Glacial Lake Columbia (GLC) existed from 15,550 (+/- 450) to 13,050 (+/- 650) years ago (Atwater, 1986) as a result of the Okanagan Lobe of the Cordilleran Ice Sheet damming the Columbia River near present-day Grand Coulee Dam. The lake deposited a fine-grained basal layer that had interbeds of coarse Missoula Flood deposits and later lake deposits above. Because these GLC deposits are present around most of the Spokane area, they are important to civil engineering and development. We sampled the basal layer of GLC soils from the Peone Prairie, WA. We performed prerequisite testing before the main experiment, with ASTM D422 for particle size along with coefficients of uniformity and curvature, D854 for specific gravity, D698 for optimal water content, and D4318 for liquid and plastic limits along with plasticity index. We performed the main experiment according to ASTM D2166 to determine unconfined compressive strength at varying compactive efforts. We performed three unconfined compressive strength tests at a CE of 7,425 ft*lbs/ft3, a CE of 12,375 ft*lbs/ft3, and a CE of 17,325 ft*lbs/ft3. The ultimate strength for a CE of 7,425 ft*lbs/ft3 is 4,290.26 psf, and the theta angle is 60°. The ultimate strength for a CE of 12,375 ft*lbs/ft3 is 5,519.07 psf, and the theta angle is 68°. The ultimate strength for a CE of 17,325 ft*lbs/ft3 is 7,077.58 psf, and the theta angle is 68°. We determined that ultimate strength increased with compactive effort. The Unified Soil Classification System name for GLC soils is ML.
Navarra, Alexander M.; Hendrickson, Dwight; and Shaw, Jaremy, "Impact of Compactive Effort on Soil Strength of Glacial Lake Columbia Soils" (2020). 2020 Symposium Posters. 35.
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