The most important route between the Croatian seaports of Split and Makarska is the D8 National Road. This road was built very near to the shoreline of the Adriatic Sea in the 1960s. Today, the road finds itself in the middle of numerous towns which have grown in the last decades. 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. DSI supplied its reliable Type 114 mm AT-Pipe Umbrella Support System, which 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 Tunnelling Method (NATM). For further tunnelling works, DSI supplied DYWI® Drill Hollow Bar Self-Drilling Anchors in lengths of 3,000 mm each to secure the heading face. However, the geology encountered often required short-term recalculations of the necessary anchoring forces. Hence, different types of DYWI® Drill Hollow Bars were used. The Hollow Bar System is designed for differing rock mass conditions: The DYWI® Drill Hollow Bar drill bit design and diameter can be easily and flexibly adjusted. Various types maintain the basic dimensioning of the required anchoring forces. Eventually, necessary functional adjustments of the required anchor lengths can be carried out easily using the appropriate couplers.
The opening of the new Omis bypass tunnel is scheduled for the end of 2012.