Scenario-based stability analysis of an embankment dam under rapid drawdown conditions

Abstract

This study presents a comprehensive assessment of the transient slope stability of the Gavoshan embankment dam, located in western Iran, under a range of rapid reservoir drawdown scenarios. The analysis was performed using a sequential seepage–stability framework, in which transient pore pressures were computed in SEEP/W and transferred to SLOPE/W for slope stability evaluation. Four drawdown rates of 0.15, 0.30, 0.60, and 1.20 m/day were modeled to represent a wide operational range, from gradual to accelerated depletion. The hydraulic response was examined through temporal variations in total head and phreatic line, while slope stability was evaluated based on the time-dependent factor of safety (FoS) for both upstream and downstream slopes. The findings show that during a rapid drawdown, reservoir lowering occurs faster than pore-pressure dissipation within the dam body. This results in temporary hydraulic disequilibrium, steep pressure gradients, and brief flow reversals in the upstream zone. The upstream slope exhibited the most critical response, with FoS decreasing from 2.04 to between 1.66 and 1.73 depending on the drawdown rate, followed by a gradual recovery as pore pressures equilibrated. In contrast, the downstream slope remained highly stable (FoS ≈ 1.97–2.08) under all conditions. A sensitivity analysis showed that clay-core permeability had a modest influence on stability; at a drawdown rate of 1.20 m/day, the FoS ranged from approximately 1.64 to 1.70, with lower permeability values producing slightly higher FoS under the investigated conditions. The findings indicate that the Gavoshan Dam maintains safe hydraulic and structural performance under both gradual and rapid drawdown, highlighting the necessity of transient coupled analyses for realistic and reliable dam safety assessment.