Centrifuge modelling of the use of discretely-spaced energy pile row to reinforce unsaturated silt

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.