Analysis of the phenomenon of material expansiveness in tunnels built in anhydrite. Outcomes and experiences

The serious geotechnical problems arising in many tunnels bored in material giving rise to stability problems as a result of being expansive, makes the water channelizers. These are materials which are easily washed with sulphates dissolving with water causing the massif to become decompressed and to remould, aggravating and transferring the problem beyond the tunnel’s immediate environment. In the particular case of layers of anhydrite between argillite, it also happens that the primary support and subsequent lining must have exceptional strength to resist the pressures the terrain may transmit in the medium to long term. This article describes the most relevant aspects of the hydromechanical behaviour of sulphated soil and rock and presents some experiments, concluding with various aspects associated to the phenomenon of swelling in tunnels and its possible treatment.