Colluvium refers to common surface deposit rolling down hillsides under the action of gravity. It differs from residual soils which, upon decomposition the discontinuity, joints and textures are preserved. The rolling action of colluvium destroys these features.
Colluvium displays some important features which deserves attention:
(i) It appears to be more resistant than residual soil to erosion and tends to offer protection to the soils beneath.
(ii) Its relatively lower permeability when compared with underlying residual soils may form a perched water table at its base during heavy rainstorm.
(iii) For residual soils, when slope cutting is carried out the presence of relict joints may affect the slope’s stability. However, the base layer of colluvium is also a plane of potential failure location.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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