Abstract
Application of Ground Source Heat Pumps (GSHP), which extract ground thermal energy, may change ground thermal conditions. These changes raise concerns for possible deformations and reductions of shear strengths in the ground. The typical GSHP range of thermal influence is until 50 m of depth and the maximum temperature applied is around 50 ° C. The range of thermal influence will include unsaturated soil layers. In this study we therefore investigated the mechanical behavior of both unsaturated and saturated soils due to temperature changes and also proposed a model for this. Two series of tests for a silt named DL clay: suction and temperature controlled tests and heating and cooling tests, were conducted with a thermal control triaxial compression apparatus for unsaturated soils. It was found from the tests that the peak strengths were affected by temperatures and the specimens with lower temperatures had higher strengths. However, the strengths at critical state were almost independent of temperatures. In the elastic region the specimens expanded and shrank due to heating and cooling, respectively. From the data obtained in this study and previous works, we formulated a thermal elasto-plastic model for unsaturated soils taking into account two thermal effects and two suction effects. We investigated the typical test results by using the elasto-plastic model. It was found from the results that the elasto-plastic model could qualitatively express the behavior.
