal specimens, the strength of the coal specimens increases with the increase of the soaking height. (2) The acoustic emission activities of complete water soaking and nonsoaking coal specimens are relatively concentrated, occurring mainly in unstable fracture expansion stage and post-peak destruction stage, and acoustic emission exhibits main-shock mode. Partially soaking coal specimens, especially the 25% water-soaking height and 50% water-soaking height coal specimens, produces obvious acoustic emission activities during the fracture expansion stabilization phase, and then generates more acoustic emission activities during the unstable expansion stage and the post-peak stage. The acoustic emission presents foreshock—main shock mode. (3) The softening effect of the water soaking on the coal specimens is obvious. It was further found that the deformation of coal specimens with partial water soaking is not synchronized in different layers, the nonuniform deformations of partially soaked coal specimens aggravate its damage.