THE COEFFICIENT OF EARTH PRESSURE AT REST

Laboratory experiments on undisturbed specimens of a large number of s oft clay deposits, as well as previous measurements on clays and granu lar soils, were used to examine and explain the magnitude and behavior of the coefficient of earth pressure at rest, K(o): (i) after sedimen tation - primary consolidation, (ii) during secondary compression agin g, (iii) after active or passive preshearing away froin the laterally constrained condition, (iv) during a decrease in effective vertical st ress, and (v) during an increase in effective vertical stress in the r ecompression or compression range, in terms of k, the slope of the eff ective horizontal (sigma(h)') versus effective vertical (sigma(v)') st ress path. The behavior of K(o) is explained using the concept of mobi lized angle of friction in laterally constrained deformation condition . The Jaky equation provides, in terms of the angle of internal fricti on, a good estimate of K(o) of sedimented. normally consolidated young clays and granular soils. as well as of K of presheared clays and san ds, and of densified granular soils that are subjected to laterally co nstrained compression from sigma(h)' = sigma(v)' = 0. Empirical equati ons provide reasonable estimates of K(o) for clays and granular soils after secondary-compression aging, after preconsolidation by unloading , and for soft clay deposits that display a preconsolidation pressure sigma(p)' greater than in situ effective vertical stress sigma(vo)'. P roposed empirical equations and methods successfully predict K(o) of p resheared clays.