Equations for effective stress and permeability of soft mud–sand mixtures

Abstract

Equations for the Terzaghi effective stress and permeability of clay–silt–sand mixtures are derived on the basis of a scale-invariant structure of the soil to enhance physical interpretation of the empirical coefficients. The behaviour of soft sediment is assumed to be dominated by the clay fraction, but the sediment may also contain silt and sand. A theoretical model is presented of the structure of the sediment, based on the concept of a scale-invariant structure of the clay–silt matrix. Using this scale-invariant model, equations for effective stress and permeability are derived. The equations take effects due to partial segregation into account. The equations for effective stress and permeability are validated against data (effective stress, permeability and particle size distributions) obtained from a consolidation experiment with a sandy soft mud. It is shown that the equation for effective stress relates the effective stress to the clay and sand volume fraction accurately for the present data set. The correspondence between modelled and measured permeabilities is only fair, which may be caused either by a shortcoming of the model or by the poor quality of the data.