Blasting milestone for Bergen road tunnels 06 Apr 2017

Final breakthrough success is achieved in Norway on the first of the major road tunnels for the E39 coastal highway near Bergen. Breakthrough completed the 1.4-km long twin tube Skogafjell Tunnel located at the southern end of the chain of E39 tunnels being constructed for the national roads authority Statens Vegvesen between Svegatjørn and Rådal, to the south west of Bergen.

Main road tunnelling at Skogafjell Tunnel

Excavation of about 12.5km of the 27.8km of tunnelling on the E39 Svegatjørn-Rådal project brings excavation to about the halfway mark.

Challenges have included high water ingress on Skogafjell Tunnel and varied rock and fault zones on the longer Lyshorn Tunnel, explained Lawrence William Nilsson, the client’s geologist for the southern lot of tunnels when contact by TunnelTalk.

E39 Svegatjørn-Rådal scope

Tunnelling began in early 2016 on the two main South and North tunnelling packages for the Svegatjørn-Rådal E39 improvements.

The South (K10) contract involves 23.1km of main drill+blast excavation, comprising the 1.4km twin-tube Skogafjell Tunnel, the 9.2km,twin-tube Lyshorn Tunneland, two non-road tunnels – a 1.7km x 22m² water tunnel at Hamre and the 300m long Tverrslag mail access tunnel (Fig 1).

Fig 1. E39 road tunnels near Bergen

The North lot includes tunnels that link the E39 into Bergen and to the city’s airport. The key tunnels are the Rå and Sørås Tunnels that include tunnel crossings and junctions (Fig 2). The package also has a 1.1km long water tunnel, connecting to Nordås lake and includes the portal at the north end of the Lyshorn Tunnel.

Consultants providing services to the project include Norconsult, providing design work; Sweco, looking at tunnel stability; and, Multiconsult, performing environmental work.

South lot progress

Veidekke is the contractor on the South lot and is using Atlas Copco 3-boom jumbos for the excavation, said Nilsson. Excavation began on the Skogafjell Tunnel in February 2016 and started at Lyshorn Tunnel in April 2016. Across the major works and the smaller tunnels on the lot, Veidekke has had up to 11 faces under excavation, said Nilsson.

The tunnels have the standard T11.5 cross-sections, with final lining of cast concrete at the lower walls and shotcrete in the crown. At regular intervals, the section widens to T14.5 profiles and the parallel Skogafjell Tunnel tubes are linked by five cross passages, at 250m intervals.

Last breakthrough at twin-tube Skogafjell Tunnel

Progress has varied across the tunnels, ranging from 50m/week/face down to 10m/week, according to Nilsson. Work at some locations has required more grout injection than expected. The required limitation on groundwater inflow is 20 litres/min/100m but has been much higher at times. “We had a lot of water inflow in Skogafjell,” said Nilsson, at up to 400 litres/min/100m, or 20 times as much.

Working from each portal, Veidekke achieved first breakthrough after almost a year of tunnelling, in mid-February 2017 and at the end of March in the parallel tube.

The longest Lyshorn Tunnel involves a total of 18,370m of main T9.5 profile excavation, widening to T12.5 profiles, and with several cross passages.

The geology beneath a cover of 10m-250m, consists mainly of gneiss, gabbro and amphibolite with quartz-rich sandstone, mica-schist, marble and green slate. The tunnel intersects more than 60 faults zones, five of which are considered major regional faults.

Advancing the Skogafjell Tunnel

Groundwater inflow is required to be limited to 5 litres/min/100m for long stretches of the Lyshorn twin tunnels, noted Nilsson.

Veidekke started blasting on the Lyshorn Tunnel in April 2016 and is working on six headings, said Nilsson, two from the south portal and four from an intermediate adit. Work at the northern end, beside and well below an underground cavern complex used for quarrying and waste disposal, is for preparation of the portal structure by the North lot contract only.

By the end of March, Veidekke had completed almost 7km, or about 38%, of the Lyshorn excavation.

North lot progress

Contractor on the North (K11) lot is Implenia Norway. By the end of March, a total 2,746m of excavation had been completed in the complex layout, or almost 52% of the total 6,605m of road tunnelling to be blasted.

Fig 2. Route and progress of Rå & Sørås tunnels

Focus on Bergen and on Norway

Bergen is host city of international tunnellers for the WTC-World Tunnel Congress 2017 in June.

Other key tunnel projects in the Bergen area include TBM boring at the New Ulriken rail tunnel and both the rail tunnel project and the E39 Svegatjørn-Rådal tunnels will feature among technical excursions for WTC delegates.

Other key projects in construction or in late stage planning in the mountainous country, include: advanced preparations for the long Romsdal subsea road tunnel to the north of Bergen; the long TBM Follo Line rail tunnels near Oslo; and, blasting for current urban and subsea road tunnels in the Ryfast scheme in Stavanger, and the world-beating Rogfast subsea road tunnel that is soon to start construction.

The WTC event is hosted in Norway by the Norwegian Tunnelling Society, Norsk Forening for Fjellsprengningsteknikk – NFF. Registration to attend the event is open, at www.wtc2017.com.