Patent for sustainable process to prevent anhydrite swelling

By introducing heat sources into the substrate, anhydrite swelling can be prevented. We own a patent for this.

Anhydrite is one of the most critical rocks in underground mining due to its massive swelling capacity through water absorption. For countless structures built on gypsum keuper (e.g. tunnels, roads, etc.), costly damage is repeatedly recorded and expensive repair measures have to be initiated. The renovation measures are extremely time-consuming and usually not sustainable. Damage caused by swelling elevations in tunnel structures in Switzerland and France as well as in the greater Stuttgart area are typical examples of this. In only short periods of time and even during the construction work, uplifts caused by swelling caused by anhydrite can occur.

In the case of anhydrite, which occurs in nature, hydration can lead to an increase in volume of up to 61% due to swelling. After that, lithological gypsum is present.

At normal pressure and freshwater conditions, the conversion of anhydrite into gypsum usually only takes place up to a temperature of 58 °C. Recent unpublished studies even assume conversion temperatures well below 58 °C.

When the subsurface is heated, the swelling rate is significantly slowed down and the swelling pressure is significantly reduced. Thus, artificial soil heating represents a sustainable and in the long term cost-effective remediation method.