Title: Simplified physically based model of earthen embankment breaching Author
|Wu, Weiming -|
Submitted to: Journal of Hydraulic Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 1, 2013
Publication Date: August 1, 2013
Citation: Wu, W. 2013. Simplified physically based model of earthen embankment breaching. Journal of Hydraulic Engineering. 139(8):837-851. Interpretive Summary: The developed model has been tested using 50 sets of laboratory experiment and field case study data. The calculated breach parameters agree well the measured data. 98, 80, and 69% of the tested cases have less than 25% errors, and the root-mean-square relative errors are 12.2, 19.3, and 37.4% for the calculated peak breach discharges, breach widths, and breach characteristic times, respectively. Shown in the selected representative cases, the temporal evolutions of breach flow, breach width, and upstream water level are reasonably well reproduced by the model. It is recognized that most field cases used to test the developed model do not have complete information, such as initial breach, clay ratio, and soil cohesion. The soil cohesion can be somehow calibrated using the known breach side slope using the slope stability model, but the initial breach and clay ratio have to be guessed. This reduces the confidence of the model. Sensitivity analysis of the model results to these important parameters will be reported in the future. In addition, erodibility varies with soil types, so that the present model needs to be further tested for soils different from the tested ones. This model could be applied to dam break and levee breaching flood study and make the computations more efficient.
Technical Abstract: A simplified physically based model has been developed to simulate the breaching processes of homogenous and composite earthen embankments owing to overtopping and piping. The breach caused by overtopping flow is approximated as a flat broad-crested weir with a trapezoidal cross section, downstream connected with a vertical drop (headcut) and a straight slope for cohesive and noncohesive homogeneous embankments, respectively. For a composite dam with a clay core, the downstream becomes two straight slopes after the core is exposed. The breach by piping is assumed to be a flat pipe with rectangular cross section until the pipe top collapses and overtopping takes place. Sediment transport and morphology changes on the breach top flat section and downstream slopes and inside the pipe are calculated using a nonequilibrium total-load sediment transport model, whereas the time-averaged headcut migration rate is determined using an empirical formula. Stabilities of the side slope, pipe top, headcut, and clay core are analyzed by comparing the driving and resistance forces. The breach side slope is set as the average of the steepest stable slope and its corresponding failure plane angle. The model is able to handle dam and levee breaching by adopting various routing algorithms for headwater and tailwater levels and allowing embankment base erosion. It has been tested using 50 sets of data from laboratory experiments and field case studies. The calculated peak breach discharges, breach widths, and breach characteristic times agree generally well with the measured data.