First Advisor

Arash Khosravifar

Date of Award

Spring 2023

Document Type


Degree Name

Master of Science (M.S.) in Civil & Environmental Engineering


Civil and Environmental Engineering




Silt -- Oregon -- Willamette River Valley, Soil liquefaction, Shear strength of soils, Geotechnical engineering




As discussed within studies from Idriss and Boulanger (2008) and Bray and Sancio (2006), the undrained cyclic shear behavior of low-plasticity fine-grained soils will transition between liquefaction (sand-like behavior) to cyclic softening (clay-like behavior) over a narrow range of plasticity index (PI). Despite not being sufficiently understood, the cyclic behavior of low plasticity silts has become an increasingly important field of study due to the significant impact it has on ground deformations and infrastructure failure in areas that are seismically active. Laboratory tests were performed on soils by third party consultants on a site located in the northern Willamette Valley, and the results were provided to Portland State University for further analysis. The soils in this study had PI values ranging from 4 to 15, and were classified as low plasticity silts and clays (ML, CL) using USCS classification. The cyclic behavior of these soils was analyzed and compared to the behavior of other Pacific Northwestern silt soils. The relationship between cyclic resistance ratio (CRR) and stress history (overconsolidation ratio) were explored in this study, as well as the relationship between post-cyclic strength degradation and excess porewater pressure during cyclic loading. The results of this study will improve our understanding of cyclic behavior of low plasticity silts in seismic evaluations of infrastructure in the Pacific Northwest.



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A research project report submitted in partial fulfillment of the requirement for the degree of Master of Science in Civil and Environmental Engineering.

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