On an Elasto-plastic Stress-Strain Relationship of the Cohesive Soils (Part.I)

One of the authors proposed in the previous paper (1) an incremental stress-strain relationship in terms of the tensor considering the subsequent anisotropy of a Sand, which can evaluate the dilatancy characteristics under multi-axial stress condition with the rotation of the principal stress axis. But it neglected the effect of time-dependancy and the influence of the stress histories on the stress-strain behaviour of soils. In this paper Part. Ⅰ, the authors attempt to apply it to the cohesive soils, which contain more significant practical problems than Sands. However, it cannot be applied to the cohesive soils a pliori, because the deformation of the cohesive soils is time-dependant, and is largely influenced by the stress histories. So, as a first step to the development of the constitutive equation of the cohesive soils, an elasto-plastic incremental stress-strain relationship is derived by considering them as strainhardening materials not only for shear but for compression, by admitting the well-known deformation characteristics reported by many investigators. In next paper Part. Ⅱ, the examination of the postulates used to derive the incremental relationship in sec. 3 will be carried out, from the results of both repeated isotropic consol. tests and repeated mean principal stress const. tests for Ariake Clay. And the verification of the incremental relationship will be done by the comparison of both calculated and observed stress-strain behaviours of Ariake Clay experienced some stress histories