Stabilization of Abutments for Dam Safety: A Case of Punatsangchhu-I Dam with Adverse Geology

Dam abutments are critical structural components which require special attention throughout the life time of the dam. Presence of adverse geological conditions in foundation and abutments causes stability problems and necessitate special care in planning and design. All dam sites with heterogeneous geological conditions in abutments are generally problematic. The problems get aggravated if dam is to be founded on deep foundation as it requires deep rock cutting in abutments also. Such deep excavation in abutment having poor geological features threatens its stability. In Punatsangchhu-I Hydroelectric Project, which is under construction in Bhutan, the foundation of concrete dam is 75 m below river bed with many adverse geological features at right abutment. Highly heterogeneous geo-technical environment has posed several challenges during construction. During excavation of dam foundation, rock slope in right abutment destabilized. This necessitated further geological investigations, extensive stabilization measures and constant monitoring. For tackling large slides in highly variable geological strata, monitoring based approach is useful as it is difficult to simulate the exact problem in a model. The paper describes challenges faced in stabilization of right dam abutment of Punatsangchhu-I Project in Bhutan.