Deterioration of Mechanical Properties of Rockfill Materials Subjected to Cyclic Wetting–Drying and Wetting

The deterioration of rockfill materials caused by different factors harms the safety and workability of rockfill dams. This has been confirmed by the increase in dam deformation resulting from initial impoundment and water level fluctuation during operation. However, the deterioration process and mechanism for rockfill materials subjected to different weathering conditions lack systematic comparison. In this study, we conduct a series of oedometer tests on rockfill materials that have undergone different wetting–drying cycles and wetting duration. The deterioration in mechanical properties as manifested by the decrease of yield stress and increase of compressibility varies nonlinearly with wetting–drying cycles and wetting duration. The degree of deterioration for rockfill samples subjected to cyclic wetting–dying is more significant than exposed to wetting alone. The relative breakage index and fractal dimension of rockfill samples subjected to cyclic wetting–drying are larger than that exposed to wetting alone, indicating more particle breakage occurred in former conditions. In addition, the scanning electron microscopy analysis and mineral composition content test are performed to investigate the deterioration mechanism of rockfill grains induced by two weathering conditions. The chemical reactions in the wetting process and the crystallization-induced stress in subsequent drying process cause the expansion of micro-cracks and the microstructural changes.