3 THE STØLSDAL TUNNEL 3.1 Project Description

At the Ulla-Førre hydropower project a 7.8 km diver-sion tunnel was bored with a 3.5 m TBM, as were 4 penstocks of about 150 m each. In addition, two intake shafts with a diameter of 1.4 m and lengths 260 and 300 m were raise drilled.

3.2 Geology

Based on sampling and laboratory tests, the rock was characterised mainly as massive and fine to coarse grained gneisses with only a faint extent of foliation.

The drilling rate index (DRI) ranged from 40 to 60, i.e.

low to high, but mainly in the high area, which indica-ted good boreability. The bit wear index was in the range of 25-35, indicating low to medium abrasiveness of the rock.

The assessed weak zones were expected to require heavier rock support works than normal for TBM tun-nels. As a conclusion, it was considered feasible to ex-cavate the tunnel with a TBM at a lower cost than con-ventional Drill & Blast excavation.

3.3 Equipment selection

When going for such a comprehensive job in hard rock, it was of vital interest to have guarantees from the TBM manufacturer linked to the rock parameters for boreability and cutter lifetime from the Norwegian Institute of Technology (NTH). This was accepted by the manufacturers, even though the NTH-index was not a well known standard at that time.

The TBM was bought from Robbins. The most impor-tant machine specifications were:

• diameter: 3.5 metres

• cutters: 27 15.5’’ including 2 double centre cutters (four rings)

• nominal thrust force: 18.2 tons per cutter

• stroke: 1.25 metres

• torque: 58 tons m.

• rotation rate: 10 rpm

• mean ring track distance: 6.5 cm

• weight: approx. 92 tons

The reason why the TBM diameter of 3.5 m was pre-ferred to 3.0 m diameter, was to give retain the possi-bility of continuing the tunnelling with conventional methods. If further boring should turn out to be impos-sible and had to be terminated, the loss would not be too high, since the total price was not much higher than for a 3.0 m machine.

3.4 Experiences

The achieved rates of advance and cutter lifetime for this project, reflect the hard, massive and abrasive rock mass which was encountered. The rock mass properti-es were indeed at the limit of what had been experien-ced within hardrock tunnel boring. Hence, the econo-mical benefit from the choice of TBM excavation in this particular case, was marginal. However, useful ex-perience was obtained, particularly in terms of identi-fying rock mass properties which were essential in the improvement of the prediction models for advance rates and cutter lifetime.

The following table shows some of the production data for this project.

Table 2. Experienced production data for the Stølsdal hydropower tunnel.

Maximum weekly advance,m 120.8

Average weekly advance,m 67.1

Maximum advance pr. shift 20.4

Net penetration rate, m/hour 1.45 - 2.80 Time consumption, boring 40.2% (of total) Time consumption, cutter change 21.6% (of total)

The basis for prediction of cutter wear and advance rates, were the index parameters DRI and BWI (dril-ling rate index and bit wear index) obtained from labo-ratory testing on rock samples collected at the surface along the tunnel. These prediction procedures proved to be inadequate as a tool for characterisation of rele-vant input data for the assessments for tunnelling.

Variations in the jointing characteristics of the rock mass turned out to be the most governing geological feature.

4 THE IVAR WATER TREATMENT PROJECT, STAVANGER

4.1 Project Description

IVAR is a joint venture of several municipalities in the northern part of Jaeren in Rogaland County, south of Stavanger. The organisation was responsible for buil-ding a transportation system and a treatment plant for sewage water. The plant is situated approximately 10 km west of the city centre of Stavanger. The system will serve an equivalent to 240,000 persons, and is de-signed for a dimensioning water flow of 1.5 m³/s, and a peak flow of 4.0 m³/s.

The transportation system includes an 8.1 km tunnel from the city centre to the treatment plant, as well as a 4.1 km outlet tunnel from the plant to the sea.

