Polygonal drum for deep compaction

By Hans-Josef Kloubert, BOMAG GmbH, Germany

The following article describes the design and effect of the single drum roller with polygonal drum for deep compaction and thick lift compaction applications.

Padfoot and smooth drum rollers are well known to projecting engineers, construction supervisors and earth construction companies with respect to application and effect. The compacting depth of this type of equipment is approx. 40 to max. 80cm, whereby lift heights of 30-40cm, as typical for earth construction, are laid. Padfoot rollers are thereby mostly used on cohesive loose ground, whereas the smooth drum roller is employed for non-cohesive loose soils. On mixed particle soils either padfoot or smooth drum rollers may be used, depending on the condition of the soil. A suitable roller shape to enable deeper compaction and to cover a more wider soil spectrum than the roller types available at this time, where not available in the market. Trying to meet these requirements of earth construction companies resulted in the development of a roller which, due to the wide ground contact area of the drum, achieves a high depth effect and, due to the flexing and kneading effect, also achieves compaction in mixed particle loose ground. These requirements are met by the polygonal drum.

The polygonal drum roller was developed by BOMAG in the early nineties and the 4th generation of this roller type is available in the market since 6 years.

Fig. 1: 26t Polygonal drum roller BW 226 DI – 4 BVC

The polygonal drum developed by BOMAG consists of three octagonal elements axially next to one another, each arranged offset to the neighbouring segment. Laterally weld on rings prevent the drum from tipping when the central element is standing exactly on the edge. Polygonal drums have 24 smooth areas and 24 edges. With full ground contact these smooth areas generate a considerably higher pressure cone, than comparable round drums. When the drums rolls on over the edges, these edges generate a particularly effective kneading and shearing effect, as well as high peak pressures, which are considerably higher than the ones achieved with padfoot drums. The combination of this special drum shape with the high dynamic forces provided by the directed vibrations of the BOMAG VARIOCONTROL system, enables optimal introduction of forces into the ground (see Fig. 2a, 2b). The VARIOCONTROL system is able to generate amplitudes of 2.85 mm and centrifugal forces of up to

530KN.

Fig. 2: Compaction effect of the polygonal drum roller

The polygonal drum roller is always equipped with a compaction measuring device (Terrameter), which measures continuously the soil stiffness modulus Evib (MN/m²). An additional documentation system (BCM05) can easily be installed in order to collect, present and evaluate all data according to various criterions. This information is very helpful for the economical use of the roller, the proof of maximum compaction achieved, the proof of uniform stiffness, for weak spot analysis and proof rolling purpose. It can also be applied as a continuous compaction control method based on correlations between density and soil stiffness modulus. All standard BOMAG single drum rollers (smooth drum / padfoot drum) can be equipped with the measuring and documentation system.

The BOMAG continuous compaction control systems (Terrameter and BCM05) are already applied on many European highway, high speed rail link, airfield and huge foundation areas projects.

Fig. 3: BOMAG Compaction measuring and documentation system

Over the last few years BOMAG conducted together with international geotechnical consulting engineers extensive examinations concerning the compaction effect of the polygonal drum roller in different soil materials and fields of application.
•  Post compaction of existing fills and natural grounds
•  Comparison of smooth / padfoot and polygonal drum rollers with different operating weights
•  Increase of lift heights for embankments in motorway and dam construction

The result of these trials revealed that the polygonal drum roller in comparison to the standard smooth and padfoot roller:
•  achieves higher degrees of compaction
•  deeper compaction depths
•  less permeability
•  higher load bearing capacities
•  substantial cost savings compared to the traditional cut and fill method using traditional 10–12t single drum rollers

Depth compaction trials   
The depth compaction trials with the polygonal drum where conducted in testing and calibration fields, following the test methods E3 and E4 of the German Earthwork regulations TP BF StB. The significant parameters for compaction
•  degree of compaction
•  load bearing capacity
•  bonding of joints between the layers
were determined by direct and indirect testing methods. The tests concerning the before mentioned parameters were carried out in the testing and calibration fields from the top level of the terrain down to a depth of 5.0m below the compaction level.

Fig. 4: 30–35cm of soil settlement after 10 passes with BW 226 DI-4 polygonal drum

Initial tests for determining the depth effect of the polygonal drum roller were conducted in 2003 (WEINGART et al, 2003). Here parameter changes down to 5m under the ground  surface were detected after compaction with a 26t polygonal drum roller. The degree of compaction increased by 5% over a depth range of approx. 2.0m. The sounding resistance of the light ram penetrometer increases by 10 blows per 10cm penetration and the peak resistance of the static pressure tube increases by 5MN/m², always across a depth range of approx. 3.0m. The surface settlement on average was 30–35cm (see Fig. 4).

German highway embankment A 20
The A 20 motorway construction required the construction of a subbase in the form of an dam layer with a thickness of up to 1.5m. For this dam construction it was examined whether the previous layer thickness of 0.3m could be increased when using the polygonal drum roller. For this purpose a wedge shaped testing field with a maximum layer thickness of 2.0m and 9 compaction tracks side by side was prepared. Always three compaction tracks were compacted in 3, 6 or 9 passes of the polygonal drum roller with an operating weight of 26t. The middle track of these three tracks were examined in 4 transverse profiles (per 0.5m increase in layer thickness).

Figure 5: Preparation of the compaction trial area

The examination revealed the required compaction of 95% of the degree of compaction over a height of 1.5m had already been reached after 3 passes. The compaction was examined over the layer thickness by calibrating the compaction against the ram penetration resistance. After testing and approval of the testing field the company DEGES constructed the A 20 motorway over a length of 20km with a layer thickness of max. 1.5m and used the polygonal drum roller for compaction.

