Railway Tunnels in Iran
Developing a railway was always a dream for Iranians. The Trans-Iranian railway was the first step towards this dream. After completion of this north-south line, works continued on the northwest and northeastern railways and other parts of the railway network continued. The main railway lines constructed between 1925 and 1978 were 4565 km long and between 1979 and 2008 about 4400 km.
Survey works for the Trans-Iranian railway started in 1925 and were completed within 19 months. The construction of Tehran’s railway station started on 16th of October 1927. At the same time railway constructions started in the south, centre and north of Iran. The Trans-Iranian railway was completed on 18th of August 1938.
The total length of the Trans-Iranian Railway from the North to the South is 1394 km. About 980 km of the alignment has wooden sleepers and 414 km metal sleepers. Along the route 224 tunnels were constructed of which 93 are located between Ghemshahr city in the north and Tehran, and 131 tunnels are positioned between Andimeshk city in the south and Tehran. The total length of these tunnels is 83666 m of which 23599 m are excavated in the northern part and 60067 m in the southern part.
In the Northern railway route four tunnels have a length of more than 1 km and nine tunnels are longer than 500 m. The Gadouk tunnel is the longest tunnel of this route with a length of 2887 m.
Veresk Tunnel and Bridge during construction (ca.1936)
Railway tunnels in Iran can be classified based on different criteria:
1) Based on lining, railway tunnels are subdivided into tunnels without lining, non-structural cover used only for protection against erosion, and with structural lining which carries load.
2) Based on material used for lining, tunnels are subdivided into masonry or concrete tunnels.
3) Based on size, tunnels are subdivided into small tunnels (mainly older tunnels), and large tunnels (mostly newly constructed tunnels with more height).
In masonry tunnels, loads applied due to arching phenomenon are carried by the walls and arc-roof. Most of the older tunnels of the northern, southern, and northwestern routes of the Iranian railway network are masonry tunnels, also known as rock tunnels.
Tunnel concrete covers can either be structural linings (load bearing) or non-structural covers. In case of non-structural covers, the load applied on the cover is minimal . In tunnels with structural lining, most loads applied from the peripheral rock material are borne by the lining. Tunnels which have concrete walls and a masonry roof are known as rock-concrete tunnels.
Most of the older tunnels with small cross sections have a height of 5.8 m (and in some cases 5.6 m). Newly constructed railway tunnels are designed based on new train sizes and have a height of at least 7 m. These tunnels have enough space for the installation of an electricity network and have also less ventilation problems.