Development Of A Suction-controlled Resonant Column Apparatus With Self-contained Bender Elements

Small-strain soil stiffness properties such as shear modulus, shear wave velocity, 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, enormously underestimate the true soil stiffness, primarily due to inaccuracies in small-strain measurements. Around the world, a great deal of research efforts has been dedicated 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. The overall purpose of this research is to study the dynamic properties of soils at very small shear strain amplitudes under different controlled matric suction states via resonant column and bender elements testing. This research work 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. The apparatus also features a full set of self-contained bender elements for simultaneous testing of small-strain dynamic properties under both techniques. A comprehensive series of suction-controlled resonant column and bender element 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 dynamic properties of the tested soil, highlighting the reliability of the novel apparatus.