Triaxial stress path tests on artificially prepared analogue alpine permafrost soil

Some degrading rock glaciers have been exhibiting deepening depressions, accelerating strain rates, and, in some rare cases, sudden release of mass movements. Warming permafrost already mobilizes lower strength as temperatures rise; however, unusual stress paths with lateral stresses greater than vertical stresses, instead of vice versa, could exacerbate this condition with lower strength at failure, and hence higher vulnerability. This paper investigates the mechanical behaviour of artificially frozen soil specimens at temperatures between –3.0 and –0.3 °C under various stress paths: axial (A) and lateral (L), compression (C), and extension (E), for total stress paths AC, AE, LE, LC. Acoustic emissions were detected during shearing to expose how the deformation mechanisms develop from a microstructural point of view. Deviatoric stress mobilized in the stress path tests was linearly dependent on the temperature (within the ranges tested): a temperature increase resulted in a decrease in residual deviatoric stress. Comparison between the residual deviatoric stresses obtained from the different stress path tests indicates that (i) values mobilized with radial stress greater than axial stress were lower than vice versa, (ii) more strength was mobilized when changing lateral stress paths than axial, with (iii) the lowest strength mobilized in AE beneath a depression.