Abstract
Water content is an important factor in the deformation-destruction process of coal bodies. To analyze the influence of water on the creep acoustic emission (AE) characteristics of coal rock surrounding a borehole, we conducted graded loading creep AE tests of single-hole specimens with different water contents (0%, 4%, 8% and water-saturation) under uniaxial loading. The findings include the following: the water content affects the creep mechanical properties of the coal body around a borehole. The creep transient strain and steady-state strain increased exponentially with rising water content; the saturated specimen showed the highest increase, reaching 44.5% and 28.6%, respectively. The specimen water content affected the cumulative ringing count (CRC) and the axial strain during creep. The axial strain increased with rising water content, the CRC increased linearly with rising axial strain. The higher the water content, the greater the CRC rise. At different stress levels, the CRC in the 4%, 8% and saturated water content specimens changed by 43%, 53% and 74%, respectively. The AE ringing rate showed a pattern of grow–decline–stabilize at each creep stage. The AEs decreased significantly with the rising water content and the creep curve lagged behind the AE data. This paper provides guidelines for gas extraction, borehole maintenance and AE detection.
Highlights
IntroductionLong-term submergence of the coal body increases the water content, which reduces its bearing capacity and strength, or even destroys it [3]
The coal rock body around a gas extraction borehole is affected by water–stress coupling; in this setting a drilled coal body can be damaged more than an intact coal rock body
In this paper, the following analyses were performed for coals with different moisture contents, the main parameters included: creep displacement, calculation of strain, acoustic emission parameters, etc
Summary
Long-term submergence of the coal body increases the water content, which reduces its bearing capacity and strength, or even destroys it [3]. This affects its macroscopic mechanical properties, and the gradual accumulation of coal body damage will eventually affect the creep deformation properties of the coal body [4,5,6]. The creep properties of pore-bearing coal bodies differ from those of intact coal bodies; few studies have investigated creep deformation of coal bodies around boreholes [7,8,9]
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