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(ø 6.96 m) were 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 was the major task to carry out. 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 was more than 5 month, day and night. The pressure was up to 2.0 bar overpressure in air. To stabilize the support pressure we used bentonite with a special mixture of high density and viscosity.
Maintenance and repair under compressed air was performed at up to 2.0 bar for works at the cutterhead. Regular compressed air and oxygen decompression was successfully in use. In total more than 2.000 h of compressed air works and more than 375 man interventions were performed. No minor case of decompression illness was reported.
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