Centrifuge Modeling of Soil-Structure Interaction in Energy Foundations

Abstract

This study presents a centrifuge modeling approach to characterize the transient thermo-mechanical response of energy foundations during heating-cooling cycles in order to provide data for calibration and validation of soil-structure interaction models. This study focuses on the response of a scale-model energy foundation installed in an unsaturated silt layer with end-bearing boundary conditions. The foundation response was assessed using embedded strain gages and thermocouples. Other variables monitored include foundation head displacements, soil surface displacements, and changes in temperature and volumetric water content in the unsaturated silt at different depths and radial locations. Measurements during the initial heating process indicate that the thermal axial stress is greater near the toe of the foundation due to the restraint associated with mobilization of side shear resistance along the length of the foundation. The thermal axial strains were close to the free-expansion thermal strain near the soil surface and decreased with depth. The thermal axial displacements calculated by integrating the thermal axial strains correspond well with the independently-measured head displacements. The mobilized side stresses calculated from the thermal axial stresses increased with height and were consistent with the shear strength of unsaturated silt. During successive heating-cooling cycles, slight decreases in upward thermal head displacement were observed due to changes in stiffness of the unsaturated soil due to thermally-induced water flow away from the foundation and potential down-drag effects. However, little change in the thermal axial stress was observed during the heating-cooling cycles.

Numerical modelling of thermo-active piles in London Clay

“…The fullscale field experiments reported by Brandl (2006), Laloui et al (2006), Bourne-Webb et al (2009), Akrouch et al (2014), Mimouni and Laloui (2015), Murphy et al (2014) and Wang et al (2015), as well as experimental set-ups by McCartney and Rosenberg (2011), Kalantidou et al (2012), Stewart and McCartney (2013), Ng et al (2014) and Yavari et al (2014a) have provided an invaluable insight into the behaviour of thermo-active piles. Moreover, the results of the first field tests (Bourne-Webb et al, 2009;Brandl, 2006;Laloui et al, 2006) have led to the development of a simplified descriptive framework for thermo-mechanical pile response (Amatya et al, 2012;Bourne-Webb et al, 2013).…”

Transparent Soil to Model Thermal Processes: An Energy Pile Example

“…This is possible owing to scaling laws derived by Savvidou (1988), who determined the time scaling factor of N 2 (N being the applied enhanced gravity in the centrifuge) for heat flow in accelerated gravity experiments, which enables multi thermal cycles to be simulated in a shorter duration (hours) that would normally take years at full field scale. Notable centrifuge investigations benefiting from this scaling relationship include Stewart and McCartney (2014), Ng et al (2014), Britto et al (1989), Goode et al (2014), and Stewart and McCartney (2012). These studies considered a range of various soil types with reported observations of increased pile settlements and ratcheting over several thermal cycles.…”

Characterisation of Ground Thermal and Thermo-Mechanical Behaviour for Shallow Geothermal Energy Applications

“…Typically, laboratory THM soil characterisation is carried out by adapting standard laboratory soil testing devices to non-isothermal conditions, mainly oedometer, direct/simple shear, and triaxial devices, and more recently by means of centrifuge modelling [213]. The temperature controlled triaxial test is one of the best-established approaches for characterising THM behavior due to its relative simplicity and capability to control key variables.…”