Tunnelling in swelling rock - a solved problem? / Vortrieb in quellendem Gebirge - ein gelöstes Problem?

In some sedimentary rocks, the admission of water results in an expansion of volume, which results from the chemical conversion of anhydrite into gypsum (anhydrite swelling) or the physical adsorption of water in certain clay minerals (clay swelling). This expansion leads to heavy loading of the tunnel lining and has already caused significant damage to some structures. In addition, sulphate attack on the lining concrete can lead to softening due to the formation of ettringite. Damage can be in the form of shear failure, spalling or bending tension cracks. The location and nature of the damage, which depends on the location of the ground containing clay or anhydrite and susceptible to swelling, is illustrated with some examples. Numerical modelling is applied to demonstrate the load transfers, which lead to these phenomena. Recent attempts to counter the problem have been based on the strengthening of the lining (resistance principle) or by installing compressible zones between rock mass and lining (yielding principle). The design rules for each principle are explained.