Modelling the plastic anisotropy of Lower Cromer Till

Experimental data on Lower Cromer Till (LCT), a sandy silty-clay, are re-evaluated enabling a study on the effects of plastic anisotropy of soil fabric. The results of virgin constant stress ratio consolidation tests reveal that an equilibrium state is achieved and maintained under any specific radial loading path, with characteristics of a unique anisotropic fabric and a unique straining mode. The inclination of the plastic dilatancy and the yield surface from the hydrostatic axis provides a means of quantifying this equilibrium state of the soil fabric. A unique fabric anisotropy at critical state is naturally obtained. Rotational hardening laws are then proposed to quantify the changes in plastic anisotropy of soil fabric for all stress ranges. Constitutive relations are formulated within the framework of Critical Sate Soil Mechanics, with a non-associated flow rule logically determined from experiments. The proposed rotational hardening laws have been systematically validated against a large bank of laboratory tests on LCT samples, covering a variety of deposition conditions, stress histories, and overconsolidation ratios. Comparisons illustrate the feasibility and efficiency of the proposed framework in describing the plastic anisotropy of LCT, which may suggest possible application to other types of clays.