Critical transportation infrastructure in Washington and Oregon is vulnerable to damage during strong earthquake shaking, including the anticipated magnitude 9 Cascadia Subduction Zone event. A major hazard to transportation infrastructure is the failure and deformation of the underlying soil. 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.

This project aims to characterize the geotechnical earthquake hazard from silt soils. Understanding the geotechnical earthquake hazard will be critical to evaluating and planning emergency transportation routes and emergency response solutions following a magnitude 9 Cascadia Subduction Zone event in Oregon and Washington. This project will develop engineering relationships between the expected loss of strength or deformations of silt soils in response to earthquake-like cyclic loading. The goal of this work will be achieved in three tasks: (1) characterize earthquake-induced settlement, (2) characterize earthquake-induced reduction in shear strength, and (3) calibrate a standard-of-practice soil model with results from the previous tasks.