Evolution of Dilatancy Angle during Shearing of Kaolin Clay with Different Microfabrics

The mechanical response of clay mass can be significantly affected by the distribution and arrangement of the particles and the interaction between them. A series of compression and extension tests under drained and undrained conditions were performed on normally consolidated and heavily over-consolidated clay specimens with different microfabric. The experimental data indicates strong influence of microfabric on the stress-strain relationship, shear strength, excess pore pressure evolution and volumetric response. This study shows that the microfabric can change the basic nature of clay. For example the normally consolidated Kaolin clay shows its dilative nature during shearing for dispersed microfabric and contractive nature for flocculated microfabric. In order to describe the mechanical behavior of such materials in the form of constitutive equations, it is imperative to perform quantitative evaluation of the volumetric response of different microfabrics during shearing and this is the focus of the present paper. The dilatancy angle (Ψ) is a measure of contractive or dilative nature of the volumetric response due to shearing. The dilatancy angle during shearing has been determined for different microfabrics, confining pressure, loading conditions, and drainage boundary conditions. This paper shows how the clay microfabric can play a significant role in the deformation behavior of soil, which can be useful for developing the constitutive equations more close to the physically observed phenomenon.