Abstract
This paper introduces the innovative technique to release the bursting liability of coal seam via microwave irradiation. To verify the feasibility of this environment-friendly technique, a series of laboratory tests incorporating acoustic emission (AE) investigation were carried out. Test results indicated that both the uniaxial compressive strength (UCS) and bursting energy index of raw and water-soaked coal samples were significantly reduced. In particular, the bursting liability was reduced by one level when the values of UCS were compared, the evidence of which is the variation of wave velocities of tested coal samples. It can also be found from the events and hits in the complete stress-strain curve and the cumulative curve of acoustic emission that the elastic modulus of the raw and water-soaked coal samples subjected to microwave irradiation decreased by 58.42% and 29.63%, respectively. This facilitates the entry into the stage of stable crack propagation more quickly, the growth rate and size of the cracks were slower and more uniform, and there were no smaller coal fragments ejecting during the failure process of the coal samples. Meanwhile, the proportion of high-energy events released in coal samples experienced a decline after the treatment of the microwave. Moreover, microwave heating principally promoted the initiation and expansion of microcracks in coal samples under the influence of microwave power of 1 kW and a heating time of 120s, which may cause the overall damage of large fractures to break into multiple small and medium cracks. Based on the experimental results, the conceptual process of using microwave in weakening the bursting liability of coal seam was then proposed, which will be the meaningful reference for microwave-assisted oil recovery and coal bed methane production.
Highlights
Rock bursts have become one of the most severe risks in underground coal mining
Indices of Bursting Liability. e sensitivity of the coal samples subjected to microwave heating and the declined strength of coal samples made it difficult to accurately control to a 75% to 85% level of the ultimate load during cyclic loading
Depending on the different failure modes, artificially subjective factors influence the calculation of the duration of dynamic fracture (DT). erefore, the bursting energy (KE) and uniaxial compressive strength (Rc), being more reliable, were selected for comparative analysis
Summary
Rock bursts have become one of the most severe risks in underground coal mining. As a typical dynamic phenomenon, it generally causes the sudden and severe damage associated with a rapid and violent release of the elastic strain energy attributed to the failure of the rock mass [1,2,3,4,5]. E average value was almost the same as that specified in identifying the result of bursting liability. Both belong to the “strong bursting liability” class. E UCS and bursting energy decreased by 73.74% and 64.54%, respectively, with the average values being 2.98 MPa and 1.78 times for the raw coal samples exposed to microwave heating (CGY). E average values of UCS and bursting energy of the water-soaked coal samples before microwave heating (HSN) were 9.10 MPa and 4.10, respectively. Compared with the CGN, the values decreased by 19.82% and 18.33% It suggests that the water intrusion had a significant weakening effect on the mechanical properties of the coal, which agrees well with such findings by other investigators [7]. When the water-soaked coal samples were irradiated by microwaves (HSY), the UCS and bursting energy index
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