Internal stability of particles in dam cores made of cohesionless broadly graded moraines

The main dam of the LG-4 project in the James Bay territory has a height of 125m and a crest length of 3800m. Piezometers have recorded abnormally high pore pressure drops in a restricted zone near the filter interface, being in the order of 50 to 80% of the reservoir head. The Figure 1 adapted from Verma et al. (1985) shows the corresponding concentration of equipotentials at the end of the reservoir filling. These measurements would indicate that the hydraulic conductivity of the broadly graded moraine is not homogeneous in the whole volume of the core but lower in its downstream part.