The Karaj – Chalous road starts in the middle of Karaj and after crossing the Alborz mountain chain, it reaches Chalous city and the Caspian sea side. At the time of constructing the Chalous road there was no other solution but to excavate a tunnel through the mountain otherwise one had to go round it. On 11th of May 1935 the first dynamite was used to create an opening from where workers continued digging with pick and chip-axes. The construction of this 1884 m long, 5.5 m wide, and 6 m high tunnel took three years and was inaugurated on 17th of May 1938.
In 1995 it was suggested to widen the road for bi-directional traffic. However due to the presence of ground water, and weakening of the rock and soil mass over the years, works progressed slowly when the old rock cover of the tunnel was removed and several collapses occurred. This project was completed after seven years in 2002.
The southern portal and inside the Kandovan Tunnel after widening
Tehran – North Expressway
The Tehran – North Expressway is part of the north – south corridor that connects countries of southeast Asia with Europe via Iran and its northern neighbours . This expressway shortens the distance from Tehran to the city of Chalous at the Caspian sea from 200 km to 121km and the travelling time from 4.5 to 1.5 hours.
The route includes 137 tunnels with a total length of 45 km in each direction (90 km all together). Ten of these tunnels have a length of more than 1 km. The longest tunnels in this route are the Taloun twin tunnels with a length of 5000 m in each direction and the Alborz twin tunnels which are 6300 m long in each direction.
The Taloun pilot tunnel is excavated using the drill and blast method and following the rules of NATM. The excavated rocks consisted mainly of Tuffs from Karaj formation. The Alborz pilot tunnel is the longest tunnel of the route and is excavated by TBM with a diameter of 5.2 m. The main tunnels will be excavated by drill and blast method.
The TBM machine at the beginning of the Alborz pilot tunnel
Khoramabad – Pol -e- Zal Expressway
The existing Khoramabad – Pol -e- Zal road with a length of 165 km is an important part of the north – south corridor. The route passes through mountains and difficult terrain of the Zagros mountain chain and ends near Pol -e- Zal ( Zal -Bridge in Farsi) almost 55 km away from Andimeshk city in Khuzestan province and is connected to the Khoramabad – Andimeshk expressway by a crossing. The length of this expressway is 104 km and consists of 25 km of twin tunnels which were excavated by drill and blast method, 14 special bridges and 270 simple bridges.
Twin tunnels in Khoramabad – Pol -e- Zal Expressway