Sensitive foundation construction
By Helen Wright14 June 2013
From dust, noise, vibration and spoil to diesel exhaust emissions, there are a lot of environmental factors to consider when installing foundations or improving soil conditions, and the bigger the project, the bigger the potential impact.
Manufacturers of foundations equipment are breaking new ground in terms of environmental sensitivity when developing their latest machines. And they are often finding efficiency and performance improvements at the same time.
For instance, vibratory hammers, which produce vertical vibrations to drive or extract foundations such as sheet piles, are growing in popularity both in their own right and as an alternative to hammering piles into the ground, according to manufacturer PTC.
PTC, which is owned by Fayat group, has seen a growing interest in its Vibrodriving technology in the offshore wind farm sector in particular. The increasing concern in reducing under water noise during offshore pile driving to protect marine life is motivating offshore wind farm contractors to start looking for more environmentally sensitive techniques.
Dong Energy tested a trio of 200HD PTC Vibrodrivers during construction of the Anholt wind farm – a 400 MW development that will become Denmark’s largest offshore wind farm when complete.
The project requires 275 tonne monopiles to be driven into the sea bed as foundations. Powered by three PTC 1200C power packs supplying a total power of 2.42 MW, the Vibrodrivers worked in synchrony to install the piles to a depth of 20 m. They achieved this in less than 30 minutes while emitting under 160 dB at 750 m distance.
PTC general manager Jean de Saint Julien said, “Offshore piling is a very important market for us to develop. Working with Dong Energy, we exceeded our expectations in terms of productivity.”
Mr Saint Julien added that the manufacturer was exporting more and more vibration foundation equipment outside its domestic French market.
“We are an international company – 15% of our turnover is generated within France, while 85% comes from export sales. Of that, 75% is generated outside the EU,” Mr Saint Julien said. “We expect turnover to increase +20% in 2013, boosted in part by the rental market – which represents between 25% and 30% of revenues.
“PTC views US and China as promising markets for two different reasons– in the US, the market for vibrodrivers is very mature but, PTC is pushing its variable moment technology, which allows the amplitude to be adjusted at any time on the jobsite and to control the vibrations emitted in the environment. In China, the market of the hydraulic vibrodrivers is emerging and has developed very fast the last five years. It is going to grow in the few next years. PTC set up PTC USA in 2010 and PTC China in 2012.
“In addition, we are pursuing our industrial partnership with Casagrande to develop piling rigs and stone column rigs,” he added.
Mr Saint Julien said the manufacturer had first developed the SC13, a rig dedicated to stone columns up to 13 m depth, and now is concentrating on the development of the PR16-S to vibrodrive 18 m piles or hammer 16 m piles.
Meanwhile, PTC’s latest Vibrodriver is the 20RHFV, which has been designed to be mounted on piling rigs. Equipped with variable moment technology, the 20RHFV boasts a reduced centre width of 450 mm, which means it can be fitted to two sheet piles when installing a sheet pile wall. Users can therefore drive or extract sheet piles more rapidly because they don’t have to stop as often due to the adjacent sheet piles.
Contractor Miller Piling, meanwhile, says cased continuous flight auger (CFA) piling is also a fast-growing sector of the foundation industry. It involves drilling to the required depth with a continuous casing and hollow stemmed flight auger and then pumping liquid concrete down the hollow stem while the casing and auger is slowly withdrawn, conveying the soil upward along the flights. Reinforcement can then be lowered into the column of liquid concrete.
This method is useful with deep basements in poor ground conditions as it prevents auger from deviating from the intended path. This is especially important when constructing a secant-piled wall where accurate alignment is essential. It is also gaining ground as a foundations technique for cities, because it causes minimal noise and vibration.
“Lots of developers now want deep basements and as projects such as this one are often in tight urban sites, cased CFA piling really comes into its own”, said Miller technical manager James Hayward.
Miller bought a 140 tonne Casagrande cased CFA piling rig – believed to be the largest such machine in the UK – to work on a number of contracts coming on stream this year.
The C850 DH can install piles up to 1 m in diameter to a depth of more than 21 m and can drive both the auger and full-length steel pile-casing simultaneously.
“The auger runs inside a 21 m casing which is spun into the ground along with the auger. These types of rigs are typically larger than conventional piling machines because of the force needed to twist the casing and auger into the ground. This machine has two rotary motors which have a drilling torque capacity of 360 and 421 kNm,” Mr Hayward explained.
