عنوان مقاله [English]
نویسندگان [English]چکیده [English]
In earth dams, the rapid drawdown process creates a pressure gradient between the embankment and reservoir. This pressure gradient which is due to the temporal delay that is required for dissipating excessive pore water pressure existing in the upstream slope, may let the upstream slope to be prone to failure. In this research, the effect of length and thickness (of horizontal drain) on upstream slope stability under rapid drawdown conditions were considered in a model of homogeneous earth dam. The factor of safety for different drain dimensions immediately after drawdown ranged within 1.5-2.6 and 1.3-2.2 for superficial and deep slips, respectively, and increased with time to 2-3 and 2.2-3 for the drain with maximum effective length and thickness. Moreover, for drawdown ratio of less than 0.3, drain with the length ratio (drain length to water depth in reservoir) of 0.43 assured the stability. For the greater ratios of drawdown, drain length ratio of 0.71 with medium thickness provided the stability against sliding.