Iranian engineers designed and built around 1000 km of new line through difficult terrain

ALTHOUGH RAI's latest railway is described as the Mashhad - Bafgh line, the new alignment starts 114 km south of Mashhad at Kashmar. The junction faces Tehran, and a loop has been built to allow trains to or from Mashhad to avoid reversal.

Leaving Kashmar, the line traverses remote desert terrain, with mountain ranges traversed between Kashmar and Torbat-e-Heydariyeh, near Tabas and north of Bafgh.

From the junction the route heads southwest towards Torbat-e-Heydariyeh with passing loops at intervals of 20 to 25 km at Nannaki, Hesar jadal, Kameh and Rokh. At each loop is a building housing signalling and telecoms equipment and a generator room. There is also a water reservoir and short platform.

Torbat-e-Heydariyeh, reached at Km107, is one of three passenger stations. The others are at Bejestan (Km234) and Tabas (Km440). In addition to all the facilities available at the loops, the passenger stations provide washing areas and prayer rooms. Wagon shops and loco maintenance depots, plus accommodation for train crews, are located at Torbat-e-Heydariyeh and Tabas.

While the alignment passes through generally arid terrain, it must cross a salt marsh near Boshrouiyeh, north of Tabas. As the area is entirely surrounded by mountains, there is no possibility for water to drain away, and during the winter the marsh becomes waterlogged. The ground consists of a weak structure formed of thin layers of silt, clay and fine-grained sand, all mixed with salt. This had to be stabilised and the upper layer of soil removed. This was replaced by a special 300 cm deep drainage layer, with drainage channels built on each side of the formation.

Because of the possibility of cement corroding in the saline atmosphere, exposed surfaces were covered with two layers of polyamide epoxy paint, with an extra layer where they face strong sunlight. Steel girder surfaces also have three layers of epoxy paint as protection.

For the first time in Iran ballastless track similar to the interlocking prefabricated design found on Japan's Shinkansen was used in the tunnels. This technique was chosen partly to reduce the depth of excavation for the tunnels and partly to save construction costs, but it will also bring lower maintenance costs over the life of the project. RAI says that the capital cost of the slab design is 1·2 times the cost of conventional ballasted track. The slabs used are 5m long by 160 cm deep, with a centrally-located mandrel preventing transverse and longitudinal movement between the slabs.

The line speed limit has been set at 160 km/h for passenger trains, with freight allowed to run at 120 km/h. Track uses B70 monobloc concrete sleepers on plain line, with wooden sleepers for points and crossings. Continuously-welded UIC60 rail is affixed using seven million Pandrol and Vossloh fastenings, and all equipment, apart from the rails, was produced in Iran.

Ballast consisting of crushed igneous rock was sourced from quarries at Sabzevar, Kashmar, Kamar, Bejestan and Shirgacht in Khorasan province, with two quarries in Yazd province supplying ballast for the southern part of the line.

Communications equipment uses optic fibre technology, and a digital telephone system and wireless radio network are provided. Computer-based interlockings are used, with CTC at Tabas controlling the movement of trains.

In overall charge of the 4 000bn rials scheme was the Construction & Development of Transport Infrastructure Co. Iranian consultants and engineers were used for the entire design process, and RAI says that 'no foreign expert was employed for studies or the construction'. Tracklaying and other railway works were carried out by Railway Services & Technical Buildings Co, an affiliate of RAI, and by CBG, a private-sector contractor.

The 148 km Sangan branch has loops or freight facilities at Khaaf, Salami, Channan, Alsad, Rashtkhar and Salar. Plans exist to extend the line east into Afghanistan, where Herat would be the obvious destination. Sangan is also the name of a locality in Afghanistan where there are further deposits of iron ore, and Iran has proposed a scheme to fund the extension. According to Alireza m Alamoti, Director-General, International Affairs, in the Ministry of Roads & Transportation, the Afghans felt that the proposal was too expensive. 'We will need to negotiate', he said.