Erosion of Zoned Earthfill Dams by Internal Instability: Laboratory Testing for Model Development

The WAC Bennett Dam is one of the largest embankment dams in North America, and one of the most instrumented and studied dams in the world. Following the 1996 sinkhole incident, considerable effort has been made to characterise the zoned materials of the dam with reference to susceptibility to internal erosion. Informed by the findings of this experience, we reflect upon the state-of-practice in dam engineering, and discuss some of its inherent limitations with reference to internal erosion, dam safety, and the management of aging embankment dams. We then describe the state-of-the-art for erosion of zoned earthfill by internal instability, a phenomenon whereby seepage flow removes a finer fraction of the soil gradation. Our paper addresses laboratory testing for materials characterization at the University of British Columbia. In collaboration with our industry research partner BC Hydro, we are seeking to advance the state-of-the-art with reference to a mechanics-based understanding of the phenomenon. We report insights gained from (i) a recent study using a flexible-wall permeameter, and (ii) the status of a new investigation using an advanced triaxial permeameter.