The last decade has been a good period for the Swedish tunneling industry and tunnels have been constructed for many purposes both in Sweden and abroad.

The Swedish mining industry, which mainly requires underground excavations, has exploited greater depths with an increased need for permanent tunnels. New and deeper mining levels are planned with increasing rock mechanic challenges. The rock stresses increase with depth. Rock burst due to large-scale instability has been observed more frequently. Rock support to stand both high static rock stresses and dynamic stresses from blasting and rock burst are two issues that are studied at our universities in order to facilitate deep mining. The deeper mining activities of LKAB (an iron mineral producer) mean that part of the Kiruna City in the northern extremity of Sweden has to be moved. Planning and preparation work has started. It is anticipated that the city will have to be moved gradually during the next 20 years.

Power thirst
Another and increasing market for tunnelling is the energy sector. Many of our hydropower plants are old and have to be renovated. This will involve changes but also installation of further turbines and enlarging the waterways. This type of tunnelling work always involves careful blasting and intricate excavation in order not to damage the installations. It is thought that this type of work will increase in the coming years.

Building storage for nuclear waste will belong to this energy sector. The nuclear waste management company in Sweden, SKB, has applied to the authorities to build underground storage in Forsmark north of Stockholm. The storage will be situated in Precambrian granitic rock at a depth of 500m and up to 60km of tunnels will be excavated. The design work has already started and it is anticipated that the excavation works will start in 2017.

Rail and road demand
Many tunnels for railways and roads have been constructed the last 10 years, and new projects are planned especially in major cities like Gothenburg and Stockholm. The Northern Link of the ring road around Stockholm is under construction in the northern part of the city. In total 11km of tunnels with motorway standard will be opened by 2015.

The Citybanan project under the centre of Stockholm is a railway tunnel with two major underground stations close to existing metro lines and other tunnels. The work is ongoing. There has been a special focus from the authorities and contractors on developing pregrouting technologies in cooperation with the Swedish Technical Universities. Normally, Swedish tunnels are only supported with rock dowels and a thin shotcrete lining. The waterproofing requirements are strict and the allowable ingress of water is in the order of one to 4 litres/min in 100m of tunnel. Pregrouting is one alternative and the other is constructing fully concrete lined tunnels that should withstand the ground water pressure. Pregrouting has so far been a competitive solution compared to the lined alternative.

Hallandsas
The 8.7km long railway tunnel through Hallandsas in the southern part of Sweden is ongoing. The project has met many problems with very severe water ingress and environmental disturbances due to chemical grouting. The geology is a very fractured and water bearing horst. One of the two railways tubes is now complete. It has passed through a 50m wide zone of completely decomposed rock situated 140m below ground water level. In order to pass through with the TBM, the silty zone had to be frozen. The TBM has been reconstructed before excavation of the second tube. Progress is very good and better than planned. As T&TI went to press, 79 per cent of tunnel work is complete. The tunnel is planned to be open to traffic in 2015.

Inbound interest
The good market has encouraged contractors from central Europe to open branch offices in Sweden. Scandinavian contractors such as NCC, Veidekke, Lemminkainen and Skanska have to compete with foreign companies such as Bilfinger Berger, Beton and Monierbau, Hochtief, Strabag, Zublin and Pihl & Son. It has in many aspects vitalised the market and the development of new technology.

The Swedish Rock Mechanic Society is hosting the Eurock conference in May. This is achance to visit Stockholm and its tunnel projects when the city is at its best.