Refurbishment of a tourist railway in the Kalavrita valley has required engineers in Greece to come up with some imaginative solutions. Narrow and restricted access, steep slopes and historic structures made the contract, to replace bridge bearings and improve the seismic response of the structures on the line, particularly challenging.
The project was first announced in 2006 by the National Railway Infrastructure Management company, a subsidiary of the Greek Railway Authority. It involved upgrading the historic cog railway in Kalavrita in the north west of the Greek Peloponnese. The northern part of the Kalavrita valley is the location of the Vouraikos gorge that was cut by the river which runs into Corinthos bay.
The construction of this route, known as the Diakofto-Kalavrita cog railway, was carried out by French contractor Aton in 1896 for Greek prime minister Charilaos Trikoupis and his government. The route runs through the gorge next to river, and it served an area lacking road access until the late 1960s.
The first steam locomotives ran on coal, while today the train consists of two carriages and is powered by a diesel engine located in the middle. Even today, the track still contains rails that are marked with the date of their production. The entire route, including all facilities such as stations, stops, and a 20m-wide zone on each side of the track has been identified as a historical monument by Unesco and the Hellenic Ministry of Culture.
Today, the route is regarded as a unique tourist attraction in Greece, as well as internationally. Τhe entire length of the track, from Diakofto station to Kalavrita is about 22km and takes about an hour to travel. On the cog sections of the route, locomotives can travel at a maximum velocity of about 12km/h, and on the friction sections they speed up to 40km/h. At its steepest, the inclination of the track is some 17.5%, explaining why a conventional train could not travel on this route. When it was built, a cog straight-edge was fitted between the rails on three parts of the route, a total length of more than 3km. This cog straight-edge locks into a mechanism in the locomotive and enables the train to ascend to almost a kilometre above sea level at Kalavrita station where the route ends. Τhis cog railway has the narrowest track gauge in Europe, at 750mm.
Initially the route is smooth and after travelling through fields along the coast, it leads into the gorge, where impressive red rock walls eroded by water form the first narrowing of the route.
After passing through numerous tunnels, the train reaches Portes, where the train enters another tunnel at the narrowest point of the gorge. The tunnel still has heavy iron doors at its two portals; in the 1930s and 1940s these doors were only opened for trains to pass and remained closed at all other times to prevent pedestrians from entering the tunnel. After ascending the last section of cog mechanism, the train reaches the station at the delightful village of Zachlorou.
But the bridges on the route are currently being upgraded to allow them to carry bigger axial loads from new, heavier locomotives, and to improve their response to seismic events. The work, which involves the replacement of bearings and strengthening, started in May this year, and is expected to be finished before the end of the year.
Design of the bridge upgrading work was carried out by Greek consultant K Mylonas & Partners, whose engineers had to overcome a large number of technical obstacles, while at the same time providing a smooth and effective construction methodology for this unusual assignment.
The contract for the work was awarded to contractor Edraco, a subsidiary of Greek contractor Edrasis, in February this year. Edrasis area managing director Aristoteles Tsagkarogiannis and site construction manager Nikos Melikidis organised a multi-disciplinary team of staff and the logistics necessary to address all the technical and safety issues, in order to complete the works as quickly as possible. This was particularly important for the local economy, which would be seriously affected by the suspension of rail services.
Specialist subcontractor Elemka was appointed to carry out the upgrading work on the ten railway bridges, five of which are arch bridges and five beam bridges. Elemka's expertise is in the inspection and maintenance of bridges, replacement of bearings and joints and so on.
The project had particular strategic importance because of its cultural significance and its role in the tourist industry. The difficulty of site access created by the local terrain meant that the only way to get materials, equipment and staff to the site was by the train itself. On top of this, the need for specialist technical solutions to accomplish the work required, all combined to characterise the project as a unique challenge in railway maintenance and bearing replacement.
Τhe steel bridges are either beam or arch structures, with subsidiary longitudinal girders that are reinforcements in three axes. All steel elements are connected using rivets and retaining plates.
Out of the ten structures, nine are single-span bridges ranging from about 10m length, to the longer arch structures of up to 26m span. The other arch bridge had three spans each 20m long, with a total length of 60m and a significant inclination of 10%.
Elemka's engineers had to address the special technical requirements of each bridge as well the requirements of the design. More precisely, with the steel structure being more than 100 years old, the steel elements of the bridge might demonstrate the effects of fatigue.
Another issue was the very difficult access to the job site. At seven out of the ten bridges there was no road access and the only means of transport was the locomotive. This had a limited capacity for cargo, in addition to which it had to respect the dimensional limits of the tunnels and the cog mechanism, in terms of materials and machinery that could be transported.
One major problem that had to be addressed was the fact that no cranes or any other lifting equipment could be used at the jobsite.
The narrow route of the railway meant that there was no storage area along the route, not to store equipment and machinery. Hence the contractor used a platform that could run on the rails, as storage area. What's more, the fact that staff had to operate in a dangerous working environment in a steep gorge, using safety harnesses and suspended working platforms meant that a safety engineer had to be in constant attendance. Another issue was the laborious and time-consuming process of demolition and drilling of masonry piers and abutments at the area where bearings were located.
As a result, Elemka had to develop a unique methodology in order to carry out the upgrading work while still meeting the requirements of the design. The company designed and built a special steel cantilever frame, which could be placed on the abutments. It had to be specially designed so it could be assembled and dismantled, transported and installed at the job-site without the use of any lifting equipment.
The resulting design was a steel frame consisting of 38 steel beams of various types (HEB 160-260), 56 connection plates and an enormous number of steel angles and bolts - some 980 bolts per frame.
Consequently it took more than 20 days to transport, assemble and install two steel frames at the job site. Another critical issue was the need for a total counterweight of 10,000kg per frame - and this was achieved using water tanks. Ten water tanks were used for each frame, filled with water that was extracted from the local river using underwater pumps. The
