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The application of thermally-activated pile foundations has received significant attention in the last decade with a number of large- and small-scale tests having been undertaken. Alongside these physical studies, a number of investigations utilising numerical analysis have been undertaken to examine the behaviour of single piles and pile groups. Focussing on studies examining single piles, it is apparent that a variety of differing domain dimensions have been used. The work presented in this paper had the objective of systematically examining the influence of the domain size and how it affects the predicted thermo-mechanical response of the pile. It shows that the domain size has an important impact on the initial distribution of mobilised shaft friction due to applied mechanical load which then impacts on the subsequent thermo-mechanical response.

Considering the need to reduce our dependence on unsustainable energy sources and reducing the carbon footprint associated with building climate control, shallow geothermal energy represents an attractive sustainable technology for providing renewable heating and cooling. The temperature field generated around ground-coupled heat exchangers, and thus their energy efficiency, fundamentally depends on the heat transfer mechanism and the thermal properties of the materials involved. While the thermal properties of materials that make up the system can be defined with some certainty, little is known about the impact of contact thermal resistance at the soil-structure interface. Contact thermal resistance will reduce heat exchange efficiency and increase mechanical impacts associated with temperature changes within energy geo-structures. This paper describes a laboratory test method to quantify the contact thermal resistance of soil-concrete interfaces. The methodology is first evaluated using numerical analysis, and then validated against a test using a limestone aggregate concrete and fine, silica sand at differing levels of compaction.

The thermal-activation of pile foundations for use within shallow geothermal energy systems has received much attention with a number of studies having reported full- and small-scale testing and/or numerical analysis. Various conditions in terms of pile type, ground profiles and thermal loading, have been considered in these studies, leading to a broad understanding of the thermo-mechanical behaviour of thermally-activated pile foundations. One area that requires further attention is the clarification of the foundation response under seasonal cyclic thermal loading. This study systematically assesses the impact of cyclic thermal loading in relation to the initial mechanical loading, for isolated floating piles and pile groups in a cohesive soil medium. For piles where the shaft resistance dominates the pile total resistance, it was found that irrecoverable movement will be small and thermal stress and pile head movements change in a cyclic and regular manner. It is shown that the effect of the coefficient of thermal expansion of the soil, is much reduced from that suggested in studies using constant thermal loads applied over long periods. The effect of the overlying building was explored and it is shown that thermal-activation of the pile foundation mitigates the effect of the imposition of a higher average temperature at the surface.

This paper presents a numerical study on the short-term bearing capacity of preloaded footings on soft clay. In practice, this situation needs to be addressed when re-using an existing foundation for a new building or when extra load is to be transmitted to an existing foundation. Previous studies have estimated the bearing capacity in this situation, allowing simply for the increase in the soil undrained strength due to the increase in effective stresses imposed by the preload. However, field and laboratory observations corroborate that there is a continuous increase in the stiffness and strength soil properties with time, even after the dissipation of the excess pore water pressures generated during the initial loading is complete. This paper quantifies the short-term bearing capacity of existing foundations allowing for the occurrence of creep deformations and associated soil hardening. The problem is investigated by means of a series of plane-strain coupled finite element analyses of a 2 m wide rough strip footing, in which the foundation soil is modelled using an overstress based elastic-viscoplastic model. The study investigates the effect of the level of preload, the applied loading rate, the creep characteristics of the foundation soil (magnitude and creep law type) and the footing geometry. It is shown that the time dependent nature of soil (e.g. occurrence of creep) accounts for a significant increase in bearing capacity.