Transient dynamics of the thermally induced deformation of sands

Currently, inconclusive evidence characterizes the thermally induced deformation of sands. In this context, the role of the transient nature of heat diffusion on the thermally induced deformation of sands has remained largely disregarded. This paper presents a theoretical and computational investigation of the transient dynamics characterizing the thermally induced deformation of sands under oedometric conditions. The study shows that heating rates determined by the pore fluid pressure dissipation timescale to ensure drained conditions can cause an important temperature nonuniformity and a breakdown of quasi-static conditions. Under these dynamic conditions, the differential expansion between the sand and the confining oedometer ring uniquely characterizes the response and is broken down into two characteristic regimes. For slow heating rates and low-expansion ring materials, a mathematical analysis shows that expansion and only expansion can occur, regardless of relative density and stress level. For fast heating rates and high-expansion ring materials, a parametric analysis establishes the possibility of a very small initial volumetric contraction for loose materials under high stress levels. In the light of the existing literature, the study shows that the intrinsic volumetric response to heating loads of sand, as a material, is only expansive; volumetric contraction may only be observed under transient conditions. This work supports a conceptual shift in the framework of analysis of thermally induced deformation of sands, from a temperature-dependent material response to a rate-dependent response of a finite volume under nonuniform conditions.