The Average Temperature of Energy Piles

The geotechnical design of energy piles requires confirmation that the foundations can continue to carry safely the required load from the overlying structure and that no detrimental effects from the additional imposed temperature changes will occur. These additional design checks require assumptions to be made about the temperature changes within the pile. However, there is no universal approach for determining these, and routine application of over-conservative pile temperatures can lead to unrealistically adverse geotechnical design scenarios. This paper considers how the average temperature of a pile can be determined based on the analysis steps already carried out for the thermal design. The aim is to be able use the calculated fluid temperatures, along with readily available pile and ground parameters, to provide better assessments of the actual pile temperature so that the outputs of the geotechnical design can be improved. Two dimensional numerical simulations are used to determine the average pile temperature for different pipe, pile and concrete properties. The results of the simulations are compared with analytical approaches, allowing these to be validated for use on a routine basis. It is shown that the temperature of the center of the pile, which can be determined easily by analytical methods, can be used as a proxy for the average pile temperature.