Mechanical Behaviour of Mixtures of Kaolin and Coarse Sand

Summary

Experimental studies have been performed in order to discover the ways in which the presence of different proportions of coarse sand (particle size ∼2mm) affects the mechanical properties of a clay (kaolin). The behaviour of the mixtures can be understood through the use of appropriate volumetric variables. At one extreme, if the coarse particles do not interact then the response of the mixture may be dependent on volumetric packing of the clay matrix which can be described through the use of clay specific volume and clay volumetric strain which treat the sand as inert space filler. At the other extreme, when the sand particles become sufficiently close to interact, a granular specific volume characterises the potential for interaction between individual sand grains.

Clayey soils are classified according to the values of index properties measured using standard procedures. The liquid limit, determined using a cone penetrometer, is found to be proportional to clay content for clay contents of the mixture between 40 and 100%. It can be inferred that the strength of the clay matrix controls the strength of the mixtures for this range of clay contents.

Direct measurements of the flow characteristics of the mixtures show that a simple relationship can be obtained between permeability of the mixture and the volumetric packing of the clay matrix, for clay contents down to 40%. The relationship in one-dimensional compression between vertical effective stress and volumetric packing of the clay matrix is also unique for vertical stresses up to 1600kPa and for clay contents down to about 40%.

The stiffness and strength characteristics of the mixtures have been studied in conventional triaxial tests. The shear stiffness, shear strength and pore pressure response are unaffected by the presence of coarse material for clay contents down to 40%. The volume changes of the different mixtures are identical when expressed in terms of the clay volumetric strains.