There is a growing need to better understand the relationship between time, strain rate, and temperature on the load-deformation behaviour of clay soils in engineering applications. These applications may include: infrastructure constructed in northern regions where climate change is a growing concern; disposal of nuclear waste; and, industrial structures, such as furnaces, foundries, and refrigeration plants. Temperature variations may induce changes in internal pressure in the soil, swelling and shrinkage, and affect the mechanical properties of the soil. This thesis presents thermal numerical modeling for two instrumented field sites in northern Manitoba. Thermal conductivity testing on samples from these sites and field data are used to calibrate these thermal numerical models. Various boundary conditions are examined. The capabilities of the models are evaluated to determine if the models adequately simulate and predict changes in temperature in geotechnical structures. A discussion is presented on the strengths and weaknesses in the models and the predictive capabilities of the models. The thesis then shifts into understanding the concepts of thermoplasticity and viscoplasticity and the mathematics relating these concepts. Mathematical models that describe these concepts are examined and compared with traditional soil mechanics approaches. The concepts of thermoplasticity and viscoplasticity are combined in an encompassing elastic thermo-viscoplastic (ETVP) model using a semi-empirical framework. A sensitivity analysis is used to evaluate quantitatively the response of the model. The model is then validated qualitatively against published laboratory data. Applications of the ETVP model are discussed.