Mechanical processing methods increase occupational health and safety on the construction sites of a network operator
Manual methods with jackhammers are generally used for the pile breaking of bored piles, but sometimes mini-excavators with mounted jackhammers are also used. Accidents caused by tipping 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 head 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 in order 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 removed. Until now, this work has been carried out with jackhammers as described above. Serious accidents have repeatedly occurred, particularly in the area of pile breaking.
Health hazards
People who are exposed to an excess of hand-arm vibrations can suffer from circulatory disorders 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 breaking methods
To minimise these risks, TenneT TSO GmbH, a high-voltage grid operator from Bavaria, looked for alternative solutions and found and tested two mechanical pile breaking methods: Pile Breaker and Brextor. During the realisation of their West Coast project, practical tests were carried out and the two methods were tested and compared directly in the field.
Method Pile-Breaker
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 cap and are driven hydraulically via the excavator or an auxiliary unit. The concrete is then removed from the pile head in slices. Ideally, the reinforcement should be encased in foam in advance so that the concrete is even easier to release. The pile breaker has a modular design and can be adapted to different pile diameters on site.
Method Brextor
Brextor does not require any work steps in upstream work processes, such as foam coating of the reinforcement at the pile 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 standing, can now be broken away with the BRC pile head crusher without risk to the concrete body or reinforcement.
The fixed connection to the carrier enables absolute control over the attachment tool at all times and therefore centimetre-precise work. This completely eliminates heavy physical labour and reduces it to just light cleaning work. The tool, which is guided in all directions, also enables the precise breaking of inclined piles. The deconstruction material that has already been processed during the work process can either be used directly in the cleanliness layer or utilised 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 savings potential for excavation work and also allow the processing of tangent pile walls.
Test evaluation Pile-Breaker
Positive
+ Reduction of heavy manual labour
+ High efficiency when the parameters are right
+ Low training costs
Negative
– Filigree coordination of earthworks/pile breaker
– 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
Test evaluation Brextor
Positive
+ Heavy physical labour is completely eliminated
+ No need for support 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 transport 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 breaking methods have the advantage that a large part of the manual processing with the pneumatic hammer can be dispensed with. On 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 Brextor, for example, is significantly quieter than conventional manual breaking.
Convincing test run
The tests with Pile-Breaker and Brextor were so successful that the company TenneT has decided to authorise pile breaking only with non-manually guided work equipment in future. “HSE guidelines stipulate that manual processing may only be used in justified exceptional cases. The advantages of automated processing are obvious. It minimises 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 favoured. In compliance with Section 2 (1) of the Construction Site Ordinance in conjunction with the principles formulated in Section 4 (Paragraphs 1 to 5) of the Occupational Health and Safety Act, manual breaking 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 has been enshrined 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 breaking 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 only mechanised work will be permitted in future. The two mechanical pile breaking 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 placed 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 transport to the landfill and the need to bring in replacement material.”
“The two mechanical pile breaking 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 breaking methods such as the Pile Breaker and Brextor. There are no people in the swivelling and danger zone of the excavator during work and there is no longer any need to manually strike and dispose of a concrete core.
TenneT TSO GmbH
BRC Swiss/Brextor
Original press release in German.