Experimental observations of behaviour of heterogeneous soils

Triaxial tests have been performed on mixtures of kaolin clay and a coarse uniform sand (d₅₀∼2 mm). Drained and undrained compression tests have been performed on isotropically normally consolidated and overconsolidated samples. It has been found that the mechanical behaviour of the mixture is dominated by the mechanical behaviour of the clay matrix until the clay content falls below 40 per cent and the volume fraction of the granular constituent reaches about 0.45. Pore pressures in undrained tests are unaffected by the presence of the sand. Volumetric strains in the clay matrix in drained tests are virtually identical to those seen in pure clay.

Calculations of mechanical response of mixtures have been made using a theoretical analysis, developed for the behaviour of composites: it is found that this analysis overestimates the effect of the granular material. Numerical analyses using a finite element program lie closer to the experimental observations but still overestimate the influence of the sand.