Volume 34, Issue 5 (September 2011)
Measurement of Small-Strain Shear Moduli of Partially Saturated Sand During Infiltration in a Geotechnical Centrifuge
This paper describes the use of bender elements to measure changes in small strain shear modulus, Gmax, of sand layers due to the change in degree of saturation during centrifuge tests. The goal of the measurements is to verify that steady-state infiltration is an appropriate technique to control the effective stress in centrifuge physical modeling of partially saturated sands. Specifically, the suitability of infiltration is assessed by checking if the measured values of Gmax of partially saturated sand layers follow a similar trend to dry and saturated sand layers when the effective stress is defined from the suction and degree of saturation profiles during steady-state infiltration. Three pairs of bender elements were installed at different depths in a container of Ottawa sand, and the shear wave velocities of the sand were measured during steady-state infiltration into the sand layer. The applied infiltration rate was varied to obtain different uniform distributions of degrees of saturation with depth. Consistent with results from suction-controlled resonant column tests performed on the same sand, the values of Gmax measured from the bender element tests varied nonlinearly with degree of saturation with a peak value at a degree of saturation between 0.3 and 0.4. When interpreted in terms of mean effective stress, the values of Gmax from the bender element tests on partially saturated sands followed a unique trend consistent with measurements for dry and saturated sands.