Excavation of three new cross passages, linking the twin bores of the River Mersey’s Kingsway road tunnel near Liverpool, England, have been completed using remote controlled single boom excavators designed primarily for demolishing concrete.
The versatility of these small, triple arm, electrohydraulic, Brokk excavators allowed them not only to operate in the limited headroom of the 3.4m diameter passages, but also to use conventional hydraulic hammers to excavate the competent bunter sandstone rock.
Gnat International, as supplier and operators of the Swedish manufactured excavators for main tunnel contractor Amco Donelon, achieved drive rates of up to 2m per 12 hour shift. Excavation was allowed only during 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 reopening for the following morning’s 6.30am rush hour.
Gnat found the machines so adaptable for tunnel driving that the company is now designing a special rotating head for use in softer clay soils.
The cross passages had been ordered by client Mersey Tunnels as part of a fire safety upgrade for the 2.4km long tunnels.
