Experimental study into the overtopping and breaching of rockfill dams with erosion protection

Embankment dams are mainly made of erodible and pervious materials and are at risk from overtopping and piping, the erosion process that initiates may ultimately lead to the dam breaching. Estimating the flood and mapping the downstream area of the dam is essential to minimize the risk in the future due to the dam’s collapse. This flood calculation requires understanding the breaching mechanism and breach opening parameters. In Norway, earthfill dams are protected by placed ripraps on the upstream, downstream, and crest. Thus, this thesis aims at adding some information to the understanding of the breaching mechanism and process, examining the breaching parameters, and calculating outflow peak discharge during the breaching. In this thesis, experiments were carried out on a scale of 1:10 on dam models with placed riprap, single-layer dumped riprap, and double-layer dumped riprap each. Through experimentation and later analysis of these experiments, it is found that both placed and dumped riprap failure starts from just downstream edge of the crest in overtopping during breaching. Breach parameters calculated from available empirical relations significantly differ from the data obtained from the experiment. The data plot revealed that we could relate inflow breach discharge and outflow peak discharge with a linear equation. During the PIV analysis, it was observed that the failure between two dumped riprap was similar while observation with placed riprap was different. Through PIV analysis, it was also found that the breach in placed riprap occurs abruptly, and failure in both dumped and placed riprap starts just downstream section of the dam.