The effects of weathering on the physical and mechanical properties of igneous and metamorphic saprolites

The present paper presents three extensive datasets of laboratory testing on weathered geomaterials, which are emblematic of soil types widely found worldwide. The overall dataset includes soils originating from igneous and metamorphic rocks, either coarse or fine grained and having either felsic or mafic minerals. In particular, the data are interpreted to highlight the effects that weathering has on the physical and mechanical properties of these natural geomaterials comparing them with published data with the aim to provide a general framework of interpretation that takes into account this geological process and links soil mechanics to engineering geology. Generally, weathering induces a reduction in the grain size, both due to physical actions (e.g. opening of grain contacts) and to the chemical decomposition of minerals resulting in the formation of clay minerals. As weathering proceeds and the soil becomes finer, the in situ specific volume and the location of the normal compression and critical state lines move upwards in the volumetric plane. On the other hand, the clay minerals cause its angle of shearing resistance to reduce. When analysing the behaviour of the intact soil, in all cases positive effects of structure, albeit small compared to some sedimentary soils, were observed and these reduced as a consequence of weathering