The D8 Adriatic Highway section between Split and Omiš is one of the most congested roads in Croatia, with an average daily traffic of 11,000 to 15,000 vehicles. As a tourist destination, during the summer these numbers rise to an astonishing 55,000 vehicles per day, which is far exceeding the capacity of this two-lane highway. In response to this issue, Hrvatske ceste d.o.o. initiated the Omiš bypass construction project in 2007., which will ultimately bring significant traffic relief to the city center of Omiš and reduce summer and tourist season congestion.
The Omiš bypass is part of the multimodal platform project for the Split agglomeration and one of the largest infrastructure projects in the Split-Dalmatia County, with a total value of 90 million euros where Institut IGH provided services for supervision. The project included the construction of new roads with a total length of 3.7 km, access roads to the tunnel with a total length of 544 meters, the construction of the new Komorjak Sjever tunnel with a length of 600 meters, the Omiš tunnel with a length of 1470 meters, the Brzet tunnel with a length of 220 meters, and the construction of a bridge over the Cetina River with a length of 225 meters.
One of the project's unique features is the road fork located in the Komorjak Sjever tunnel, which is part of the connecting road to the state road DC70. The tunnel will accommodate two-lane traffic, with a road width of 7.10 meters and a height of 6.85 meters measured at the tunnel crown. The tunnel was constructed using the NATM technology, the most advanced tunneling method available.
Directly from the tunnel heading east, one reaches the Cetina Bridge. The bridge is a continuous beam span of 30.00+152.00+30.00 meters, based at the ends of the tunnels Komorjak Sjever and Omiš, with the largest span of 152 meters between two supports. The slender structure of the bridge, a closed steel box of variable height (2.50 m - 6.50 m), fits seamlessly into the environment without obstructing the view of the Cetina canyon. For the construction of the bridge, 1280 tons of steel was used. The assembly and erection of the bridge halves were conducted in the Komorjak Sjever and Omiš tunnels, with the final joining completed 70 meters above the Cetina River using special hanging scaffolds.
From the Cetina bridge, one immediately enters the next tunnel called Omiš, which is 1470 meters long. The tunnel begins at about 70 meters in height, on a steep cliff above the Cetina River, and runs east and northeast of the old town center of Omiš through the slopes of the Omiš Dinara massif. The tunnel is initially straight, then in a right curve, followed by another straight section and a right curve, and finally a left curve. The total road width in the tunnel is 7.1 meters, with a maximum clear width of 9.9 meters and a clear height in the center of the road of 6.85 meters. The road structure is 55 cm high, consisting of a wearing course (3.5 cm), a binding layer (5.5 cm), a bituminous base layer (7 cm), and a mechanically compacted layer (40 cm). Additionally, two evacuation tunnels were constructed within the existing Omiš tunnel, measuring 339 and 205 meters in length, respectively.
To complete the bypass and the Split – Omiš highway one smaller tunnel was needed. Tunnel Brzet, 220 meters long, which connects the expressway to the Adriatic Highway DC8. The tunnel is initially in a right curve, ending in a left curve, with the grade beginning to decline and continuing in a convex curve to the end of the tunnel. The road width, maximum clear width of the tunnel tube, and clear height in the center of the road are the same as in the Omiš tunnel, as are the road structure, drainage, and waterproofing. The portals are formed with a frontal wall that laterally connects to the embankment wall, and as it is a smaller tunnel, no longitudinal ventilation is planned.
We congratulate the investor, Hrvatske ceste d.o.o. on another successful project, as well as the contractors Viadukt d.d., Strabag d.o.o. and our amazing team of experts in the field of supervision. It is an exceptional honor for us to provide our services on yet another significant infrastructure project of great importance for the Republic of Croatia. We look forward to our continued partnership and collaboration.
