Hohlgangsanlage 1 - Construction and Design

Construction and Design

The tunnels were dug into the sides of hills, into rock. This means that incomplete tunnels remain mostly intact, due to the strength of the unsupported rock. Completed sections are lined with concrete floors, walls, and ceilings.

There was a basic design of storage and personnel tunnel. Storage tunnels incorporated a 600 mm gauge railway in a loop running around the whole complex and a small platform for loading supplies; they usually had two entrances so that vehicles could continuously enter and exit the complex. Personnel tunnels were built like a grid; the railway was often removed after construction was complete. Completed tunnels would have been lined in concrete, and have drainage, lighting and air conditioning systems.

In all, 19-25 storage tunnels were planned, but due to the almost wholesale destruction of primary source material before the surrender the exact number is unknown (although the number where work began is known).

Where possible, the tunnel routes avoided granite and instead they were routed through looser shale rock formations. The tunnels were dug by the traditional method of drilling and blasting. When the tunnels were bored out they were lined with concrete. First the floor was lined, followed by the walls and finally the roof. The walls were concreted using wooden shuttering, the space between the shuttering and the rock face was filled with concrete, and the shuttering subsequently removed. The roof was made in the same way, but using curved shuttering balancing on the concrete walls. Concrete was poured down the escape shafts rather than through the tunnel entrances to avoid contamination with the rock leaving the tunnel; these shoots can still be seen in many of the tunnels. Contrary to popular belief there were relatively few accidents and deaths in the building programme itself, but many slave labourers died of starvation.