Svartisen Hydroelectric Project

Project Overview

Approximately 99 percent of the total electric power in Norway is derived through hydroelectric projects, making these large schemes a key part of the country’s infrastructure.   Norway’s use of hydropower dates back to 1877, when its first hydro project reached completion. By 1990, Norway had more than 170 underground hydro facilities comprising approximately 3,500 km (2,175 mi) of tunnels throughout the country. Owner-contractor Statkraft plans, builds and operates all central government hydropower plants, which produce 28 percent of Norway’s total annual hydroelectric power output. The Svartisen project, located just north of the Arctic Circle, consists of 46 shafts connected to 40 km (25 mi) of 3.5 m (11.5 ft) to 5 m (16.4 ft) diameter tunnels.  The tunnels are designed to collect and carry water from the glacier-covered Trollberget Mountains to Lake Storglomvatnet, the project’s reservoir. From there, the water is fed through a 7 km (4.4 mi) headrace tunnel to a sea-level power plant at Kilvik, Holandsfjorden. There are also two gutter tunnels to catch additional water from hillside inlets.

In 1988, Statkraft contracted Robbins to supply five machines to bore 57 km (35 mi) of tunnel for the new Svartisen Hydro Project, or 62 percent of the tunnels needed for the project. Two of the machines were veteran TBMs, 8.5 m (27.9 ft) and 3.5 m (11.5 ft) in diameter, and bored 7.3 km (4.4 mi) and 15.4 km (9.6 mi) of tunnel, respectively. Also employed on the project were three new Robbins High Performance (HP) TBMs capable of high thrust loads up to 312 kN per 19 in (483 mm) cutter.  These first HP TBMs were revolutionary machines that paved the way for hard rock tunneling as we know it today.

Geology

The area’s geology consisted mainly of mica schist and mica gneiss (80 percent); metasandstone (pure quartzite), granite and granitic gneiss (13 percent); and limestone and marble (7 percent). The limestone beds varied in thickness from a few centimeters to more than 100 m (328 ft). Caves and underground drainage features were evident from the surface as well. The unconfined compressive strength of the Svartisen geologic formations varied from 100 MPa to more than 300 MPa (43,500 psi). Also, the steep, uneven topography caused irregular stress on rock masses which were subject to extreme tectonic and residual pressures. Because stable, hard rock conditions were present in more than 95 percent of the tunnel, no lining was required.

High Performance TBMs

All three HP machines were equipped with 19 in (483 mm) diameter disc cutters, which were developed by Robbins for the Svartisen Project. In addition to the larger cutters, the machines were built stronger than standard TBMs and had tri-axial main bearings to withstand higher loads. The two 4.3 m (14.1 ft) diameter HP machines weighed 262 metric tons (289 US tons) and supplied 2,345 kW (3,143 hp) of power to their cutterheads, allowing each machine to reach 9,048 kN (2,034,071 lb) of thrust at the face. A conversion kit was supplied for one of the machines that allowed it to bore at 5 m (16.4 ft) diameter instead of 4.3 m (14.1 ft) and also added six cutters, bringing the total weight of the machine to 290 metric tons (319 US tons). The third HP machine, weighing 180 metric tons (198 US tons), was 3.5 m (11.5 ft) in diameter and was supplied with 1,340 kW (1,796 hp) of power to the cutterhead giving it a total 7,800 kN (1,753,509 lb) of thrust. The cutterhead featured twenty-five 19 in (483 mm) diameter disc cutters.

In addition to higher penetration rates and advance rates, the new generation of TBMs enabled efficient use of the crew. Each machine was teamed with a back-up system equipped with remote controls and television cameras, and only required a four-person crew per shift – one to operate the machine and load the rail cars, a locomotive operator, an electrician and a mechanic to handle the extension of rail, cables, ventilation and hoses.

Tunnel Excavation

All three HP machines achieved very impressive results throughout the project. The first of two 4.3 m (14.1 ft) diameter machines excavated 6,021 m (19,754 ft) of tunnel between September 1989 and October 1990, averaging 3.8 m (12.5 ft) per hour on its first drive. In its 5 m (16.4 ft) mode, it averaged 2.74 m (9 ft) per hour. The machine had a best day advance of 75.8 m (248.7 ft), best weekly advance of 312 m (1,024 ft) and best month of 1,068 m (3,504 ft) which were all Norwegian records.

The second 4.3 m machine bored 11,861 m (38,914 ft) of tunnel between September 1989 and April 1991, averaging 3.5 m (11.5 ft) per hour. In the process, the TBM set world performance records for machines in its 4 to 5 m ( 13 to 16 ft) diameter size class: best shift of 61.2 m (200.8 ft), best day of 90.2 m (296 ft), best week of 360.5 m (1,182.7 ft) and most material excavated in 24 hours: 1,309 m³(1,700 cubic yards).

The third machine began boring in July 1990 from a junction about 4 km (2.5 mi) from the crosscut area. In May 1991, about 4,700 m (15,420 ft) into the drive, the machine experienced poor ground and water inflows which slowed excavation for about 4 months. However, despite the poor conditions, the machine still averaged an overall advance rate of 3.7 m (12.1 ft) per hour while capturing a single shift record of 55.5 m (182.1 ft).