Stresses and conjugate strain-increments in plotting experimental data for unsaturated soils

摘要

The development of an equation describing the stress regime in an unsaturated soil is presented. The analysis is contrasted with Bishop's (1959) modified effective stress equation for unsaturated soils and a more recent analysis by Houlsby (1997) of the work input to an unsaturated soil. The equation is presented in terms of the stress state variables (sigma_(ij) - u_a delta_(ij)) and (u_a - u_w) along with the volumes through which the stresses act. The analysis is extended to triaxial stress conditions and to the development of work input equations that give the work conjugate strain-increments. The conjugate strain-increments are those within the volumes through which the stress state variables act. The development of a stress-strain model and constitutive relations from experimental data requires careful consideration to be given to the choice of the stress state variables and the strain-increments if they are to be work conjugate. Plots of triaxial experimental results for a kaolin specimen are presented and illustrate the use of the conjugate variables.