Localization and deformation in laponite sand mixtures

Presence of small amounts of cohesion or fines in a granular ensemble usually restricts the particle rearrangement and, in effect, changes the ensemble’s mechanical response. Plastic fines, such as clay particles present in the sand, impart enhanced ductility. A series of orthogonal cutting experiments were carried out on laponite clay-sand mixtures to understand the effect of the presence of highly plastic fines on the formation of zones or regions of localizations/shear bands. Clay suspension was prepared by dispersing laponite in water, which was further mixed with sands. The sand-laponite mixture was characterized by unconfined compression tests at different loading rates. The laponite provides an interesting interstitial scaffold in the sand particle ensemble, in effect, hindering particle rearrangement in such mixtures via its thixotropic properties. Gelation of the laponite in the pore spaces caused rate-dependent strength enhancement to the model soil. Severe plastic deformation followed by separation of the soil wedge via fracturing was observed as a cyclic mechanism of cutting in sand-laponite. Load response during cutting was observed to be a function of rate and depth.