Particle orientation and its influence on the mechanical behaviour of isotropically consolidated reconstituted clay

The behaviour of naturally occurring geological materials such as clay and sand depends on many factors. For example, stresses, strains, previous stress history, mineralogy and the depositional environment all contribute in some degree to a characteristic that all natural soils share, namely “structure”. The structure of clay, or more generally, the microstructure of microscopically sized clay mineral particles, is just as important as the many other parameters that are used to quantify the performance of clays. This paper examines the microstructure that results from the particle arrangement brought about during reconstitution in the laboratory and considers its relevance to the resulting stress–strain behaviour.

Samples of reconstituted kaolin clay were produced using two different procedures. In the first series of tests, kaolin slurry was simply isotropically compressed in one increment. In the second series, the slurry was first isotropically compressed to a low pressure and then completely remoulded. This was followed by isotropic compression to the same pressure as the other series. Specimens were taken from the two series of samples, reconsolidated at various isotropic pressures, and sheared under undrained conditions.

Scanning Electron Microscope (SEM) images indicated that the monotonically compressed samples (Series 1) exhibited an anisotropic microstructure that was distinct from the remoulded (Series 2) samples. Significant differences were also found in the consolidation and stress–strain characteristics of the samples produced in the two series.