Wirth Gripper TBM Drives Alborz Tunnel on Shomal Freeway near TehranToday only a two-lane highway with a length of 200 km connects Tehran and the city of Chalus at the Caspian Sea. By 2010 both cities should be connected by a four-lane freeway shortening the distance to 121 km. On upward slopes an additional lane would be added for slow speed vehicles. More than 40 twin-tube tunnels making 2 x 40 km will be required. The Alborz tunnel at an altitude of 2,450 m is the longest twin-bored tunnel in the project with a length of 6.3 km.The gripper type TBM TB III/ 520E of Wirth is well into the excavation of the service tunnel in the middle between the two main tunnels. Another goal of this service tunnel is to gain more knowledge about the geology for the later excavation of these main tunnels. It is planned that this first drive will be followed by boring also the pilot tunnels for the actual freeway tunnels followed by an enlargement to the final diameter of approximately 14 m. The complete TBM, the complete trailer as well as all auxiliary equipment for its operation were designed and supplied by Wirth. Visit www.wirth-europe.comThe service tunnel is being lined with rock bolts, wire mesh and shotcrete. Rock bolters are integrated into the machine and cover a roof section of 120 deg. In addition to the rock bolters, the TBM is equipped with a ring beam lining device. Thus a lining system can also be placed safely in very adverse rock conditions.The rock is conveyed out by means of muck trains (locos with side dump cars). Works are carried out by Taloon Construction under the Swiss-based work supervision consultants Amberg Engineering. The latter is also responsible for the client's consultancy, the design and layout of the service tunnel. Visit www.ambergengineering.comThe boring diameter of the TBM is 5.20 m, with a cutterhead drive power of 1,200 kW, advance thrust of 8,400 kN, cutterhead speed of 8.6 rpm max., nominal torque of 1,260 kNm, breakout torque of 2,000 kNm and total clamping force of 22,000 kN. There are 24 clamping cylinders. The total installed power is 1,500 kW. Behind the face, a 800 mm-wide belt collects the material at a speed of 0-2 m/s and a capacity of 480 cu m/h. The TBM started tunnelling in early September 2004. At present the machine has passed the 2,500 m mark. Rock conditions were sometimes very unfavourable with some significant rock falls. Click ir/15. 05/06. Click to enlarge