Next Generation of Hybrid TBMs for Mixed Ground

Hybrid EPBs, such as this 10 m diameter Robbins machine supplied for India’s Sleemanabad Carrier Canal, are gaining in popularity

Hybrid EPB/Single Shield machines often include an oversized, reinforced screw conveyor for more abrasive ground conditions, and a convertible belt conveyor that can be changed out in the tunnel

For machines over 12 m in diameter, a new type of setup is available. This Robbins hybrid EPB features a hydraulic muck ring that allows both the screw and belt conveyor (in pink) to stay in place – thereby drastically reducing in-tunnel conversion time between modes

A side view of the large diameter Robbins hybrid EPB design in hard rock mode. A muck chute (blue) transfers rock chips through the screw conveyor (in red) onto the belt conveyor

The use of hybrid TBMs in a mixed and unpredictable underground environment is increasing. This report concentrates on the advances achieved by hybrid TBMs, focusing on what is likely the most common type: A cross between a hard rock single shield TBM and an EPB.

In a mixed and unpredictable underground environment the increasing use of hybrid TBMs is one that goes with the territory. Where multiple machine types might have once been used for different sections of rock and soft ground, a hybrid machine can excavate the entire tunnel. New designs are making this versatile take on tunnelling more efficient, even at larger diameters of 10 m or more.

For the purposes of this article, the focus will be on what is likely the most common type of hybrid machine: a cross between a hard rock single shield TBM and an EPB. Typically these TBMs bore tunnels with...