Liquefaction analysis of Duncan Dam using strength ratios

Abstract

B.C. Hydro performed extensive seismic safety studies for Duncan Dam in the late 1980s and early 1990s. The results of these studies indicated that Duncan Dam was reasonably safe from liquefaction-induced failure. A recently proposed liquefaction analysis procedure that uses strength ratios to assess liquefaction triggering and post-triggering stability was used to revisit the liquefaction analysis of Duncan Dam. When compared to the detailed field and analytical studies performed by B.C. Hydro, the proposed liquefaction analysis procedure predicts: (i) similar zones of liquefaction within a contractive unit of foundation sand; (ii) similar shear strengths at the triggering of liquefaction (yield shear strength) and at large strain (liquefied shear strength); and (iii) similar post-triggering factors of safety for slope stability. The good agreement suggests that the strength ratio based liquefaction analysis approach is relatively robust and is suitable for screening level studies for large projects or may serve as the primary analysis procedure for less complex projects.Key words: liquefaction, liquefied shear strength, yield shear strength, laboratory tests, penetration tests, Duncan Dam.