Tasked with one of New Zealand’s key roading projects, the Peka Peka north of Otaki Expressway (PP20), Higgins Group require smart heavy equipment solutions to maintain their project schedule. Having lost time to the Covid-19 pandemic, Higgins were looking for gaps in efficiency, and found room for improvement as stabilisation of the highway base layer began. The objective of this stage in the roading project was to create 250mm layers at a time; ensuring cost and time spent was kept within their targets. Before exploring alternative options, their initial workflow was not only high cost regarding labour, but also resource use and time spent.
The first stage of stabilisation required a 16 ton construction roller to compact the bottom layer, but were noticing that after the 16 required passes, the top layer would begin to break down. To rectify this, the next step in their process was to follow up with an oscillating2 roller to smooth the upper section of the 250mm layers. Finally, the team at Higgins would finish each section with a PTR roller to seal the top layer.
This traditional compaction plant model was costing significant time and man-power, and the Higgins Group saw an opportunity to improve: the BOMAG 213 BVC D-5 roller. Supplied by Porter Equipment, the BOMAG 213 BVC D-5 utilises the patented VARIOCONTROL Bomag technology, providing targeted compaction energy which is automatically adjusted to match the conditions on the ground. By replacing the previous compaction model with the 213 BVC D-5, Higgins were able to reduce the cost of two rollers and operators, significantly simplifying their compaction workflow.
PLANT USED BEFORE BOMAG BW213BVC D-5
PLANT USED AFTER BOMAG BW213BVC D-5
• Pre-moisture NDM check (to decide % amount of water to add to bring to optimum moisture content).
• Commence hoe adding pre-determined water.
• Commence rolling with construction rollers on High Vibe to pre-determined amount passes from plateau. Once complete, move over and continue until all runs have had correct number of passes.
• Commence grading after high vibe rolling on 2nd run is complete.
• 1 x construction roller to work in conjunction with grader on low vibe until pre-determined amount of passes from plateau is complete on each run.
• Once grading and construction rolling is complete twin steels then do their pre-determined amount of passes on each run.
• Water is added to surface and PTR begins surface finishing works and drag brooming begins.
• Once all high vibes are complete on section 1, hoeing begins on section 2 and all steps from section 1 are repeated.
• Pre-moisture NDM check (to decide % amount of water to add to bring to above optimum moisture content 7%t).
• Commence hoe adding pre-determined water (from step above).
• Commence rolling with Bomag 213 BVC construction rollers on manual setting 6 max depth/max amplitude until half the required passes are completed.
• Once complete, move over and continue until all runs have had correct number of passes.
• Commence grading after max setting vibe rolling on 2nd run is complete.
• Once grading is completed to required height, Bomag 213 BVC rollers finish their required amount of passes on max setting for each run.
• One Bomag 213 BVC roller then begins secondary compaction with the required number of oscillation passes per run.
• Water is added to surface and PTR begins surface finishing works if needed and drag brooming begins.
• Once all manual setting 6 max depth/max amplitude passes are complete on section 1, hoeing begins on section 2 and all steps from section 1 are repeated apart from High Vibe correlation plateau undertaken to determine compaction densities are equal.
KEY BOMAG BENEFITS
With VARIOCONTROL, the amplitude can be adjusted exactly to the requirements of the site. The environment is protected from unwanted vibrations, without wasting compaction power. When the amplitude is increased to maximum, the single drum roller meets the performance of its weight class, and also handles applications for heavier machines. The BW 213 BVC-5 uses directed compaction force to achieve an amplitude value of more than 2mm. This corresponds to the compaction power of a 16 ton standard roller and is therefore producing 20% higher performance than standard rollers with circular exciters in the 13 t class. With VARIOCONTROL, thicker fill layers can be compacted or for the same layer thickness, the number of passes can be reduced.
Another issue which every roller operator knows well can be solved by VARIOCONTROL: the vibration direction is automatically switched to the driving direction. Material is no longer pushed in a bow wave in front of the roller, but is always pulled under the drum. This also improves traction. Furthermore, amplitude is automatically set to minimum during standstill, which prevents the drum from digging in.
Due to the counter-rotation, the individual centrifugal forces overlap so that the force produced is only effective on one plane. This produces directed vibration. The effective direction of this vibration is changed by slewing the complete exciter unit. Thus the drum is able to vibrate in a vertical or horizontal direction, or any angle in between. This change in direction of vibration is equivalent to a change in the vertical amplitude and therefore to the compaction energy transferred into the material.
In order to determine the optimal amplitude, two acceleration transducers permanently measure the movement of the drum on the ground. This signal is then used to calculate the dynamic stiffness of the soil EVIB in MN/m2. If the dynamic stiffness of the soil increases – in other words, the degree of compaction – the ground contact force will also increase. The movement of the drum then changes, which the sensors detect.
Based on these measuring values, the system will calculate and adjust the optimal amplitude in fractions of a second.