The most important route between the Croatian seaports of Split and Makarska is the D8 National Road.
Due to continuously increasing traffic volume, the government decided to expand this coast road and to construct spacious bypasses for several towns. A critical part of this infrastructure upgrade project was the construction of a 1,471 m long tunnel as part of the bypass of the town of Omis, some 25 km south of Split.
Due to the comparatively small depth of cover at the tunnel location, it was necessary to start with a pipe umbrella support at the portal. The pipe umbrella support system provided the protection and safety for the first tunnel driving work. Tunneling was carried out mechanically using excavators and shotcrete in accordance with the New Austrian Tunneling Method (NATM).
For further tunneling works, the contractor used anchor bolt in lengths of 3m each to secure the heading face.
However, the geology encountered often required short-term recalculations of the necessary anchoring forces. Hence, different types of anchor bolts were used. The anchor bolt system is designed for differing rock mass conditions: The drill bit design and diameter can be easily and flexibly adjusted. Various types maintain the basic dimension of the required anchoring forces. Eventually, necessary functional adjustments of the required anchor lengths can be carried out easily using the appropriate coupler. The application of anchor bolt has guaranteed the project quality and progress.