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Olympian task

Vast investment in new underground infrastructure has put Greece on the tunnelling map. Adrian Greeman travelled west from Athens to see new road and rail tunnels being carved through the faulted and tectonic-shattered mountains.

Few countries have as much tunnelling under way as Greece right now.

Economic growth and the freedom to tap Brussels support funds through its European Union membership have led to massive infrastructure growth. And of course the 2004 Olympics are coming.

New motorways and the Athens metro are all generating work. The 680km Egnatia road in the north has 75 tunnels, the longest being 4.6km long. For the Patras-Athens-Thessalonica (PATHE) highway, a 5km immersed tube link is being studied and the just-completed metro is being immediately expanded by another 14km.

But some of the most spectacular and technically difficult work being carried out is on the railways.

Upgrading of the north-south line between Athens and second city Thessalonica will see the line modernised to European strategic standards. Single track is being doubled and the line continuously electrified.

The work will also see completely new sections built to replace the current single track which winds through the mountains at 60km/hr. To achieve this some 35km of tunnel is required.

The largest project is at Kallidromo in central Greece where two parallel single track tunnels, each 9km long, are being built.

However, the upgrading also continues west from the capital to Corinth and eventually on to the western Peloponnese port of Patras. Here the old Peloponnese 1m narrow gauge line is being replaced by twin track standard gauge electrified line, and will be capable of running 200km/hour trains.

It is this section that sees the most challenging tunnelling condition as about 30km beyond Athens the Attica flat land gives way to the Grecian hills and mountains. Several tunnels from 800m to 2km long are needed.

The most difficult tunnel is at Kakia Skalas where a 400m high limestone escarpment plunges into the sea. At this point the recently built PATHE motorway also gives way to a two way national road, winding for 8km around 60degrees slopes.

The project will create a route through the mountain for both new rail and motorway. Twin bored motorway tunnels and viaducts will run 20m to 40m above a single double track tunnel for the railway on a subparallel alignment. Each route has two main stretches of tunnel.

The railway has the 2,380m long S1/2 tunnel and 1,537m long S3 tunnel, linked in the middle by viaduct. Additional lengths of viaduct and embankment complete the western end of the mountain crossing.

Motorway authority PATHE has been seconded to carry out the design work on these tunnels for specially created railway client Erga Ose, which is also building the other new rail infrastructure in Greece.

'It did not make sense to split the design, ' says Dr George Tsifoutidis, a Durham-trained geotechnical engineer with the Erga Ose. Instead, a single £110M contract for the rail and road work was let and work has been under way since January 1999.

Typically for Greece, the four firm Kakia Skalas joint venture has subdivided the work, with experienced tunnellers Aktor and TEV tackling all the higher, larger diameter road tunnels.

Aegek, also highly experienced underground, is working on the eastern end of the parallel S1/2 rail tunnel. Alte, a large general contractor new to tunnel contruction, is handling the easier, western end of this longer tunnel.

Aegek is also constructing the second, shorter and more straightforward S3 section of rail tunnel.

Originally the scheme was designed with three rail tunnels.

Trains were to have entered a 667m long twin track tunnel at the east end and cross a viaduct into a second 420m long tunnel before passing over longer viaducts into the S3 tunnel.

'But after the Athens earthquake in September 1999, the designers became worried about founding high viaducts on slopes up to 70degrees, ' says Tsifoutidis. 'Particularly as there is a fault system passing through here, ' he adds.

Although the fault is last known to have moved 6000 years ago, the first 3km of the alignment was altered to set its course back into the hill to create a single, longer 2,380m S1/2 tunnel, thus also eliminating three viaducts.

But the fault, which runs more or less along the line of the tunnels, is still a significant factor for the tunnelling and creates frequent changes in the rock for up to 60m either side. As a precaution, an extra 500mm is allowed in the tunnels' diameter as they cross the main fault line to allow for a possible future seismic movement.

As everywhere in Greece, faults and shattering in the rock are commonplace due to the major tectonic activity. Rock, predominantly Triassic and Cretaceous limestone, has gone through compression followed by dilation and tension cracking.

Greek tunnellers cope with this often mixed and shattered ground by using conventional drill and blast techniques combined with rock support which varies according to observation and classification of the rock mass. This technique is loosely describable as 'sub-NATM'.

Heavy use of steel sets is the answer, particularly in the S1/2 tunnel, along with mesh, bolts and self drilling Belloni and Dywidag Mai rock bolts. On both tunnels the design gives five combinations of rock support to cope with increasingly severe conditions.

'In all categories we use a CIFA robot shotcreter to apply a steel fibre mix to the walls and crown, ' explains site manager for Alte, Michael Kapnoutzis. He is working on the western end of the S1/2 rail tunnel with two Tamrock jumbos for its face work, which make about 4m a day.

An O&K loader and backhoe clear the spoil which is then transported 6km in Mercedes and Scania trucks to an old quarry. This huge cavity will be landscaped when filled to be turned into an amenity for the local town of Megara, an ancient community dating back to 1400BC.

At the eastern end, the most difficult part of the S1/2 rail tunnel, water draining through the rock discontinuities has left the large solution features. These voids, often man-entry size, are typically filled with loose, weathered limestone and rock.

However, the effect is localised, perhaps because the immediate rock formation drains straight through to the sea and the whole rocky headland is dry, even by Greek standards, due to a very low water table.

In general the Cretaceous limestone structure has large blocks, normally over 1m on each side. These are sometimes embedded in softer material.

'Blocks frequently act like wedges or keystones and if they are shifted and fall they allow a mass of other material to follow, ' says Tsifoutidis.

In general the strategy is to keep as much rock in place as possible using spiles through the blocks, and the arches. Most of five categories of support also use 5m long grouted passive anchors and 4m long Superswellex rockbolts in the crown.

Putzmeister and Normet shotcrete units are used to apply the 50kg/m 3steel fibre shotcrete at between 100mm and 250mm in thickness.

Contractor Aegek started with drill and blast excavation techniques. But according to Tsifoutidis: 'It has proved impossible for most of the work because the blast gases simply escape through the rock voids. We did try grouting but after losing some 90t of grout we concluded it was simply going straight through to the sea.'

Aegek is now working carefully forwards 1m at time using a hydraulic breaker, a Rammer mounted on a Cat 245 excavator.

The best progress on a top heading is about 3m each day. A single bench follows some distance behind, explains the contractor's engineer at the site, James Siampos.

The second S3 tunnel westwards is much more straightforward and here Aegek is achieving progress of up to 6m a day using a Tamrock 206 jumbo on the eastern face.

In this region, the Triassic limestone has a much smaller and tighter block structure although it also has fault and tectonic shattering discontinuities.

Caterpillar wheel loaders and articulated trucks do the mucking out on both tunnels along with Mercedes highway trucks.

All the tunnelling is expected to be completed in 2003.

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