Hitachi dealer HM Plant supplied Carey with a Hitachi Zaxis ZX225USRLC-3 with a clamshell telescopic arm to remove material from 21m below ground.
The machine worked on the site between January and June 2012, excavating several basement levels that belonged to the neighbouring British Museum, which remained open throughout the work. With excavation complete, five new storeys will now be constructed below ground level to house scientific research facilities, storage and study rooms when the Centre opens in 2014.
Equipped with a 0.8 cubic metre bucket, the Hitachi excavator loaded an average of 45 trucks per day. Its productivity was an important factor, according to Carey assistant project manager David Kyari. “It takes approximately 12 minutes to fill each truck; eight seconds for the arm to extend and ten seconds for it to retract,” he explained. “It’s important for the process to be as fast and smooth as possible, as the trucks are not allowed to queue on the street adjacent to the site, due to parking restrictions and emissions regulations.”
Without the Hitachi ZX225USRLC-3, the excavation process would have been slower and less safe. “We would have had to use skips, conveyor belts and a crane to lift the skips to remove the material, which would then have been stockpiled on site,” said Mr Kyari. “With this machine, we can do both the excavating and loading, and it is up to three times quicker than the traditional method.”
HM Plant operations director David Hearne added that the use of tower cranes and skips would have meant more moving parts to the process: “This has implications for safety risks on such a busy site. Enhanced safety is one of the most important benefits of this excavator to the Carey Group, because it is always a top priority for the company.”
Further benefits of the ZX225USRLC-3 for job sites like this include the sliding cab. “It is positioned 700mm further forward than on a conventional Hitachi excavator,” said Mr Hearne, “and it has the capacity to slide a further 1,300mm forward, allowing for an additional two metres of visibility through the glass floor.”
Carey invested in the Hitachi ZX225USRLC-3 following a visit to Düsseldorf to see a similar model working on an underground car park. “They were so impressed with its performance that they immediately ordered the excavator for this job,” said Mr Hearne. “They were particularly impressed by the compact size of the machine, which makes it suitable for working at pavement level on busy, urban sites and within small hoardings.”
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