A study of the effects of weathering on soils derived from decomposed volcanic rocks

A comprehensive investigation was made of the effects of weathering on the nature and mechanics of volcanic saprolites from Hong Kong. Few such studies have been conducted in volcanic weathered soils and the application of a critical state type of framework that accounts for the effects of structure, as has been used here, is especially novel. The investigation examined the effects of spatial variations of the effects of weathering both vertically as the weathering degree alters, and horizontally through comparing data from different sites. In addition to index tests, SEM and XRD, an extensive series of oedometer, triaxial and multi-directional bender elements tests was carried out, comparing the behaviour of samples from different locations and depths in both intact and reconstituted states. This meant that the changes to the intrinsic (reconstituted) behaviour could be traced throughout different degrees of weathering along with the effects of changing structure on the mechanical behaviour of the intact soils. The intrinsic properties changed in a manner that was broadly consistent with the increasing of fines content and plasticity due to weathering. The effects of meso-structure were small to medium in compression, and in shearing they were generally even less evident, both at small strains and failure. The degrees of anisotropy of stiffness for both intact and reconstituted samples were mostly quite small.