Journal of Cold Regions Engineering

The large strain nonlinear thaw consolidation model developed by Dumais and Konrad is used to analyze the Inuvik experimental warm-oil pipeline built on ice-rich permafrost foundations. The predictions for the thaw penetration rate, the final thaw settlements, the settlement rate, and the maximum excess pore water pressure compare favorably with the field observations. The modeling results are compared with the results obtained by the small strain linear thaw consolidation theory formulated by Morgenstern and Nixon. The Dumais and Konrad model offers a notable increase in precision given the large strain configuration used for the definition of the thaw penetration rate and the nonlinear characterization of the $e-{\sigma }_v^{\prime }$ and $e-k_{vT}$ relationships. The Dumais and Konrad model improves on the formulation of one-dimensional thaw consolidation theory to yield a lifelike assessment of thaw consolidation by the introduction of a second moving boundary at the surface and by considering the changes of soil properties as thaw consolidation proceeds. An important practical implication of the model is the ability to handle a complex initial frozen soil profile and its corresponding soil properties.

The in-situ lateral temperature around freezing pipes in an artificially frozen shaft lining (FSL) is always nonuniform. In order to obtain a better understanding of the radial thermal gradient–dependent deformation behaviors of frozen soils, a test apparatus for a frozen hollow cylinder (FHC) under a radial thermal gradient and the matching specimen preparation device were developed. The results obtained showed that the temperature precision was within $\pm 0.05°\mathrm{C}$ and the measured thermal gradient fluctuation was within $\pm 0.03°\mathrm{C}/\mathrm{cm}$ by circulating refrigerants rapidly through the confined cells. The initiation and growth of the thermal gradient significantly lowered the elastic modulus and the peak strength but had little effect on the strain-softening behavior. The inclination angle of the observed shear band exhibited a slight increase as the thermal gradient increased. Further, a linear response was detected between the heterogeneity level and the peak strength, and it was independent of soil types and temperatures. These observations were fundamentally distinguished from previous studies on frozen soil specimens under a vertical thermal gradient and contributed to developing a practical technique to decrease the temperatures at the inner surface and thermal gradient near the inner surface of the FSL.

One of the main problems of wide expressway construction in permafrost regions involves protection of the thermal stability of roadbed. Although ventilating ducts and crushed-rock layers have been successfully used in railway embankment construction, their effects may fail to reach the requirements of large-width expressways. This paper proposes Convection-intensifying composite embankments composed of perforated ventilation ducts and crushed-rock layers and numerically studied their cooling effects. A numerical model for composite embankments in permafrost regions is established considering air flow and heat transfer characteristics in porous media. Temperature fields and cooling effects are simulated, and the results show that when the underlying permafrost temperature decreases, the position of the 0°C isotherm increases significantly. The installed position of the ventilation duct and the thickness of crushed-rock layer have a significant influence on thermal status of the underlying permafrost. The new convection-intensifying composite embankment is a potential cooling measure for high-grade, large-width highway construction in permafrost regions.

Two high-salinity soils with different types of salts were tested to assess the effects of freeze-thaw (F-T) cycles on their volumetric and low-temperature shear behavior. The testing program, including freeze-thaw cycling and triaxial testing, is described in detail. Experimental results, including volumetric change and low-temperature stress-strain behavior and shear strength parameters are presented, and the causes of changes in shear strength parameters are analyzed. The research results show that soils with a high chloride salt content ($\ge 15\%$) and a low sulfate salt content ($\le 0.5\%$) exhibited very small volumetric contractions, whereas soils with a low chloride-salt content ($\le 5\%$) and a high sulfate-salt content ($\ge 1.5\%$) demonstrated very large volumetric expansion after freeze-thaw cycling. There appears to be a residual state for saline soils, at which the void ratio and the stress-strain behavior remains unchanged with an increasing number of F-T cycles. The residual void ratio and the stress-strain behavior at the residual state are much different from those at the initial state for soils with low chloride-salt content and high sulfate-salt content. The large salt expansion and the drop in the apparent cohesion of the soil with a low chloride-salt content and a high sulfate-salt content after F-T cycling is of concern for engineering purposes. These volumetric change and shear strength parameters have a direct or indirect impact on geotechnical analyses, such as assessments of slope stability and bearing capacity and/or load capacity of shallow and deep foundations in similar saline soils.

A vertical riser pipe is often mounted on the leg of an offshore platform to transport oil and gas. However, severe ice-induced vibrations and low-cycle fatigue damage of welded joints have been observed on the outside vertical riser of a platform when ice sheets interact with the riser in the Bohai Sea. In this study, an irregular cone is first proposed and mounted on the platform to decrease ice-induced vibrations. The vibration responses and the numerical analysis of the riser are then measured and simulated, respectively. The observed data and security analysis indicate that the stress amplitude of the welded joints on the riser structure compromises the endurance limit on fatigue damage. The security of the riser structure is found to be substantially stronger after mounting the irregular cone, thus providing a reference design for outside riser structures to reduce ice-induced vibrations.