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Mega TBM heads for Madrid assignment

WHAT IS claimed to be the world's largest tunnel boring machine has been built for a Madrid road tunnel project.

The Herrenknecht Mega S-300 TBM is soon expected to begin its journey to Spain on two container ships. A year ago, Herrenknecht received the order for one of the most technically demanding machines in the company's 28-year history.

Spanish construction firms Necso Entrecanales Cubiertas and Ferrovial Agroman ordered an EPB shield with a drilling diameter of over 15m for the excavation of the 3.65km long north tunnel of Madrid's urban M-30 motorway.

Herrenknecht, based in southern Germany, says it is the world's largest excavation diameter. Engineers developed a unique cutting wheel consisting of a 7m diameter central wheel and an outer one with a maximum excavation diameter of 15.2m.

Both can be rotated independently clockwise and anti-clockwise.

Three screw conveyors are integrated in the shield. Two large ones remove the spoil of the outer cutting wheel to a conveyor belt in the rear.

A smaller screw conveyor, installed in the bottom section, clears spoil from the central cutting wheel.

The giant TBM weighs 4,364t and has a thrust force of 316,000kN at 400bar. Herrenknecht claims it has the highest torque ever installed in a TBM and at 125,268kNm would be enough to lift a fully loaded Boeing 747, weighing 410t, with a 30m long lever arm.

Site assembly is scheduled to start next month in the launch shaft in downtown Madrid. The inner diameter of the tunnel will be 13.45m, providing three lanes for heavyweight traffic in one direction as well as sidewalks on both sides.

The TBM is due to start excavation this autumn and the tunnel is scheduled to open for traffic in 2008.

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