Annual Journal of Hydraulic Engineering, JSCE, Vol.53, 2009, February NUMERICAL AND EXPERIMENTAL STUDY ON 3D TRANSIENT SEEPAGE AND SLOPE STABILITY OF LANDSLIDE DAM FAILURE Ripendra AWAL 1 , Hajime NAKAGAWA 2 , Kenji KAWAIKE 3 , Yasuyuki BABA 4 and Hao ZHANG 4 1 Student Member of JSCE, Graduate Student, Department of Civil and Earth Resources Engineering, Kyoto University (Katsura Campus, Nishikyo-ku, Kyoto, 615-8540, Japan) 2 Member of JSCE, Dr. of Eng., Professor, Disaster Prevention Research Institute, Kyoto University (Shimomisu, Yoko-oji, Fushimi-ku, Kyoto 612-8235, Japan) 3 Member of JSCE, Dr. of Eng., Associate Professor, Disaster Prevention Research Institute, Kyoto University (Shimomisu, Yoko-oji, Fushimi-ku, Kyoto 612-8235, Japan) 4 Member of JSCE, Dr. of Eng., Assistant Professor, Disaster Prevention Research Institute, Kyoto University (Shimomisu, Yoko-oji, Fushimi-ku, Kyoto 612-8235, Japan) The failure of landslide dam may occur with a variety of failure processes which includes overtopping, seepage or piping, and sudden sliding etc. This study focuses on three-dimensional (3D) transient seepage and slope stability analysis of landslide dam and prediction of the failure due to sudden sliding through flume experiments and numerical simulations. The 3D slope stability model coupled with transient seepage flow model is developed by using the limit equilibrium method. The proposed model is capable to predict time to failure by sliding according to pore water pressure and moisture movement in the dam body. Comparisons show that results of numerical simulations and experimental measurements are quite close in terms of movement of moisture in the dam body and predicted critical slip surface. However the time to failure of the dam body is earlier in the experiment compared with simulation. Key Words : seepage flow, slope stability, 3D model, numerical simulation, laboratory experiment 1. INTRODUCTION Temporary or permanent stream blockages by mass movements commonly occur in mountainous area due to heavy rains or earthquakes. Landslide dam formed by this process may fail by erosion due to overtopping, abrupt collapse of the dam body or progressive failure 1) . Water infiltrates through the landslide dam in a transient manner, so the slope stability analysis coupled with transient seepage analysis is useful to study stability of landslide dam. Many researchers used different slope stability analysis method combined with hydrological model to analyse slope stability of natural slopes. Wilkinson et al. 2) used a combined hydrology and slope stability model by incorporating an automated non-circular search technique into the Janbu’s method. Tsutsumi et al. 3) used combined hydrology and slope stability model to analyse deep-seated landslide triggered by the Typhoon in Taketa City, Oita Prefecture. Some researchers focused on transient stability analysis of a collapsible dam using dynamic programming combined with finite element stress fields (e.g. Pereira et al. 4) ; Brito et al. 5) ) and very few studies analysed transient slope stability of embankments (e.g. Staiano et al. 6) , Gitirana and Freduland 7) ). Most of these studies are limited to 2D (two-dimensional) analysis. A 2D analysis is only valid for slopes which are long in the third dimension. However, failure of natural slopes and landslide dams confined in a narrow U- or V-shaped valley occurs in three dimensions. Therefore 3D (three-dimensional) approach is more appropriate to analyze such stability problems. This study focuses on 3D transient slope stability analysis of landslide dam and prediction of the failure due to sudden sliding through flume experiments and numerical simulations. The Annual Journal of Hydraulic Engineering, JSCE, Vol.53, 2009, February - 61 -