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Double Shield Tunnel Boring Machines

A Double Shield TBM consists of a rotating cutterhead mounted to the cutterhead support, followed by three shields: a telescopic shield (a smaller diameter inner shield which slides within the larger outer shield), a gripper shield and a tail shield.

In normal operation (“double shield mode”), the gripper shoes are energized, pushing against the tunnel walls to react the boring forces. The main propel cylinders are then extended to push the cutterhead support and cutterhead forward. The rotating cutterhead cuts the rock. The telescopic shield extends as the machine advances keeping everything in the machine under cover and protected from the ground surrounding it.

Features & Benefits

Flat, low profile cutterhead to enhance face support in broken rock.

Recessed muck bucket openings with grill bars to prevent ingestion of large rock blocks.

Back-loading cutters for safe cutter changing in unstable rock conditions.

Dual thrust-reaction systems, enabling thrust reaction from the tunnel walls or the tunnel lining.

High-speed segment erector (single- or dual-arm depending on machine diameter) installs pre-cast concrete segments with precision.

Two-piece articulated telescopic shield offers safety, access to surrounding ground for examination and treatment, and smooth steering through curves.

Digital guidance system for continuous information on alignment for maintaining strict control of tunnel line and grade.

Digital guidance system for continuous information on alignment for maintaining strict control of tunnel line and grade.

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