uncertainties in mechanical behavior of rockfills during first impounding of rockfill dams

Rockfills are used vastly as materials for shells of earth dams, changing their name to rockfill dams. During construction of a rockfill dam, rockfill layers are placed and compacted often dry, with no moisture added, due to extra costs and times required for moistening. During first impounding of the reservoir, when the sealing element is embedded in the structure (e.g. clay core, asphalt core), the upstream shell becomes saturated immediately. This will degrade rapidly mechanical parameters, including strength and deformation parameters of the rockfill materials, resulting in relatively large settlements in the upstream side of the structure. This phenomenon is named saturation collapse/ or compression in the literature. As far as deformation behavior and safety of the dam are concerned, it is of vital importance to estimate, as realistic as possible, the degree of degradation in strength and stiffness parameters of the saturated rockfill materials. There is no clear, unanimous view in the literature on the mechanism of collapse saturation phenomena, as well as the degree of induced degradations in the mechanical parameters of different types of rockfills upon their first saturation. This paper first reviews effects of water on behavior of rock particles and rockfills subjected to loading. Also the paper discusses various factors responsible for the saturation-induced mechanical degradation; among the factors are: rockfills particle sizes, initial void ratio, compaction level of rockfills, type of rock minerals, and weathering degrees. Also the paper investigates and proposes a mechanism for the phenomena.