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BUYING BEHAVIOUR

PLANT FOCUS

There are numerous issues driving plant design, including environmental considerations and the need for power, many of which appear to be in conflict.

To understand the direction in which construction plant is moving requires first an understanding of the direction that construction is moving. In the UK, this means an increasing amount of building on difficult brownfield land.

lanning regulations are restricting new developments primarily to sites that have been used before, on what may be contaminated or geologically diffi cult land. The sites are often in built-up areas and small pockets of land with difficult access and restricted space for moving around on site.

'The redevelopment of brownfi eld sites is certainly on the up, with the result that traditional techniques don't get a look in so much, ' says Roger Bullivant associate director Andy Preece. 'Because the ground is not so good, a more engineered solution is required.'

'The industry is becoming more specialised, ' says Terry Bolsher, managing director of Aarsleff, which specialises in precast concrete piles. 'As methods become more specialised so the plant becomes more specialised.'

But as Keller commercial director Trevor Snell says: 'There is always a balance between the right technical solution for the site and the environmental impact of the system you use.'

In essence, this usually means making a compromise. There are regulatory requirements to observe, such as the Control of Noise Regulations 2006; there may be adjacent structures that cannot be damaged, which means controlling vibration;

and there are commercial pressures.

After all, every construction job is a compromise between speed, price and quality. Snell believes that continuous fl ght auger (CFA) boring remains the best option for eliminating vibration.

'In the past two years CFA has grown up quickly, ' says Antonello Verdolini, export manager of Italian manufacturer Tes Car. 'Engineers choose CFA to work faster and cleaner. I have noticed an increase in enquiries for CFAs machines of at least 40% compared with 2004.'

But in the UK, the cost of landfill and handling spoil is an increasing issue for contractors. Methods that bring spoil to the surface, such as traditional or CFA boring, are giving way to displacement techniques, although re-using extracted spoil can sometimes be designed into a project.

'The cost of handling spoil is having a big impact on the industry. Engineers are looking at displacement techniques that prevent bringing spoil to the surface, ' says Marc Evans, technical director of ground improvement specialist Pennine.

he contractor buys base machines and builds its own front-end equipment and has a proprietary design with a special rubber insert that minimises vibration to protect operators.

With operations in the UK, Dubai, Spain and the US, it has standardised on Caterpillar base machines because of the worldwide availability of spare parts and service.

Driven piling is the traditional displacement technique. Shrouded hammers have reduced noise to a significant degree, but more could be done, Snell believes. 'The industry wants a quieter system for driven concrete piles, ' he says. 'It's an area that more work needs to be done in.

Several contractors have produced their own solutions (see box).

Another displacement technique growing in popularity, according to Preece, is continual helical displacement (CHD). With this technique the auger leaves a screw-shaped pattern in the ground that is lled with concrete, without any spoil removal. Bullivant, which builds its own piling rigs, has just built its fth CHD rig in ve years. It can produce 600mm diameter piles, 20m deep, with no spoil. Bachy offers the same concept, under the name Screwsol.

'In the right groundconditions it produces a much better pile than CFA, uses less concrete and there is no spoil, ' Preece says. Bullivant has now developed a mini-CHD piling rig as well.

However, some people question the robustness of a helical pile, citing the potential for fragility in the wings. In the quest for a different kind of displacement solution Rock & Alluvium worked with Italian manufacturer Soilmec on the development of a compact piling rig - called compact not because of its size but because it works by reverse screwing to push material down into the ground. 'It relies on a lot of pulldown and brute force to displace the material - 26t/m as opposed to eight or nine, ' says the rm's operations director Roger Cox.

Cox says it is like a CFA machine, only shorter and more powerful. Delivered just last year, it has already proved itself on an eightmonth contract on the redevelopment of Plough Lane, former home of Wimbledon FC.

Multi-purpose rigs Van Elle director, Andy Sneddon says one of the biggest changes in recent years is the growing trend for multi-purpose piling rigs. 'Gone are the days when you just get a CFA rig. Now you get multi-discipline rigs. Most manufacturers do that now, ' he says.

Verdolini says: 'Now, from the customer point of view, the most important thing is to have drilling equipment that can be used in a multi-functional way. For this reason Tes Car has been equipping almost all drilling machines not only for kelly bar work, but also for CFA and soil mixing. The future will be to those companies able to provide more versatile drilling machines.'

That said, it seems the advent of multi-discipline rigs might be more signi ant for manufacturers than their customers. It enables manufacturers to rationalise product lines. A single machine doing various tasks sounds attractive, but not every one sees the need for a multi-discipline rig. 'We've tailored our eet to the market we want to aim at, ' says Sneddon. Despite the fact that Van Elle does both CFA boring and pile driving, Sneddon says: 'We are happy with what we've got.'

Other examples of multi-purpose machines include Soilmec's sixmodel range of SC crawler crane carriers, which can be equipped with various foundations attachments, and Liebherr's LRB series.

The LRBs consists of four base models with weights from 40t to 140t, each of which can be used for piling jobs with vibrator and hydraulic hammer as well as drilling jobs with double rotary head, CFA and kelly drilling equipment. The LRBs also allows operations with a hydraulic press or vibro-drilling.

RTG Rammtechnik, a Bauer company, also emphasises the multipurpose characteristics of its rigs. Its new RG 25 S can vibrate up to 25m long sheet piles into the ground, install piles with the VdW double rotary drilling system, carry out soil mixing by way of the CSM process and also the MIP process using the triple auger system. It can also install soil displacement piles and drill with a kelly bar. Torque is 250kNm and extraction force is 530kN.

