A pile boring rig is used as a base machine.
Bauer delves into new territory
Foundation engineering specialist Bauer Maschinen – which has led the industry with innovative drilling rigs – is now developing a new cutter-soil-mixing technique to create watertight walls for foundation works.
01 October 2004
Bauer Maschinen of Germany, in co-operation with Soletanche-Bachy of France, is developing and testing an innovative ‘cutter-soil-mixing’ (CSM) technique, which the company claims is a specialist foundation construction process that will provide excellent results.
The CSM technique is a process for the formation of consolidated soil elements by the introduction of hydraulic binders into the ground.
All known soil mixing processes use the principle of mixing the prevailing soil with suspension grout utilising mixing tools that rotate about a vertical axis. By developing sets of triple mixing tools, wall panels can be formed. These processes are based on the principle of the rotary drilling technique.
“In contrast, to the existing systems and techniques, the new CSM process is derived from the cutter diaphragm walling technique,” says a company spokesman.
“The soil is broken down by cutter wheels rotating about a horizontal axis and mixed in-situ by the rotating wheels with the self-hardening slurry introduced into the ground between the two wheels to form a soil-cement mortar.”
“The technique finds valuable use in the construction of watertight walls in place of conventional diaphragm, bored pile or sheet pile walls and can therefore be deployed to construct cut-off walls as well as structural load-bearing retaining walls,” he adds.
“This innovative concept has been demonstrated convincingly in practical use in a large-scale field trial in which 28 wall panels with a combined surface area of approximately 1,000 sq m were constructed in a sandy/gravel soil,” he says.
“In addition, a new generation of mixing wheels was deployed on a project for a Japanese client this May, and the company claims to have achieved good mixing results with a net productivity rate of 40 sq m/h in clayey fine-sandy soil.
“While further testing and development work on the technique will revolve round the aspects of optimisation of cutting and mixing geometry of the cutter wheels, it will also extend possible applications both in cohesive and coarse-grained soils,” he says.
The plant
At the heart of the system are two cutter gear drives each driving a standard cutter wheel. In contrast to ‘normal’ cutter operation, the cutter wheels can be driven in both directions. The slurry is pumped through a central nozzle between the two cutter wheels and mixed with the loosened soil material by the rotating wheels.
“The rotating cutter wheels and vertical deflector bars mounted between the cutter teeth have the effect of a compulsory mixer,” explains the spokesman. “The soil is fluidised and forced upwards at both sides of the mixing unit, which is mounted on a kelly bar. The hollow stem of the kelly bar houses both the slurry hose pipe and the hydraulic hoses for supplying power to the mixer unit. The types of drilling rigs deployed as base machines for the cutter gear drive unit mounted on the kelly bar range from BG 15H to BG 25, depending on the required depth of penetration.”
The minimum plan area of a mixed slurry-soil panel is 2.20 m by 0.50 m.
Strengths
The CSM technique offers significant advantages over conventional soil mixing techniques:
• Compared to methods involving soil excavation (diaphragm wall, bored pile wall), the technique can utilise the existing soil as construction material; and it calls for minimal soil removal, as a majority of the surplus soil-cement mixture can be regenerated and recycled for further use. The residual soil material can be removed off site as dry material.
• Compared to other soil mixing techniques (multiple auger or mixing paddle based), the CMS technique achieves wall depths of 25 m and daily outputs of 200 sq m with base machines of operating weights ranging from 70 to 90 tonnes and installed power outputs of 260 to 300 kW. High vertical accuracy of the wall panels is achieved by counter-rotating cutter wheels. The system enables clean and trouble-free joint construction as result of cutter wheel principle for wall panels of different age (for example, after weekend rest periods or stoppages during work process). As a pile boring rig is used as base machine, the refit from standard drilling rig to CSM carrier rig is accomplished within a few hours. It offers a vibration-free and low-noise process for deployment in inner city areas.
In addition, hard soil strata can easily be penetrated by using the cutter wheels as loosening and mixing tool; the continuous display of important production parameters supports the rig operator in controlling the production process.
Bauer Maschinen came into being in 2001 following a restructuring of the Bauer Group.
Bauer’s Equipment Manufacturing Division, which had over 30 years experience as a specialist foundation construction equipment manufacturer, became an independent player, opening up new opportunities for the company in equipment manufacturing in the market place, says the spokesman.
Based on the experiences gained on construction sites and a willingness to innovate, a complete range of equipment for specialist foundation construction was assembled under the roof of the Bauer Group.
Bauer Maschinen has led through innovation since its inception, offering the market place the first anchor drilling rig capable of delivering optimum results for the then newly developed anchor drilling technique – followed by the first BG7, a heavy-duty rotary drilling rig which is claimed to have revolutionized drilling technology.
Today, Bauer Maschinen is the world leader in the foundation equipment sector, he says.
At this year’s bauma construction equipment show held earlier this year in Munich, Germany, the company introduced and showcased a host of products that range from drilling rigs to diaphragm wall cutters. The machines include:
BG series
The biggest rotary drilling rig showcased at the bauma by Bauer was a BG 40 equipped with a double-head rotary drilling system. Over recent years, this technique has proved itself on numerous occasions and has resulted in outstanding rates of production when drilling in the most difficult ground conditions, says the spokesman. The double-head rotary drilling system deploys two rotary drives: by concurrently drilling a continuous flight auger into the ground and – in opposite direction – a string of drill casing, piles of 1,200 mm diameter can be constructed in one continuous operation to depths of up to 18 m.
The rotary drilling rigs of the BG series for large diameter boreholes represent the core manufacturing sector of Bauer Maschinen.
With an overall height of 32 m and a torque of 468 kNm, the BG 48 is the biggest rig designed and built by the company. The rig is capable of drilling 3 m diameter boreholes with full torque to a depth of up to 70 m.
The rig has a total weight of 260 tonnes, an overall height of 36 m and has been designed for boreholes to a depth of 100 m.
BC 32
Bauer Maschinen also showcased its 100th diaphragm wall cutter straight off the production line. The BC 32 cutter designed for depths of up to 35 m is mounted on the mast of a BG 25 large diameter rotary drilling rig. If and when required, the rig can also be refitted for deployment as a large diameter rotary drilling rig.
VDW 6035
RTG Rammtechik, an important centre of competence within the Bauer Maschinen Group of companies, displayed its VDW 6035.
The system has a double-head rotary drilling system mounted on a RG 16T base machine for installing cased CFA cast in-situ concrete piles. It deploys two rotary drives: by drilling a continuous flight auger into the ground with one rotary drive while the second rotary drive drills down casing (which is rotated in opposite direction), CFA piles of 406 mm diameter can be constructed to depths of up to 14 m.
MG15
The MG15, a brand new drilling rig for installing soil displacement piles up to 400 mm in diameter was also on display at the Bauma. The maximum torque produced by the rig is in the region of 150 kNm, which is achieved by a rotating casing clamp mounted at the bottom of the leader. Crowd pressure is provided via the rig’s telescopic leader.
“Our sales and service network extends across the globe, in some countries Bauer machines and equipment are manufactured locally for regional market requirements. In almost every country, Bauer has its own sales offices and representatives who are able to provide advice and support to customers,” the spokesman concludes.
