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CLEAN SHEETS

PLANT FOCUS

Sheet piling specialists are combating vibration and noise.

Steel sheet piling is often associated with temporary works.

However, it is increasingly being used in foundations and other permanent applications. Sheet piling contractor Dew Piling managing director Bob James says it is being used for large basement structures.

The company, acquired last year by Belfast-based Lagan Holdings, says, for example, it can take axial loads of the walls as well as retaining earth.

With contractors being demanded to turn the noise down, hammers are giving way to variable moment high-frequency vibrators. Fussey Piling, for example, another specialist in the fi eld, has two Bauer RTG 16T telescopic leader rigs with 90t variable-moment, high-frequency vibrator and a PVE 2316 crane-suspended, variable-moment, high-frequency vibrator.

The high frequency of vibrators also reduces vibration allowing piles to be pressed in much closer to existing structures, an important feature, particularly on urban redevelopment projects.

Fussey recently traded in a pair of RTG 15T machines for the 16Ts.

The new machines give an extra metre of depth (16m instead of 15m). But that was not the issue, says contracts manager, Graham Hall, so much as the extra power that the newer machines have, with maximum centrifugal force in the hammer up from 90t to 100t.

Many sheet piling contractors are also able to offer the Japanese pile pressing system, which is both silent and vibration-free. The system was invented by Giken way back in 1967 and the Silent Piler is still offered today. A similar product, the Still Worker, is produced by Kowan (formerly known as Tosa), which is also Japanese.

The concept is that the first three sheets are pushed in hydraulically by fi xing the pressing rig to a reaction rig.

For subsequent piles, the press grips previously installed piles and uses their reaction force for leverage. It then self travels on to those just installed ready for the next pile to be installed. Piles are extracted in the same way.

Fussey is increasingly using its silent and vibration-free equipment, and has a Tosa WP-150 Still Worker with up to 150t of hydraulic pressing force to install U-section piles.

The Still Worker can be diesel or electric powered and is commonly used in sands, gravels, clays or tills.

It can drive sheets into soils with N values as high as 30. If supplemented with a water jet, it can be used in soils with an N value as high as 50.

It is typically 10% to 15% more expensive than using an RTG type rig, Hall says, but there has been signifi cant growth in use of such systems in the last fi ve years, particularly in the South East.

Although it remains a niche market, environmental demands are leading a growing number of these machines in the UK. There are close to 20 in the UK, estimates Kowan's European agent Watson & Hillhouse managing director Phil Bell, of which seven were sold by his company in 2006. 'Silent piling is growing, there's no question about it, ' Bell says.

Kowan this year unveiled a new Tosa press at the Bauma Fair, the ZU-100, the fi rst press in the world that can install Z section piles as well as U piles, according to Bell.

Kowan's rival, Giken, has a Z pile press already, but not a combination machine, he says.

The ZU-100 can press Z piles that are 575mm to 700mm wide and U piles of 700mm to 750mm width.

Bell says the initial target market is mainly northern Europe - Germany, the Netherlands and Scandinavia - where Z piles are more commonly used. Since Arcelor acquired the sheet piling business of Corus in 2004 it has started to promote Z piles in the UK, he says. 'But the UK is still very much a 600mm U pile market and will remain so for some time, ' he says.

Hall is not sure the 100t pressing force of the ZU-100 is enough for the UK market anyway. 'We are frequently using more than 100t just for U piles so we think it may be of limited use in the UK, ' he says.

There are also Japanese presses available designed for H section piles. However, while the press for U piles only needs a reaction stand to install the first three piles, and subsequently grips installed piles to react against, for H piles the reaction stand needs to be used every time and moved around the site.

There is also a rig for pressing interlocking tubes to form a contiguous wall. It is used in Japan but is yet to be seen in Europe. 'I can see a time when we would bring it in, ' Bell says. 'Maybe within ve years.'

Hall says developments from sheet pile producers are generally not in synch with what plant manufacturers offer. Sheet pile producers are always trying to develop everwider piles, he says, which have benets for designers.

But he adds that a wide vibrator or drop hammer may be the only way of installing them, since neither of the Japanese press manufacturers have a machine even on the drawing board for 750mm wide piles in the of ng. 'We are being told that wider piles are the way forward, but machines aren't being developed, ' Hall says.

'It's like a bullet manufacturer developing a wonderful bullet with no gun to re it.'

Hall cites the case of one manufacturer who developed a hydro-press to drive a particular pile pro le, only to nd the pro le go out of mainstream production almost immediately, making the machine obsolete.

Design of modern sheet piles demands that new machines are more powerful than their predecessors. Loose clutches on old Corus steel piles made them easy to install but prone to leaking, Hall says. New Arcelor ones have tight clutches, but 7% of the hammer energy is lost to overcoming clutch friction.

In general, however, manufacturers appear to be making every effort to meet customer demand in terms of power and versatility. Liebherr launched a leader-mounted steel sheet pile press at Bauma last month that can install both U and Z section piles. Previously it had different frames for different proles.

The LRB 255 has 125t of pressing force and the LRB 155 and 125 models have 80t. A system that uses four U section sheets locked together to form a box, installed with an LRB 255, is promoted in the UK by its dealer Dawson Construction Plant.

Another sheet pile launch at Bauma was the universal HPZ 500720 hydro-press system from ABI Mobilram. This can install nearly all common Z pro les with section width from 500mm to 720mm, ABI claims.

It can be adjusted for different sheet pile types setting section width and angle. No adapters or adjustments of hydraulics are necessary.

Each of its four clamps has a pressing force of 800kN and an extraction force of 600kN per clamp. Stroke is 400mm.

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