Tunnel Boring Machine

Overview

A tunnel boring machine excavates a circular tunnel in a single continuous operation, replacing drill-and-blast methods with a rotating full-face cutting wheel. This earth-pressure-balance variant is built for soft ground and mixed-face conditions: it holds the excavation chamber under controlled pressure so the tunnel face cannot collapse or flood while the Cutterhead grinds forward. The whole machine is a self-contained underground factory, it cuts ground, removes spoil through the Muck Removal System system, and builds a watertight concrete lining behind itself as it advances.

The working end is the shielded boring unit; a long Trailing Gantry towed behind carries the transformers, pumps, and material supply that the front cannot house.

How it works

The Cutterhead is a welded steel wheel studded with disc cutters. A ring of electric drive motors turns it through reduction gearboxes and a single large Main Bearing, the most heavily loaded component in the machine. The disc cutters roll under enormous load against the rock, propagating cracks that spall chips off the face; softer ground is simply scraped and mixed into a paste.

Forward force comes from the Thrust & Gripper System. Hydraulic propulsion cylinders push off the last completed lining ring, driving the whole shield ahead by one segment width per cycle. Excavated material enters the pressurised chamber and is drawn out by a screw conveyor that meters spoil while maintaining face pressure, then dropped onto a belt that runs the length of the machine.

Once the shield has advanced a full stroke, the Segment Erector rotates precast concrete segments into place to build the next ring; the thrust cylinders then push off this fresh ring. Every function, thrust, steering, erector, screw, is driven by the Hydraulic Power Pack pack. The Guidance & Control System system references a tunnel laser against a target on the shield, continuously correcting line and grade by extending the thrust cylinders unevenly, with the operator overseeing it from the Operator Cab.