BauPortal 2023: New solutions for pile breaking

Bird's eye view of piles
A bird’s eye view of bored piles.

Machine processing methods increase occupational health and safety on a network operator’s construction sites

Manual methods with caulking hammers are generally used for the pile head processing of bored piles, but sometimes mini-excavators with mounted caulking hammers are also used. Accidents caused by tipping bored pile heads and serious health problems induced by noise, vibrations and dust are side effects for the personnel carrying out the work. As the safety and health of employees on construction sites are also the responsibility of the client under the Construction Site Ordinance (Section 2 [1]), TenneT TSO GmbH, a grid operator from Bavaria, decided to demand new solutions with a higher level of protection for employees when working on pile heads.

High-voltage pylons are often founded on bored piles. The pile heads of these piles, on which the mast foundations are placed, must be machined to ensure a secure and high-quality connection to the foundation. The process involves drilling a pile from the top edge of the ground to the target depth. The soil around the pile head is then excavated to create the embedment length of the pile reinforcement in the foundation reinforcement in accordance with the structural specifications. As a result, the concrete around the reinforcement must be chiseled off. Until now, this work has been carried out with pneumatic hammers as described above. Serious accidents have repeatedly occurred, particularly in the area of pile head processing.

Health hazards

HAVS syndrome

People who are exposed to excessive hand-arm vibrations may experience impaired blood circulation in the fingers and neurological and motor dysfunctions in the hands and arms.
Picture: © BRC

The use of hand-held pneumatic hammers causes vibrations to enter the hand-arm area and can lead to damage known as hand-arm vibration syndrome (HAVS). In the worst case scenario, this can extend to incapacity for work.

Two mechanical pile head processing methods

To minimize these risks, TenneT TSO GmbH, a high-voltage grid operator from Bavaria, looked for alternative solutions and found and tested two mechanical pile head processing methods: Pile Breaker and Brextor. During the implementation of their West Coast project, practical tests were carried out and the two methods were tested and compared directly in the field.

Pile-Breaker method

After pile production, the pile breaker (a ring-shaped arrangement of hydraulic chisels) is lifted over the pile head to be removed using an excavator. The chisels work like individual caulking hammers, except that they act concentrically around the pile head and are driven hydraulically via the excavator or an auxiliary unit. The concrete is then removed from the pile head in sections. Ideally, the reinforcement is coated with foam in advance to make it even easier for the concrete to release. The pile breaker has a modular design and can be adapted to different pile diameters on site.

Brextor method

Brextor does not require any work steps in upstream work processes, such as foam coating of the reinforcement at the head. A hydraulic drive attached to an excavator operates the Brextor milling tools. This means that the concrete inside and outside the reinforcement is removed in a 100% controlled working process. The inner cutter breaks the core tension and the outer cutter breaks the surface tension. The remaining concrete edge, in which the undamaged reinforcement is located, can now be broken away with the BRC pile head bit without risk to the concrete body or reinforcement.

The fixed connection to the carrier device enables absolute control over the attachment tool at all times and therefore centimeter-precise work. This completely eliminates heavy physical labor and reduces it to light cleaning work. The tool, which is guided in all directions, also enables the precise processing of inclined piles. The deconstruction material that has already been processed during the work process can either be incorporated directly into the clean layer or used as recycling material in another measure. The milling tools, which can be adapted to the pile sizes, considerably reduce the lateral working space, enable a large saving potential in excavation work and also the processing of tangential pile walls.

Test rating Pile-Breaker

Positive

+ Reduction of heavy manual labor

+ High efficiency if the parameters are right

+ Low training costs

Negative

– Filigree coordination of earthworks/pile cutter

– No or poor correction of errors made during pile production

– Limited use (inclined piles, pile walls)

– Cross on the top reinforcement ring of the reinforcement cage is obstructive

Pile Breaker
After pile production, the pile breaker (a ring-shaped arrangement of hydraulic chisels) is lifted over the pile head to be removed. The chisels chisel the concrete from the reinforcement slice by slice without destroying it. The removed concrete residue can then be lifted away and disposed of.

Pile cutter
A hydraulic drive attached to an excavator operates the Brextor milling tools, which are used to remove the concrete inside and outside the reinforcement.

Brextor test rating

Positive

+ Heavy physical labor is completely eliminated

+ No need for auxiliary personnel to remain in the danger zone during the work process

+ High working accuracy

+ High efficiency in the overall work process

+ Predictable, reliable performance

+ Dismantling material already recycled

+ Less resource consumption

+ Less transportation required (therefore less CO2)

Negative

– Correct configuration of the carrier device required

– Training costs for operating personnel

– More work process planning

– Cross on the top reinforcement ring of the reinforcement cage is obstructive

Conclusion on the two methods

The two mechanical pile head processing methods have the advantage that a large part of the manual processing with the pneumatic hammer can be dispensed with. On the one hand, this means that fewer staff are required and, on the other, employees are not exposed to noise and exhaust fumes. Noise measurements on the construction site have shown that the Brextor, for example, is significantly quieter than conventional manual chiseling.

Convincing test run

breaking of inclined piles
The remaining concrete edge, in which the undamaged reinforcement is located, can be broken away without risk to the concrete body or reinforcement.

The tests with Pile-Breaker and Brextor were so successful that the company TenneT has decided to only allow pile capping with non-manually guided work equipment in future. “HSE guidelines stipulate that manual processing is only permitted in justified exceptional cases. The advantages of mechanical processing are obvious. It minimizes the risk of accidents at work and protects employees from HAVS, which is hazardous to health. If there is a technical solution to prevent accidents at work and reduce the exposure of workers to vibrations, this should be preferred. In compliance with § 2 (1) of the Construction Site Ordinance in conjunction with the principles formulated in § 4 (para. 1 to 5) of the Occupational Health and Safety Act, manual chiselling should only be used in exceptional cases on all construction sites in Germany. The consequences for individuals, society and companies if employees are absent or suffer an accident at work due to HAVS are too high. This decision was anchored in the company’s HSE guidelines and is therefore binding for all future projects,” says Christoph Brüggemann, HSE expert at TenneT.

Dominik Gorgulla, the project manager responsible for TenneT’s West Coast project, confirms the positive experience with the new pile head processing methods. “We want to protect the health of our employees and reduce the number of accidents at work. For this reason, the project has decided that in future only mechanical work will be permitted. The two mechanical pile head processing methods not only have the advantage of being safer and healthier for the employees, they also have other advantages. Machine processing of the piles is much faster and the material can be inserted directly into the clean layer using the milling method, so that the bulky concrete parts do not have to be reduced in size and disposed of. This also saves on transportation to the landfill and the need to bring in replacement material.”

“The two mechanical pile head processing methods not only have the advantage of being safer and healthier for employees, but also have other benefits.”
(Dominik Gorgulla, TenneT)

On the way to greater occupational health and safety

Overall, it is clear that TenneT has taken an important step towards occupational health and safety in this area with the introduction of mechanical pile head processing methods such as the Pile Breaker and Brextor. There are no people in the swivel and danger zone of the excavator during work and no concrete core has to be struck and disposed of manually.

TenneT TSO GmbH
BRC Swiss/Brextor

Original press release in German.

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