The Design of Thermal Tunnel Energy Segments for Crossrail

The shallow ground has a large potential of low enthalpy energy that can be used for heating and cooling purposes. With the advances in ground source heat pump technology it becomes increasingly feasible to capitalise on this geothermal energy present in the ground. The biggest advantage of the geothermal energy is that the soil temperature reaches a constant at a depth of approximately 10 to 15 m below surface. For example, in central London the soil temperature at 14 m below surface remains undisturbed at 14 °C. Outside London, the soil temperature is slightly lower.

Recent development has seen the use of foundation piles, diaphragm walls, and base slabs as ground heat exchangers (Adam and Markiewicz, 2009; Brandl et al, 2006; Fry, 2009). For example, thermal piles and walls involve attaching polymer absorber pipes to the reinforcement cages and this approach has been applied to Crossrail stations. Other application examples involving sprayed concrete linings include the tunnels at Stuttgart Metro U6 (Schneider, Moormann, 2010), Lainzer Tunnel (Franzius et al, 2011) and the metro stations (Brandl et al, 2010). Heat-exchange pipes have been placed along the lengths of the Channel Tunnel to extract heat from inside the tunnel (Personal communications).