The coefficient of earth pressure at rest

Abstract

Laboratory experiments on undisturbed specimens of a large number of soft clay deposits, as well as previous measurements on clays and granular soils, were used to examine and explain the magnitude and behavior of the coefficient of earth pressure at rest, K0: (i) after sedimentation – primary consolidation, (ii) during secondary-compression aging, (iii) after active or passive preshearing away from the laterally constrained condition, (iv) during a decrease in effective vertical stress, and (v) during an increase in effective vertical stress in the recompression or compression range, in terms of [Formula: see text], the slope of the effective horizontal [Formula: see text] versus effective vertical[Formula: see text] stress path. The behavior of K0 is explained using the concept of mobilized angle of friction in laterally constrained deformation condition. The Jaky equation provides, in terms of the angle of internal friction, a good estimate of K0 of sedimented, normally consolidated young clays and granular soils, as well as of [Formula: see text] of presheared clays and sands, and of densified granular soils that are subjected to laterally constrained compression from [Formula: see text]. Empirical equations provide reasonable estimates of K0 for clays and granular soils after secondary-compression aging, after preconsolidation by unloading, and for soft clay deposits that display a preconsolidation pressure [Formula: see text] greater than in situ effective vertical stress [Formula: see text]. Proposed empirical equations and methods successfully predict K0 of presheared clays. Key words: coefficient of earth pressure at rest, soft clays, granular soils, presheared soils, sampling and laboratory testing.