On estimating Ko for overconsolidated granular soils

Abstract

It is possible for horizontal stresses to be significantly different at the same depth within two deposits. The stress-path dependency of load-deformation behaviour in tests must be taken into account when assessing their use. Thus the estimation of ko, the in situ ratio of the horizontal effective stress to the vertical effective stress, is of major importance. The author reviews the results of the laboratory evaluation of ko for various materials and gives details of his work on Ham River sand at various void ratios. Samples were set up in a stress path cell with two LVDT transducers to obtain axial deformations relatively free of bedding errors. A lateral strain gauge was installed at the mid-height of the sample to control or obtain the lateral deformation of the sample as required. Typical stress-paths during the loading and unloading are plotted. The rate of increase of ko was always greater in dense than in loose samples. Observations based on Lambe's plot showed that the unloading paths can be approximated to straight lines up to ocr of 7 used. An equation is given to express ko in terms of the slope of the unloading stress-path and ratio of the change in effective horizontal stress to the change in effective vertical stress. (TRRL)