Genesis of transitional behaviour in geomaterials: a review and gap analysis

There has been sporadic but increasing reporting regarding the intermediate character of natural geomaterials which neither conforms to the general behaviour of fine-grained (clay-like) nor coarse-grained (sand-like) soils. Nonetheless, geoscience considers such soils as non-textbook or challenging geomaterials. The literature attempts to identify and analyse a range of threshold manifestations of their behaviour (e.g. liquefaction). However, the physics behind their transient nature is not described in a generic manner. Transitional behaviour (TB) is observed more often in soils containing measurable amounts of silt-size particles. The complexity of their structure–greatly dependent on a number of interrelated micro and macro parameters–is believed to discourage generalisation of the behaviour. This review collates the factors potentially controlling the reported transient character. In order to illustrate a more holistic picture of transitional soils, the available characterisation findings are critically categorised based on purpose and/or testing technique. Collective understanding of transitional soils can ultimately provide a more confident prediction of their ramifications in a wide spectrum of applications. The present initiative is meant to attract attention to the need for multidisciplinary research on quantifying the controversial character of this class of geomaterials. It is also attempted to highlight relevant discrepancies and identify research gaps.