MECHANISED TUNNELLING | BTS HARDING PRIZE COMPETITION 2025
● Four lifting beams were lowered into the gap, and end base plates were bolted to the extrados of the last full ring. The gap between the beam and segment was filled with grout;
● A lifting beam (without segments) was lowered and placed over the centre of the bridge beam, then bolted to the axis segments of the exposed ring in the shaft; and,
● Once the lifting beams were installed, the TBM was ready to resume advancement.
TAILSKIN BRUSH REPLACEMENT The tailskin brushes were originally scheduled for replacement in the Kidbrooke shaft; however, due to re-sequencing of works at New Cross, an enforced downtime created an opportunity to complete the replacement earlier. The team adapted their plans and carried out the brush replacement while still in the ground. This replacement was essential due to the wear
sustained by the brushes throughout the tunnel excavation. Failure of the brushes could result in water and grout ingress, as well as a loss of pressure. This approach minimised risk for the remaining 4km of tunnelling to Eltham, where non-cohesive deposits and groundwater inflows were anticipated. Two of the three rows of brushes were replaced, ensuring optimal sealing. The previous two rings were secured by longitudinal strapping between each ring and radial strapping between each segment. To access the brushes, it was necessary to dismantle
Above: The TBM had to stop exactly at this point for the removal of the screw Below: The 10m-long screw split in half to aid in removal
a ring after mining. The last constructed ring followed a U11 sequencing pattern, so the subsequent sequence required an even number and selecting U12 positioned the key segment at the top of the ring. This placement was optimal for its removal, as the key segment needed to be extracted first. The ring designated for dismantling was constructed without dowels to facilitate the removal of segments after assembly, while bolts were installed to secure the ring in place. The thrust cylinders were extended to 1600 mm,
following a safe stop procedure. After allowing an hour for the grout to settle, an additional 100 mm extension was applied to separate the tailskin brushes from the grouted gap seal. At this stage, the key segment was carefully removed using the erector, which was specifically designed to extract segments to aid with tailskin brush replacement and placed onto the segment feeder. The thrust cylinders were then incrementally extended farther until the second row of brushes was exposed. Once the brushes were exposed, the remaining
segments—except for the invert—were removed using the erector and placed on the segment feeder in their original order for easy reinstallation. The invert segment was then lifted onto the tailskin after pulling back the feeder. Before replacing the brushes, accumulated dry grout and grease were jet washed. The old brushes were then removed and replaced with new ones, ensuring no gaps that could allow water ingress. To ensure thorough lubrication of the tailskin brushes,
WR90 grease was applied using an injection lance, ensuring the grease penetrated all areas within the brush assembly. In some instances, manual application with a brush was necessary to guarantee complete coverage of hard-to-reach spots. The entire greasing process required three 8-hour shifts to complete, ensuring optimal lubrication and functionality of the brushes. After the brushes were installed and greased, the ring was reassembled following the sequence below:
14 | July 2025
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