RESEARCH ON CAUSE OF DAM FAILURE FROM VIEWPOINT OF HYDRAULIC FRACTURING – CASE STUDY OF A DAM FAILURE IN VIETNAM

It is widely believed that hydraulic fracturing will occur in a fill dam when the stress in the dam is reduced to levels that are lower than the water pressure, a condition which allows for crack propagation in the dam body. The risk of hydraulic fracturing may increase when arching action occurs in the dam body. The aim of this study is to explain the cause of a dam failure using the finite element method. A case study, KE 2/20 REC dam, investigates a dam in Vietnam that failed a little under one year after it was put into operation at positions adjacent to the culvert. A build-up model is taken to simulate the stress-strain state in the dam body. Research reveals that the normal stress around the culvert was reduced to levels much lower than the water pressure. This reduction was due to the arching action associated with the effects of the culvert shape and the foundation. The findings suggest that the cause of the dam failure was related to the hydraulic fracturing phenomenon. Based on this conclusion, two countermeasures are proposed. These countermeasures are combinations created by changing the culvert shape and either shifting the position of the excavation slope 5.0 meters away from the former position or replacing the fill soil between the culvert and the excavation slope with a concrete block. The countermeasures are then verified by numerical models. The results show the effectiveness of the countermeasures for reducing the risk of hydraulic fracturing.