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Discretely spaced reinforced concrete (RC) energy pile rows have been proposed to be installed at the mid-height of soil slopes. Although the pile row can provide mechanical reinforcement to slopes, the piles can also potentially be used to (a) intercept solar energy from roadways for heat storage in the ground to mitigate extremely high carriageway temperatures and (b) to extract shallow geothermal energy for road surface de-icing. In this study, a series of centrifuge model tests was conducted to evaluate the shearing behaviour of unsaturated silt with and without reinforcement by conventional piles and energy piles. Three-dimensional finite-element coupled water-vapour-heat transport analysis was also performed to understand further the effects of pile heating on the responses of temperature and pore-water pressure of the soil. The measured and computed results revealed that the primary effect of pile heating was an increase in soil hydraulic conductivity due to the heat-induced reduction in water viscosity. The heated soil had enhanced water flow and hence developed higher suction. When subjected to translational slip, the silt reinforced by a row of closely spaced RC energy piles exhibited a more ductile shearing response and a lower peak shear resistance, compared to that reinforced by conventional piles. The peak bending moments mobilised in the energy piles in the stable stratum were also smaller. At larger shear displacements, however, the shear resistance converged to a similar value, regardless of the suction and temperature. These findings suggest that piles modified with additional energy transfer functionality can continue to act as reinforcement, potentially preventing soil from a sudden brittle failure, without attracting additional flexural stresses onto the piles. © 2021 Thomas Telford Ltd.

Discretely spaced reinforced concrete (RC) energy pile rows have been proposed to be installed at the mid-height of soil slopes. Although the pile row can provide mechanical reinforcement to slopes, the piles can also potentially be used to (a) intercept solar energy from roadways for heat storage in the ground to mitigate extremely high carriageway temperatures and (b) to extract shallow geothermal energy for road surface de-icing. In this study, a series of centrifuge model tests was conducted to evaluate the shearing behaviour of unsaturated silt with and without reinforcement by conventional piles and energy piles. Three-dimensional finite-element coupled water-vapour-heat transport analysis was also performed to understand further the effects of pile heating on the responses of temperature and pore-water pressure of the soil. The measured and computed results revealed that the primary effect of pile heating was an increase in soil hydraulic conductivity due to the heat-induced reduction in water viscosity. The heated soil had enhanced water flow and hence developed higher suction. When subjected to translational slip, the silt reinforced by a row of closely spaced RC energy piles exhibited a more ductile shearing response and a lower peak shear resistance, compared to that reinforced by conventional piles. The peak bending moments mobilised in the energy piles in the stable stratum were also smaller. At larger shear displacements, however, the shear resistance converged to a similar value, regardless of the suction and temperature. These findings suggest that piles modified with additional energy transfer functionality can continue to act as reinforcement, potentially preventing soil from a sudden brittle failure, without attracting additional flexural stresses onto the piles. © 2021 Thomas Telford Ltd.

Installing a row of discretely-spaced energy piles at the mid-height of an unsaturated soil slope has been proposed as an innovative means to increase the slope stability and also to harvest solar and geothermal energy for road surface de-icing. Centrifuge modelling of the thermomechanical interaction between unsaturated soils and energy piles is challenging. This paper aims to share three new inventions to improve our capabilities of modelling unsaturated soil-energy structure interaction in a geotechnical centrifuge, namely (i) small-scale model reinforced concrete (RC), to capture the thermomechanical behaviour and nonlinear quasi-brittleness of RC energy piles in prototype; (ii) centrifuge-mounted heating system, to deliver/extract heat energy into/from a model structure during a centrifuge flight; and (iii) large-size direct-shear box apparatus, to test the shearing behaviour of unsaturated soils, with and without reinforcing elements, under realistic stress and suction regimes. The performance of these inventions on an unsaturated soil-energy pile system relevant to the engineering application above is discussed in this paper. Copyright © Soil Mechanics and Geotechnical Engineering, ARC 2019.All rights reserved.

Small-scale physical model tests have been increasingly used to study the thermomechanical soil-pile interaction, but existing model piles are highly simplified and do not have representative thermal properties or the quasi-brittle mechanical behavior of RC. This study aims to overcome these shortcomings by presenting a new type of model RC. This consists of a mortar (plaster, sand, and water) with copper powder added to tune the mixture's thermal properties, along with a steel reinforcing cage. Fine sand was used to represent geometrical scaling of the prototype aggregates to correctly capture the quasi-brittle structural response. Adding copper powder content of 6% (by volume) matched the coefficient of thermal expansion and thermal conductivity of prototype concrete without changing the axial and flexural properties of model piles. In 1g soil-structure interaction tests, the model pile was able to serve as an effective heat exchanger for transferring heat from a water-carrying pipe embedded within the mortar to the surrounding soil. The model RC exhibited cyclic pile head settlement due to repeated pile heating and cooling. (c) 2020 American Society of Civil Engineers.

The use of thermo-active geo-structures has been recognised to be a sustainable engineering solution that can reduce carbon emissions from civil infrastructure. Physical modelling in a geotechnical centrifuge has been increasingly used to study the behaviour of this kind of geo-structures and their interaction with the surrounding soil under cyclic heating/cooling loads. Previous studies have been limited by the choice of materials used to model thermo-active geo-structures (such as aluminium and conventional concrete), due to inaccurate scaling of the thermal properties and the inability to capture the quasi-brittleness and strength properties of reinforced concrete (RC) due to improper scaling of aggregate sizes. The paper aims to develop a new thermally-enhanced plaster-based model concrete which can realistically reproduce both the thermal and mechanical properties that are representative of concrete at prototype scale. The new model concrete, combined with steel wire reinforcement (i.e. geometrically scaled reinforcing bars and stirrups), was then used to create 1:20 scaled RC thermo-active piles. Effects of temperature on their thermomechanical behaviour, including the coefficient of thermal expansion, moment capacity and flexural stiffness, were investigated. The suitability of using the newly-developed RC thermo-active piles for future centrifuge testing is discussed. © 2016 Taylor & Francis Group, London.