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Case for space

An innovative way to fit more into landfill sites is to create new holes in existing sites says Lisa Russell.

Even an apparently full landfill site has potential space lurking within, and creating deep holes in it might prove the way to exploit it. Kimbolton- based PTC Piling hopes to build on work carried out by manufacturer Leffer in Germany and persuade British landfill operators to try the system.

The principle is very simple. PTC's sales and marketing manager Rod Collerton explains that a casing of 1.5m-2.5m diameter is pushed in, displacing and hence laterally compacting the landfill material as it goes. Remove the casing, and the hole can be filled with fresh waste, compacted as it is installed. And the casing and displacement shoe are ready for re-use - repeating the process across the site.

The casing is brought to position by crane, and dropped into the Leffer RDM type motorised hydraulic casing rotator. Once plumbed up, it is held by a hydraulic clamp. The tube is then rotated into the ground, crowded down by four rams, with a stroke of about 0.5m, after which they are reset. Rotation is at up to 1.1rpm, with a torque of 3,700kNm.

Only two operators should be needed, says Collerton - the crane driver and a banksman as the equipment is controlled remotely.

The double walled hollow casing has a cutting shoe at its end, working like a hollow drill to install a void perhaps 15m deep. The idea is similar in principle to installing a compacted displacement pile, adds Collerton.

And there is no reason why, once the site has been peppered with holes, the machine cannot be brought back to make more space in between the newly- filled voids, 'similar to installing hard-soft piles', remarks Collerton. 'It can increase the volume available for landfilling by up to 7m3/m2..'

The idea seems brilliantly simple; what is less clear is how well the economics would work in the UK. Collerton puts the costs to buy the equipment outright at DM1.6M (£550,000), though there could be options for hire.

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