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Energies 2017, 10(5), 612;

Grain Size Distribution Effect on the Hydraulic Properties of Disintegrated Coal Mixtures

1,2,3,* , 1,* , 2
School of Resources & Safety Engineering, Central South University, Changsha 410083, Hunan, China
State Key Laboratory for Geomechanics & Deep Underground Engineering, China University of Mining & Technology, Xuzhou 221116, Jiangsu, China
GeoEnergy Research Centre (GERC), University of Nottingham, Nottingham NG7 2RD, UK
Authors to whom correspondence should be addressed.
Academic Editor: Mehrdad Massoudi
Received: 6 April 2017 / Revised: 25 April 2017 / Accepted: 27 April 2017 / Published: 29 April 2017
(This article belongs to the Special Issue Mathematical and Computational Modeling in Geothermal Engineering)
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In order to better understand groundwater influx and protection in coal mining extraction works, an in-house water flow apparatus coupled with an industrial rock testing system, known as MTS 815.02, were used to study the effects of grain size mixtures on the compaction and flow properties of disintegrated, or non-cemented, coal samples. From the Reynolds number evaluation of the samples with different grain mixtures, and the relationship between the water flow velocity and pore pressure gradient differences, it was found that seepage through the mixtures are of non-Darcy flow type. The porosity of coal specimens was found to be highly affected by compaction, and the variations of the porosity were also influenced by the samples’ grain size distribution. It was found that the sample porosity decreases with increasing compaction and decreasing grain sizes. Grain crushing during compaction was observed to be the main cause of the appearance of fine grains, and the washing away of fine grains was consequently the main contributing factor for the weight loss due to water seepage. It was observed that during the tests and with the progression of compaction, permeability k decreases and non-Darcy factor β increases with decreasing porosity φ. The k-φ and β-φ plots show that as the sizes of disintegrated coal samples are getting smaller, there are more fluctuations between the porosity values with their corresponding values of k and β. The permeability value of the sample with smallest grains was observed to be considerably lower than that of the sample with largest grains. Non-Darcy behavior could reduce the hydraulic conductivity. It was found that the porosity, grain breakage and hydraulic properties of coal samples are related to grain sizes and compaction levels, as well as to the arrangement of the grains. At high compaction levels, the porosity of disintegrated coal samples decreased strongly, resulting in a significant decrease of the permeability at its full compression state; Non-Darcy flow behavior has the slightest effect in uniform samples, therefore, indicating that disintegrated coal in uniform grain size mixtures could be treated as an aquicluding (water-resisting) stratum. View Full-Text
Keywords: water influx; mining; coal grain; hydraulic properties; compaction water influx; mining; coal grain; hydraulic properties; compaction

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Ma, D.; Zhou, Z.; Wu, J.; Li, Q.; Bai, H. Grain Size Distribution Effect on the Hydraulic Properties of Disintegrated Coal Mixtures. Energies 2017, 10, 612.

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