Thermal volume change of poorly draining soils I: Critical assessment of volume change mechanisms

Abstract

a b s t r a c tThe thermal volume change of soils is typically interpreted using the stress history and changes in yield stress with temperature (thermal softening). However, the path followed to reach a given stress state may lead to different thermal volume changes. Alternative mechanisms of thermal volume change are explored using data from the literature and isotropic, drained heating tests on compacted silt. No relationship between thermal volume change and degree of saturation was observed. However, a clear relationship with the secondary compression prior to heating was observed, indicating that thermally accelerated creep may provide better thermal volume change predictions than thermal softening.

Thermal Volume Change of Unsaturated Silt under Different Stress States and Suction Magnitudes

“…Inconsistent trends in thermal contraction were observed for normally consolidated specimens with decreasing degree of saturation, similar to the lack of trend with this variable observed by Uchaipichat and Khalili (2009). Coccia and McCartney (2016a) proposed that thermal volume change may instead be due to thermally-accelerated secondary creep under the previously applied mechanical stress.…”

Thermal volume change of poorly draining soils II: Model development and experimental validation

“…However, studies by Towhata et al [35] and Burghignoli et al [5] observed that clays with an OCR as high as 56 may either expand or contract during drained heating depending on the sequence of loading prior to the change in temperature. Coccia and McCartney [9] re-evaluated these results and found a clear relationship between the secondary compression index of soil measured prior to heating and the resulting thermal volume change. This relationship serves as the basis of a new effective-stress based constitutive model for the thermal volume change of saturated and unsaturated soils presented in this paper.…”

“…Following the re-examination of the experimental observations of Houston et al [20], Towhata et al [35], Burghignoli et al [5], as well as an independent study performed on Bonny silt by Coccia and McCartney [9] using the experimental approach described by Coccia [8] and Coccia and McCartney [10], the hypothesis of this constitutive model proposed in this study is that the thermal volume change response of saturated and unsaturated soils is due to the thermally-enhanced creep associated with the most recently applied change in effective stress. Particularly, heating of normally consolidated soils will cause an acceleration of the secondary compression process occurring prior to the start of heating, leading to contraction, while heating of overconsolidated soils will lead to either expansion or contraction depending on the direction of the most recent change in effective stress (i.e.…”

“…To assess the use of the function, H(T), to characterize the relationship between the total change in void ratio during heating and that expected due to ambient secondary creep, the ratio De total (t, T)/De a (t, T 0 ) for Bonny silt from Coccia and McCartney [9], as well as MC clay and Todi clay from Towhata et al [35] and Burghignoli et al [5], respectively, has been compared with H(T) as defined in Eq. (13) in Fig.…”

“…A critical assessment of the mechanisms of thermal volume change in saturated and unsaturated soils was presented in the companion paper by Coccia and McCartney [9], and an alternate volume change mechanism related to the effects of thermallyaccelerated secondary compression arising from changes in stress prior to heating was found to help explain some discrepancies in data reported in the technical literature. Thermal volume changes are typically estimated using empirical thermal softening equations that predict elastic expansion for overconsolidated soils and plastic contraction for normally consolidated soils during drained heating.…”