Physical modelling of cyclically thermally-activated helical piles under tensile loading

Using physical modelling, this study investigates the response of helical piles under tension loading and subjected to thermal cycles. Helical piles with single and double helices were installed in dry, medium dense sand and subjected to tension mechanical loading, thermal loading (TL) only and thermomechanical (TM) loading. Irrecoverable displacements were observed in all the thermal tests with those in the TM set being larger than those in the TL set. Within the TM set, the settlements were mitigated by about 50% when the pile had two helices rather than one, and about 30% when the global factor of safety was increased. The load–displacement responses demonstrated that more thermal cycles and cycling at lower factor of safety led to increased initial stiffness, ductility and load resistance for the helical piles. However, the maximum increase in tension bearing capacity was no more than 16%, and generally was less than 10%, which is comparable to the variation in repeat isothermal tests and thus, was not considered significant. The effect of thermal cycles on the helical piles under tension loading is less pronounced than for compressive loading and can be mitigated by using an appropriate factor of safety and/or adding a second helix.