Effect of stress history of saturated clay on engineering behaviour of an energy pile

Abstract

The mechanical properties of soil could be affected by its temperature change and these effects may lead to additional issues in the thermo-mechanical behaviour of energy piles. Laboratory experiments were conducted to assess the thermo-mechanical behaviour of a small-scale instrumented energy pile installed in a saturated clay at different stress histories. The energy pile was subjected to five heating/cooling cycles. The experimental programme involved monitoring the changes in the surrounding soil temperature, pile-head displacement, pile axial load and pile-tip resistance as the temperature of the pile changed. The results show that the thermo-mechanical behaviour of the energy pile depended on the stress history of the surrounding saturated clay. The normally consolidated clay showed a higher irreversible pile-head settlement and pile-tip resistance compared with the overconsolidated clay. This behaviour could be explained in light of the expected contraction thermally induced volume change of the normally consolidated clay that could induce an additional negative skin friction on the pile. Moreover, the observed mechanical engineering behaviour of the energy pile under thermal heating/cooling cycles could be explained in terms of the expected degradation of shaft friction due to the cyclic thermally induced interface shear stress.

Cyclically thermally-activated pile under combined axial/horizontal loads in clay

“…The gradual accumulation of thermally-induced irreversible horizontal displacements during thermal cycles could be caused by thermally-induced passive soil resistance mobilization. This kind of ratcheting response was similarly observed for axially-loaded energy piles embedded in clay reported by Nguyen et al (2020), Wu et al (2020) and Ng et al (2014Ng et al ( , 2021a, and for horizontally-loaded energy pile embedded in dry sand reported by Zhao et al (2022). 13…”

“…Additionally, thermally-induced soil consolidation and creep could contribute in turn to a time-dependent increase in horizontal displacement during the recovery phase. Evidence of these phenomena are available in previous works (Akrouch et al 2014;Wu et al 2020;Ng et al 2014Ng et al , 2021a. The gradual accumulation of thermally-induced irreversible horizontal displacements during thermal cycles could be caused by thermally-induced passive soil resistance mobilization.…”

“…Previous studies revealed that cyclic thermally-induced volume changes are much more predominant in clayey soils compared to sandy soils. Nevertheless, only a limited number of studies focused on the influence of thermal loading on the mechanical response of axially-loaded energy piles embedded in clayey soils by performing full-scale tests (Laloui et al 2006;Bourne-Webb et al 2009;Akrouch et al 2014), centrifuge model tests (Stewart & McCartney 2014;Ng et al 2014Ng et al , 2021a and 1-g small-scale physical model tests (Yavari et al 2016;Wu et al 2020;Yazdani et al 2019;Nguyen et al 2020;Tang et al, 2021). To the authors knowledge, the works of Vitali et al (2022) and Zhao et al (2022) are the only available studies using centrifuge model tests to investigate the influence of monotonic heating and heating-cooling cycles, respectively, on the flexural behaviour of horizontally-loaded energy piles in sands.…”

Simulation and Analysis of the Thermal-Mechanical Response of an Energy Pile

“…Scholars at home and abroad have carried out much research in the related areas of this study [19,20,[24][25][26][27][28]. Wu et al [29] started with the stress history of soil and found that compared with overconsolidated clay, normally consolidated clay exhibits higher irreversible pile head settlement and pile end resistance. Through laboratory experiments, Liu et al [30] found that the moisture content of the sand around the energy pile affects the frictional resistance at the pile-soil interface caused by temperature.…”