Abstract
The Kantalai reservoir dam collapsed in April, 1986. National and international investigators have observed that the failure could have occurred mainly due to three reasons.
Firstly, failure of mortar joints in the sluice barrel, secondly, vibration effect that may have affected while installing a pump house by driving piles. Finally, dewatering of seepage water from the intake well during the stage of excavation for the same construction.
A brief geological investigation in the area around the dam-site of the oldest reservoir in Sri Lanka was carried out within the first 48 hours of the disaster. Geological structure, rock types and weathering conditions of the foundation rocks were visually observed with special attention to the locations where the failure occurred.
The block material, charnockite. is an excellent rock but showed signs of extensive spheroidal weathering. The author wishes to point cut that the failure to remove these weak residual materials prior to construction of the dam could have been a major contributing factor that led to reservoir leakage through these materials. Continuation of further weathering and erosion of finer particles due to leakage could have been another factor to accelerate the process of collapse of the dam. Observations evidenced that the joint orientation, rock foliation and its structure do not comply with the ideal geological requirements for a dam-site.
