Computing the stability of clay fill dams under construction

The increasing number of failures of clayey fills by sliding in the past decade, in France (Mirgenbach, Mondeley) and in other countries (Carsington and Acu) demonstrates the difficulty of checking increases in pore pressure during construction of this kind of dam. A computer program called UDAM has been developed to forecast pore pressure, and to evaluate the safety of the fill material. It is based on a three-phase approach to soil behaviour. Air pressure, water pressure and displacements are the unknown nodal variables, and the local safety factor is calculated at each element. The unsaturated constitutive equations are developed from the state surfaces model developed by Alonso. The main hypotheses are presented here, and the advantages of the program are demonstrated with examples of the method.