Size matters The market seems to be demanding both bigger and smaller machines.

Bolsher says the tendency is towards bigger plant. But Cox says demand is for smaller, more powerful machines.

Snell says: 'There is a push towards putting bigger piles in, particularly with retaining walls, to try to avoid propping.' With construction more often focused on tight urban sites, space is at a premium and propping takes up space.

According to Evans: 'We are using smaller machines with lower bearing capacities.'

So what is really happening?

With progress it is inevitable that advances in hydraulics engineering and materials science mean faster, more powerful machines can be built using higher grade, lighter steel. This means an equivalent performance can be delivered today by a machine that ve or10 years ago would have been signicantly bigger.

Abbey Pynford has recently taken delivery of a 13.5t Soiltec CFA rig that can install piles 10m deep.

Chairman Paul Kiss says that in the past he would have had to buy a rig weighing 30t to achieve the necessary performance. This is an important development - and one that is certain to continue - not just for reasons of transport, logistics and site access.

The Federation of Piling Specialists' safe platforms initiative, decreeing that the working surface is part of the temporary works and therefore must be designed accordingly, has been a signi ant driver for reducing ground bearing pressure.

Other matters Another driver is the so-called 'modern methods of construction' movement and the push for more off-site construction and prefabrication.

Evans says: 'Off-site construction is starting to affect us because it often leads to lower foundation loads.' This supports the use of ground improvement techniques rather than piling, he says. 'It opens up more opportunities for us [as a ground improvement specialist].

Or, if you are using piles, it means smaller piles.'

Other trends indicate the industry's direction. As Pennine rebuilds its eet it looks to use biodegradable hydraulic oil and have double-skin fuel tanks on the machine that can hold a week's fuel, eliminating the need for bowsers on site. Sneddon says: 'Environmental matters are going to come to the fore.' He envisages biodegradable oils becoming standard. 'Everyone gets oil spills and pipes that leak, ' he says.

It seems noise, vibration, landll, land use, and oil spills - environmental matters of every kind - impact on what plant buyers need.

To buy or to build It is difcult for manufacturers to standardise, observes Van Elle director Andy Sneddon, because regulations vary so much from country to country.

In the UK, for example, auger cleaners are required and noise regulations are tough. 'Piling companies all want something special, ' says Sneddon. 'Little things are tweaked here and there - bits added and taken off. Some people build their own rigs, but with what's out there, I'd prefer a second-hand rig from a known manufacturer than to build our own.'

'We have tried building our own rigs, ' says Abbey Pynford chairman Paul Kiss. 'These things look simple but it's never as easy as it looks. We prefer to buy.'

Keller commercial director Trevor Snell says, in general, drilling rigs can be bought off the shelf, although instrumentation may need adjusting. For driven piling, however, there are fewer options and more adjustments may be required depending on techniques used, such as with the number of winches.

Roger Bullivant is a notable self-builder. 'When you can build your own machine, you can build it to your own specication, not to the specication that someone else thinks you need, ' says associate director Andy Preece. 'We know how they work so we can service it. It gives us better control of the machine.'

Bullivant uses standard JCB or Komatsu base machines and adds its own front-end equipment.

'You can't buy on the market what we want so we developed our own hammers, ' says Preece.

The hammers are shrouded to make them up to 15% quieter than standard hammers, he says.

Bullivant specialises in segmented precast piles, which means the mast can be shorter, lowering not only the rig's height, but also its centre of gravity. Its own rigs are smaller and lighter than others available, Preece says, so they are easier to move between sites and do not need such a substantial pile mat.

Aarsleff has also recently developed its silent hammer, in conjunction with Danish parent company Per Aarsleff. 'We needed to meet a number of requirements very specically, ' says managing director Terry Bolsher.'Although there were some products that purport to do what we wanted, they all fell short. They are designed for general purpose needs and are either too heavy, too long or need too much energy to drive them.'

Aarsleff's apability ems from its acquisition of the design rights of the Swedish Uddcomb hammer. It is steel-cased and lled with lead to maximise the blow energy. The new hammer was designed to meet the requirements for installing 200mm and 250mm 2 section precast concrete piles, predominantly used in the house building sector, rather than larger pile sections.

An independent noise survey carried out for Aarsleff on a piling contract for Persimmon Homes at Weston-super-Mare, by specialist noise and vibration consultant Philip Acoustics, shows that the Banut 500 piling rig, equipped with the silenced hammer, is more than twice as quiet as the rig with the standard un-silenced version.

Average noise levels, taken at 10m from the pile in front of the rig, were 80.2dBA Leq for the silenced version, compared with 87.9dBA Leq for the standard hammer.

The 7.7dBA Leq reduction is considerable as a 3dBA cut is equivalent to halving the noise.

Results taken at the same positions over the entire pile driving cycle showed noise levels at 76.1dBA Leq compared with 85.4dBA Leq.

'We were condent that we could build an effective silenced hammer, but we have been very impressed with these results, ' says Bolsher. 'In addition to the silenced hammer being two and a half times' quieter than our standard hammer, it has also proved to be more fuel efcient.

'So far both reliability and speed of performance are also improved with the added benet of a much more pilefriendly blow characteristic.

'Following successful field trials we have made a commitment to build two more silenced hammers, which will join the company's eet early in 2007.'

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