Coupled Effects of Moisture Content and Inherent Clay Minerals on the Cohesive Strength of Remodelled Coal

Hongwei Zhang,Dan Ma,Peng Zhou,Zhijun Wan,Bo Zhang

doi:10.3390/en10081234

Abstract

Injecting water into a coal seam to enhance the cohesive strength of coal and thus minimize and reduce the coal wall spalling risk must be considered in underground coal mining systems. In general, coal with low cohesive strength contains clay minerals which may affect the stability of coal by interacting with water. Therefore, the coupled effects of moisture content and inherent clay minerals on the physical properties (i.e., cohesive strength and internal friction angle) of coal samples should be addressed. In this paper, direct shear tests were conducted by remodelling the Yiluo coal with various moisture contents ranging from 6.6% to 20.7%. According to Mohr–Coulomb failure criterion, cohesive strength and internal friction angle of coal were obtained. Afterwards, effects of moisture content and clay minerals (i.e., Kaolinite, Smectite and Illite) on the cohesive strength of coal were analysed using X-ray diffraction (XRD) method. The results show that cohesive strength increases when the moisture content rises from 6.6% to 17.6%, after which it decreases with increasing moisture content. This trend can be well illustrated by the relationship between typical water retention curve (WRC) and suction stress of soil. Therefore, a moisture content of 17.6% would be an optimal value to enhance the stability of the Yiluo coal seam.

Highlights

In underground coal mining systems, coal wall spalling, gas emissions, and unexpected roof falling are serious disasters increasing the economic cost and challenging the security of coal production, especially when the coal seam is soft and weak [1,2,3]
Remodelling of coal specimens is a repeated method which would be helpful to explore the effect of moisture content on mechanical properties of soft coal
Normal of 100and kPa, 200 kPa, 300 kPa and 400 kPa were applied on specimens with a specific moisture content

Summary

Introduction

In underground coal mining systems, coal wall spalling, gas emissions, and unexpected roof falling are serious disasters increasing the economic cost and challenging the security of coal production, especially when the coal seam is soft and weak [1,2,3]. To enhance the strength of soft coal seam, increasing the moisture content of coal to a certain degree via hydraulic measures has been developed rapidly in recent years. Clay minerals in soft coal may, to a greater or lesser degree, affect the cohesive strength of coal by interacting with water [8]. Broken and can be mouldedIntroduction or shaped, especially when wet It does not expand contactsor with water. Broken and canwhen be moulded shaped, especially when wet. It does not large expand when contacts with water.to. That canand absorb quantities of water, masses.to many times their original volume, and give rise to (Al,Mg)2 [Si4 O10 ](OH)2 ·nH2ofOgel-like swelling.

Methods

Results

Discussion

Conclusion