Concreting in now under way in the southern bore of the twin-tube Gorgier tunnel in Switzerland’s Jura mountains, part of works for the new A5 highway. Breakthrough by hard rock TBM in the 11.7m diameter tunnel was in mid-June after a
ten-month drive beginning one month after breakthrough on the northern drive. Ground conditions on this double 2.72km drive included limestone marls and loose ground plus a small river crossing with just 0.5m cover. Despite artesian water in the marls there was little inflow, although in an earlier drive for the Sauges tunnel karstic, flows of up to 1m³/sec were encountered. The same contractor is due to begin work on a third A5 project, the Laengholz tunnel, in 2003.
