Temperature effects become important in a number of geotechnical applications, such as nuclear waste disposal facilities, buried high-voltage cables, pavement, energy geostructures and geothermal energy. On the other hand, soft soils act time- and strain rate dependent. Both temperature and strain rate influence soil behavior, affecting stiffness, strength, and deformation even under constant stress levels. A model to predict temperature and loading rate effects on soil behavior is presented in this article. The model is based on a simple visco-hypooplastic model for clays and encompasses key aspects of coupled rate- and temperature-dependent soil behavior such as (partially irreversible) thermal expansion, heating-induced irreversible compression, stress history, drained heating/cooling cycles, as well as mechanical and thermal creep, incorporating isotachs, and isotherms.

This article experimentally evaluates the influence of shearing rate on the monotonic and cyclic response of isotropically-consolidated samples of Malaysian kaolin. On the one hand, a series of undrained monotonic triaxial tests were performed with varying shearing displacement rate. On the other hand, undrained cyclic triaxial tests were conducted considering different deviatoric stress amplitudes and loading frequencies. The well-known soil rate-dependency under monotonic loading was confirmed up to a displacement rate threshold. The experimental results under cyclic loading suggest that for the given loading frequency, the variation of the deviatoric stress amplitude remarkably influences the strains and pore water pressure accumulation rates. In addition, the results suggest that depending on the loading frequency different shapes of mobilized effective stress loops are obtained. Larger loading frequencies lead to banana-shaped effective stress loops, while smaller frequencies reproduce eight-shaped effective stress loops. Furthermore, higher loading frequencies result in a larger number of cycles required to reach failure conditions. The reasons for the observed differences in the behavior are thoroughly analyzed and discussed.

Many geotechnical failures are associated with degradation of the soil strength over time. The time-dependency behavior of unsaturated loess is often required to evaluate the long-time behavior of geotechnical engineering in loess areas. To investigate such strain rate response and stress relaxation behavior of intact loess, a series of oedometric compression and relaxation tests were conducted under different suctions and strain rates. Water retention behaviors and microstructures were also measured to characterize the tested loess. The more rapid strain rate, leading to larger yield stress at relatively low suctions (0 and 50 kPa) and roughly paralleled onedimensional normal compression lines (1D-NCL) conformed to the isotache approach. In contrast, the weakening effect of a more rapid strain rate on the clay cementation, resulted in smaller yield stress when the suction was larger than 100 kPa, which was an apparent deviation from the conception of the isotache. The reason might be that the microstructure developed during the long term (slow strain rate) under the relatively larger suction, which may increase the inter-particle bonding and structural strength. The relaxation behavior of unsaturated loess depended on suction and prerelaxation stress, which cannot be well described by the model with a soil constant viscosity I v . The results of two viscous effects (rate-dependency and relaxation) in loess demonstrated that they could not altogether be explained within the isotache concept. (c) 2024 Production and hosting by Elsevier B.V. on behalf of The Japanese Geotechnical Society. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).