Energy geo-structures in transport infrastructure: Are they feasible?

Ground source heat pump (GSHP) systems use the ground as a source of sustainable thermal energy. This shallow geothermal energy technology has proven to efficiently provide renewable energy for space heating and cooling. While the use of purposely built boreholes is widespread, it is becoming increasingly common to attempt to use any geo-structure in contact with the ground as the ground heat exchangers (GHEs) of GSHP systems. In this way, major capital cost savings are potentially achieved since the highest additional costs associated with geothermal technology are drilling and trenching, already required for structural purposes. In transport infrastructure, sub-surface structures designed for stability are abundant. They can be used to also exchange heat with the surrounding ground, converting them into energy geo- structures. This paper summarises the potential of applying this technology to piles, soldier pile retaining walls, diaphragm retaining walls, slabs, road bases and tunnel linings. These are geo-structures that are commonly found in rail and highway projects such as the Melbourne and Sydney Metro Projects, and the West Gate Tunnel Project to name a few. Detailed 3D finite element models have been developed to investigate the thermal performance of these systems, exemplified herein on an energy wall. The applicability of this technology is discussed for different thermal load scenarios, showing the importance of the thermal load distribution balance. Barriers to adoption are also briefly discussed.