The Samsun-Kalın heritage railway line was one of the first built by the Republic of Turkey, and required comprehensive modernisation of its 378 km single-track, non-electrified line. This extensive overhaul means faster, more comfortable travel for the local residents along the line, and heavier options for the wider transport corridor between the Black Sea and the Mediterranean. 

Appointed by a Joint Venture including Çelikler-Gülermak-AZD, Arup provided multidisciplinary engineering design services for both the preliminary and detailed construction design, including civil engineering, geotechnics, structures and bridge assessment and strengthening, restoration of historical bridges, permanent way/track, drainage, tunnelling, as well as Traffic Control Center Building (architectural, structural, mechanical and electrical) design services. This included the challenges of working with infrastructure that also has protected historic status, for example assessing and strengthening 41 historical protected bridges for increased loads.  

Average train speeds will increase as a result of the modernization, reducing overall travel times by nearly 50%, while more than doubling the line’s daily capacity, allowing for better transport flows and resulting in fewer delays. As a bridge between East and West, Turkey’s railway infrastructure plays a strategically important role for Europe, Asia and the Middle East. This train line is part of a wider transport corridor between the Black Sea and the Mediterranean through Kalın and is among a series of initiatives backed by the EU to link Turkey with the European railway network.

Rail design and engineering support

Upgrading an existing rail link throws up significant challenges. Cutting through the Pontic mountains, the line’s geographic conditions rendered the topographic site surveys difficult, while the high gradients and tight curves of the line itself made soil investigation and improvement works similarly challenging.  

The historical design constraints of the existing infrastructure also made remediation and upgrade works a complex task. The historical tunnel’s steam-era cross section had to be adjusted to accommodate changes to the superstructure including increasing loading gauges, as well as securing the height clearance required to fit electric installations.  
 
With 47 tunnels including 8 avalanche tunnels, the line includes about 7,790 m of tunnels throughout, with the longest tunnel alone measuring 586 m. 

Other structure upgrades in the project include the retrofitting of 29 station and stabling yards to make them universally accessible to pedestrians including under- and overpasses. In addition, a total of 1,253 hydraulic structures were designed for this project, a key element for this region that receives heavy rainfall throughout the year. 

Aerial view of Samun Kalin railway link in Turkey

The modernised line will result in a 50% reduction in journey times.

Engineering to preserve and protect historical bridges

The assessment and strengthening of historical protected bridges was a key aspect of the project. The work includes 38 new bridges, as well as infrastructure and superstructure upgrade works on 41 historical bridges that have been assessed for increased axle load and combined seismic events. The 3D point cloud scanning of existing historical bridges and for some tunnels provided highly accurate data sets, which allowed the project to progress seamlessly to the next phases. The whole project was designed in less than 36 months, with works underway simultaneously across the line, allowing for a speedier project delivery that helped keep the budget under control.