Dubai seaport extension
Apart from extensive experiences on constructions sites in Germany, excellent results were also achieved with the polygonal drum roller in international backfilling, dam construction and land reclamation projects. There are currently 10 machines involved in land reclamation measures in the Persian Gulf.

For the extension of the Jebel Ali seaport in Dubai the area of the container terminal is extended as the first of 14 project phases by using the dredging/flushing method. The offshore dredging vessels dredge gravelly, sandy soils, which are partly heavily loaded with rock material, from the bottom of the sea and flush these to the shore. According to the original plan the new container area was to be built up in layers of 30cm, starting from 1.5m above seal level to a height of 3.80m above seal level, and compacted with 12t single drum rollers. For the existing terrain, which has already been flushed up to a height of 1.50m, subsequent compaction to 90% of the modified Proctor density is required. For the layers on top of this terrain up to a height of 3.80m above sea level a compaction of 95% modified Proctor density is specified.

Fig. 6: Compaction of soil to 1.50m with BW 226 DI-4 BVC  and compaction tests at various depths on trial area

Extensive compaction trials including a BW 226 DI-4 BVC with polygonal drum revealed that a subsequent compaction on the terrain level was possible down to a depth of 1.50m and that the following build up can be made in two layers of 1.35m each.

Two testing fields, 20m in width x 50m in length, were prepared to measure the density with an isotope gauge  and the sand replacement method at  depths of 0.30m, 0.80m and 1.50m after 6, 8, 10 and 12 passes with water contents in the range of 6% ≤ Wn ≤ Wopt ~ 10%.

The tests revealed that successful subsequent compaction of the dredged and flushed terrain down to a depth of 1.50m after 8 passes is assured. For the additional build up in two layers of 1.35m each a total of 12 passes was found to be adequate to achieve a compaction of 95% modified Proctor density. With the use of the polygonal drum roller from BOMAG the entire construction process – application of soil by dredging / flushing, distribution by bulldozer, compaction with roller – could be significantly accelerated and executed more economically, because of the roller's higher depth effect when compared with conventional single drum rollers.

Singapore Jurong Island
Two units with BW 226 DI-4 BVC polygonal drum machines were delivered to Singapore in 2007 for post compaction, backfilling and proof rolling purpose of a mid size land reclamation project. Around 500,000m² of the area was to be developed for heavy industrial installations. The existing ground, mainly brown sand with at least 30% of sea shell content and a density of around 85–90% MDD, had to be compacted to a depth of 2.0m in one layer with at least 95% MDD at a depth of 1.0m. Uniform compaction had to be achieved.

Fig. 7: Post compaction of existing ground on Jurong Island at depths of >1.5m with
BW 226 DI – 4 BVC equipped with BCM05

On the Jurong Island project compaction trials were set up and it was found that compaction requirements were achieved after 14-16 passes at an operating speed of 2.0-2.5km/h.
The documentation of the soil stiffness data measured by the roller itself provide very useful information about compacted soil quality and uniformity of compaction (Fig. 8).

Fig. 8: Mapping of soil stiffness Evib, right for one track, left for an area of 3000m² showing uniform compaction on a high bearing capacity level

Conclusion
For the construction practice the available results from the testing fields and the practical applications mean that the polygonal drum roller in comparison to traditional single drum rollers:
•  deep compaction capability of >1m
•  Thick lifts application
•  high compaction performance (500-1500m³/h)
•  considerable reduction of construction time
•  the on board compaction measuring system together with the BCM05 documentation system provide continuous proof rolling documentation
•  suitable for granular, mixed and cohesive soils

With the polygonal drum roller the market offers a machine which, apart from the original requirements – higher depth effect, compaction of sandy, gravely, silty, mixed and cohesive soils – can be universally and economically used in earth and dam construction.

The company:
BOMAG is a global market leader in compaction technology. The company, situated in Boppard, Germany, belongs to the French FAYAT Group and produces compaction machines, stabilisers/recyclers, milling machines and pavers. In 2007, around 2,000 employees achieved a turnover of 634 million Euros. Six branches within Germany, 11 subsidiaries worldwide and more than 500 dealers in over 120 countries guarantee global distribution and service.
 
Literature
• Floss, R. (2001): Compaction Technology in Earthwork, Highway and Transportation Engineering Volume 1, BOMAG GmbH, Boppard
• Weingart, W.; Körner, M.; Saal, S. (2003): Investigation into the compaction in depth effect of a vibratory roller with polygonal drum. German version published in Strasse und Autobahn , 2003, Kirschbaum Verlag GmbH, Bonn, Germany
• BOMAG (2004): Company documents Polygonal Drum Roller
• FUGRO (2004): Technical test report - Examination of the compaction effect of various BOMAG single drum rollers by means of direct and indirect testing methods Construction: Testing field BOMAG
• Thiele, R. (2005): Experience with the use of a single drum roller with polygonal drum for in-depth compaction, Expert Meeting Road Construction, Civil Engineering and Earthwork 2005
• ZTV-E-StB (1994 / 1997): German Earthwork Regulations
• FGSV (1994): German technical testing instructions for soils and field in TP BF-StB, part E 3, Examination and compaction by test compaction and work instructions
• Kloubert, H.-J. (2006): Construction site report about the use of a polygonal drum roller BW 226 DI-4 BVC in the Jebel Ali harbour extension project in Dubai, BOMAG GmbH, Boppard, not published 
• Ong, K.L. (2008): Experience report with polygonal drum roller BW 226 DI-4 BVC on Jurong Island Project , Singapore; BOMAG GmbH, not published