Degradation mechanism in dispersive-soil earthen dams under climatic conditions: A case study from Song Sat reservoir, Khanh Hoa, Vietnam

Abstract

The safety of earthen dams remains a critical global concern, particularly in the context of climate change and the increasing frequency of extreme weather events. Highly dispersive soils and climate stress in South Central Vietnam are causing dam degradation and downstream slope failure. The combined approach, which involves both field observations and laboratory experiments, is employed to provide a comprehensive understanding of the underlying mechanism. The statistical results elucidate the annual progression in the number and size of sinkholes, thereby revealing patterns of erosion development over time and in relation to climatic conditions. In which the number of sinkholes on the downstream slope increased from 20 in 2014 to 626 in 2023, a rise of more than 30-fold, including a sharp seasonal escalation of over 70% during the 2020–2023 rainy periods alone. In parallel, laboratory tests-including Pinhole, Crumb, and Exchangeable Sodium Percentage (ESP) tests-were conducted to confirm the strong dispersivity of the dam fill soil, with ESP values ranging from 16% to 31%, and Pinhole and Crumb tests consistently classifying the soil as dispersive. The results show that the soil in this region has a high and is highly prone to structural breakdown upon contact with water. This research provides both scientific and practical foundations for proposing appropriate engineering solutions, and application of automated monitoring technologies, thereby contributing to improved dam-safety management under increasingly extreme climatic conditions.