Probabilistic Analysis of Dams Built with Collapsible Material

Abstract

Poorly compacted soils with collapsible behavior are sometimes employed in the construction of emergency dams. This paper introduces a probabilistic approach to the coupled analysis of collapsible earth dams. Both the construction and the first impoundment are simulated for three different sections: a homogeneous section containing soil compacted at optimum conditions, a homogeneous section made of poorly compacted collapsible soil, and a mixed section built with both materials. Stability was assessed using a finite element based method, and the Barcelona Basic Model (BBM) was used to describe the mechanical behavior. Following preliminary deterministic studies, the variability of the parameters was considered in the stability analyses to account for laboratory limitations. First, a sensitivity study was performed without the need for numerical simulations. The most relevant variables were then selected to calculate the probability of failure using the point estimation method (PEM). The results show that the deterministic studies are misleading when attesting the safety of the mixed section, which returned a probability of failure of at least 6% for the first impoundment. In addition, the role of collapsibility on the dams' behavior was assessed using a statistic based approach. Collapsibility was shown to attribute significant skewness and variability to the factor of safety (FS) distribution since the sections containing collapsible material presented a standard deviation at least two times higher than the optimum section after the first impoundment. The results discourage the use of poorly compacted material and prove rigorous compaction as a measure for avoiding serious uncertainties when dealing with potentially collapsible soils.