The measurement of small strains and K-o-values in triaxial tests on clay-shales

Improved laboratory techniques for measuring deformations of triaxial specimens of soft rocks are described, and the stress-strain behaviour of an uncementeded and a strongly cemented clay-shale during K-o-consolidation (loading and unloading) and subsequent shearing, are compared. The displacement measurements are made directly on the surface of the specimen, thus reducing the uncertainties connected with measurements made outside the rubber membrane. Internally measured vertical strains (i.e. measured directly on the specimen to avoid end effects) are compared with externally measured vertical strains. The K-o-values during loading were very similar for the two clay-shales, approximately 0.6. However, during unloading, while K-o for the uncemented material increased to 0.9 at an overconsolidation ratio of 2.5, the value for the strongly cemented material decreased to 0.35.