Enough room to swing a cat

John Holland mechanical supervisor Mark McLean said the company’s tunnelling experience meant they knew exactly what specification they needed for the excavator.“We are looking to put the largest excavator we could operate in the small work area of the shaft,” he said. “We have a set of criteria the machine had to conform to, including being about 20-tonne size, having a zero-swing radius, a short stick, an operator protective structure cabin and specifications for buckets and work tools.”The boom on the 321D LCR is repositioned toward the centre of the machine compared to a standard excavator, reducing the front swing radius when the boom is pulled back and the stick brought in fully. This also increases the machine’s lift capacity.The machine underwent a series of modifications to suit John Holland’s requirements. The boom has been reinforced and shortened 1.2m less than standard while the stick is the shortest specification available to make the machine even more compact than standard. The machine also has a unique centralised lifting point. “We can now attach one shackle on the machine and hook it on our crane and can quickly lower the machine down the shaft,” McLean said.“The Cat started working at ground level and has been digging material as well as ripping or hammering when needed. If we encounter hard rock conditions, such as on our stage two sites, we drill and blast and then use the excavator to muck out the spoil.“We also have a twin header attachment, which is a hydraulic drive rotating head with picks to dig through the softer ground – this gives us the exact profile needed in the tunnel because the closer we get to the profile the less concrete we have to place afterwards.“I’m confident, based on the work we have completed on the EastLink project and now on the Northern Sewerage Project, that we will keep the machine for use on another project because it has been such an effective tool

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