The effect of embedded gypsum streaks on the dissolution of dam foundation: a case study in Iran

Abstract

Evaporative rocks are known to have a high susceptibility to dissolution in fresh water. Substantial evidence all over the world has shown that the dissolution of evaporative rocks in the foundations of dams and basins can lead to unfortunate disasters. In a basin located in Iran, owing to dissolution of evaporative rock in the foundation on the south side, some hazardous events, such as unexpected subsidence, ground collapse, and water escape from the reservoir, have been reported. Comprehensive geological and geophysical surveys along with detailed geotechnical investigations were performed in order to assess the reasons. By analyzing the site investigation results, it is recognized that even though the foundation of the basin is composed of impervious marl layer, the dissolution of thin streaks of gypsum embedded inside the marl layer provides interconnected paths for the flow of water into the lower depths of the foundation in order to reach to halite layer located inside the marl. The geophysical survey results indicate that the zone with defects is limited to the specific area of the basin where the halite layer is located relatively near the ground surface. However, if the reservoir is filled completely again, the dissolution front may advance to other zones of the basin, and more area of the basin ground may be affected by subsidence and other relevant phenomena.