The Bibra Tunnel runs through rock formations of the Middle Bundsandstein along its entire length, primarily the Hardegsen formation.
The ground conditions are characterised by layers of sandstone, shale and siltstone that belong stratigraphically to the Middle Buntsandstein and, in particular, to the Hardegsen and Solling formations. The layers of the Solling formation are cut through only in the easternmost part of the tunnel. After the portal areas, the tunnel varies in depth from around 15 to 50 metres below the surface. The mountain groundwater level is generally around 30 metres under the floor of the tunnel. However, it can be expected that the tunnel will cut through layers of water.