Brokk machines in Mersey tunnel link by David Hayward
(Courtesy of BTi magazine)
Three remote controlled Brokk demolition machines have just completed the excavation of new cross passages linking the twin bores of the River Mersey's Kingsway Road Tunnel. The cross passages had been ordered by client Mersey Tunnels as part of a fire safety upgrade for the 2.4km long tunnels.

The versatility of these small triple boom electro-hydraulic excavators allowed them not only to operate in the limited headroom of the 3.4 diameter passages, but also to use conventional hydraulic hammers to peck at the bunter sandstone rock.

"Our machines only weigh 3.5 tonnes but have the power of an excavator four times heavier" said Nick Turnbull, director of specialist demolition contractor Gnat International.
"Their articulated booms can operate horizontally and, like a human arm, push forward into the face".

Gnat International, as supplier and operators of the Brokk excavators for main tunnel contractor Amco Donelon, achieved drive rates of up to 2m in a 12 hour shift. Excavation was allowed only during regular night time possessions, when one of the main tunnel bores could be closed. All equipment and materials had to be removed, and the closed bore cleaned, by the end of each possession allowing the tunnel to reopen for the start of the following morning's 6.30 am rush hour.

"A conventional large roadheader would have proved impractical for such short 17m drives but the Brokks, with their excellent size to power ratio, could remain in the crossover tunnels during the day," said Amco Donelon site manager Jim Yerkess.
Gnat found the Brokks so adaptable for tunnel driving that the company is now designing a special rotating head for use in the softer clay soils.