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Sv. Rok Vehicular Tunnel

BASIC INFORMATION


Employer:

Hrvatske autoceste, d.o.o., Zagreb

Location:

Sv. Rok – Maslenica Section in the central part of the Split-Zagreb
Highway running through the Velebit Mountain, Croatia

Design:

Institut građevinarstva Hrvatske d.d., Zagreb

Construction Period:

October 1996 – June 2003

BRIEF DESCRIPTION OF WORK:


The SV.ROK Tunnel on the Sv. Rok – Maslenica Section of the Split-Zagreb Highway is currently the longest vehicular tunnel in Croatia.

It is located in the central part of the Split-Zagreb Highway. It runs through the Southern Velebit
Mountain near the area of Tulove Grede where the Obrovac - Sv. Rok Road was constructed in 1832, which road was used as an access to the southern and northern portals.

For construction of this tunnel it was required to perform very extensive preliminaries. They involved
blasting large areas to provide access to the site, repair of 13km long transmission lines and the construction of a highly complex water supply system requiring raising water to 420m. The excavation and support works ran parallel with site arrangements for building material supply. The first
700m of the tunnel were driven with the assistance of a diesel generating set. Thereafter, a normal electric power supply from the repaired transmission lines was secured for the works. The SV.ROK Tunnel was designed to have two tunnel tubes at 35.0m centering. The phased construction was proposed. The difference in height between the entrance and exit portals is 51m while the thickness of the ground above the tunnel averages 450m. The carriageway 2 x 3.85m wide is at 0.4 and 1.5% gradient and 1.5–2.5% crossfall. The clear span is 58.09m2, while excavation face varied between 72.97m2 and 86.21m2 in normal cross-section profile of the tunnel. In niches and turnarounds, the profile amounted to 99m2. The 30cm thick concrete lining was made with CG 30 and provided with reinforcement in its major part.

The works completed under Phase 1 included formation of the right tunnel tube, construction of
four (4) turnarounds and a 1,322m long service tunnel which connects the 3rd and 4th turnarounds of the left tunnel tube. Also constructed were six (6) stopping niches to house transformer substations
to supply the tunnel with electricity, 14 emergency footways which connect the left and the right tunnel tubes and 56 emergency telephone and electrical installation niches.
Work on the 5,661m long right tunnel tube began in February 1997 and ended at the beginning of October 1999. KONSTRUKTOR did the excavation and support work for 3,391.5m long section or 60% of the proposed work. The excavation and transport of excavated material accounted for 750,000m3 of inter-grown material.

The New Austrian Tunneling Method (NATM) was applied in the works because it provided optimal
effectiveness regarding composition of the rock mass, which is featured by a diversity of rock classes.
Excavation was performed in full profile with the exception of rock Classes 4th and 5th where
phased advance was applied. During work for the SV. ROK Tunnel, non-electric detonators were
used for the first time in Croatia which resulted in a higher safety level in tunneling. Primary support for the tunnel excavation was provided in accordance with the Geo-Technical Report which involved
classification of the rock mass and the use of adhesion and expansion anchors, steel arches and plates, reinforcement netting and 5-20cm thick shotcrete layers for support. In addition to standard design solutions, the application of specific solutions for probing cavernous areas was required.

The equipment used in tunneling was adapted to the applied technology of the works. The new equipment supplied for major works included the following:

  • a drilling machine with three (3) booms, 
  • a shotcrete gun,
  • dump trucks for transporting excavated material equipped with a single-axis articulation and purpose constructed for mining works,
  • fans with a capacity of 65 m3/s with frequency-controlled operation.

The tunnel was concreted in 6 and 12m segments behind metal shuttering (Cifa) newly supplied for
this Project. It is suitable for concreting the standard diameter as well as greater diameter components
such as niches and turnarounds due to its expansion by telescoping. Also provided for the works was
the supply of a mobile stone crusher for the manufacture of aggregates from the excavated rock.
The left tunnel tube is 5,682m long. Included under the contract was rough tunneling only. The plans for providing the tunnel lining have not yet been defined. This tunnel tube will be used for redirecting traffic in case of an emergency in the right tube.

Communication between the right and left tunnel tubes is provided by two corridors cross cut in four (4) turnarounds. These passages will be equipped with sliding doors and the intended uses are maintenance and traffic control re-regulation in case of accidents in the Sv. Rok Tunnel.
The material from excavation in favorable geological zones was used for the manufacture of aggregates. Therefore, concrete for the secondary tunnel lining was produced with an admixture of these aggregates. It involved the use of approx. 80,000m3 of CG30. Mention should be made that drainage provided within the fabric of the carriageway in the tunnel accounted for 500mm diameter asbestos-cement drain pipes for the central pipeline and 400mm diameter PEHD pipes for the secondary network. The secondary network is comprised of pipe branches draining large water in-flows from the tunnel flanks. It is designed to collect such water in two (2) onsite water storage tanks providing that surplus quantities would be discharged over the overflow. Mention should be made that this water could be used for drinking because it originates from a pollution-free environment. Also, the fact it runs through Velebit Mountain from a height of 450m provides an efficient filtration.

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