Abstract
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.
Highlights
Water-conducting fissures will be formed in overburden strata during the coal mining process, which results in a large amount of mine water in gob area [1]
In order to study the influence of the soaking height on the water absorption law of coal specimens, In order to study the influence of the soaking height on the water absorption law of coal the water-soaking tests of the coal specimens under five different soaking heights were carried out
The results showed that the evolution of water content of coal specimens with 25 mm, 50 mm, 75 mm, and 100 mm water-soaking heights was almost the same
Summary
Water-conducting fissures will be formed in overburden strata during the coal mining process, which results in a large amount of mine water in gob area [1]. The coal and rock mass around gob will inevitably be in a certain mine water environment [2]. Due to the difference in water supply and drainage in the gob, the amount of water in the gob will be different. The water-preventing coal pillars may be soaked in water-accumulated gob with different water amounts, the soaked height of the coal pillars in the gob water will be different. Coal is a porous medium [3], water will be absorbed from the bottom to the upper part of the coal pillar due to capillary force, while the gravity will hinder.
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