Soilmec has also launched a new CFA rig – the SR-90 Turbojet for deeper cased secant and CFA piles. Like the three other new models in the SR range of foundation rigs, it can be fitted with US Tier 3 or Tier 4 interim-compliant engines that are said to boost efficiency and productivity. The new generation SR rigs also boast more powerful and lightweight rotaries with torque increased by up to +20%.
The other new SR rigs are the SR-60 for large diameter piles, SR-65 for displacement piles and SR-100 for cased secant piles.
The manufacturer also introduced new SM drilling rigs for micropiling and anchoring which can also be powered by Tier 3 or Tier 4 engines for high performance and low diesel exhaust emissions.
Developed jointly by Soilmec and Puntel, five new SM rigs were on show at Bauma – the SM-3 for CFA piles, SM-5G for soil investigation, SM-8 multi-purpose micropiling rig, SM-14 with jet grouting, and SM-17 with a double rotary.
Soilmec has also developed a new electric multipurpose drill rig – the SM-5E – for work in tunnels or other restricted spaces where diesel engine emissions would be harmful.
The SM-5E comes directly from the SM-5 and has the same main features, including rotary heads with torque ranging from 687 to 972 daNm, and maximum drilling speeds of between 98 and 862 rpm. The power source, however, has been changed to a 75 kW ABB electric motor.
As well as having a compact design, the SM-5 is a multipurpose machine – its optimised mast articulation and large range of rotary heads ensures that it covers a broad application field from anchoring and tiebacks to micro-piles, jet grouting (fitted with a special extension), coring, well drilling, tunnelling and radial soil consolidation.
And demand for multipurpose foundation equipment is increasing, according to Bauer, which has developed a new piece of soil mixing equipment together with its subsidiary RTG Rammtechnik. The SCM-DH Single Column-Double Head tool is said to represent a significant improvement on existing technology.
Bauer said it was responding to a growing number of enquiries for soil mixing columns with ever increasing diameters.
The SCM-DH has two counter-rotating mixing components that are said to be capable of achieving exceptionally intensive levels of mixing and homogenisation of the soil with the slurry. The tool is well-suited to sandy soil as well as for the construction of soil mixing columns in cohesive soils.
SCM-DH mixing tools are available for column diameters of 1.8 m and 2.4 m. The tool can be carried by either by a double-head rotary drive rig, like a RTG Rammtechnik DKS 100/200-02 or DKS 50/100, or a KDK rotary drive like the Bauer BG rotary drilling rigs in combination with a BTM torque multiplier.
The SCM-DH tool was tested in a large-scale field trial, attached to an RG 25S fixed leader rig and driven by the DKS 100/200-02 double rotary drive. Bauer said the installed engine power of 570 kW proved particularly beneficial in maintaining a high rotational speed throughout the mixing process, despite an increase in soil resistance. It said the maximum mixing depth attainable with an RG 25S machine was approximately 23.5 m.
Junttan has developed new technology aimed at improving the management of piling jobs. The Junttan X controller system and iPiler software can control all functions and collect data about the piling process. Exact piling instructions can be prepared at the office and sent to the control system for the operator to follow, while data is collected during piling and sent back to the office for verification as well as pro-active maintenance.
Modular software and hardware configuration are said to make upgrading and adding new features fast and easy, while the components of the Junttan X control system are built of robust machine control electronics that were especially developed for harsh conditions.
New technology for the foundations sector has also been launched by Trimble in the form of its DPS900 Drilling and Piling System. This machine control technology gives contractors the ability to precisely drill to the specified location, depth, orientation and inclination angle, and has been designed to help promote site safety by minimising the need for stakes, construction surveying and personnel near machines during drilling.
The Trimble DPS900 is also part of the Trimble Connected Site portfolio and can be integrated with Trimble Business Center HCE software in the office, for instance. Using HCE in the office and DPS900 in the field allows contractors to optimise drilling and piling plans and send them wirelessly to the rig. Comprehensive quality and production reports from site can also be transmitted back to the office.
From the latest software to new foundations installation techniques, it is clear that developments in the sector are moving fast. And it will be interesting to see how technology plays a role in increasing efficiency and reducing the environmental impact of foundations machines in the future.