One-dimensional compression

Abstract

In the previous chapters the deformation of soils has been separated into pure compression and pure shear. Pure compression is a change of volume in the absence of any change of shape, whereas pure shear is a change of shape, at constant volume. Ideally laboratory tests should be of constant shape or constant volume type, but that is not so simple. An ideal compression test would require isotropic loading of a sample, that should be free to deform in all directions. Although tests on spherical samples are indeed possible, it is more common to perform a compression test in which no horizontal deformation is allowed, by enclosing the sample in a rigid steel ring, and then deform the sample in vertical direction. In such a test the deformation consists mainly of a change of volume, but some change of shape also occurs. The main mode of deformation is compression, however.