- The project has created a database on landslides and their characteristics; and clarified some affecting factors to landslides on slopes in dam reservoir areas (including slopes in the upstream area) in Central Vietnam. Topography, morphology, geology, tectonics and climate settings are main contributing factors while rainfall with high intensity and long duration is the trigger for the sliding.
- Soil testing is carried to measure some physical parameters of sliding surface samples of the landslides, which is useful for slope stability analysis. It indicates that landslide materials with a high percentage of clayed minerals that is very prone to soil moisture, resulting in shear resistance reduction and structural connection within soil layers and causing the landslides. In additions, landslide materials are mostly soils with a high permeability that are derived from the moderate to strong weathering of bedrock. This condition favors the water permeability deeply into the slopes to build up high pore water pressure for the landslide initiation.
- Ring shear apparatus tests were conducted on sliding surface samples in order to investigate the landslide mechanisms. Test results present that samples failed at a high pore water pressure ratio (ru > 0,50). For the large scale landslide near Song Bung-5 hydropower, this ratio is 0,57.
- The simulation of the initiation and motion processes of a rapid landslide in the dam reservoir area of Rao Trang 4 was successfully conducted in accordance with recorded data and site evidences. The Song Bung-5 landslide is likely to move down at pore pressure ratio of 0,55, which puts a high risk to the hydropower facilities.
- The study has also investigated and evaluated some of the main impacts of landslides in dam reservoir areas in Central Vietnam, including economic losses due to damage to the facilities and effects to the project progress; losses causing by debris flows and flash floods and other threatens to dam safety operation such as reservoir sediments.
Methods using in this project can be applied to other areas with the similar conditions of geology, topograpy and climate. Besides, this study has proposed some countermeasure for landslide risk reduction in reservoir areas.