Risk assessment of internal erosion in till core dams at the Keeyask generating station

The 698 MW Keeyask scheme in Northern Manitoba represents one of the largest hydropower developments in Canada. The project presents a number of geotechnical challenges, including the construction of more than 22 km of dams and dykes on a variety of foundations. One of the risks associated with the project is the use of a broadly graded till as the impervious core in the zoned embankments that, in certain circumstances, can be susceptible to internal erosion. Given that this represents the second most common cause of embankment dam failure, Manitoba Hydro undertook a thorough assessment of the potential for internal erosion. This paper presents details of the results , and of the factors which lead to internal erosion. Material characteristics, critical stress and critical hydraulic load are discussed, as well as the mitigation measures developed to improve the performance of till cores and fine filters at Keeyask.