The UK’s largest telescopic clamshell excavator is poised to start work on Crossrail. Geoff Ashcroft reports.
Hertfordshire-based M O’Brien Plant Hire has taken delivery of the UK’s largest clamshell telescopic arm excavator, ready for deployment on London’s Crossrail project. The specialist machine is designed to combine a compact footprint with long-reach capability, making it ideally suited for foundation works, underground renovations and canal clearance, according to its maker, Hitachi.
“We’ve had specialist excavators before, but this is our first telescopic excavator,” says O’Brien director James O’Donnell. “It is quite an innovative machine and gives us endless possibilities when it comes to deep excavations.”
On Crossrail the 42t telescopic excavator - based on a Hitachi ZX series machine - will extract material from supplementary plant working a long way below ground. “Smaller machines will stockpile material at an access shaft, where the ZX will be working from above ground,” explains O’Donnell. “It will be used to remove material and load it directly into trucks for recycling.”
The specially modified machine has a Hitachi ZX350LC excavator as its base, but has undergone considerable changes to its specification - most notably the boom and arm configuration. It has been equipped with a two-stage telescopic arm that gives it a vertical digging depth of 25.2m, and fitted with a 1.3m3 clamshell bucket.
O’Brien’s telescopic excavator is one of two such conversions carried out by the Japanese maker. The second is a smaller machine, based on its short radius ZX225USRLC-3 excavator, which offers a 21m dig depth with a 800mm3 bucket. Civils contractor Careys owns the smaller version, and O’Brien did consider buying this model too.
“The short radius excavator offered its own appeal for working in tight spaces, but we opted for the ZX350 purely for its superior digging depth,” says O’Donnell, while hinting that the large specialist machine may not be the only telescopic excavator that finds its way onto O’Brien’s books. “Depending on how successful this machine is, we can see a lot of different applications for having a smaller, more manoeuverable version in our fleet,” he says.
“It offers a tremendous solution for those looking to go deep into the ground as part of inner city or urban regeneration”
David Hearne, HM Plant
According to HM Plant operations director David Hearne, who supplied the machine, only four clamshell telescopic arm excavators are made available to the European market every year.
“There is a six to nine month waiting list on this type of specialist conversion,” he says. “But it does offer a tremendous solution for those looking to go deep into the ground as part of inner city or urban regeneration, where the only place left to build is below ground level.”
Hitachi has engineered a range of novel solutions to adapt the machine for deep vertical digging, including addressing the traditional problem of hydraulic pipes snagging on the clamshell. This has been overcome by creating a double-ended hydraulic cylinder that is fed with oil from a top entry point close to the bucket’s coupling.
“The hydraulic cylinder used for the clamshell operation is a very neat solution to an age-old problem, and it’s an area of machine design that we really like,” says O’Donnell.”
The slim construction of the telescopic arm also helps to resist damage when operating in deep, narrow excavation shafts.
Full extension in 10 seconds
The ZX350 can move rapidly to and from its 25.2m maximum digging depth, taking just 10 seconds to achieve full extension or full retraction, thanks to a combination of wire ropes and hydraulic cylinders. This helps to keep production cycles short and speeds up the removal of material from site.
The telescopic arm system uses dual wire ropes as an additional safety precaution against losing the entire telescopic structure in the event of rope failure, and there are indicators in the cab to keep the operator informed of rope status. To help the operator to see what’s going on at that depth, Hitachi has fitted a camera on the telescopic arm, which relays an image of the clamshell bucket to an in-cab screen.
Visibility is also enhanced by giving the machine a sliding cab. Using a hydraulic cylinder beneath the cab structure, the operator can push the cab forward by an additional 1.3m from its standard location to make it easier to see into the deep excavation.
The cab also has a window in the floor, though its installation has required the tracking pedal valves to be relocated in an offset position to the left side of their usual position on the cab floor. As a result, Hitachi has designed specially shaped tracking levers that put the controls back into a central position for the operator.