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.