A siphon drainage method for stabilizing bank slopes under water drawdown condition

Drawdown of reservoir water level is unfavorable to the bank slope stability due to the large seepage force. In this paper, the siphon drainage method is proposed to decrease the water table as well as the seepage force in the bank slope. The novelty of the siphon drainage used in the bank slope is that it will automatically start working when the drawdown of the reservoir water level occurs. To validate the feasibility of the proposed method, a numerical method which combines GeoStudio and spreadsheet is used to investigate the pore water pressure distribution and evaluate the safety of the bank slope. The “air element method” is adopted in GeoStudio to simulate siphon drains. Chen-Morgenstern generalized equations are modified to consider the hydrostatic force of reservoir water and the suction strength of unsaturated soil. The modified equations are then incorporated in the spreadsheet to calculate the FOS of the bank slopes with siphon drains. The proposed method is illustrated and validated with the Shuping landslide, China. The advantages of the siphon drains are also discussed by comparing with traditional horizontal drains.