An experimental investigation challenging the thermal collapse of sand

Currently, highly contradictory knowledge characterises the thermally induced deformation of sands and the occurrence of the thermal collapse phenomenon: a volumetric contraction of such granular materials upon heating, which has been observed in some laboratory studies as opposed to a volumetric expansion. In this context, the effects of applied stress level and relative density, which seem to account for the inconclusive findings, remain disputed. A key challenge inherent to investigations of the thermally induced deformation of sands is the requirement for tremendous measurement accuracy (i.e. trueness and precision) and the ability to minimise measurement errors. This paper addresses this challenge and the conflicts presently characterising this subject by reporting a laboratory experimental campaign that accurately and repeatedly measures the thermally induced deformation of sand for different relative densities, stress levels and particle shapes by means of temperature-controlled oedometer tests. The results of this study show a monotonic volumetric expansion of sand upon heating and contraction upon cooling, with an irreversible contractive deformation remaining after one heating–cooling cycle. Specifically, irrespective of the stress level, relative density or particle shape, no thermal collapse is observed, challenging the actual occurrence of such a phenomenon in sands.