Safety analysis of rockfill dams during overspill phenomena

Abstract

An increasing interest is rising on the study of rockfill embankment dams during overspilling. Design criteria of earth dams are being reviewed in many countries to guarantee an increasing safety level in front of an exceptional flooding. The possibility of studying the failure process is currently limited by the lack of a precise knowledge and by the absence of a suitable computational method which can predict accurately the onset and evolution of breaching. The analysis of the possible consequences of an accidental overspill is then impossible or very imprecise and the necessary economical measures for solving the problem are then inefficient. An appropriate computational method will help to reduce the economic impact of the investments in dam safety and in emergency plans for embankment dams. The dam failure is mainly due to the hydrodynamic forces acting on the rockfill material in the downstream face. Two failure mechanisms occur in an alternative or combined mode: dragging of rockfill particles with erosive effects, and loss of stability of a part of the downstream region due to the slippage of a bulk mass of the rockfill material. The loss of a relevant part of the rockfill material in the downstream side of the dam, can lead to mechanical failure of the impervious region, either if this is formed by a concrete (or asphalt) face, or by a clay core. In the latter case, erosion of the cohesive material can also influence the failure process, but the scale time of appearance of this erosion phenomenon is so different from the principal erosion of the rockfill part, that this second one is not taken into account. The objectives of the current work is to develop and validate a new computational method of general applicability that allows treating above problems. The method will combine advanced finite element and particle techniques. Fluid-structure interaction effects and non-linear geometrical and mechanical effects in the dam material will be considered. The specific features of the analysis method proposed make it appropriate to treat the rockfill material adjacent to the downstream surface where a transfer of momentum between the water running over the dam surface and that moving through the interior due to seepage occurs.