Swelling laws for clay-sulfate rocks revisited

The swelling of clay-sulfate rocks is a major threat in tunnel engineering and in the installation of shallow geothermal systems. It can cause serious damage to tunnels and buildings; and produce high additional costs during tunnel construction and operation. The swelling may result in a heave of the tunnel invert, destruction of the lining or uplift of the entire tunnel section. Heave–pressure–time relations are therefore needed in order to predict the mechanical behavior of swelling rock as a basis for an optimal tunnel design. The present study revisits different stress–strain relations (“swelling laws”) for swelling clay-sulfate rocks proposed by various authors. Published laboratory data from oedometric swelling tests are presented that may confirm the proposed stress–strain relationships. These data are re-examined by testing each of the different data sets with the different proposed relations. One main outcome of this study is that different interpretations of stress–strain data are possible and none of the swelling laws proposed in the literature could be generally confirmed or rejected. We conclude that a generally valid swelling law in the form of a stress–strain relation does not yet exist. A promising approach to describe the swelling behavior of clay-sulfate rocks, however, is process-based numerical modeling, which is also briefly introduced in this study.