Failure of a geomembrane lined embankment dam - Case study

The right wing embankment of the headrace channel of a hydropower plant, failed adjacent to the concrete intake structure. The failure also caused damages of the penstocks and flooding of the powerhouse. The root-cause analysis showed that water from the reservoir entered, through an open joint in the adjacent concrete structure, the geomembrane lined homogeneous embankment dam fill. This seepage water had eroded dam material from below the geomembrane and transported it to the drainage zones located at the interface of the embankment and concrete structures. Due to continuing seepage and erosion of dam material the geomembrane ruptured and this resulted in the full reservoir head being applied to the embankment fill material. This increased the seepage through the dam fill and caused concentrated leak erosion of the fine-grained material at the contact with the concrete structure, and this lead to the failure of the embankment.