Unsaturated Soil Response under Plane Strain Conditions Using a Servo/Suction-Controlled Biaxial Apparatus

Abstract

The engineering response of a vast majority of geotechnical infrastructure, including earth slopes, embankments, tunnels and pavements, may be most accurately modelled using plane strain analyses, given the particular geometries, stress paths and boundary conditions that such geosystems normally feature or undergo in the field. Biaxial devices allow for direct testing of soils under truly plane strain conditions, facilitating a more accurate assessment of shear banding phenomena and stress-strain-strength parameters under these conditions. However, most conventional biaxial devices reported to date only allow for soil testing under dried or saturated conditions. This paper introduces a suction-controlled biaxial apparatus that is suitable for soil testing under controlled-suction states via axis-translation technique. The design of its core system is based upon the original Vardoulakis type of biaxial apparatus. In this work, biaxial specimens are prepared by uniaxial consolidation of a slurry mixture, made of 75% silty sand and 25% kaolin clay, into an acrylic custom-made biaxial consolidation mold. The results from a short series of constant-suction tests reflect the important role played by matric suction in the stress-strain response of unsaturated soils under plane strain conditions.