University of Cambridge > > Engineering Department Geotechnical Research Seminars > Predicting Long Runout Landslides

Predicting Long Runout Landslides

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If you have a question about this talk, please contact Magdalena Charytoniuk.

While our technical ability to model short runout landslides is advanced, we are weak at predicting when a landslide will suddenly liquefy and run out much farther than expected. For example, the 2014 SR 530 (Oso) Landslide in Washington State collapsed and traveled 450m, engulfing a neighborhood and killing 43 people. That same year, the West Salt Creek Landslide in Colorado abruptly liquefied, traveling almost 5km at speeds exceeding 65 kph and killing three. Although there were mapped, prehistoric events of similar runout length in these areas, each recent event came as a surprise to the community. While there is no systematic way to accurately predict landslide runout distance, there are several factors that can be used to estimate both the occurrence of long runout landslides and the expected distance traveled. The H/L (vertical drop over distance traveled) ratio has long been used to characterize landslide movement, but recent studies have shown the possibility of using H/L ratios measured from landslides in similar geologic settings, coupled with landslide area, to establish predictive ranges of future movement. We have also shown that contractive soil behavior, or densification upon movement with a corresponding jump in porewater pressure, is related to landslide mobility, and this can be predicted as a function of dry density, clay content, and liquid limit. Contractive behavior can be induced in soils below critical-state density, and tests we developed using a lightweight deflectometer and modified slump test both help predict high soil mobility. Density is affected by field conditions in the vicinity of a potential landslide, so loose materials, tension cracks, and previous landslide movement all contribute to lower density and higher potential for contractive behavior. Finally, landslide runout can also be shown to relate to upstream drainage basin contributing area and proximity to surface water features.

This talk is part of the Engineering Department Geotechnical Research Seminars series.

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