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PASS THE PORT

GEOTECHNICS OF TRANSPORT

Finland's capital is expanding seawards with the building of a new harbour.

Damon Schünmann reports on tunnelling for its underground railway link.

The Finnish capital Helsinki is seeing construction of a third harbour to amalgamate freight transfer from its two older facilities. Vuosaari, the new harbour, is being built partly on the site of an old shipyard and partly on 90ha of reclaimed land.

Fill materials - red granite and black gneiss - will be sourced from drill and blast excavations at nearby tunnelling for a freight rail link to the mainline network.

The tunnelling will allow the line to pass under urban infrastructure and a conservation area east of the city. The new railway, which is expected to handle about 10 trains a day in either direction, will run through two tunnels for a total of 14km of its 19km length.

The E65M (£45M) allocated to the railway excavation work is split over six contracts, TU1 to TU6 (see box).

YIT Infra Construction, which claims to be Finland's biggest contractor with 22,000 employees based mainly in Sweden, Norway and Russia, won two of the six contracts. Site engineer Ari-Pekka Manninen says: 'We are doing about 50% of the tunnel and are blasting 240,000m 3 for TU5 and 170,000m 3 for TU2.'

Skanska Group won TU1, the section nearest the harbour, which is largely overland with only a comparatively short 0.5km section of rail tunnel.

Skanska has also built a longer stretch of twin bore road tunnel as part of TU1. The 1.7km road tunnel, completed in February, was included under a £16M slice of funding and will form part of a new route linking the harbour with the national motorway network.

TU2 to TU6 are for railway tunnel sections.

As soon as it leaves the harbour in the south of the project area, the railway line will cross a bridge over Porvarinlahti Bay. Then it will run under Labbacka Natura 2000 (the conservation zone) for about 0.6km in the first tunnel.

The second tunnel will begin just south of the Porvoo motorway and extend to Savio where it will join the main line. The route will run underground to minimise environmental impact and disturbance.

The largely impermeable ground is good for tunnelling in terms of water ingress. 'There is only 7080l/m on our TU5 3.5km section which is very good, ' Manninen says.

The client for the overall scheme is Vuoli-Projekti, a consortium of the Port of Helsinki and the Finnish maritime, road and rail authorities.

The project includes a further £17M funding for superstructure work and £7M for operating systems.

YIT is using the latest Atlas Copco plant to build the tunnels, including cutting edge rock drilling and grouting rigs. Atlas Copco's key account manager Sami Niiranen says: 'YIT are doing TU2 and TU5 with equipment and techniques such as Forcit emulsion-based foam explosives, that make this one of the most advanced construction sites in Finland.' He says this is the first time this explosive has been used for construction in Finland.

On the £9M TU5 contract, YIT is burrowing outwards in two directions simultaneously from a roughly central access ramp.

'The first part of the construction process is blasting the arch then blasting drainage channels either side of the tunnel' says Manninen.

'We then rock bolt the arch before shotcreting it with a 100mm thick lining. Pipework for the drainage channels and rails will be installed later, although not by us.

'Sometimes we need a bit of safety shotcreting and rock bolting [immediately after blasting] in areas of bad ground to prevent possible rock falls before we do the final bolting and shotcreting.'

Vertical access shafts, about 3km apart, ventilate the tunnel at either end of TU5, 40m deep at the south end and 20m at the north. These vents will also act as escape shafts for the final tunnel.

Manninen says the big challenges for YIT surround the use of new techniques and equipment. 'We have many brand new machines that had not been seen anywhere else in the world and these needed newly trained operators.

'There is also a new charging system being done by a modified Normet rig. We needed to develop it as there wasn't anything in Finland that could work with remote control for the operator and data logging to monitor quantities of emulsion used.

'The second big challenge is a very tight schedule that only allows one spare week over a two-year programme. This took a lot of planning but we are slightly ahead of schedule.

'To keep things on track we have to know exactly what is happening underground, so we use VHF radios which is new for construction - they are more commonly used in the mining industry. We only use one channel, so we all hear everything - this helps with safety as well.'

For drilling, YIT is using an Atlas Copco WL4C30 equipped with COP 3038 rock drills. The Swedish manufacturer says the four-boom rig with the 3038s attached is the fastest rock drilling machine in the world, and the first Atlas Copco to feature four booms.

'We can do between 3m and 3.5m per minute [with 51mm diameter drill bits] which is good going, ' says Manninen. 'Before we were using an older XL3 1838, a three boom rig fi tted with COP 1838 rock drills, and the most we could manage was 2m to 2.5m.'

The manufacturer says the rig is particularly efficient as all four booms can be supervised by one operator. The Helsinki site was the world's fi rst to have one of the new machines when it arrived last year.

During GE's March site visit the machine was drilling to 6.2m depth, but an operator working from a basket can add more rods when drilling to 20m is required.

Grouting is being done by a machine specially built for the project. The Unigrout EH400-100135WB truck is the result of a twoyear design process between YIT and Atlas Copco.

'It has four pumps and is the first rig of this size to have eight grouting lines, ' says Niiranen. 'This means an operator can be grouting four lines while the other four are being prepared.'

YIT also built the rail yard in the harbour and did surface blasting of a hill in preparation for a business park there.

The contractor is due to complete the £7.7M TU2 contract next March and TU5, which began in December 2004, should fi nish in February 2007. The harbour railway line is scheduled to open in 2008.

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