Undrained Cyclic Loading of Low Plasticity Silty Soils in the Pacific Northwest Using Laboratory and Field Cyclic Shear Testing

Abstract

The cyclic behavior of a fine-grained low plasticity silty soil (plasticity index of approximately 15) at a site in Portland, Oregon, is characterized using a field and laboratory cyclic shear test program. The field cyclic tests were performed using the NHERI@UTexas large mobile shakers T-Rex and Rattler. The laboratory tests were performed using resonant column torsional shear and cyclic direct simple shear devices. This testing program's results were used to evaluate the soil's potential to develop excess pore water pressure with cyclic shear strains ranging from 0.00001% to 3%. The laboratory cyclic test results are compared against field cyclic test results to predict the soil's cyclic behavior during earthquakes. These data will contribute to the larger body of knowledge of the cyclic behavior of low plasticity silts. This study includes additional laboratory cyclic shear tests from the following: low plasticity silts from Longview, Washington, diatomaceous soils (high plasticity silts) obtained from Klamath Falls, Oregon, silty sands from the Columbia River Slough in Oregon, and low plasticity silt and low plasticity clay from Beaverton, Oregon. The objective of the cyclic shear tests on different soils is to understand how these soils may potentially behave in the event of a large magnitude earthquake.