F. Geiser

Automated Digital Image Processing for Volume Change Measurement in Triaxial Cells

An automated digital image processing technique is presented for the measurement of specimen volume change during triaxial testing. A digital camera is fixed at a constant distance from the triaxial cell. Pictures taken at various intervals are processed (e.g. using contouring techniques) to extract specimen volume and thus volumetric strain. A calibration procedure requiring a rigid specimen is used to correlate specimen image with specimen volume. The accuracy of the method is discussed on the basis of experimental results. This technique is of particular interest for cases where conventional use of pore-water volume exchange cannot be used to extract total volumetric strain, as is the case when testing unsaturated soils.

Constitutive modelling of unsaturated soils

ABSTRACT Research interest on the behaviour of unsaturated soils is growing as a result of an increasing number of geomechanical problems involving suction effects and multiphase flow. It is, therefore, necessary to understand the suction-induced effects on soils and then to use the appropriate constitutive models for the numerical simulation of such phenomena. This paper addresses elementary concepts concerning the constitutive modelling of unsaturated soils. Starting from experimental evidences, the presentation of the general form of a constitutive model is then made within the framework of hardening plasticity. Numerical simulations support the theoretical formulations by showing performances of constitutive modelling.