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Project of the Year incl. Renovation (up to €50M)

Lower Otta Hydropower Project

nedre-otta-draft-tube
Nedre Otta Hydropower Project (Lower Otta HPP) is situated on the Otta river, one of the tributariesto Lågen river that further connects to Glomma, which is the longest river in Norway. The scope of works is the construction of an intake structure with a 200 m2 trash rack area and two intake gates, 10.1 km unlined headrace and tailrace tunnel (90 m2), surge tunnels upstream and downstream, Powerhouse 65,000 m3 with15,000 m3 concrete works.

The project consists of 11km of tunnels with a cross section up to 90 m2 (waterway), an underground powerhouse of 65,000 m3 with 2 Kaplan units (90 m3/s each)The project was split into multiple construction and supply contracts and coordinated by the Management and Supervision Team from Hafslund-ECO with support of Norconsult AS as the Owners Designer and Technical Advisor.

The project was based on a Virtual Design and Construction (VDC) process where a “digital twin” was established with input from all disciplines and suppliers. The construction was performed directly based on the BIM without production of 2D drawing. The underground works (tunnel and caverns) were preformed in a very efficent manner. Skanska utilized two Atlas Copco XE3 jumbos with 3 booms for the tunnelling works, drilling 5.2 m rounds to 2/8 full cross section. The loading was done with a 51
ton Cat 988. Transportation of the tunnel muck was performed with Cat 772 trucks with a maximum payload of 51.6 tons. At the maximum they had 6 trucks in operation at the site. In practice, there was one set of dump trucks that served both tunnel fronts. They achieved (slightly better than planned) average production rates 55 m/week with production of up to 68 m/week in some weeks for the headrace and tailrace tunnels with cross section of 90m2.

Project of the Year incl. Renovation (up to €50M)

FEDRO’s Tunnel Renovation Method – renovation of a non-reinforced primary lining using night shifts while keeping all traffic lanes open during the day

3-final-state
This project consists in the removal of part of primary lining, installation of drainage & sealing systems, final lining with self-compacting concrete, construction of verges incl. drainage, renewal of road surface, installation of electrical equipment.

To secure the availability and usability of the motorway network, the Federal Roads Office (FEDRO) developed new solutions for the renovation of road tunnels while keeping them open to traffic, and initiated an innovative project. Completely replacing the primary lining could not be regarded as a standard solution because the secondary lining could not guarantee stability and the demolition work could endanger road users. The solution that was ultimately considered was to partially remove the primary lining,install drainage and sealing systems and then construct a new final lining.

The stability of the weakened arch could be secured using temporary rock bolts, and traffic diversions would only take place at night when work was being carried out in the tunnel.

The new arch of self-compacting concrete in tunnel T3 was constructed in a single step and is designed solely to provide the necessary stability. To maintain two-lane traffic during the day, aspecial tunnel formwork had to be conceived. For this project, two sealing systems were tested and compared: conventional synthetic sealing membranes and a sprayed sealing system.