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Greece is the word

Greece has sun, sea, sand… and an awful road fatality record. The new Corinth to Kalamata motorway − with its five tunnels − should help improve statistics. Jessica Rowson reports

Motoring around the Peloponnese, mainland Greece’s southernmost region, it is not hard to see why the country’s national accident statistics are so bad. The beautiful mountainous scenery lends itself to treacherous winding roads with hairpin bends and even along the coast, where the topography is flatter, driving is hazardous.

Now the Greek government is taking a hard look at its highways and pumping serious investment into its infrastructure. Most advanced of its schemes is the 185km long Corinth to Kalamata motorway whose development includes upgrading an existing motorway and many kilometres of new build.

“The new route will bring major benefits. At the moment there are twisting sections, HGVs crawling along and volumes of traffic that can be horrendous at Easter and in the summer.”

Phil Shuttleworth, Aecom

A design, build, finance, operate & maintain contract was awarded to concessionaire Moreas in January 2007. Moreas comprises Greek construction firms Elliniki Technodomiki, Pantechnikis and Intracom Holdings. It in turn has given design and construct duties to its own subsidiaries – Aktor, Pantechniki and Intrakat respectively.

Of its many structures, it is the motorway’s tunnels that have dominated construction so far. These are being built to remove tight bends, to ease traffic flow and – crucially – to greatly improve safe driving conditions.

Independent engineer for the project is Aecom. “The new route will bring major benefits,” says Aecom associate director Phil Shuttleworth. “At the moment there are twisting sections, HGVs crawling along and volumes of traffic that can be horrendous at Easter and in the summer.”

His comments are amplified by the general manager of concessionaire Moreas SA George Sirianos: “Heavy vehicles crawl up the hills, people get frustrated, try to overtake and then crash. There are lots of accidents.” Greece’s motorway projects (see map) are “absolutely necessary”, he says, and not just for safety. “New motorways are crucial also for economic development and tourism.”

Work began on site in March 2008. The motorway route runs from the north east corner of the Peloponnese peninsula at Corinth, diagonally down to Tripoli (all upgrade) and then onwards (all as new build) to Lefktro where it splits – one branch extending to olive exporting Kalamata on the coast, the other to the ancient city of Sparta.

Corinth to Tripoli

The motorway’s first section, from Corinth to Tripoli, involves upgrading an existing motorway.

This was constructed between 1989 and 1994. Before that, the road connecting Corinth to Tripoli was a very low quality two-lane road. This still exists but is now only used by local traffic.

The then-new motorway made transportation much faster, easier, and safer, and led to increased development of Tripoli. Now more modern motorway standards are being applied. The motorway is being widened to include an adequate hard shoulder, which means extensions to existing structures to accommodate the widened cross section.

“It’s a lot of work to create what may be only one or two metres extra width,” says Aecom associate director Phil Shuttleworth. “You have to widen bridges, replace side drains and so on.”

 

Altogether five major tunnelling schemes are under way, several nearing completion. Two new tunnels have been built as part of the motorway upgrade works between Corinth and Tripoli: the Neochori tunnel and the Sterna tunnel, both approximately 750m long. These will take the motorway through the shoulder of a mountain, removing sharp bends where there have been fatalities.

Two tunnels are also under construction along the new section of motorway between Tripoli and Lefktro: the Kalogeriko tunnel and the Rapsomati tunnel. These are intended to ease the alignment of the new road where it cuts through ridges of high ground.

The fifth tunnel duals the existing single bore Artemission tunnel, which is 1.35km long and at an altitude of 750m. Each bore will carry traffic in one direction. The original tunnel was built around 15 years ago and the idea to dual it is not new. A second bore was started at one time but stopped after around 30m.

Different stages

All five tunnels have been built using a similar process but are all at different stages. They are being excavated in two phases. Phase A involves creating a semi-circular arch for each tunnel’s roof which is carried out by drilling and blasting 3m lengths at a time. The phase B bench is then excavated conventionally. For Phase A, holes are drilled in semi-circular lines concentric to the centre of the arch using a drilling machine with two drill drives.

The holes are at around 500mm to 900mm centres and penetrate about 1m to 3m into the rock. They are packed with explosives which are then set off with an electronic delay of around 1.5 seconds, starting off at the centre and moving outwards. “The inner holes are fired first and the blast moves progressively outwards to the profile of the tunnel. It would damage the rock mass and create considerable overbreak if all the holes were fired at the same time,” says Shuttleworth.

“The inner holes are fired first and the blast moves progressively outwards to the profile of the tunnel. It would damage the rock mass and create considerable overbreak if all the holes were fired at the same time.”

Phil Shuttleworth, Aecom

The roof vault is then stabilised initially with sprayed concrete and mesh before 4m long, 25mm diameter dowels are installed perpendicular to the rock surface to increase the structural stability of the rock. The length and number of the dowels is increased in weaker rock. Additional sprayed concrete is then applied to give a thickness of 250mm to 350mm depending on rock classification.

“Standard concrete is used with an accelerator which minimises rebound and hardens in under an hour,” says Shuttleworth. In the areas of weaker rock, arches are installed in addition to the sprayed concrete. In Rapsomati for example, Moreas JV found that the tunnel was overbreaking – more material was coming away from the tunnel walls than the contractor wanted. By using arches to control the excavation it avoided further overbreak.

Existing cavities were encountered while excavating Neochori. Arches helped to support the rock and prevent further deterioration while solutions were devised. The contractor subsequently went back and filled the holes with concrete and built up the side of the tunnel – which all cost time and money.

