ABSTRACT
Small-strain soil stiffness properties such as shear wave velocity, shear modulus, and material damping, are key subsoil parameters for an adequate analysis and design of unsaturated earth structures subject to static and non-static loading. Most conventional geotechnical testing techniques, however, are not able to capture this small-strain behavior and, hence, vastly underestimate the true soil stiffness, mainly due to inaccuracies in small-strain measurements. In the United States, a great deal of research efforts has been devoted to field and laboratory based measurements of soil suction, assessments of soil-water retention properties, and analyses of swell-collapse behavior. However, very few efforts have been focused on small-strain response of unsaturated soils and their dynamic characterization at small strains. This paper introduces a suction-controlled, proximitor-based resonant column device featuring a PCP-15U pressure control panel that allows for the implementation of the axis-translation technique via the independent control of pore-air and pore-water pressures in the specimen. A preliminary series of resonant column tests were conducted on statically compacted samples of silty sand for a range of constant suction states between 50 kPa and 400 kPa, at different net confining pressures. Results show the critical role of matric suction on the soil’s small-strain response. The apparatus also features a full set of self-contained bender elements for simultaneous testing under both techniques. However, preliminary results from an on-going bender element testing program are beyond the scope of the present work.
