Colloid-chemical and mineralogical differences of smectites taken from argillized layers, both from within and outside the slip surfaces in the Kamenose landslide

Abstract

Colloid-chemical activity of three smectitic clays taken both from within and outside the slip surfaces in the Kamenose landslide was assessed in terms of the relative viscosity increment (RVI) and sediment volume (SV) of the clay sol saturated with sodium and calcium. The RVI and SV are fundamentally determined by the average thickness of smectite particles in the sol that swell osmotically after Na-saturation and form larger packets after Ca-saturation. Among the three smectites, the smectite taken from the argillized layer where no slip surface developed showed the lowest degree of osmotic swelling and packet formation. This smectite was found to be composed of montmorillonite and beidellite-nontronite in a roughly equal amount, whereas the smectites from the slip surfaces were mostly of montmorillonite-type. The residual strengths of the Kamenose soils are considerably varied at the effective normal stress below 100 kPa. This variation of the residual strengths was not well explained by the differences in the <2-μm clay fraction and smectite contents and in the exchangeable cation composition. However, the colloid-chemical differences are inversely correlated with the residual strengths of those smectite-dominated soils. The high colloid-chemical activity of smectite possibly leads to lowering of the residual strength, through promoting reorientation of particles on the shear surface.