期刊
GAS SCIENCE AND ENGINEERING
卷 111, 期 -, 页码 -出版社
ELSEVIER
DOI: 10.1016/j.jgsce.2023.204927
关键词
Pre-drilled coal; True triaxial stress; Mechanical response; Flow characteristics; Coal and gas outburst
True triaxial experiments were conducted to study the mechanical response and gas flow characteristics of pre-drilled coal samples. The results showed that the gas flow rate of pre-drilled coal samples increased with strain, presenting an S-shaped trend. The failure mode of pre-drilled coal samples was mainly shear-type, with V-shaped macro-fractures observed when the boreholes were perpendicular to bedding planes and parallel to face cleats. The mechanical responses and flow characteristics of pre-drilled coal will provide guidance for borehole layout design and prevention of coal dynamic disasters.
Many gas pre-drainage boreholes are generally constructed in coal seams to ensure safe underground operation. True triaxial experiments were conducted to study the mechanical response and gas flow characteristics of pre-drilled coal to reveal the in-situ behavior at pre-drilled regions in coal seams. The mechanical parameters, failure modes, and flow rate evolutions of pre-drilled coal samples were collected. The gas flow rate of pre-drilled coal samples showed an S-shaped trend with the increase of strain, and no obvious descending progress was found the flow rate-strain curves. The typical failure mode for pre-drilled coal samples was shear-type during the true triaxial stress compression. V-shaped macro-fractures around the boreholes were observed when boreholes were perpendicular to bedding planes and parallel to face cleats. In contrast, single shear macro-fractures around the boreholes were observed when boreholes were parallel to butt cleats. The pre-drilled coal samples exhibited lower peak strength values when boreholes were parallel to butt cleats, induced by the relatively low cohesion parameter. Pre-drilled coal's initial flow rates perpendicular to bedding planes and parallel to butt cleats di-rections were only 33.33% and 41.67% of values measured along face cleats. More complex macro-fractures were formed, and up to a 39.30% decrease in strength was observed in pre-drilled coal samples under true triaxial unloading stress paths. The variations in volumetric strain level and the flow rate evolution were further dis-cussed with an anisotropic conceptual failure model. These mechanical responses and flow characteristics of pre-drilled coal would guide the design of borehole layout and prevention of coal dynamic disasters.
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