Laboratory testing on an unsaturated soil: equipment, procedures, and first experimental results

This paper describes two new apparatuses recently developed at the Universi ta di Napoli Federico II (Italy) in order to test soils under unsaturated c onditions. The related experimental procedures and the first results obtain ed on a dynamically compacted silty sand are also discussed. The devices me ntioned are a Bishop and Wesley stress-path cell and a Wissa oedometer, mod ified to control matric suction and to measure all the stress-strain variab les relevant to unsaturated soil mechanics. Specific experimental procedure s were established to perform tests under general conditions and were caref ully verified during several tests. Using the triaxial cell, isotropic and anisotropic compression stages were carried out under constant suction leve ls of 0, 100, 200, and 300 kPa. Furthermore, two deviator stages were perfo rmed following different stress paths and water drainage conditions. Using the oedometer, an additional suction level (400 kPa) was investigated durin g compression tests driven up to 5 MPa of vertical net stress (sigma(v) - u (a)). This research is a part of a major project in progress at the Diparti mento di Ingegneria Geotecnica of Naples; it is aimed at the experimental a nalysis of the behaviour of several dynamically compacted soils and at the numerical modelling of boundary problems related to earth structures.