Estimation of fast groundwater flow velocity from thermal response test results

Abstract

This study proposes a practical approach for the simultaneous determination of both the groundwater velocity and the effective thermal conductivity of the soil by using the moving line source theory. It is especially the process for verifying that the theory can be applied to the area where the groundwater velocity exceeds 100 m/y. Thermal response test (TRT) is carried out in Kazuno City, Japan having alluvial gravel deposits of 100 m in its depth. A borehole thermal resistance is calculated by a numerical simulation considering the effect of the groundwater velocity under the condition in which an inside borehole was filled with the porous material having a high permeability. A radius of an equivalent single pipe instead of the borehole radius is applied to the calculation model to calculate the circulating fluid temperature. The method can calculate the temperature variations of the equivalent pipe wall, reflecting a grout thermal resistance affected by the groundwater velocity. The groundwater velocity and the effective thermal conductivity of the soil are determined by using root mean square error between the calculated results and the TRT data. As a result, the groundwater velocity and the effective thermal conductivity of soil calculated by the moving line source theory were 120 m/y and 4.7 W/(m K), respectively.