Figure 1.
The image shows a three-dimensional cutaway of an underground tunnel section surrounded by soil. The tunnel lining consists of cylindrical segments forming the tunnel wall. One segment is labelled as an equipped lining segment. A main heat pipe runs longitudinally along the inner side of the tunnel crown. An embedded pipe system is integrated within the lining segments and arranged in repeated curved loops around the tunnel circumference. The pipes are shown distributed along multiple rings of the lining, indicating a system designed for heat transfer between the tunnel structure and the surrounding ground.Schematic representation of a tunnel segmental lining equipped as a ground heat exchanger