Brextor: a quantum leap in pile head processing

By Alois Portmann, BRC Engineering AG

All graphics and photos courtesy of BRC Engineering AG.

Due to increased dense construction and building in exposed locations, pile foundations continue to gain in importance. Previous pile-heading methods involve risks that can be avoided with the newly developed Brextor method.

BORED PILES AND PREVIOUS PROCESSING METHODS

The world is becoming increasingly crowded. The annual population growth rate is currently two per cent. The necessary building land is becoming increasingly rare, and thus the call for denser construction is becoming stronger. The available building ground is more and more often in exposed locations and of poor bearing capacity. Pile foundations are the solution to ensure a safe foundation in such conditions. For this reason, pile foundations are becoming increasingly important. The pile head is the connection to the foundation. Highest quality without compromise is required. A foundation failure can end in disaster.

Up to now, bored piles have mainly been processed with air or hydraulic hammers. Air or hydraulic hammers work with a vertical impact energy. This processing energy cannot be controlled. Thus, there is a risk of cracks in the concrete body and spalling on the outer skin of the pile. This can cause corrosion damage in the medium term. Bent or torn reinforcements caused by air or hydraulic hammers additionally reduce the absorption capacity of the tensile load. Due to the design-related mode of operation of these devices, a correspondingly large working space is required. Furthermore, narrow and long reinforcements are difficult to process, and large obstructions occur with existing spiral reinforcement in the excavation area. In order to ensure quality and to break the surface tension, a cut must also be made to the definitive height. The last 30 to 50 centimetres are only possible with a lot of manual work.

BREXTOR With Brextor, the working process remains under control. The horizontal force application allows 100 per cent control of the applied processing energy. In addition to the best possible quality, the pile head is handed over to the succeeding gear with precise accuracy (height accuracy +/- one centimetre). Also, the concrete structure and reinforcements remain intact.

The core tension is broken with the Brextor internal cutter. The surface tension is broken with the Brextor external cutter. The remaining concrete border with the reinforcement inside can be broken away with the Brextor crusher without risk of damage. Thus, the finished bored pile head is achieved in four working steps:

1) prepare the pile with the milling disc, 2) mill to level (+/- one centimetre height accuracy), 3) break out the remaining concrete with the BRC pile head crusher, and 4) clean and align the reinforcement.

Brextor is manufactured in Switzerland is a CAD drawn design and incorporates precision CNC machined parts. The process is patented worldwide.

NEW APPLICATIONS Brextor’s design allows it to be used with very little or even no lateral working space. This means that excavation can be saved. The cut at finished excavation level to break surface tension is made automatically with the external cutter. The clean-up effort is minimized to cleaning work. Brextor is suitable for all pile types/walls. The system uniformity allows easier use by site staff (one system for all uses – bored pile, bored pile wall, earth auger). In addition, the excavated material (80 per cent 0-30 millimetre gravel) can very often be processed directly on site.

FOUR-LANE EXPANSION LIESTAL, SWITZERLAND Brextor was used for the four-lane expansion at Liestal station, which was carried out by Implenia. The expansion of the northern and southern station entrances to four lanes should ensure significantly fewer crossing conflicts and more punctual and disruption-free rail traffic for long-distance, regional, and freight traffic.

“With manual removal by hydraulic hammer, there would always be a risk of damaging reinforcements and disturbing the concrete quality at the pile head. I minimize this risk with Brextor,” confirms Stefan Lang, site manager at Implenia.

TIME AND WORKSPACE SAVING

The client attaches great importance to timely execution of the work; after all, the four-track expansion is being carried out during ongoing rail operations.

“The time pressure on this construction site is huge, as various milestones have to be met,” notes Lang. “We only have a limited time window available and if this cannot be massively extended, such an undertaking would only be possible with a lot of resources and personnel without the Brextor.”

Time as a decisive factor was supplemented by the challenge of very little space. “We would also need more space, which would be a big challenge here because you don’t have enough room for a pick hammer between the nail wall and the pile head.” For this reason, it would be necessary to move back the wall, which is up to six metres high, over a length of 300 metres, just to create enough space for the pile head to be worked. This would mean a massive increase in costs. Thanks to Brextor, these costs are saved,” says Lang.

In the case of a railroad line extension, 80 centimetres of working space could be dispensed with on the rear side. With an embankment of six metres, over 300 metres, this results in 1,440 m3 excavation (fixed measure) which did not have to be made.

Besides the enormous cost savings for excavation, transport, landfill fee and material replacement, Brextor has made a great contribution to the environment and to the population. At least 280 truck trips of 40 kilometres each could be saved. Thus, the CO2 footprint was reduced and the population benefited from a less polluted road network. l