Microstructure and water holding characteristics of pre-disintegrated carbonaceous mudstone under the action of wetting and drying cycles

The microstructure and pore size distribution characteristics of pre-disintegrated carbonaceous mudstone in different numbers of dry and wet cycles were studied by scanning electron microscopy and mercury-pressure test, and soil-water characteristic curve test and permeability test of pre-disintegrated carbonaceous mudstone were carried out to study the evolution of water-holding characteristics of pre-disintegrated carbonaceous mudstone under long-term atmospheric influence. The unsaturated permeability coefficient of pre-disintegrated carbonaceous mudstone was estimated using a modified model of soil-water characteristic curve of pre-disintegrated carbonaceous mudstone based on the Van Genuchten model that took account of the effect of dry and wet cycles. The results show that the dry and wet cycles can promote the continued disintegration of pre-disintegrated carbonaceous mudstone, resulting in the increase of large pore volume and porosity, and the soil structure becomes loose, but porosity stabilizes after six dry and wet cycles. The dry and wet cycles have significant effects on the water-holdingcharacteristics of pre-disintegrated carbonaceous mudstone, and the soil-water characteristic curve shifts to the left with the increase of the number of dry and wet cycles, and the value of soil air intake decreases. In the high matric suction stage, the predicted unsaturated permeability coefficient of the pre-disintegrated carbonaceous mudstone remains essentially the same after multiple wet and dry cycles, indicating that the pre-disintegrated carbonaceous mudstone is unaffected by changes in permeability. © 2023 Central South University of Technology. All rights reserved.