Actual and nominal pore water pressure distribution in earth dams

In assessing dam safety with respect to global instability, nominal pore water pressure distributions are often adopted for each stage of a dam's life, referring to a hypothetical "expected performance" of the different dam components. However, seepage phenomena taking place within the dam may substantially modify pore water pressure distributions. In this context, the present paper represents and interprets the singular pore water pressure distributions measured within an Italian earth dam, pertaining to the type of zoned earth dam with an internal clay core. Pore water pressure interpretation is supported by the representation of the evolution of the measured seepage flows. The work shows that pore water pressure may differ strongly from the nominal distribution during the first stages of the dam's life, when, if nearly undrained conditions take place, pore water pressures are discontinuous as a result of their dependency on total stresses. Pore water pressure may also assume other than expected distributions after some decades of operation, this time as a result of suffusion phenomena induced by seepage processes within the dam embankment. Measured pore water pressure distribution, suitably interpreted as piezometric head contours, clearly show that part of the downstream shell contributes to embankment water-tightness. © 2012 ejge.