Dynapac roller cuts fuel consumption in HS2 trial

A Dynapac vibratory roller recorded fuel consumption 20–32% lower than a comparable machine during an HS2 earthworks trial near Birmingham, while both machines achieved the required ground compaction standard.

The evaluation compared a Dynapac CA6000D SEISMIC with another 19-tonne roller on parallel test areas prepared using 6F8 crushed limestone. Balfour Beatty VINCI (BBV), SMT GB, and Dynapac carried out the comparison to assess whether adaptive vibration could reduce diesel use without compromising the performance of the compacted material.

Both machines met the specified compaction requirements, but the Dynapac roller delivered improved density close to the finished surface following its final passes. Fuel consumption was measured using machine telematics, with the reported reduction applying to the monitored operating periods rather than a complete construction programme.

The difference centres on how vibration energy is transferred into the ground. Conventional vibratory rollers typically operate at a selected frequency and amplitude, applying repeated dynamic loads through the drum as the machine travels across the material.

These loads cause aggregate particles to rearrange and settle into a denser configuration. The process reduces air voids and increases the stiffness of the compacted layer, helping it provide a stable formation for subsequent construction. The results depend on the material grading, moisture content, layer thickness, underlying support, and the characteristics of the applied loading.

Dynapac’s patented SEISMIC system changes the vibration frequency automatically in response to the material beneath the drum. Its control system identifies the resonant frequency of the roller and ground combination and adjusts the excitation system to operate closer to that frequency.

As compaction progresses, the ground becomes stiffer and its response to vibration changes. A frequency selected at the beginning of the operation may therefore become less effective as the material approaches the required density. Adaptive control is intended to maintain efficient energy transfer without relying on a fixed operating frequency throughout the compaction sequence.

That adjustment does not eliminate the energy required to compact the material. Instead, it changes the relationship between the energy generated by the vibrating drum and the mechanical response of the ground. The trial indicates that this approach can reduce the diesel consumed during the operation while retaining the required engineering performance.

BBV tested the machines on parallel sections of 6F8 crushed limestone, with a reported material grading of 0–40mm. Both rollers worked under comparable conditions, providing a basis for assessing differences in the resulting compaction and fuel consumption.

Density measurements were taken at multiple depths using a nuclear density gauge. The instrument provides measurements associated with the compacted condition of the material, allowing the project team to evaluate whether the required density had been achieved at selected testing locations.

Layer stiffness was assessed using a falling weight deflectometer. This equipment applies a controlled loading pulse and measures the resulting surface deflection, providing information about the response of the compacted layer under load.

Density and stiffness describe different aspects of ground performance. A material may meet its density requirement while exhibiting a different response to loading, depending on its composition, moisture, and supporting formation. Testing both characteristics provided a more complete assessment than relying on machine operating data alone.

The Dynapac roller achieved improved near-surface density after the finishing passes, with the trial also identifying reduced surface loosening and a smoother final condition. BBV concluded that this performance could remove the need for an additional pneumatic tyre roller previously used to finish comparable work.

That possibility has not been established as a universal change to the construction method. Removing a secondary finishing operation would require confirmation that the completed layer meets the relevant project specification under the conditions encountered on each site.

Where an additional machine can be omitted, the potential benefits extend beyond the fuel consumed by the principal roller. Fewer equipment movements and finishing passes could reduce plant operating hours, simplify the sequence of earthworks, and release resources for other construction activities.

The published trial does not quantify those wider savings. It provides a measured comparison of fuel consumption and compaction performance, together with an assessment of how improved surface density might affect subsequent operations.

Operator feedback also indicated quieter and more comfortable working conditions when using the adaptive system. The participants associated this with the optimised vibration, although the evaluation did not establish independently measured reductions in noise exposure or whole-body vibration.

The distinction is important because perceived improvements in operating comfort do not automatically demonstrate compliance with occupational exposure limits or establish a specific health benefit. Those outcomes require appropriate measurements under representative operating conditions.

Compaction forms a substantial part of major earthworks programmes. Engineered fill is placed in successive layers, with each layer compacted and tested before further material or construction activities can proceed. The number of passes needed to meet the specification influences the rate at which individual work areas can be completed.

Roller productivity is therefore affected by both the time spent compacting and the quality of the finished layer. Equipment that consumes less fuel but requires substantially more passes may offer a different overall result from a machine that meets the specification with fewer operations.

The HS2 trial did not establish a complete comparison of lifetime machine costs, maintenance requirements, or productivity across different materials. However, it demonstrated that two machines of comparable operating weight could achieve the required compaction while recording different levels of diesel consumption.

Lower diesel consumption also reduces the emissions associated with the fuel burned during operation, although the published results do not provide a verified calculation of total project carbon savings. Such an assessment would need to account for operating hours, machine utilisation, additional equipment, and any changes to the construction sequence.

Further testing across different soil types and site conditions would establish how consistently adaptive vibration performs outside the trial environment. Cohesive soils, variable moisture conditions, and different aggregate gradings may respond differently to changes in vibration frequency.

The comparative results provide evidence of reduced fuel consumption and improved surface density during a defined HS2 application. Wider deployment will depend on whether those improvements can be reproduced while meeting the compaction specifications and operating requirements of other projects.