DOI: 10.17603/ds2-81g3-ef87
title: Collaborative Study on Dynamic Response of Transitional Soils
title: in Collaborative Research: Bridging the In-situ and Elemental Cyclic Response of Transitional Soils

description: NHERI@UTexas team conducted field seismic testing to evaluate the response of transitional silty soils to seismic loading. Test results from two field sites are presented in the project. The first site, named Port of Longview site, is located in Longview, WA. The second site, named Troutdale site, is located in Portland, OR. This field study is part of the collaborative research project with Prof. Armin W. Stuedlein and his research group at Oregon State University (OSU). 
The field experiments were conducted at six test panels during three visits to the site in 2016 and 2019. The soil specimens being tested at four of the six test panels consist primarily of silty soils with Plasticity Index (PI) ranging from 11 to 20. The ground water table at the test site varies between 1.2 m to 1.9 m. At each test panel, the dynamic field testing include (1) direct-push crosshole (DPCH) testing to measure the small-strain VS and VP, (2) liquefaction screening test to locate the potentially liquefiable soils, and (3) staged-loading nonlinear shaking tests to obtain the to determine the nonlinear shear modulus, G, and excess pore-water pressure ratio, ru, of the soil deposits as functions of number of cycles of loading, N, over a range of induced cyclic shear strains, γ. 
The newly developed liquefaction screening test has been utilized in this field project. The screening test aims to quickly locate the liquefiable soil deposits below the ground surface. The staged-loading, field shaking tests have been improved to increase the maximum shear strain that can be induced in the instrumented soil zone so that excess pore water pressure generation of soils can be evaluated over a larger strain range.  As a result of the improvements to the field shaking test procedure, the maximum shear strain level in the shaking tests has been increased to better characterize the excess pore water pressure vs strain relationships of silty soils with some plasticity. Results show that the threshold shear strain at which excess pore water pressure begins to be generated increases as the plasticity index of the silty soils increases. The normalized shear modulus vs strain relationships are also determined for the tested soils using the staged-loading, field shaking tests and laboratory resonant column and torsional shear testing. Despite the various level of the plasticity in the sandy and silty soils, the normalized shear modulus vs strain relationships determined at all the six test panels fall in a narrow range.
description: Researchers from Oregon State University (OSU) and members of the NHERI@UTexas conducted field seismic testing to evaluate the response of transitional silty soils to seismic loading. Test results from two field sites are presented in the project. The first site, named Port of Longview site, is located in Longview, WA. The second site, named Troutdale site, is located in Portland, OR. The field experiments were conducted at seven test panels during three visits to the site in 2016 and 2019. The soil specimens being tested at five of the seven test panels consist primarily of silty soils with Plasticity Index (PI) ranging from approximately 11 to 20. The ground water table at the test site varies between 1.2 m to 1.9 m. Test panels typically included: (1) direct-push crosshole (DPCH) testing to measure the small-strain VS and VP, (2) liquefaction screening test to locate the potentially liquefiable soils, and (3) staged-loading nonlinear shaking tests to obtain the to determine the nonlinear shear modulus, G, and excess pore-water pressure ratio, ru, of the soil deposits as functions of number of cycles of loading, N, over a range of induced cyclic shear strains, γ. One test panel, termed the OSU Blast Array, was also subjected to controlled blasting to increase the range in dynamic shear strains applied. The newly developed liquefaction screening test has been utilized in this field project. The screening test aims to quickly locate the liquefiable soil deposits below the ground surface. The staged-loading, field shaking tests have been improved to increase the maximum shear strain that can be induced in the instrumented soil zone so that excess pore water pressure generation of soils can be evaluated over a larger strain range. As a result of the improvements to the field shaking test procedure, the maximum shear strain level in the shaking tests has been increased to better characterize the excess pore water pressure vs strain relationships of silty soils with some plasticity. Results show that the threshold shear strain at which excess pore water pressure begins to be generated increases as the plasticity index of the silty soils increases. The normalized shear modulus vs strain relationships are also determined for the tested soils using the staged-loading, field shaking tests and laboratory resonant column and torsional shear testing. Despite the various level of the plasticity in the sandy and silty soils, the normalized shear modulus vs strain relationships determined at all the six test panels where RCTS was conducted fall in a narrow range. The excellent agreement between the excess pore pressure and shear modulus variation with shear strain between the mobile shaking and controlled blasting experiments validate the novel blasting technique for the determination of in-situ dynamic soil properties.