A Simplified Breaching Model for Cohesive Embankments: Fid-Bau Portal

A Simplified Breaching Model for Cohesive Embankments

Wu, Weiming / Kang, Yunghee

This paper presents enhancement of an existing simplified breach model to simulate the embankment breaching processes in the form of headcut migration and the breaching of composite embankment with a clay core. The existing model approximates the breach caused by overtopping flow as a flat top section connected with a straight slope in the downstream and simplifies the breach cross-section as trapezoidal or rectangular. The flow at the breach is estimated using the broad-crested weir equation, and sediment transports at the breach flat top section and on the downstream slope are calculated using the non-equilibrium sediment transport equation. In the case of piping, the model assumes the breach flow through a pipe with rectangular cross-section at the initial stage, and the pipe is enlarged uniformly along its length based on the eroded sediment at each time step until the collapse of the top part of the dam. Considering that most of cohesive embankments erode in the form of headcut migration, the model is enhanced with empirical formulas to calculate the time-average headcut migration rate and an algorithm to analyze the stability of the embankment body upstream of the headcut. In the case of composite embankment with a clay core, the erosion of non-cohesive (or less cohesive) materials on the dam crest and downstream shoulder is first calculated using the non-equilibrium sediment transport model until the clay core is exposed to and eroded by the breach flow. The stability of the clay core is then analyzed by comparing the driving and resistance forces. Once the clay core fails, the breach will continue to enlarge until the water in the reservoir is depleted or the downstream water surface rises to a certain level. The enhanced model capabilities have been tested using available laboratory and field experiment data.