Multilayer-concept thermal response test: Measurement and analysis methodologies with a case study

A multilayer-concept thermal response test is proposed by incorporating the standard test with a pair of fiber-optic distributed temperature sensors in the U-tube. The heating exchange rates in any vertical segment are estimated from the sequential temperature data. The ground thermal conductivity of each sub-layer is calculated using the line heat source model, in which the heating exchange rates and the temporal temperature slopes are determined at their convergence as the thickness increases. The convergence analysis continues downward until reaching the borehole bottom to obtain the stepwise conductivity. A case study of Sapporo, Japan, is shown with the sensitivity analysis of the convergence threshold.