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Technical report #2

02 Feb 2021


By Andreas Persson, Dynapac Technical Specialist 

For decades, compaction levels have been achieved by machines compressing layers of materials, whilst operators undertake the number of passes they have been instructed to complete by site managers or by using industry guidelines. This outdated approach doesn't focus on achieving optimised compaction levels as it's unable to consider variables like site conditions which can potentially lead to both under and over compaction.

But thanks to advances brought about by observing mother nature, this is all about to change. This is because a new technical breakthrough is set to resonate around the industry, with our Seismic System launch. It takes an entirely new approach to compaction that supports increased performance and fuel savings by working in harmony with the soil.

This not only optimises compaction to eliminate rework but due to the technology it also has the possibility to complete the compaction tasks with fewer passes, increasing efficiency and productivity on site, whilst saving time, fuel and their associated project costs.

What is currently the norm for Intelligent or 'Smart' Compaction, is the use of compaction equipment operating at a fixed frequency and variable 'forced' amplitude. These types of products are much more complex to design and maintain, delivering a higher cost of purchase and ownership to the customer throughout a machines operating lifecycle. 

Forced amplitude relates to how a machine delivers forced vibrations into the soil using a fixed frequency. The compaction effort in a forced amplitude machine is adjusted by changing the exciter inside the drum in a mechanical way, which requires a complex sensitive and expensive mechanism. 

However, after close to five years of research, our engineering team has made a significant breakthrough in what we see as a Seismic shift away from a 'forced' amplitude approach to a resonance-controlled system. It's a breakthrough that uses the laws of mother nature to deliver lifecycle cost savings of up to 25% in fuel burn when combined with the Dynapac Eco-mode. 

Created to be in-tune with mother nature instead of forcing compaction, Seismic mimics the natural behaviours of materials as they are compacted. This is achieved by adjusting the frequency of the drum in a "smart way" by benefiting from the resonant frequency of the drum-soil system. The resonance achieved by this approach delivers a much simpler compaction solution with better results, less fuel burn and a reduced machine lifecycle cost. 

By using a much simpler solution, than the expensive advanced mechanics used by forced amplitude machines, Seismic adjusts the drum amplitude to match that of the soil. This then supports a natural phenomenon of enhanced compaction with the support of 'mother nature' to deliver all-round better performance.

This article will explain the differences between the two approaches of 'Forced' amplitude systems and the Seismic resonance system. This in-turn will demonstrate the overall impact we believe Seismic will have on the worksite and operators' wellbeing, particularly as we roll out our latest emission's compliant ranges with Seismic on-board.

The basics of compaction 

Going back to basics, good compaction is all about taking loose soils with poor load support and compacting it to the optimum level that improves the overall load support of the finished area. This process is usually achieved by vibration or impact, producing stress‐waves that rearrange the soil particles into an even denser state.

When you compact soils, you want to introduce as much energy as possible into the material, without crushing or over compacting it. With energy efficiency and fuel consumption now a key factor in purchasing equipment, it's important to carry out the compaction process in the most environmentally friendly and cost-effective way.

Of course, there are job sites which require different approaches depending on the layering of material, so Seismic has been developed for all applications to achieve compaction in the most productive way as possible, whilst using the minimum amount of fuel. 

To do this, we need to look at the behaviour of different types of material. We then need to magnify the forces delivered by the roller drum at all stages of compaction. Understanding mother nature is so important, as we know that all dynamic systems show a phenomenon called a "resonant frequency" where vibrations are greatly amplified. In practical terms, we feed in the energy from the machine to the soil at exactly the right time maximising compaction, whilst minimising the energy or fuel needed to achieve this. 

Put in simple terms. If you can continue to match the material's resonant frequency as you pass over it, you can continue to achieve this optimised compaction. It sounds straightforward, but the challenge in achieving this relates to how to continuously calculate the resonance frequency of the drum-soil system and adjust the machine accordingly. This is because with each pass, the stiffness of the material increases and changes the resonant frequency of the drum soil system.

Add into this the presence of 'Soft Spots' over different areas from weaker soils and it becomes impossible to monitor and change the frequency of the roller drum manually. This is why the Seismic system has been designed to monitor material conditions continuously, to automatically adjusting the drum frequency. 

How does Seismic measure and automatically adjust drum frequency?

The critical components at the heart of the Seismic system are the on-board machine control unit and a next-generation compaction meter. This device has been designed to sense the dynamic characteristics of the material being compacted. In turn, this allows Seismic to calculate the optimum frequency required to achieve the 'resonant frequency' needed to optimise compaction. 

This is achieved using advanced data flow from the Seismic Compaction Meter to the on-board machine control unit, which controls the machine's hydraulics. This means that drum frequency can be changed hydraulically every 0.2 seconds to ensure that both compaction performance and energy efficiency are maximised at all times.

