The microfabric of deformed kaolin

SUMMARY Samples of remoulded kaolin have been subjected to varying consolidation and shearing stress conditions, and the resulting microfabric has been examined using a scanning electron microscopy and an X‐ray texture diffractometer. Preparation of samples for observation in the SEM involved both freeze‐drying and critical point drying methods. In consolidation experiments, a significant regional variation in the degree of orientation is observed in each sample. An increase in orientation is seen near drainage surfaces. Observations from areas remote from these surfaces on samples consolidated one‐dimensionally show that from 0 kPa to 100 kPa there is little increase in the general degree of orientation. However, the large decrease in voids ratio associated with this change of stress level is achieved by aggregation of particles into domains, the latter being randomly orientated with respect to one another. Above 100 kPa, the degree of orientation increases, as the particles show a tendency to align with their normal vectors parallel to the principal stress direction. These findings are in agreement with the X‐ray texture goniometer studies on impregnated specimens cut from parts of the consolidated samples adjacent to those for scanning electron microscopy studies. The surfaces of specimens for the X‐ray studies were cut orthogonal either to the major principal stress direction or to the space diagonal in σ 1 , σ 2 , σ 3 space. Micrographs of kaolin consolidated one‐dimensionally in one direction and then to a higher stress level in an orthogonal direction show a closely packed near random fabrics. Examination of samples deformed in shear reveal narrow zones, although regular herring‐bone‐shaped kink bands have been seen in the region between two parallel shear zones.