Performance Evaluation of A High Geomembrane Faced Rockfill Dam In Case of Liner Rupture and Earthquake Risks

This paper presents stability and seepage evaluation of a high rockfill dam with a geomembrane seepage barrier by considering scenarios of a possible occurrence of a large earthquake due to the active faults in the region and also a seepage flow in the dam due to a possible rupture of the geomembrane liner. For this purpose, finite element transient seepage and pseudo static slope stability analyses were both carried out together to assess the critical potential failure surfaces and safety factors of the rockfill slopes. Therefore, pore water pressures on the failure surfaces were first calculated using the time varying (transient) numerical seepage analyses method which is essentially important to determine the time dependent variations of seepage paths and water pressures within the rockfill as well. In the analyses, it was determined that the most critical slope failure case is when a geomembrane liner tears at the time of the highest reservoir water elevation since the hydraulic head is maximum and causes the largest seepage pressure in the rockfill there. Analyses showed that if a strong earthquake struck the region, both the upstream and downstream slopes are safe with sufficiently high safety factors. In addition, in case of a possible tear and leakage on the geomembrane liner, the dam will also withstand well with 2.25 horizontal to 1 vertical slopes. However, it is recommended that constructing a downstream toe drain or a relief well will provide an additional safety measure against any heave occurrence or instability of the rockfill since the embankment and bedrock foundation are pervious causing high seepage pressures at the downstream toe of the dam