Influence of cyclic wetting‐drying on the mechanical strength characteristics of coal samples: A laboratory‐scale study

Abstract

Water‐coal interactions have gained much recent attention, although few studies focus on the strength of coal under wetting‐drying cycles. This study investigates changes in the microstructure and mechanical strength of coal that are induced by water‐coal interactions, at the macroscale and microscale. Fourteen specimens after continuous wetting and fourteen specimens after wetting‐drying cycles were tested, indicating that peak stress and elastic modulus decrease with increasing continuous wetting time and number of wetting‐drying cycles, while peak strain increases. We analyzed changes in the coal microstructure using a scanning electron microscope (SEM) and the Image Pro Plus 6.0 (IPP 6.0) software. The regression model for cyclic wetting‐drying reveals that porosity and pore circularity are the main correlation indicators associated with uniaxial compressive strength. Therefore, different numbers of wetting‐drying cycles could induce different degrees of damage to coal, which increases progressively through gradual changes to its microstructure. These findings indicate that wetting‐drying cycles have a more significant impact on the stability of coal mass than continuous wetting. Our results are of use in determining the size of coal pillars, and expanding the knowledge base related to the mechanical properties of coal mass, water bursting, water recharge channels, and the stress‐crack‐permeability evolution law in mines.

Deterioration of Physical and Mechanical Properties of Rocks by Cyclic Drying and Wetting

“…The strength properties of rocks would be significantly deteriorated after the cyclic dry-wet treatment. Khanlari et al [22], Özbek [21], Zhao et al [32], Huang et al [40], and Chen et al [41] performed static compression tests after dry and wet cycles on sandstone, melted limestone, mudstone, and coalstone, respectively. All of the results shown that with the increase of the number of dry and wet cycles, the uniaxial compressive strength and triaxial compressive strength of the rock sample decreased to varying degrees.…”

Experimental Study on Mechanical Properties of Briquette Coal Samples with Different Moisture Content

“…Talapatra et al (2020) revealed the evolution law of coal deformation and strain and described the influence of moisture content on the permeability of coal through porous media in wet reservoir [26]. studied the influence of water-coal interaction on the mechanical strength of coal [27]. The results showed that with the increase of continuous wetting time and the number of dry and wet cycles, the peak stress and elastic modulus decreased and the peak strain increased.…”

Experimental Study on the Mechanical Properties of Sandstone under the Action of Chemical Erosion and Freeze‐Thaw Cycles

“…e subsurface works in the western part of China is not only affected by the low temperature environment and freezethaw cycles but also influenced by factors such as acid rain and groundwater erosion. Not only hydrochemical reaction causes elements to redistribute between rocks and water [1], the volume expansion of water in the pores will also produce freezing force during the freeze-thaw cycles [2,3]. e freezing force leads to the expansion of the original defect and the generation and expansion of new cracks, which cause imbalances within its soil particles, water molecules, and ions and decrease in strength and increase in compressibility.…”