Small strain shear modulus and damping ratio of two unsaturated lateritic sandy clays

In this study, resonant column tests carried out to investigate the influence of suction on the shear modulus and damping ratio of two compacted lateritic sandy clays from Ghana (GL) and Nigeria (NL) are reported. Each type of soil was tested under two confining pressures and at three suctions. The microstructure of the soils was also studied through a scanning electron microscope. It was found that the effects of suction on maximum shear modulus (G₀ ) are about 10% larger for GL than NL, mainly due to the existence of smaller aggregates in GL. Moreover, an increase in suction from 0 to 300 kPa for both soils resulted in a lower elastic threshold shear strain, different from the behaviour of other soils reported in the literature. The uniqueness of lateritic soils is likely attributable to their high sesquioxide content and much larger aggregates, which shrink upon an increase in suction. Drying of specimens from 0 to 300 kPa resulted in an increase of about 22% and 100% in initial damping ratio (D₀ ) for GL and NL, respectively. The difference in D₀ for GL and NL is attributed to larger aggregation of NL because of its higher iron sesquioxide content, leading to more cladding.