ANALYSIS OF OVERTOPPING FAILURE OF HONGSHIHE LANDSLIDE DAM AFTER WENCHUAN EARTHQUAKE

The Hongshihe landslide dam, located at Qingchuan County, Sichuan Province, is one of the 34 large-scale landslide dams induced by the Great Wenchuan Earthquake on May 12, 2008. The Hongshi River was blocked by the Donghekou Landslide. The landslide debris formed the Hongshihe landslide dam approximately 50 m in height, 250 m in width, 500 m in length along the river. The dam reservoir capacity was estimated to be 6106m3. Field tests were conducted at the Hongshihe landslide dam after its breaching. The tests include soil erodibility tests and basic soil property tests. Based on in situ soil erosion resistance data, the breaching failure risk was studied. It is shown that the landslide soils can be eroded as long as there is overflow, which means the overtopping breaching failure risk of the Hongshihe landslide dam is quite high. Moreover, the breaching time is evaluated based on newly introduced empirical equations and is about 4.5 days. As the presence of boulders is not included in the analysis, the actual failure time could be longer than our estimation. The trend of soil erosion depth with time is also investigated. The methodology presented in the paper may provide some guidance in handling similar incidences in the future.