ABSTRACT
The design of two large dams, Mangla and Kalabagh has given the profession a very useful insight on the behaviour and engineering characteristics of the soft rocks in general and sheared clays in particular. Mangla was designed when the concept of long-term stability of slopes underwent radical changes. The design of the project had to be modified during construction as it was realized that shearing in clays was far more extensive than what had been assumed during the design stage. Design parameters were revised and residual strength of clays was adopted instead of peak strength, owing to which major design changes had to be incorporated. The research conducted at Mangla on the properties of these over-consolidated clays is a landmark and has provided an important guidance for dealing with such foundations in the future projects. The experience of design, construction and monitoring during operation of Mangla dam and later the design of Kalabagh dam, afforded the profession an excellent opportunity for the study of these soft rocks. The special design features adopted for these large projects will also be of considerable help for the designers dealing with similar foundation conditions.
