Thermally induced deformation of coarse-grained soils under nearly zero vertical stress

In the last few decades, the deformation of soils induced by temperature variations has received increasing attention due to the limited understanding of its governing mechanisms and variables, and the rising significance of such phenomenon for science and engineering. This paper provides new competence on this subject, with a focus on coarse-grained soils. Specifically, this study presents experimental laboratory investigations and discrete element simulations addressing the thermally induced deformation of coarse-grained soils at different length scales. For the first time, the influence of relative density has been studied considering minimal levels of applied vertical stress. The results show expansive deformation of coarse-grained soils upon heating and contractive deformation upon cooling for all relative densities. The magnitude of the contraction is more significant than the expansion, leading to a residual contractive deformation over one heating-cooling cycle. Microscopic insights drawn from numerical simulations highlight an increase in grain rearrangement through inter-particle sliding during both heating and cooling. These results also show that denser soils exhibit larger heating expansion and particle sliding, corroborating the existence of expansive grain rearrangement that can be linked to a mobilisation of dilatancy arising from thermally induced deviatoric stress.