Loessification of Residual and Deltaic Sands

The concept of “loessification,” introduced by Berg in 1916, describes the transition of non-loess ground to loess ground via weathering. The theory dismisses the aeolian deposition phase in loess cycle, and is heavily centred around pedogenic processes, climate actions and interaction between residual sands/silts and neighbouring soil sequences. The role of loess constituting sand and silt particles, their size and shape, and the effect of these on structures evolving from isotropic consolidation is largely ignored. This paper makes use of scale-dependent porosity indices to explain the role of sand shape in formation of structures through fines migration and isotropic consolidation. Compared to residual sands, deltaic sands are more likely to become collapsible via isotropic consolidation. Overall, the influx of fines restricts the ability of isotropic consolidation to facilitate the loessification. The collapsibility of loess soils is evident through their shift from a state of random loose packing to random close packing. In the case of residual sands, this transition is most prominent at a fines content of 30 wt.% when subjected to confinement levels as low as 100 kPa, and at lower fines content of 20 wt.% under higher confinement levels. Conversely, for deltaic sands, the transition remains unaffected by the degree of confinement and is most marked at a fines content of 30 wt.%.