pacific nw transportation consortium region 10 Pactrans

Examining the Geotechnical Earthquake Hazard to Transportation Assets in Oregon and Washington: Characterizing Earthquake-Induced Deformations of Silt Soils

PI: Diane Moug (PSU), dmoug@pdx.edu, ORCID:

Co PIs: none

AMOUNT & MATCH: $48,000 federal from PacTrans; $48,000 federal Match

PERFORMANCE PERIOD: 8/16/2023 – 8/15/2025

STATUS: Active

CATEGORIES: Earthquakes, Mobility, Transportation

UTC PROJECT DOCUMENTATION:

FINAL PROJECT REPORT: will be available once completed

PROJECT DATA: will be available once completed

DESCRIPTION:  Although current engineering practice has methods to estimate earthquake-induced deformations for sand and clay soils, there is little guidance for assessing the geotechnical earthquake hazard for other soil types. This is a particular challenge in Oregon and Washington, where soils intermediate to sands and clays (i.e., silts) are prolific throughout the Willamette Valley, including beneath the I-5 interstate bridge, the Puget Sound area, and at Port of Portland facilities. Research is needed to characterize the geotechnical earthquake hazard of silt soils. Geotechnical earthquake hazards include liquefaction, where earthquake loading generates considerable excess porewater pressures and significant strength loss in sand-like soils, and cyclic softening, the fatigue-like strength loss of clay-like soils. Liquefaction can induce large lateral ground movements and/or settlements, which have caused bridge failures, foundation failures, and road embankment failures. Similarly, cyclic softening can cause foundation failures and lateral ground movements. A significant knowledge gap in silt soils is understanding their susceptibility to either liquefaction or cyclic softening and the likely hazard from earthquake loading. Characterizing the geotechnical earthquake hazards will impact engineering practice and transportation seismic risk assessment in Oregon and Washington and other seismic regions with silt soils (e.g., British Columbia, Alaska, New Zealand, and Turkey).

Soils can undergo large deformations and strength loss when subjected to strong earthquake shaking. Current engineering practice has established guidance for estimating earthquake hazards for clay and sand soils. However, there is a lack of knowledge regarding silt soils, which are prolific throughout Oregon and Washington. Excess porewater pressures (i.e., ru) are produced during earthquake soil loading. If ru are large enough, liquefaction will be triggered where the soil drastically loses strength. Even if liquefaction is not triggered, severe soil deformations and loss of strength can. This experimental program will test the hypothesis that the earthquake hazard for silt soils relates to ru and plasticity.