Journal of Cold Regions Engineering

This paper describes a high-pressure, low-temperature triaxial testing system that has been specifically designed and built at the Massachusettes Institute of Technology in order to study the physical mechanisms controlling the strength-deformation behavior of frozen sands. The computer controlled system is capable of performing high-stress monotonic triaxial compression tests on specimens measuring $D=3.6\mathrm{cm}\times H=7.6\mathrm{cm}$ and incorporates advanced technology for temperature, strain rate, and loading control. One of the most important and unique features of the system is the technology used for the measurement of small axial strains that makes use of two miniature submersible linear variable differential transformers mounted on a pair of yokes that clamp to the specimen. A description of the specimen preparation equipment and triaxial testing techniques is presented to aid in developing standardized testing approaches, which are currently lacking in the literature. Representative test results on frozen Manchester fine sand are presented to demonstrate the capability of this system to accurately characterize the entire stress-strain and volumetric strain behavior in triaxial compression. Results are provided to illustrate the influence of relative density, confining pressure, strain rate, and temperature.

Permafrost (permanently frozen ground) underlies approximately 25% of the world’s land surface. Construction of surface facilities in these regions presents unique engineering challenges due to the alteration of the thermal regime at the ground surface. Even moderate disturbance of the preexisting ground surface energy balance can induce permafrost thawing with consequent settlement and damage to roadway or railway embankments. Railway embankments are particularly susceptible to thaw settlement damage because of the need to maintain the alignment and even grade of the rails. The present work examines the heat transfer and thermal characteristics of railway embankments constructed of unconventional, highly porous materials. It is possible to produce a passive cooling effect with such embankments because of the unstable density stratification and resulting natural convection that can occur during winter months. The convection enhances the upward transport of heat out of the embankment during winter, thus cooling the lower portions of the embankment and underlying foundation soil. Numerical results have been obtained with an unsteady two-dimensional finite-element model that is capable of solving the coupled governing equations of pore air flow and energy transport. The numerical results are obtained for conditions typical of those found in railway configurations which allow open exchange of air between the embankment structure and the surrounding ambient air mass.