Depending on ground conditions and rock classification, the arches are spaced at anything from 700mm to 3m, using either a prefabricated lattice of reinforcing steel or rolled I-beams. The rolled I-beams are used in the weakest ground conditions. The arches are erected straight away and are fully embedded in the temporary lining.

“The whole mass is very stable as the sprayed concrete adheres to the rock and in addition it is fixed by the rock dowels,” says Shuttleworth. “So when the Phase B bench [in section, the rectangle below the Phase A semicircle] is excavated, the temporary support of the roof remains intact.”

Any steel supporting arches present are then extended to reach the floor of the tunnel before applying the sprayed concrete and mesh to the walls of the Phase B excavation to complete the temporary support. If the rock is found to be very weak, as was the case at the entrances to the Artemission and Kalogeriko tunnels, the excavation is only advanced by 700mm to 1.5m per shift instead of 3m.

Support and stability

Sometimes roof sections of the tunnels in very weak rock have had to be strengthened by forepoling, where the perimeter of the tunnel outline is reinforced with scaffold-like poles. These are grouted in to give support to the excavation and temporary stability while tunnelling. This technique was used in the Artemission tunnel during excavations from the northern portal, over a length of 30m.

Each tunnel’s final concrete lining will extend 10m to 15m beyond its portals to create shields to protect against  falling stone. “Typically the rock is not as good close to the surface at the portal areas as it is in the middle of the mountain,” says Shuttleworth. In the vicinity of the Sterna and Neochori tunnels the rock is a dolomitic limestone which has provided aggregate for concrete and the motorway’s asphalt pavement. South of Tripoli there is a mixture of limestone and a thinly layered sedimentary rock called flysch. In this area, the tunnels are still drill and blasted but the material is slightly softer.

Once the tunnels have had all the materials removed, work can begin on the permanent lining.

“The contractor prefers to complete the tunnel excavations before starting the concrete lining and in any case you can’t excavate and construct tunnel linings at the same time using the same tunnel portal.”

Phil Shuttleworth, Aecom

“The contractor prefers to complete the tunnel excavations before starting the concrete lining and in any case you can’t excavate and construct tunnel linings at the same time using the same tunnel portal,” says Shuttleworth. “Once you’ve hauled all the excavated rock out, you can start on the lining.”

Excavation is now complete in the Neochori and Sterna drives and construction of the permanent concrete lining is under way in both tunnels. First waterproofing plastic membranes are being installed against the tunnel walls. It is intended that water percolating through to the structures will run down the back of the membranes and into slotted drain pipes located at the base of the tunnel walls. These slotted pipes discharge every 25m into a central drainage channel.

Short dowels are installed to act as a support for the final reinforcement which is fixed well ahead of concreting. “When the concreting train and shield move in, the lining is poured in 12m bays,” says Shuttleworth. “The shield moves one section each day and having the reinforcement placed well in advance means better productivity.”

He says that if the reinforcement was installed when the shield was already in place, only a few people could work around the equipment. “There would also be a worry about the rebar moving during concreting,” he says. Concrete lining is currently being poured in the Neochori tunnel – pumped to a thickness of 400mm to 500mm behind the steel formwork sections.

Project details

The Corinth to Kalamata highway project is being built by Moreas JV – a joint venture of Greek contractors Aktor, Pantechniki and Intrakat under a design & construct contract awarded by Moreas SA, the concessionaire for the scheme

  • Independent engineer for the project is Aecom
  • Value of design & construct contract: £738M
  • Start date: March 2008
  • Construction stage complete: August 2012
  • Concession contract runs for 30 years to March 2038

 

On the Kalogeriko and Rapsomati tunnels, work is still be carried out on their Phase B excavations. Artemission tunnel’s second bore is in the final stages of construction, however. The permanent concrete lining has been completed and now work is concentrating on creating concrete trench walls for cables and fire fighting services. The road was paved at the beginning of August ready for opening the tunnel to traffic before Greece’s 15 August national holiday.

By staggering the work on the tunnels, resources can be moved from one tunnel to the next as phases finish. This well honed operation has the feel of a tunnel production line, but problems have arisen along the route to put a spanner in the works.

“Typically the structures are constructed first and then the earthworks and road pavement construction take place,” says Shuttleworth. “If organised well, in a good sequence, all activity progresses naturally. The sequence can be broken up, of course. For example, if land is not released to the contractor on time or a new archaeological site is found.”

“Our whole motorway project is high risk in archaeology terms”

Phil Shuttleworth, Aecom

The Peloponnese is rich in ancient history. “Our whole motorway project from Corinth to Kalamata and the spur to Sparta is high risk in archaeology terms,” says Shuttleworth.

“Ten kilometres after the Artemission tunnel we found an ancient wine press. Wherever you dig you might find something.”

The new motorway runs in the environs of an ancient Palladian temple, and an ancient cobbled road has also been encountered. Ground conditions vary along the route: “One of the big challenges has been resolving the technical ground problems in a few areas,” says Shuttleworth. In the Lefktro to Paradissia section, the ground is mainly a silty expansive clay with high swell capacity, vulnerable to heave.

“Moreas JV is mixing the clay on site with fly ash from a nearby power station.”

A tractor/trailer unit deposits the fly ash on the surface of the earthworks layer then a machine with rotavator blades adds water and mixes and grades it. This is followed by a vibrating roller for compaction. Alternative designs are currently being considered for consolidating the ground along several kilometres of the route where the foundations are weak and very high in moisture.

 

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