This paper aims to assess the characteristics of the strength and creep properties of frozen soil under triaxial stress conditions at temperatures close to the thawing point. A series of triaxial constant rate of strain (CRS) and constant stress creep (CSC) tests was carried out in axial compression on artificially frozen soil samples at temperatures between –3.0 and –0.3 °C. Acoustic emissions, with a frequency range of 100–1000 kHz, were measured using a wide-band piezoelectric sensor to understand the mechanisms of the deformation behaviour and microstructural effects that control the response of the frozen soil specimens during the tests, especially at yield and approaching failure. The test results showed that the influence of a temperature increase close to the thawing point led to reduced shear strength and increased minimum axial strain rate. The test results were compared with data from similar experiments on artificial frozen and alpine permafrost specimens obtained from a past research project. It was observed that the acoustic emission response indicates a change in the physical process of deformation between microcrack formation and the reorientation of ice granules, depending on the strain rate.

This paper presents an experimental investigation aimed at studying the hydromechanical behaviour of a silty sand from a steep slope in Ruedlingen in the northeast of Switzerland, where a landslide-triggering experiment was carried out. The hydromechanical behaviour of the statically compacted Ruedlingen silty sand has been studied under saturated and unsaturated conditions, beginning with different initial void ratios and water contents. The specimens were prepared in the laboratory using static compaction, to reproduce the mean dry density and mean water content expected in natural unsaturated in situ conditions, thus promoting specimen homogeneity and test repeatability. The choice of compaction parameters was supported by a detailed physical and microstructural investigation to produce laboratory specimens with a similar microstructure to that of the natural soil. The aim of the work was to characterize the mechanical behaviour of the soil at different gravimetric water contents in a triaxial stress path apparatus and to link the mechanical behaviour with the soil-water retention curve obtained under suction-controlled conditions with different void ratios. Soil specimens with three different gravimetric water contents were exposed to conventional isotropically consolidated drained and undrained stress paths for the water phase and to stress paths simulating in situ anisotropic compression followed by a decrease of mean effective stress at constant axial load. The radial deformation of the unsaturated specimens was measured with a laser device installed in a triaxial stress path cell. Results have been interpreted using a Bishop stress approach, evaluating the suction through the water retention curve. A simple equation has been proposed to model the compressibility behaviour of the soil tested, which depends on the parameter and the stress ratio . Possible unstable response along the stress path analysed has been investigated by means of second-order work and the validity of a unified framework has also been verified under unsaturated conditions. Key words: unsaturated soil, shallow landslide, water retention curve, instability, triaxial stress path tests. Résumé :Cet article présente une étude expérimentale visant à étudier le comportement hydromécanique d'un sable silteux provenant d'une pente raide à Ruedlingen dans le nord-est de la Suisse, où un essai de glissement de terrain provoqué a été réalisé. Le comportement hydromécanique du sable silteux de Ruedlingen, compacté statiquement, a été étudié en conditions saturées et non saturées, en débutant avec différents indices des vides et teneurs en eau initiaux. Les échantillons ont été préparés au laboratoire par compaction statique afin de reproduire la densité sèche moyenne et la teneur en eau moyenne réalistes dans des conditions naturelles in situ, et de favoriser l'homogénéité des échantillons et la reproductibilité des essais. Le choix des paramètres de compaction s'est fait selon une étude détaillée des paramètres physiques et microstruct...