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

Abstract

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.

Transient dynamics of the thermally induced deformation of sands

“…The developed investigations address the response of a cylindrical sand sample to heating under constant vertical applied stress in oedometric conditions. These conditions are chosen to match most of the experimental literature (e.g., 18,21,25,26 ) and highlight the effects of the differential expansion with the boundary ring, which are expected to become prevalent with temperature nonuniformity. The reference case of a loose sample of Toyoura sand, defined hereafter, is used throughout the paper to illustrate the effects of the sample size, heating rate, and ring material on the response.…”

“…First, the axisymmetric heat Equation ( 4) is solved for a temperature increment 𝛿𝑇 = 10 • C, chosen in accordance with most of the experiments from the literature. 18,[23][24][25] An implicit backward difference with a timestep of 0.1 s and a second order central difference with a step of 0.75 mm are again used for temporal and spatial discretization, respectively. Second, the spatial-temporal temperature distribution obtained is used to solve for the heating of the material under constant vertical stress 𝜎 𝑧 = 1 MPa.…”

“…Then, parametric investigations of the thermally induced deformation are conducted for the reference case to illustrate and inform the previously established general considerations. The particular values of 𝛽 ring = 3.6 × 10 −6 1/ • C, corresponding to the low thermal expansion metal invar used by Pan et al, 25 and 𝛽 ring = 4.95 × 10 −5 1/ • C, corresponding to the high thermal expansion 316 stainless steel used by Agar et al 18 are considered. The combined effects of the sample size and heating rate are characterized by the dimensionless thermal diffusivity 𝛼 * 𝑑 .…”

“…[9][10][11][12][13][14][15][16][17] For coarse-grained soils (e.g., sand), thermal expansion of individual grains, which alters the contact force network and causes grain rearrangement, has been considered responsible for the thermally induced deformation of such materials within the same temperature range. [18][19][20][21][22][23][24][25][26] This peculiar nature of thermally induced deformations in coarse-grained soils has been supported by theoretical, 27 experimental, 28 and numerical evidence resorting to particle-scale simulations, [29][30][31][32][33][34][35][36] considering clean sands pertaining to classes SW or SP (i.e., wellgraded and poorly graded gravelly sands, with little or no fines) according to the Unified Soil Classification System, for which there is no potential influence of the plasticity of fine grains and their chemo-physical interaction with water.…”

“…In fact, some experimental studies report an initial irreversible contraction of sand upon heating at very high relative density, 18,21 while others report only reversible expansion 23,24 . Other works show either only contraction at high stress level, 26 or only expansion at very low stress, 25 regardless of the relative density. Instabilities of the fragile granular assemblies 37,38 and shear induced by temperature gradients and differential expansion of the container 39,40 have been reported as the two major potential mechanisms for the contraction upon heating.…”