A review on the thermo-mechanical response of energy piles and soil to thermal loading

The effects of climate change increasingly felt today have led to the energy transition from the use of fossil fuels to the use of renewable sources of energy. Today, geothermal energy is increasingly getting attention and, recently, energy piles and underground structures have found increasing use in the exploitation of these resources. This energy is more economic as it saves about 250,000t of fuel each year, more reliable as it is continuous and more environmentally friendly as it releases little or no greenhouse gases in the atmosphere. The energy role added to the structural role of piles increases the loads and stresses on the foundation and therefore can have an impact on them. Moreover, the temperature variation imposed on the piles and the soil alter the soil-structure interaction, of which the effects can be above design limits. The response of energy piles to thermal loading depends on many factors such as soil properties, pile layout and dimensions, boundary conditions, frequency of loading, making their behavior complex compared to conventional piles. This knowledge gap in soil-structure interaction and the lack of appropriate design method of energy piles are some reasons for the potential of geothermal energy being untapped, despite its interesting features. As such, this paper presents the state of art on the thermal and mechanical changes of piles and soils due to thermal loading. The paper starts by explaining the current state of knowledge on energy piles and then it identifies the gaps in existing studies for potential future research. This review on past research about this topic provides a comprehensive framework for future studies, one of which is the use of energy micropiles.