Estimating the thermal properties of soil and concrete piles from thermal response tests (TRTs) for energy piles with spiral tubes

Accurate estimation of the thermal properties of soil and concrete piles is critical for designing energy piles. This paper proposes an algorithm that can simultaneously estimate the thermal conductivities and diffusivities of soil (k_s and a_s, respectively) and concrete piles (k_b and ab, respectively) using data from thermal response tests (TRTs). The outstanding feature of the algorithm is its use of a composite-medium cylindrical-surface heat source solution. The proposed algorithm is a theoretically complete short-term solution that considers the heat capacity of the concrete pile and the difference in thermal properties between the soil and concrete pile. Sensitivity analysis shows that the data of early-time TRTs reduce the linear dependence of the parameters, thereby allowing the simultaneous estimation of k_s, a_s, k_b, and a_b. The new algorithm is validated using the reported TRT data. Results show that the four parameters could be estimated with high accuracy by using the data sampled between 10 and 50 h. Moreover, k_s and k_b have relative errors of 11.05% and 24.47%, respectively. In conclusion, the proposed algorithm is easy to implement and computationally more efficient compared with algorithms using numerical models. Thus, the use of this algorithm may potentially reduce the time and cost of TRTs.