Title:    Foundation Treatment of Concrete Dams Then and Now


 Speaker:  Dr. V M Sharma

 Date :  24 March 2009

ABSTRACT:

For all kinds of dams, foundations are one of the major reasons for its failure, more so for concrete dams. The talk describes  various kinds of problems faced in concrete dam foundations. The treatment  methods which have been used for a long time are discussed. These methods  are based on experimental work done with the photo-elastic testing  apparatus, which in other words means, based on theory of elasticity.  In today's context, most of the problems of the foundation can be analyzed  with the help of numerical tools. It is not necessary to assume the  material to be elastic and other material models like Mohr Coulomb or Hoek  and Brown can be used. Surprisingly it does not show much difference  between the final outcomes done on the basis of empirical formulae and the  numerical analysis, except in some cases.  To illustrate the kind of problems faced on concrete dams of our country  case histories of three projects are presented.  The first case is that of Salal Hydroelectric Project. Here the Spillway  was sited on top of a ridge which apparently had bedding planes and shear   seams dipping upstream. It was discovered during the construction of the  dam that in addition it also had some seams which were dipping downstream  causing shearing sliding stability problem. The problem as so acute that  even after spending a considerable amount of money it was considered  whether the project should be abandoned.  The second case history relates to Indirasagar Project in Madhya Pradesh.  The dam had a shear zone running skew to the axis and there were  apprehensions about its behaviour. Numerical modeling was done both in two  dimensions and in three dimensions to carry out parametric studies and  finalize the designs.  The third case relates to Omkareshwar Project in Madhya Pradesh.. The  foundations consisted of layered formations and sliding was apprehended  along the interface of the layered formations. A shear key was provided  towards the downstream area to improve its sliding stability. Three  dimensional Numerical models were created to work out the details  including the values of normal and shear stiffness along the interface.  The talk ends with listing out some of the grey areas in the design of  foundations of dams where more research is required.