The Biaxial Apparatus
The biaxial apparatus is a Geotest-type plane-strain device, initially designed by Professor A. Drescher and I. Vardoulakis (1988). The apparatus consists of a 50kN loading frame and a biaxial cell. The loading frame is equipted with an external 50kN load cell, installed on upper load beam. The frame is displacement controlled (0-6.35mm/min). The biaxial apparatus is equipted with on-sample displacement trasducers, which monitor the axial and lateral displacement of the prismatic specimen. A displacement transducer monitors the movement of the sled. Three pressure lines, each one equipted with a system of de-airing block with on-off valves and analog & digital pressure transducers, are connected to the cell, pedestal and top cap lines. An automatic volume change apparatus is also installed to the pedestal pressure line, in order to measure the volume change of the specimen. The axial load, applied to the specimen, is measured in two levels, one at the top cap (submesible load cell) and the other pedestal level (three miniature load cells). In this way, the friction developed at the two glass side walls may be calculated, as well as the axial load eccentricity.
The biaxial apparatus is suitable for measuring the friction and dilatancy angle of a granular material during a test, as the shear band may freely develop.A detailed description, technical references, manuals and calibration spreadsheets of the apparatus may be found in the Handbook of GeoLab GeoBiax (~11Mb) (Georgopoulos, I.-O. and Vardoulakis, I., 2005).
In due time, detailed description and pictures of the apparatus will be available.