Authors: Sílvia Amaral, Teresa Alvarez, Laura Caldeira, Teresa Viseu, Rui Ferreira

The flow originated by a dam failure is a complex 3D two-phase flow (water and sediments) where several spatial scales are present and thus the breaching process details can only be addressed with comprehensive and controlled laboratorial work. This study represents a contribution to achieve this goal and is based on laboratory tests with homogenous earthfill dams with high fines content (with a cohesive mechanical behavior), performed in a medium-scale facility at the Portuguese National Laboratory for Civil Engineering. These were performed under hydraulic and geotechnical controlled conditions: i) to provide practical rules for soil selection and procedures for embankment compaction for dam-breach experiments; ii) to develop novel estimates of the breach effluent hydrographs based on local data; and iii) to advance the state-of-the-art in the relation between the flow hydrodynamics and the breach morphologic evolution during the overtopping process. In general, soils within maximum fines content of 30% and compaction by vibration were found adequate for dam breach experiments for the tested soils range. The novel estimates of the breach effluent flow showed good agreement with traditional ones, hence indicating the need to study in the detail the breaching process. The latter demonstrated that the breach effluent flow presents a gradual increase, rather than sudden, in response to the occurrence of soil mass detachments. Finally, it should be mentioned that the results herein achieved were only possible due to the use of recent instrumentation, as well as to the adoption of innovative measuring methods and by extracting the goal variables through image post-processing techniques here presented.

Sílvia Amaral^{1 |} Teresa Alvarez^{1,2 |} Laura Caldeira^{1 |} Teresa Viseu^{1 |} Rui Ferreira²
1Laboratório Nacional de Engenharia Civil (LNEC), Portugal
2CERIS-IST, Instituto Superior Técnico, Universidade de Lisboa, Portugal