Field performances of energy pile based on the secondary utilization of sonic logging pipes

Abstract

An energy pile has dual functions of bearing the upper structure load and transferring shallow ground temperature energy. Cross-hole sonic logging (CSL) is used to evaluate the integrity of large-diameter bored piles. CSL test tubes are usually abandoned after integrity tests. A secondary utilization of tubes can be advocated to save resources. In this paper, a new scheme is proposed to connect the bottom end of the access tube in a CSL test to form a new type of loop in the energy pile. A CSL tube is made of galvanized steel pipe (GSP). The thermal and thermomechanical performance of the energy pile with GSP loops and conventional polyethylene (PE) loops is measured by a thermal performance test at the cooling phase. The influence of the modified GSP tubes on the pile integrity can be neglected in the integrity test (CSL test). The heat exchange performance indicates that secondary utilization technology has good prospects. Owing to the discrepancies of different tube materials (thermal conductivity, heat capacity, and thermal coefficient), the heat exchange rate of the energy pile with GSP loops is approximately 26% higher than that of the energy pile with PE loops. The displacements at the pile top with GSP and PE loops after 120 h cooling are 0.15% and 0.083% times the pile diameter, respectively.