Evaluating up to higher terms of power-series expansion of exponential integral E(X), which appears in Kelvin′s line source function used for analyzing data of thermal response test (TRT), leads to an asymptotic solution that closely corresponds to the exact solution. This quasi-exact solution is used together with Powell′s optimization method to inversely identify both of thermal conductivity and a parameter relating to volumetric heat capacity of soils. The proposed method was verified by applying to test cases and then satisfactory adopted to real field cases operated under different conditions. A method of activating early data of TRT made it possible to identify intrinsic thermal conductivity efficiently without introducting man-made evaluation errors and to reduce operation cost and duration for TRT.

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The water characteristic curve is one of the important properties of soil required for the evaluation of groundwater flow in the unsaturated zone. Unsaturated zones occur below the water table when there is fluctuation of the water table depth. In such zones, it is not well understood how the trapped air behaves and how it affects water saturation. In this study, we estimated the water characteristic curves based on the water pressure and water saturation. The water saturation was monitored for wetting and re-saturation cycles where the water pressure was gradually increased up to 5.5 kPa using a one-dimensional sand-filled column. In the wetting cycle, the water characteristic curve was obtained assuming that the pore air pressure was atmospheric. In the re-saturation cycle, how the water characteristic curve would extend was estimated by neglecting the effect of air pressure in the discrete air bubbles. The experimental results showed that the water saturation under positive water pressure, i.e., below the water table, increased with water pressure and exceeded that at the water table level. It was concluded that the rate of increase of water saturation resulted not only from the discrete air bubbles being compressed but also being forced up as the water table gradually moved up. Not considering the increase in water saturation in the unsaturated zone below the water table could result in a significant underestimation of hydraulic conductivity in such a zone.

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