Increasing compaction efficiency on soils - and saving costs - using cutting-edge technology

Major soil engineering projects incorporate demanding specifications for compaction, as exemplified by land reclamation, embankments, the construction of dams, airports and motorways. On one hand, the requirement looks for high effectiveness, i.e. to compact as much material volume as possible in the fewest passes. On the other hand, compaction should be uniform and applied in a controlled manner across the entire area. It is in projects such as these that the use of BOMAG cutting-edge technology increases efficiency and saves costs.

In the past it was virtually impossible to achieve higher compaction performance with single drum rollers other than by increasing the operating weight. In response to this, BOMAG set new levels of performance a few years ago with its 26 ton class roller. To increase output and performance further, entirely new concepts were needed. BOMAG engineers discovered that another quantum leap in compaction output was possible using new vibration exciters and special drum shapes. The result was a revolution: the BOMAG BW 226 DI-BVC single drum roller with VARIOCONTROL and polygonal drum. This technology has been used successfully on numerous projects in the Gulf region. This is the story.

The unique polygonal drum represents a break from previous roller shapes. Instead of being round, the polygonal drum is octagonal. Three octagonal segments are arranged across the drum in a staggered formation adjacent to each other. With ground contact there is an energy interchange between the plate and the octagon edges, whereby vibration forces are directed vertically and targeted, giving deep soil penetration. Shortly afterwards the edge engages the ground which introduces horizontal thrust forces to the surface. This prevents excessive compaction at the surface which leads to the "top-compacted surface effect" of conventional roller drums and to less compaction energy being delivered at depth. The polygonal drum gives a depth effect unachievable with round drums. A positive side effect of the angular drum is better bonding between layers. Furthermore, the angular drum shape gives better traction. Polygonal drums offer unique versatility as they can be used on nearly all types of soil. They can even replace conventional padfoot roller drums. Polygonal drums do not require energy-sapping scrapers thanks to their own self-cleaning capability.

To exploit the full potential of the polygonal drum, it is combined with the BOMAG VARIOCONTROL vibration system – BVC for short. On conventional vibration systems, the forces rotate in a circular path. This means that the drum also moves the same way. The BVC has succeeded in directing forces in a single direction. The drum only vibrates in the required direction and vibration forces enter the soil in a targeted way. The driver can adjust the force direction between horizontal and vertical in 6 stages. A horizontal setting would be used to avoid damage to aggregate, to compact thin layers near to the surface or to reduce the vibration load on the environment. The amplitude is adjusted to vertical for maximum depth effect and highest productivity. Thanks to the BVC, exciter forces are now possible that were inconceivable with a circular exciter. The BW 226 DI-BVC offers an amplitude of 2.7 mm with a 530 kN centrifugal force – unique values.

The result: by combining the polygonal drum with BOMAG VARIOCONTROL thicker fill layers are possible. In comparison with conventional rollers with the same operating weight, layers can be compacted at twice the depth.

And the BVC can do more: in automatic mode, the system recognises which setting is optimum and regulates vibration without driver input. At the same time, soil stiffness is continually monitored. This is done by measuring the movement of the drum on the subsurface using two acceleration sensors. An electronic system then uses these measured values to calculate the current soil stiffness. The driver just enters the target value for the specified soil stiffness. The system automatically adapts to this target value by adjusting the vibration amplitude. This means output is increased if high compaction energy is still needed; and compaction energy is progressively reduced for those areas where soil stiffness is approaching or has reached the target value. This gives exceptionally uniform compaction over the entire area. In addition, it avoids unwanted over-compaction and destruction of the soil structure. Another advantage is that drum bounce is eliminated.

The measured compaction values are not only used to regulate vibration, they are also used for information and documentation purposes in the form of surface covering dynamic compaction control. The measuring system calculates the "Evib" value (developed by BOMAG after years of research) as a measure for soil stiffness. An advantage of Evib when compared to other values is the direct correlation with the values EV1 and EV2 in MN/m2 from plate bearing tests according to DIN 18134. The Evib value means that for the first time there is a unit capable of delivering a comparable, absolute measured variable in MN/m2 irrespective of the roller type. The roller driver can see the Evib value on the display, which shows when compaction is finished - when the set target value has been exceeded or the system has recognised that there is no further increase in compaction. This avoids unnecessary passes.

The measured values can be documented in different ways. All BVC machines have a printer installed as standard. A printout can show Evib values for individual tracks as a line diagram. A more convenient way is to document results with the optional "BOMAG COMPACTION MANAGEMENT BCM05" laptop. This computer saves all tracks, fields and layers and has proven itself on many construction sites. Data management is easy using the associated software. Soft spots are easily identified and there is an unbroken chain documenting compaction progress. The high-spec version of the BCM05 can be fitted with a GPS receiver. BOMAG exclusively offers the "StarFire" receiver which achieves a precision of 15 cm with an integrated reference signal. Alternatively, other GPS receivers can be used, taking advantage of pre-existing infrastructures on-site. This makes BCM05 an exceptionally convenient documentation system. Evib values are saved and displayed with their respective position data. Mistakes and manipulation are avoided. Risks normally associated with compaction is minimised.

The advantages of this BOMAG technology come to the fore on major projects. For example, BOMAG single drum rollers were put to the test during the development of the Jebel Ali container port in Dubai. Originally, this project involved compaction of an embankment 1.5 m above sea level using conventional 12 ton single drum rollers. The rollers were to be used to handle layers of just 30 cm at 3.80 m above sea level and to compact these layers to 95 % Proctor density. However, a BW 226 DI- BVC single drum roller with polygonal drum and VARIOCONTROL achieved the same result with 1.35m layers. A gain in productivity of 450 %! In addition to this, compaction of the 1.5 m high embankment was finished in just 8 passes. BOMAG technology really accelerated construction progress.

BOMAG single drum rollers have also been used successfully in other projects in the Arab world. For example, a 26 ton polygonal roller with BVC replaced several conventional 12 ton rollers on the Qassim-Hail motorway in Saudi Arabia. And on a landfill project in Cairo, Egypt, the tight schedule for reclaiming new areas was achieved using super-efficient BOMAG rolling technology. And sites in Qatar, Iran and other countries in the Near and Middle East have also employed numerous BW 226 DI- BVC rollers.

Contact details:
BOMAG GmbH   
Hellerwald               
D-56154 Boppard

Dr Iris v. Kirschbaum                                       
Head of Communication                                
T: +49 / 6742/100-234                                 
F: +49 / 6742/100-378                                 
E: iris.kirschbaum@bomag.com              

Holger Winkelsträter
Press/PR
T: +49 / 6742/100-688
F: +49 / 6742/100-109
E: holger.winkelstraeter@bomag.com

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