ANALYSIS OF GRAVITY DAM-FOUNDATION INTERACTION

Abstract

A 192 m high straight concrete gravity dam has been proposed at Lakhwar across river Yamuna in District Dehradun of Uttarakhand. The dam foundation is very complex and consists of quartzitic slates, traps and thinly foliated slates. Besides, a 1.5m thick shear zone exists about 70 m below the toe of the dam and traverses into the left abutment. A 3D Finite Element analysis has been done on the concrete gravity dam using the software ABAQUS 6.9. The analysis is done in three cases i.e., only dam fixed at base, dam-foundation without interface element and dam-foundation with interface element. Each case is analyzed with four load combinations. The present study of concrete gravity dam shows that maximum horizontal deformation at the crest of the dam is 44.8 cm when only dam is considered, 30 cm at the. crest and 3.8 cm at the toe in the case of dam-foundation without interface element and 22 cm at the crest and 8.7 cm at the toe in the case of dam-foundation with interface element. The maximum vertical settlement at toe is 11.0 cm and 12.4 cm in case of dam-foundation without interface element and dam-foundation with interface element respectively. However, due to shear zone existing in the left abutment, deformations in the left abutment are much more as compared to the deformations in the right, abutment. The study shows that the deformations are within reasonable limits. But high tensile stresses along right bank and high compressive stresses along shear zone on left bank are developing. The tensile stresses can be taken care of by choosing suitable shape and curvature of the dam or alternatively, tying the right abutment by means of .suitable anchors but the compressive stresses along the shear zone on left bank may force sliding along the shear zone. Thus, special treatment of left bank shall be needed. A suitable layout along with the treatment of left bank will attribute to the suitability of the concrete gravity Dam at Lakhwar.