Description of compression behaviour of structured soils and its application

One of the most distinct characteristics of structured soils is the nonlinearity in the normal compression lines in a plot of specific volume or voids ratio against logarithmic mean or vertical effective stresses, when compared with reconstituted soils. The change in the compressibility (or compression index) with loading is attributed to structure degradation and is expressed as a function of the plastic straining. A direct description of the compression behaviour of structured soil is then established. The validity of this approach is examined via merely incorporating the newly defined normal compression line into the modified Cam-Clay constitutive model. Comparisons against a series of experiments on different types of soils illustrate the feasibility and advantage of the adopted methodology. The dependence of shear strength on the compression behaviour considered initially in critical-state soil mechanics is reemphasized here for structured soils. Analysis also indicates that the stiffness sensitivity coefficient, S-lambda, should be considered together with the traditional strength (or stress) sensitivity coefficient, S-t (or S-sigma), to better characterize the sensitivity of structured soils.