Seismic Compression of Unsaturated Sand under Undrained Conditions: Fid-Bau Portal

Seismic Compression of Unsaturated Sand under Undrained Conditions

Rong, Wenyong / McCartney, John S.

Seismic compression is defined as the accrual of contractive volumetric strains in soils when subjected to earthquake shaking and has been recognized as a crucial cause of seismically induced damage to geotechnical structures. In earthquake-prone areas, seismic compression of unsaturated backfill soils is critical to predict as small settlements may have significant impacts on the performance of overlying infrastructure like bridge decks, roadways, or railways. Accordingly, the goal of this paper is to describe the results from a series of fully undrained cyclic simple shear tests on unsaturated sand specimens subjected to an intermediate shear strain of 1% with separate measurements of pore air and pore water pressures. Sand specimens having a similar initial relative density representative of the backfill used in a recent set of mechanically-stabilized earth (MSE) bridge abutment shaking table experiments were tested, with the initial degrees of saturation and matric suctions in the funicular regime controlled using the hanging column approach. Test results showed a nonlinear relation between the volumetric strains and the degrees of saturation, with the maximum value for an intermediate degree of saturation around 0.3. This was found to be due to the reduction in mean effective stress during cyclic shearing.