Geo-Institute/Seattle Section Geotechnical Group – September Meeting
Thursday, September 30th, 12pm to 1pm
Webinar presentation: A new probabilistic common-origin approach to level-ground liquefaction susceptibility and triggering in all CPT-compatible soils using DQ and its application in engineering design
Scott M. Olson, PhD, PE and Kevin W. Franke, PhD, PE
Based on a comprehensive database involving 401 cases of observed liquefaction (or no liquefaction), the authors developed a new probabilistic procedure to simultaneously assess liquefaction susceptibility and triggering for nearly all CPT-compatible soils ranging from non-sensitive clays to clean sands. This procedure has several advantages, including (1) it eliminates the need for a fines content adjustment; (2) it identifies a threshold for fine-grained soils that are not susceptible to liquefaction and large strength loss; and (3) it differentiates the liquefaction resistance of clean sands with differing mineralogy and compressibility, as reflected in CPT parameters. At the same time, based in part on conversations with numerous practitioners, the authors have identified two troubling trends in probabilistic liquefaction triggering analyses. Firstly, many engineers employ only model uncertainty in probabilistic liquefaction triggering analyses, which may significantly underestimate the total uncertainty involved in an analysis. Secondly, many engineers apply a factor of safety “buffer” to deterministic liquefaction triggering curves defined from probabilistic studies. This combination may result in significant (over)conservativism in a triggering analysis. When considered jointly with all the conditional probabilities associated with unacceptable liquefaction hazard (e.g., ground motions, triggering, and consequences), it appears that we, as a profession, often over-predict the actual risks from liquefaction-related effects.
For more information on the presentation and biographies, visit the Events page at https://seattlegeotech.org/eventlist.
Zoom Link: https://us06web.zoom.us/j/88612944518