11.1 Introduction
In laboratory triaxial or shear tests, and in the ground, soil is loaded from some initial
state and it will ultimately reach a critical state. (If the soil is clay it may go on to
a residual state.) In Chapter 8 I described the behaviour of soils during isotropic and
one-dimensional compression and swelling and I showed how these were related. If the
history of isotropic or one-dimensional loading and unloading is known the initial
state described by the current effective stress, specific volume and overconsolidation
ratio are fixed. Notice that the conditions in a shear test when the shear stress is zero
are the same as those in a one-dimensional compression test and the conditions in a
triaxial test when q = 0 (i.e. when σa = σr) are the same as those in an isotropic
compression test.