Numerical Investigation of the Embankment Dam Safety during Rapid Drawdown Conditions Using Horizontal Drains

Rapid drawdown loading condition is a critical state that can cause failure of the upstream slope in earthen dams. Applying upstream horizontal drains has been a prevalent solution to prevent such potential failure. However, existing literature tends to focus on the drains’ geometric and material properties, neglecting the impact of the drawdown rate and geotechnical properties of the dam on the upstream drainage systems’ effectiveness. The present research employs a Finite Element Method, utilizing GeoStudio software, to comprehensively assess the performance of upstream horizontal drains in enhancing slope stability of a homogeneous embankment during rapid drawdown scenarios under varied rates of drawdown and dam properties. The stability analysis results indicated that the factors of safety of the upstream slope at a drawdown rate of 1 m/d and a permeability rate of 10–2 m/d satisfy the minimum safety limits. Notably, introducing upstream drains substantially increased the factors of safety, particularly in scenarios involving faster drawdown rates and slower permeability rates. It was found that the required number of horizontal drains for ensuring the stability of the upstream slope primarily depended on drawdown and permeability rates. However, the presence of upstream drains increased seepage through the upstream face and dam bodies.