Time-scales for the redistribution of stress in the course of pressuremeter creep tests in permafrost

• Pressuremeter tests in frozen soil must incorporate a concept for the stress redistribution phenomenon caused by nonlinear creep.
• Non-stationary creep cannot be analysed in a closed form.
• The mathematical model used to represent the actual pressuremeter tests affects the stress redistribution phenomenon.
• Redistribution times decrease with an increase in the net cavity pressure for a given redistribution index and creep parameters.
• All conditions being similar, for a constant net cavity pressure, the redistribution time decreases with an increase in the modulus of elasticity

This study deals with nonlinear creep and the time taken for completion of the stress redistribution process within a borehole scenario. Specifically, the pressuremeter test, with emphasis on a step loading of long duration, in ice saturated frozen soils is analyzed. A closed form stationary creep solution based on the model of a thick cylinder under plane strain condition, that considers large strains, is first developed. Subsequently non-stationary creep finite element analyses were carried out via this model and an assumption-relaxed model that considers the actual geometry of a typical pressuremeter test (where the net cavity pressure is applied only on a portion of the borehole cavity). Finally estimates of the extent to which stress redistribution occurs is numerically considered by revisiting classical theories and proposing a time scale by introducing a redistribution index, RI.