How does Seismic prevent over compaction?

Operators of equipment not having the Seismic system, experience more 'double jumping' or bouncing, due to over compaction. This is because they don’t have Seismic’s ‘Active Bouncing Control’. This system automatically prevents harmful compaction energy from returning from the ground into the machine, by switching off the drum's vibration. This sends a real-world signal to the operator to stop compaction, and even if he must continue driving to the end of an already compacted pass, the material won't be vibration compacted any further. 

What we have also found with the Seismic system is that we can dramatically reduce over compaction because we are controlling the machine to operate in 'harmony with the soil'. This means that compared to 'forced vibratory compaction' the Seismic controlled machine operator will notice a reduction in the double jumping or bouncing associated with over compaction as it is much more unlikely to occur.

How does compaction carried out with the Seismic system differ from conventional compaction?

Having carried out extensive independently verified tests*1 in both lab and different site conditions, we have demonstrated the exact differences between the two. The first relates to the 20-30% reduction in vibration power needed to deliver the required compaction forces. This is because in most cases, the compaction frequency required is much lower compared to the fixed frequency used with conventional 'forced amplitude' compaction. 

In addition, we have found that with the Seismic system, the machine works in harmony with the material being compacted. This leads to better overall compaction, capable of reducing the overall number of passes required. 

This translates to a lifetime saving of 10% in fuel burn, which can be added up to an additional 25% if a compaction job uses the Dynapac ECO-mode fitted to all new Seismic machines. Reductions in vibration power also mean that fewer stresses are placed on the wear parts of the machine. This significantly impacts the maintenance of hydraulic and mechanical components within the machine's powertrain in particular. It also leads to a smoother ride for the operator and reduced noise emitted from the compaction process. And with overall maintenance and lifecycle costs reduced, owners will find that Seismic supports better residual values.

Linking Seismic with Dynalyzer our Continuous Compaction Control system

Of course, for Seismic machine users who want all of the compaction data for record taking, all of this information can be recorded using our Dynalyzer software. 

This is our continuous compaction control system that comes as an option with the machine. It uses the on-board removable tablet in the cab to record each pass, vibration settings used and compaction meter values, such as CMV, Evib1 and Evib2. This information is also linked to the GPS positioning data of the machine whilst compacting. So even though Seismic doesn't need to record data to ensure compaction, this is a great way of recording the progress on site. It also means that site managers can access the data to add it into as-built models, confirming compaction and working out how to manage the project in the best way.

With all of the positive environmental impacts, better and simpler compaction, there are significant benefits from the resonance controlled approach of Seismic, which is no surprise when mother nature had her hand in its design. 

Seismic Benefits at a Glance and independent testing

  • *1 Independent tests 
    To prove the performance of the new Seismic system, Dynapac commissioned an extensive independent test program. This was carried out by Dr. Carl Wersäll at KTH Royal Institute of Technology. Dr. Wersäll and his team compared compaction performance in several successful field trials in controlled conditions. These tests were carried out with the Seismic system turned on and off, respectively on the same roller.

The findings outlined from the independent tests conclude that:

  • Vibratory compaction is most efficient if it is carried out with a compaction frequency close to the resonant frequency (SEISMIC system) of the drum-soil system
  • From tests on crushed gravel, the number of passes until a specific compaction target is reached can be reduced with up to 30 %, if compaction is carried out with the Seismic system compared to conventional compaction at a higher fixed frequency.
  • The surface loosening effect in granular materials that is a common problem for conventional compaction is more or less eliminated on granular soils, meaning that the static passes towards the end of the compaction process for “finish compaction” might be omitted.
  • The Seismic system allows for fuel savings of up to 10 % compared to conventional compaction. Combined with Dynapac´s ECO-mode, that always comes with the Seismic machines, fuel savings of up to 25 % can be expected.
  • Compaction in Seismic mode utilises lower frequencies compared to conventional compaction. This saves fuel and energy, but also clearly states that centrifugal force is not a good measure of the compaction performance.
  • The lower operating frequency also means a significant decrease in machine wear and noise levels.

For more information on the Dynapac Seismic system, please contact:  
Andreas Persson, Vehicle Dynamics, Structural Analysis, Technical Specialist
Office: +46455306267
Mobile: +46764961745

Fredrik Åkesson, Product Portfolio Manager, Rollers
Office: +46455306095
Mobile: +46705769981

About Dynapac 
Dynapac is a leading supplier of high tech soil and asphalt rollers, light equipment and pavers, committed to strengthen customer performance by being a partner on the road ahead. Dynapac is represented worldwide via its own regional sales- and service offices, and cooperates with an extensive and professional distribution network. Headquartered in Wardenburg, Germany, Dynapac has production facilities in Europe, South America and Asia. Dynapac is part of the FAYAT Group.