Engineering Properties Determination of In Situ Glacial Till and Lacustrine Silt Associated with Remediation of Deep Seated Abutment Movement Downstream of Nesbitt Dam

Nesbitt Dam is a composite earth-fill embankment with stone masonry core wall, non-overflow and spillway section. Historical survey data indicate that the downstream hillside and right abutment has been subjected to movement over a 60 year period from 1920 to 1980s. Inclinometers established during a 2007 subsurface investigation depicted 12.7 millimeters (0.5 inches) of movement within a lacustrine silt stratum at a depth of approximately 30 meters (100 feet) six months after installation. This paper presents the procedures and analyses used by Gannett Fleming to identify, model, and design a remedial solution to limit future hillside instability. This paper focuses on the extensive laboratory testing program conducted on the lacustrine silt and adjacent strata to thoroughly establish the engineering properties of site soils.