MECHANISED TUNNELLING | BTS HARDING PRIZE COMPETITION 2025
Above: Drawing showing anti roll brackets supporting the rings and the relative position of the screw post breakthrough
TBM SEQUENCING INSIDE THE SHAFT
When the TBM cut through the concrete portal and the cutterhead was exposed in the shaft, the following activities took place: ● A mini digger was lifted into the Kidbrooke shaft to remove broken concrete via a boat skip and the excavation chamber of the TBM was completely emptied of broken concrete;
● The screw conveyor was inspected, revealing considerable damage to the wear plates due to mining through various ground conditions. Consequently, a decision was made to replace the screw conveyor; and,
● The cutterhead tools, particularly the over-cutters, were found to be worn and required replacement.
TEMPORARY WORKS FOR TRANSITION A concrete plinth was built before the breakthrough at Kidbrooke. After the cutterhead breakthrough, grouting
operations proceeded as usual for the first two rings. However, during the excavation of the third ring, with the tailskin no longer within the ground, grout began to seep into the shaft, necessitating an immediate halt to the grouting process. I ensured effective communication between the miners operating in the TBM and the personnel in the shaft, which was crucial to promptly cease grouting activities.
Supporting Rings inside the Shaft To support the rings that were no longer within the tailskin, a combination of bullflex and lytag support systems was utilised to bear the load of the TBM.
1. Upon full exposure of a ring in the shaft, a specifically designed bullflex sock was positioned beneath the ring at the inbye and outbye circle joints;
2. A grout mixer pan and pump were used to batch and inject OPC cement into the bullflex until air and water seepage confirmed full saturation and hardening;
3. The gaps between the bullflex seals were shuttered at the concrete plinth;
4. Using a piccolo pump, lytag was injected into the gap until refusal; and,
Right:
(Top) Crown Segments removed from shaft; (Bottom) Segments removed from the first ring in the shaft
5. This process was repeated for each ring that extended beyond the tailskin within the shaft.
Knee Support and Ring Anti-Roll Brackets In addition to invert support, the tunnel rings required knee support and anti-roll brackets. As the cutterhead rotates in one direction, the shield tends to rotate in the opposite direction. This effect is particularly pronounced for rings in free air, necessitating adequate support measures. At Kidbrooke intermediate shaft, the following
supports measures were put in place: 1. An 1800mm super slim soldier was vertically bolted to the concrete plinth on each side of the ring;
2. Two 720mm super slim soldiers were installed diagonally, bracing the vertical soldier on either side of the ring;
12 | July 2025
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