Geotechnical properties, one-dimensional consolidation behavior and liquefaction susceptibility of the glaciolacustrine clay samples from the Oso landslide

Mert, Ahmet Ali
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Involving a wide range of ground movements, such as rock falls, deep slope failures, and shallow flows of debris, landslides may cause damage to property, injury, and death. Such a landslide occurred in Washington state, near Oso, in 2014. Synthesized available literature on identical soil material was used for the investigation. On the two samples, S1 and D5 from the event site, plasticity tests and one-dimensional consolidation testing were performed. Main objectives were to compare the volume of the 2014 debris run-out with the volume of the colluvium at the toe of the slope prior to the 2014 slide, to estimate the properties of the colluvium, to explore hypotheses about how the strength of the colluvium reduced enough for it to flow like a liquid, and to provide guidance for future projects to identify the possibility of a large run-out like this event. To achieve these objectives, a literature review and an experimental program comprised compiling all the available information about the 2014 debris flow, conducting supplementary laboratory testing on remolded samples from the slope, summarizing the synthesized available literature on the mechanisms of the 2014 debris flow, and investigating hypotheses to explain the Oso debris flow. Provided the conducted test results and the obtained available data from the literature, two conclusions may be drawn:

  1. The debris flow volume included more than only colluvium, with previously in-place materials behind it,
  2. It is hard to explain whether the debris flowed like a liquid based on the critical state line, liquidity indices, or undrained remolded shear strengths obtained.