A laboratory technique for investigating the deformation microstructures of water-rich sediments

Abstract

Summary Experimental deformation is a particularly valuable means of investigating the mechanical behaviour of water-rich sediments. Techniques have been developed for preparing and deforming wet sediments in the laboratory and petrographically examining the resulting microstructures. Clays marketed for the ceramic industry are more useful than natural clays because of their consistent properties. They are mixed with sea-water, aged, and consolidated to the desired value either by self-weight or in a simple levered oedometer. Argillaceous sediments with water contents of about 50% and lower are routinely produced. Wetter materials are extremely delicate and vulnerable to non-testing artefacts. In an attempt to circumvent this problem a device has been designed which enables slurries to be sedimented directly on to the base of a triaxial compression cell. The prepared specimens are tested in a conventional ‘direct’ shear box, or in ‘distributed’ shear which subjects the whole block to shear displacement, or in triaxial compression. The latter tests can be undrained, or partially/intermittently drained, from the top and/or the bottom of the sample. After testing, slabs are cut from the specimen with a wire-saw and impregnated with Carbowax P.E.G. 8000 to allow thin-section preparation and examination.