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  Swelling Control in Tunnelling by Heating

  As illustrated by a number of tunnels, swelling of anhydritic claystones results in relevant deformations of the tunnel cross section, development of high pressures on (and damage to) the tunnel lining or, in the case of a small - moderate depths of covers, even heave of the entire lining and of the overlying ground up to the surface. This paper presents a conceptual study for a swelling mitigation method, which makes use of well-known thermodynamic and kinetic properties of the anhydrite-gypsum system. More specifically, moderate heating of the rock to 35 - 50 °C retards or even completely stops the anhydrite to gypsum transformation. The paper shows that rock heating can be technically implemented in situ; the operational cost (energy consumption) is low relatively to other measures; and potential environmental impacts or other side effects such as acceleration of the alkali–aggregate reaction in the concrete lining are manageable.

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