Relative to the study of creep, the stress relaxation phenomenon has been overlooked in research on salt rocks, especially with respect to the behavior of salt in deep underground mining environments. In the laboratory tests described in this paper, deformational properties of potash were first studied by performing reverse-loading tests that approximately simulate in situ loading paths during excavation of underground cavities. Potash relaxation properties were then investigated by multiple-stage, repeated relaxation tests along the reverse-loading path. Results show that potash behavior along a reverse-loading path is highly stress rate dependent and is reflected in the dependence of the initial axial deformation modulus, ductile point, and post-yield behavior on the rate at which the deviatoric stress is applied to the specimen. The inserted relaxation phases did not significantly affect the subsequent behavior of the potash, and therefore inserted relaxation tests are useful for investigating time-dependent behavior at various stages of deformation. A linear relationship exists between normalized stress drop and logarithm of time, which might imply that potash has no creep limit. Finally, an attempt was made to extend a uniaxial strain hardening constitutive law postulated by another researcher to include confining pressure, and the experimental data were found to approximately fit the proposed constitutive model. Key words : potash, stress relaxation, triaxial tests, constitutive model.
Constitutive Modeling of Time-Dependent Response of Human Plantar Aponeurosis
