The behaviour of a structurally complex clay from an Italian landslide
This thesis looks at the behaviour of a structurally complex clay formation from a landslide site in the Southern Italian Apennines. The argille scagliose or scaly clays which form the greater part of the argillaceous component of the geological sequence consist of small shear lenses (or scales) of clay, whose orientation may change within a few centimetres. These clays have a very complex structure in that they are both bonded and discontinuous. As a result of the tectonic history of these materials, they have a bonded micro-structure consisting of composite particles of clay minerals and a fissured macro-structure. The behaviour of these soils was investigated using S.E.M., Atterberg limit, triaxial and ring shear tests in the laboratory. This research has considered soils with four different types of structure: natural samples from the underlying formation; soil from the landslide body which had been remoulded as a result of the landslide activity; and two different types of reconstituted samples (reconstituted and minced) prepared with different amounts of remoulding energy. The effect of different macro- and microstructures could therefore be assessed by comparing the behavio.urs of these different materials with those of corresponding reconstituted samples, normalised where appropriate to account for their different stress states, specific volumes and natures. Several negative effects of structure on the strength and compressibility of these materials were observed. Samples which were vigorously disaggregated (minced) were able to exist at specific volumes not possible in the sample prepared using a less destructive method (reconstituted), whilst the scaly formation material sheared at its estimated in-situ stress level achieved strengths which were lower than those of the corresponding reconstituted samples at their critical states. The effect of landsliding on the material behaviour was also assessed by comparing the behaviours of samples from inside and outside the landslide body, normalised with respect to that of a corresponding reconstituted sample. Remoulding as the result of the landslide activity showed a change in the appearance of these materials from a scaly clay to a clay matrix containing lithorelicts. This change in the macro-structure of the natural material, due to remoulding within the landslide body, resulted in a soil behaviour which was more similar to that of the reconstituted material than the underlying formation.