Estimation of ground thermal conductivity through indicator kriging: Nation-scale application and vertical profile analysis in Japan

摘要

The estimation of ground thermal conductivity using indicator kriging and surrounding borehole data at 5-m intervals to a depth of 200 m on regular 0.5-km cells of Japan was demonstrated. The probabilities of occurrence of eight soil/rock types were estimated for their most likely thicknesses and used as weights for estimation of ground thermal conductivity. Individual thermal conductivity of each soil/rock type is determined to obtain sufficient agreements of ground thermal conductivities between estimates and in-situ measurements. The estimation was performed over the land with 46 thousand borehole data. Local maps of Kanto showed the relation of soil/rock types and ground thermal conductivities with five topographic categories. Averaged 10-km-cell maps of Japan indicated the sudden changes of ground thermal conductivity even among adjacent cells due to geologic complexity. Vertical increases of ground thermal conductivity were statistically observed in all topographic categories, and the vertical profile of each location followed a logarithmic curve without or with a peak.