Evolution Characteristics of the Cracks in the Completely Disintegrated Carbonaceous Mudstone Subjected to Cyclic Wetting and Drying

Completely disintegrated carbonaceous mudstone, a common embankment material, has significant swelling-shrinkage behavior under cyclic wetting and drying, which often causes the instability of embankments. In this paper, the evolution of the cracks in the completely disintegrated carbonaceous mudstone subjected to cyclic wetting and drying was studied by laboratory tests. The vacuum saturation method and the drying method based on heat lamps and a fan were employed to simulate the wetting and drying processes, respectively. The image processing technique was used to treat the images of the sample surface. Afterward, various geometric parameters of the cracks appeared on the sample surface were measured, and the evolution characteristics of the cracks were analyzed. The results show that with the increase in the number of wetting and drying cycles, the number of cracks on the sample surface gradually increases. After four wetting and drying cycles, the existing cracks produce a large number of small branches, which are connected to form irregular polygonal grids. The development of the cracks in the completely disintegrated carbonaceous mudstone sample can be divided into three stages, i.e., slow development, rapid development, and stable development. Both the surface density of crack and the crack rate first increase and then tend to be stable with the increasing number of wetting and drying cycles. New cracks are mainly generated on the basis of the existing cracks, and some cracks appear to heal under cyclic wetting and drying. The early cracks are mainly developed in the directions of 0°–90° and 300°–360°, and the development rate of the cracks in the directions of 30°, 90°, 140°–150°, and 180°–270° is significantly higher than that of the cracks in other directions.

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