Elastic stress paths and small strains
Although soils and soft rocks do not generally behave in the linear and reversible manner of an elastic material, it is often found convenient, and sufﬁciently accurate, to assume elastic behaviour in the calculation of soil movements or stress changes in a soil mass arising from changes in boundary loading conditions. Immediate settlements of foundations on clay are commonly calculated using an elastic formula with an elastic modulus, obtained from undrained triaxial tests. The longterm settlements are calculated from deformation characteristics determined in consolidation tests, and stress changes in the soil below the foundation obtained from elastic formulae. Both the immediate and long-term settlements are based essentially on measured, large strain, deformation characteristics, which can be broadly distinguished as strains exceeding 0.1%. Increasing attention, however, is being paid to small strain behaviour, such as represented by the initial slopes of stress-strain curves. The assumption of elastic behaviour at these small strains is likely to be much more valid than for large strains.