4.2 Geology

The tunnels are located entirely inside an allochtonous unit in the Caledonian orogeny consisting of sediments with medium to high metamorphic grade. Phyllite and micaschist are the dominating rock types. The phyllite showed significant variations in mineral composition and structures. Frequently it appeared as a greyish gre-en, fine grained micaschist with a strongly foliated curled structure. In local zones the phyllite occurred with well developed planar foliation with slickensided discontinuity surfaces, sometimes with graphite joint fillings.

Inside the phyllite, quartz appeared as a fine grained base structure and as irregular veins. The quartz con-tent normally varied between 10 and 50 %.

4.3 Equipment selection

The contractor chose to purchase a new Atlas Copco Jarva MK12. The most important machine specificati-ons were:

• Diameter: 3.5 metres

• Cutter head

• Effect: 900 kW

• Rotation rate: 12.2 rpm

• Torque: 705 kNm

• Available thrust force: 6,350 kN

• Stroke advance: 1.5 m

• Engines: 4 x 225 kW

• Gripper force: 18,870 kN

• Gripper configuration: T-shaped, front and rear

• Capacity for muck handling: 6 m tunnel per hour

• Machine weight: approx. 160 tons

• Cutter diameter: 413 mm

4.4 Experience

The boring of this tunnel turned out to be a major suc-cess, both in terms of achieved advance rates and im-proved cutter technology.

The phyllite turned out be extremely variable in terms of abrasivity. Hence, extremely high degrees of cutter wear were experienced. This was explained by the rare type of phyllite which was encountered in parts of the tunnel. This abrasive phyllite consisted of quartz grains in the clay fraction. «Normal» phyllites, with high content of clay minerals, were interbedded with the quartz phyllite, giving rapid changes in ad-vance rates and cutter wear. Under these conditions the weekly advance rate varied between 40 and 210 m (2 -4 meters per hour net penetration).

Cutter rings with a heavy duty alloy proved to be fa-vourable for these adverse boreability conditions.

In the «normal» phyllite, record advance rates were achieved several times.

Table 3. Production data from tunnel boring at the IVAR project.

Maximum advance pr. shift (10 hours) 53.7 m Maximum advance per week (106 hours) 350.8 m Average advance per week (106 hours) 159.3 m Average net penetration rate 4.3 m/hour Net penetration rate in «normal» phyllite 3.7 - 4.9 m/hour

Average utilisation grade 37.2%

LITERATURE

Flønes, O. (1981): TBM-tunnelling at The Orkla-Grana Hydropower Project. Norwegian Tunnelling Conference, Oslo, 1981 (Norw.)

Holen, H. (1982): Fullface and raise drilling in hard rock at The Ulla-Førre Hydropower Project.

Norwegian Tunnelling Conference, Oslo, 1982 (Norw.)

Larsen, S. I. (1983): TBM-tunnelling at Mosvik Hydropower. Norwegian Tunnelling Conference, Oslo, 1983 (Norw.)

Asting, G. (1990): North Jaeren central sewage treat-ment plant in rock. Norwegian Tunnelling Conference, Oslo, 1990 (Norw.)

1 INTRODUCTION

Meråker is located 80 km east of Trondheim. Five small hydropower stations were built in the years 1890 to 1915 to provide electric power to the Meraaker Smelter. In 1987 it was decided to upgrade and replace four of the generating facilities, increasing the annual output from 200 GWh to 590 GWh.

Fig. 1 Overview of the Meråker Project 2 TIME SCHEDULE

The construction started in September 1990, and the power plants, tunnels and dams were commissioned 1994. By the end of 1992, all 44 km of tunnels had been completed, approximately nine months ahead of schedule.

3 CONTRACTS

The client, Nord-Trøndelag Energy, invited bidding, and the civil works were divided into two contracts:

The Tevla Power Station contract including 17 km of tunnels and two rock fill dams, was signed with the VSF-Group, a joint venture consisting of A/S Veidekke and Selmer A/S.

The Meråker Power Station contract with 27 km of tunnels, was awarded to Merkraft, a joint venture con-sisting of Eeg-Henriksen Anlegg A/S and A/S Veidekke.