A vibro hammer will only perform as well as the power pack allows. We should look at the power pack’s specifications before the vibro’s specs. This article by Prof Dr. Holeyman of the university of Leuven in Belgium will prove why we are right to point our clients in that direction!

The power pack functions like a heart, it is connected by hoses (arteries) to hammer and clamps (the limbs and muscles) and drives the whole body. The research article we are sharing today presents findings on the importance of the power source for piling. In this posting we have taken the main findings of the paper and explained them so that a regular user can understand them. If you want the full article with all the graphs and references, please click the link at the bottom of this page to download it. 

The hammer's frequency is dependent on the capability of the hydraulic pump to provide the flow required to keep it working at the required frequency when driving through soil with higher friction resistance.

The experiment results show the vibration frequency is often lower than the theoretical frequency of the vibratory hammer. Further analysis of the data has brought to light that the reduction in frequency is due to insufficient power (kW) provided by the power source (hydraulic power pack).

The findings of 13 test piles on a jobsite in Merville France are illustrated in the figure below. For this test the vibro hammer and clay soil conditions were invariable, and the pile types were variables. The piles frequency (left) and the hydraulic power supply (right) were measured in real-time as a function of driving depth.

As the pile is driven deeper the hydraulic power supply increases to overcome the soil’s friction resistance. The figure shows the increase in kW as the pile penetrates the soil. When maximum power (in this case 300kW) is exceeded the vibro hammer’s frequency significantly reduces.

The graph further shows that the relationship between frequency and power is unaffected by pile type. Therefore, it is possible to make an estimation of the power usage by monitoring the progression of the vibro’s frequency.

Practically this means that to keep the vibro operating at its specification it is necessary to pay attention to the power pack’s pump and engine. ICE’s power pack design is optimized to meet these requirements: a variable pump and effective cooling of the power pack offer optimum working conditions for the pump.

While it is common practice to choose a larger vibratory hammer when a pile meets refusal, the data shows that for heavy driving conditions it could be more beneficial to increase the power supply and keep the hammer unchanged.

To compare different hammer models or brands you can determine the ratio [max centrifugal force kN hammer] and [engine max power kW of the power pack] which will predict the performance of the equipment. If you are unsure about the accuracy of the specs provided by a supplier, you can easily check the frequency of the vibro with a handheld RPM-meter to see if it matches the data provided by the manufacturer.

References:

“Sheet pile vibro-driving: Power pack-vibrator-sheet pile-soil interactions“ Holeyman, A.； Universite´ Catholique de Louvain, Louvain-la-Neuve, Belgium, Whenham, V.；Belgian Building Research Institute, Brussels, Belgium. In: Science, Technology and Practice, 2008 IOS Press, ISBN 978-1-58603-909-7 

The full article can be downloaded here:

https://www.fondytest.com/Alain-Holeyman-s-publications/pdf/2008-8th-Stress-Wave-2.pdf

“Intrillen van damplanken: Invloedparameters en voorspellingsmethodes” Dr.ir. Valérie Whenham WTCB Ir. Noël Huybrechts WTCB Prof.dr.ir. Alain Holeyman Université catholique de Louvain (UCL), in

GEOTECHNIEK, December 2011