Abstract: Moluocun landslide lies on the left bank of the Dadu river and at the tail of Houziyan reservoir. It is at the toe of Suopo deposit, on which the renowned Danba watchtowers concentrate. Due to their unique historical, cultural and sightseeing values, the stability of the landslide is important both to the preservation of the towers and to the selection of rational reservoir level. After introduction to local geoenvironmental conditions, the formation and stability of both Suopo deposit and Moluocun landslide are analyzed based on site investigation and field reconnaissance, numerical evaluation is also made to the stability of the landslide under different reservoir levels and operation schemes by three dimensional strength reduction technique and two dimensional limit equilibrium method. Results show that: Suopo deposit is the result of glaciations. Moluocun landslide is formed due to the long-term creep and disintegration of the toe of Suopo deposit in the past 3 300 years and its total volume is around 40×106 m3. The two diversion ditches constructed after year 1983 raised the water level in the landslide, worsened its stability and made its head and toe crack successively. Under present state, the landslide is in critical state and its safety factor is 1.048 and 1.070 obtained by using 2D limit equilibrium method and 3D strength reduction method respectively. Whether the reservoir level is 1 842 m or 1 852 m, the influence of reservoir impounding and operation on landslide stability is quite small. Drainage is the most efficient measure to maintain the landslide stability and to preserve the watchtowers.

Key words: Suopo deposit, Moluocun landslide, geological cause, reservoir impounding, stability evaluation