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The first and currently only Junttan PM23LC fixed leader self erecting piling rig in the UK has exceeded the expectations of owner and piling contractor Stent Foundations. The company bought the hydraulically operated rig, with its extensive mast manoeuvrability, specifically to modernise and replace its crane mounted suspended leader rigs, which are now about 30 years old. There were some initial concerns that the new 60 t rig would be too large, but these have proved unfounded following the successful completion of a variety of different contracts.
  
The PM23LC’s leader mast geometry allows the mast to be positioned up to 6.65m in front of the tracks (left). Click images to enlarge.
Stent is using the Junttan HHK 4A accelerated hammer, which has shown to achieve impact energy 25% above the theoretical maximum, to install 40 piles/day at Avonmouth (middle). Click images to enlarge.
Stent bought the hydraulically operated Junttan PM23LC, with its extensive mast manoeuvrability, to modernise and replace its crane mounted suspended leader rigs (right). Click images to enlarge.
“We were initially sceptical and thought the PM23LC might prove to be too big for our type of work,” says Stent Foundations operations manager Malcolm O’Sullivan. “But from the experience we have gained with it, on the wide range of projects we have used it in the 10 months we have had it, the rig has shown to be extremely versatile and far better than expected.”
Malcolm O’Sullivan was speaking about the rig during a pile installation project in Avonmouth. Stent Foundations was using the Junttan PM23LC to install 872 precast concrete piles at an average rate of 40/day on a warehouse development for St Modwen Properties PLC. Stent Foundations, working for Barnwood Construction Limited, had to install roughly equal numbers of 235mm and 275mm square section pointed toe piles, all 15m long and jointed in two equal length sections. The piles were driven to a set through made ground and soft alluvium to penetrate 2m into underlying mudstone.
Stent’s standard PM23LC rig, fitted with a 4t Junttan HHK 4A impact hammer, is capable of pitching and driving piles up to a maximum single length of 15m and can be ready for work within a short time of arriving on site. Despite the rig’s complex leader mast geometry, rigging and derigging can be achieved in less than an hour on site, including the hammer, which is carried on and under the mast during transportation. The long undercarriage and extendable tracks, coupled with a low centre of gravity, make the rig very stable.
The PM23LC has exceptional manoeuvrability of its mast, which allows the rig to work on normal level ground or on embankments or in shallow cuttings. In addition to normal side-to-side and backward and forward rake, the leader mast can be raised vertically 4.7m above and lowered 4.3m below ground level. The leader can also be positioned up to 6.65m in front of the tracks and this exceptional reach and overall working envelope allows easy and fast spotting of the piles during pitching without having to constantly move the rig. “I believe the PM23LC is more sophisticated and more versatile than any other piling rig in the UK at the moment and to achieve that kind of reach you would have to revert to using a crane mounted rig with hanging leaders,” adds Malcolm O’Sullivan. “We have made use of this feature on projects where we have stood the rig on top of an embankment and driven piles into the slope below and similarly stood in a cutting and driven piles into the level ground above. It’s very very versatile and can handle all our precast concrete pile sections from
187mm square up to 400mm square and steel tubes up to 760mm diameter and also steel sheets, steel bearing piles and timber piles.”
Stent Foundations has chosen the HHK 4A hammer, with its single piece drop weight, which also has the possibility of operating as a 5t impact hammer by adding a 1t block to the drop weight. The impact hammer, operated from the host rig’s hydraulic system, hydraulically accelerates the drop weight during the fall, boosting the impact energy and increasing by up to 20% the efficiency at full stroke over a conventional free fall drop hammer of the same weight. “The Junttan 4t hammer we are using on this rig is another key to the machine’s overall success,” adds Stent Foundations works manager Andrew Parker. “We can adjust blow rate up to 100 blows/minute and drop height from 50mm up to 1.2m. And during independent monitoring it has shown to achieve impact energy 25% above the theoretical maximum.”
The HHK 4A hammer produces maximum impact energy of 47kNm at full drop height of 1.2 m. Impact energy, drop height and blow rate can be infinitely adjusted by the operator to suit ground conditions and pile type. All relevant data is displayed on the rig’s computer screen in the operator’s cab. The HHK 4A hammer, one of 11 in the new generation Junttan A series, is suitable for driving all types of piles, such as steel tubes, H sections, steel sheets, precast concrete and timber piles. The rig’s hydraulic system is also filled with biodegradable oil, because, with its reach, it can be used to work near water, in environmentally sensitive areas or even directly for the Environment Agency.
“We are pleased with its reliability, speed and performance,” adds Malcolm O’Sullivan. “We did consider and evaluate alternative rigs before opting for the Junttan PM23LC, which complements our existing Junttan rigs, comprising seven PM20s and a PM16 with another PM16 low headroom version due in August 2007.”
For further information please contact:
Jeremy Pilch, Junttan UK
London House, 266 Fulham Road
London SW10 9EL
Tel: +44 (0) 207 351 3130
Email: junttanuk@aol.com
Web: www.junttan.com
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