FOUNDATION TREATMENT OF MASONRY DAMS WITH SPECIAL REFERENCE TO HIDKAL DAM AND MALAPRABHA DAM

Abstract

The internal configuration of the rock mass conditioned by number of faults, folds, joint system, fractures etc. needs proper treatment so as to serve as a proper foundation for large masonry gravity dams. in foreign countries during 1930's, the foundation treat» ment techniques registered an accelerated development when builds. ing up of high dams was started on imperfect foundations. Notable among to the technique of drilling and pressure grouting which reduces seepage and hydrostatic uplift pressures beneath the dam, improves bearing capacity and increases the moduli of elasticity of rock mass. Under certain geologic conditions, proper exca* vation and plugging serve the purpose. However, in case where the sliding of the dams is iiaaminent along the horizontal bedding planes within shale layers which possess low shear strength, modern practices like concrete thrust blocks or vertical or inclined prestressed cables are necessary. Different such treatments have been discussed in details. Their theoretical and constructional aspects have been brought out. Various problems encountered in the foundation treatment at Hidkal and Malaprabha Darns have been dealt at length and remedial measures adopted have been discussed. Geological formations on which 175 ft. (54.3 M) high Hidkal Dam is founded consist of stratified thin beds of quart-xite and shale layers, possessing low shear strength=. whereas the 147 ft. (45..6 M) high Malaprabha Dam is founded on hard and t tough quartzite with joints and fissures but devoid of shale beds. Both the Dams are under construction presently. Foundation problems encountered at Hidkal and Malaprabha Dams, details of laboratory and field tests conducted on found-ation materials of Hidkal Dam and various treatments in general. and some of the special treatments - have been dealt with in detail. The special treatments like concrete plugging with intensive grouting, provision of concrete thrust blok at the toe of the dam. (which is a special feature in the construction of Hidkal Dam) against danger of sliding along the bedding plane of shale and their design aspects alongdth typical design calcu-lations have been fully described in the dissertation. Case histories of some of the large dams in India and foreign countries, especially their geology of the dam site, and parallel treat-ments adopted have been quoted.