Book excerpt: Sulphatic claystones are among the most problematic rocks in tunnelling due to their distinctive swelling properties. They are known to have caused severe damage, for example, to numerous tunnels excavated in the Gypsum Keuper formation. The repairs were extremely costly and time-consuming, and often provided only a temporary solution. The setbacks experienced in tunnelling through Gypsum Keuper may be attributed, among other things, to our limited knowledge of the macroscopic principles governing the swelling process and the underlying microscopic mechanisms. The issues in question have formed the focal point of long-standing research in the Chair of Underground Construction at ETH Zurich. A series of theoretical and experimental research projects are being conducted to investigate the interactions between chemical reactions, transport processes and the observed macroscopic behaviour. The objective of the investigations is to improve our understanding of swelling processes in order to yield a scientifically established basis for design. This work has achieved important progress towards this objective. It has systematically and comprehensively analysed the thermodynamics and the kinetics of the chemical reactions involved in the swelling process, as well as their interplay with advective and diffusive ion transport. The topic is of great value in terms of further investigation in this area.