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

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.

Damage Deformation and Acoustic Emission Characteristics of Raw Coal under Different Moisture Contents

“…The results show that temperature changes the intensity of the water-rock interactions. Qian et al [8] performed uniaxial compressive tests on coal specimens with different water-soaking heights to gain an improved understanding of different water-soaking height-induced weakening characteristics of coal. The results show that the AE activities of complete water-soaking and non-soaking coal specimens are relatively concentrated, occurring mainly in the unstable fracture expansion and post-peak destruction stages, and AE exhibits a main-shock mode.…”

Experimental Study of Coal Sample Damage in Acidic Water Environments

“…For soft coal, as the water saturation increases, the uniaxial compressive strength first increases and then decreases (Gu et al 2019). For ordinary rocks and hard coal, water generally only leads to strength reduction (Feng et al 2019;Qian et al 2019) because the water-rock interaction reduces rock cohesion (Guo et al 2018;, degrades fracture toughness, and promotes subcritical crack propagation (Hao et al 2015;Ma et al 2018).…”

Experimental Study of Creep Acoustic Emission Characteristics of Coal Bodies around Boreholes under Different Moisture Contents

“…This process concluded that the weakening of the peak stress and strength, elastic, strain, and the post-peak Energies 2021, 14, 3103 2 of 13 modulus decreased to some extent with increasing moisture content and loading rate. To understand the weakening characteristics of coal induced by different water content levels, Qian et al [17] tested coal samples with different water contents and found that the acoustic emission phenomenon was relatively obvious for fully saturated and non-saturated coal specimens. In the process of exploring the main factors affecting water-rock interaction, Heggheim et al [18] analyzed the softening behavior of sandstone by analyzing the sandstone grain variation, pore morphology and pore size.…”