1 Scope

Experience from two case histories of tunnels where swelling involving sulfates and gypsum will be presented. Unexpected swelling phenomena were observed of the invert in both tunnels. One tunnel is located at the northern edge of the Triassic Keuper formation in Luxembourg: Tunnel Markusberg of motorway A 13 near Schengen. The other tunnel in the Swiss Alps crosses the formation of Bündner Schist: Gotschna Tunnel of motorway A 28 on the by-pass road of Klosters.

2 Extension of sweling zones and observed heave

In both tunnels the zones with heave are limited in length. In the dual tube motorway tunnel Markusberg the swelling zone extends over about 50 meters, about 200 m from the East portal of the tunnel and severe swelling has been observed, beginning weeks after excavating the horseshoe shaped tunnel. Initially the heave of the tunnel floor was re-excavated and the swollen material removed periodically. In the Gotschna tunnel heave in three different sections, about 100 m long, and spaced about one kilometer each, were observed. Different rates of heave (Tab. 1) are observed in the three sections that depend on type of applied invert or the support pressure.

2.1 Observations in Tunel Markusberg

The observations at Tunnel have been described by Steiner et al. (2015). The swelling zone has a small overburden of 25 m only (Fig. 1), on the ground surface in the vineyard actually gypsum can be observed in the red marl. As substantial heave was observed, a void was left below the roadway and the swollen and heaved ground was periodically removed (Fig. 1).

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