Abstract

Long term records indicate that on-going global warming has resulted in the thawing of some permafrost regions, which led to extensive geological disasters including slumps and ground settlements that were causing damage to infrastructures. An accurate characterization of the temperature-dependent mechanical properties of frozen clay soils is critical for predicting and preventing geological disasters in cold regions. This thesis presents the experimental investigations on measuring mechanical properties of two artificial frozen clay soils (kaolinite-sand and bentonite-sand) at different temperatures. A practical approach for preparing artificial frozen clay soils samples is proposed. The reason for using artificial frozen clay is to enable control and repeatability. The approaches of split cylinder test and double punch test are applied to measure the tensile strength. Uniaxial compressive tests are used to measure the uniaxial compressive strength, Young’s modulus, Poisson’s ratio, and stress relaxation characteristics. The tests are conducted at different deformation rates in a temperature-controlled cold room.
The results show that the double punch test approach is more effective in measuring the tensile strength of artificially frozen clay soil when compared with the split cylinder approach. The effects of temperature and deformation rates on the sample’s tensile and compressive strengths are significant. Low temperature and a high deformation rate tend to generate brittle failure with post-peak softening behavior. A temperature close to the frozen fringe and a low deformation rate results in a diffuse failure associated with strain hardening. The temperature-dependent mechanical property relationships for the frozen kaolinite-sand and frozen bentonite-sand are modeled using a power-law function which covers a broad temperature range from -15°C to 0°C. The parameters for the modeling function are highly dependent on the applied deformation rates. Since the artificial frozen clay soils have pre-determined mineralogical composition, stress history, water content, and pore fluid salinity, these experimental results can be used as a considerable data resource for theoretical modeling the failure behavior of frozen clay soils.
Keywords: Artificially frozen clay soil, double punch test, tensile strength, temperature-dependent properties, strain rate effect, uniaxial compressive behavior.