On 27 April, contractors broke through on the top heading of the second 1300m long US$24.2M Nollingerberg tunnel, in southwestern Germany, several months ahead of schedule. Contractor joint venture Östu Stettin/Hinteregger/Jäger used NATM to excavate the 100m2 face area tunnel.

The designer for the contractor is a joint venture comprising iC consulenten and Laabmayr & Partner. Client, the Baden Würtemberg state government, has been represented on-site by Strassenbauamt Bad Säckingen.

Drill and blast was used to excavate a hard rock section of the tunnel with two twin boom Atlas Copco 352 drill jumbos.

Approximately 600m of tunnel was excavated in this manner through limestone, where advance rates of eight 1.5m rounds every 24 hours became the regular production rate. Where the ground was weaker and soft to strong gypsum bearing strata was encountered, a rate of six rounds every 24 hours was still achieved.

For sections of soft or mixed ground a Liebherr 932 excavator was used and forepoling had to be used in one instance of poor ground. Whilst tunnelling through the soft ground, radial deformations became quite significant.

The tunnel alignment follows a 900m long site investigation tunnel that was completed in 2000. This runs parallel to the first tunnel and will be used as an emergency egress and access tunnel when the two lane motorway tunnels go into operation.

During excavation of the first tunnel, three pedestrian and one vehicular cross passages were built and will now be incorporated into this second tunnel arrangement. The bench and invert are scheduled for completion at the end of May.