A laboratory investigation on the thermo-mechanical behaviour of thermal piles in sand

This paper reports on an investigation on the behaviour of base and shaft resistant piles embedded in sand subject to heating and cooling cycles. It describes the 1 g laboratory model developed at University College London. The test pile consists of a hollow stainless steel tube which is instrumented using Fibre Bragg Grating (FBG) sensors that allow measurement of strain and temperature profiles along the pile length and the surrounding soil. The pile is subjected to two heating-cooling cycles. Water held at 50°C is circulated inside the pile for 24 hours; this is followed by a 24-hour cooling period during which the temperature of the water is allowed to fall back to ambient conditions. The results show that small irreversible settlements occurred during this period. Additionally, it is found that the degree of freedom varies between 0.9 and 1.0 which indicate low levels of restraint are present. Nevertheless, considerable axial load and axial stress is induced in the pile. Moreover, significant shaft friction is mobilized during both heating and cooling periods.