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Esfahan Metro Tunnel

Welding & Preservation

The Esfahan Metro Tunnel

The Esfahan Metro Tunnel is a 4.550 m long twin tube between Shohada Aquare and Azadi Aquare. The west and the east tunnel crosses the river Zayandehrood in the south of Esfahan, Iran. The two EPB TBM’s (Æ 6.96 m) are in use to excavate the tunnel in soft alluvium strata. The strata are mainly silt, fine sand and gravel.

 The tunnel invert’s deepest point is 20 m below street level and river.

Welding in compressed air is the major task to carry out. But this time the job is more extreme. The 8 cutterhead arms of the TBM had to be renewed more or less completely from the front side and the cutterhead edge of both machines from the back side. Therefore we welded new vertical side plates and new cover plates on the arms of the cutterhead and new hardox plates on the cutterhead edge.

The total time of this work will take more than 6 month, day and night. The pressure is up to 2.0 bar overpressure in air. To keep the support pressure stable we used bentonite with a special mixture of high density and viscosity. 

Maintenance and repair under compressed air is performed at up to 2.0 bar air pressure for works at the cutterhead. Regular compressed air and oxygen decompression is successfully in use. In total more than 2.000 h of compressed air works and more than 375 man interventions until 31.03.2010 are performed. No minor case of decompression illness is reported.