Thermal performance design and analysis method for energy cast-in-place piles (E-CIPs) installed in diaphragm walls

The diaphragm wall is a temporary supporting structure installed to prevent the collapse of excavation surfaces and groundwater leakage while conducting deep excavations. In a diaphragm wall system, cast-in-place piles (CIPs) are usually installed in a row, comprising deformed rebars and H-beams. In this study, a novel geothermal energy structure, called an energy CIP (E-CIP), was devised to use a diaphragm wall as a ground heat exchanger; E-CIPSP consisting of steel pipes substituting for deformed rebars and E-CIPDI consisting of double-I-beans substituting for H-beams, respectively. In addition to the role of temporary support, heat exchange with ground formations was induced by circulating a working fluid through the hollow space inside the steel pipes of E-CIPSP or the closed double-I-beams of E-CIPDI. Based on a series of thermal performance tests, both the E-CIPSP and E-CIPDI installed in the test bed demonstrated stable heat exchange performance. In addition, a computational fluid dynamics (CFD) model for the E-CIPSP was developed by calibrating the thermal conductivity of the ground formations, which allows to develop a design method for the E-CIPSP installed within a diaphragm wall.