BTS | HARDING PRIZE COMPETITION 2023
Articulation cylinder is closed
Concrete segment 01 (Ring)
Thrust ring
Above, figure 8: Schematic showing the possible pathway found by the water through the gasket of the ring
The team called for an emergency meeting with
the designer to propose a quick and feasible solution that would permit the operation to continue. The solution was to reinforce the joint by adding stiffeners to different locations, so the bolted connection was better reinforced to carry on with the excavation. Further investigations followed, and a better detail for
this connection would be designed and prepared for the relaunch at Greenwich. After the remedial works agreed with the designer
were completed at Silvertown, the launch restarted. More attention was paid to any big difference between the forces so that almost no eccentricity could result, and the relative movement was better balanced.
As the TBM continued to the last strokes, the trailing
edge of the concrete ring passed through the in-bye rubber seal inside the seal can. It was spotted that some water came inside the TBM. This had found a pathway through the gasket of the key segment that was not fully in contact with the leading edge of the steel ring. An expansive foam that reacted with humidity had to be injected to stop the ingress of water into the tunnel. With the pathway sealed the TBM could continue the last metre to reach its final position. Seven days after the TBM started its journey at
Silvertown, the launch of the machine using the Pressure Ring System was successfully completed. Upon completion of the launch, the machine
continued excavating using its own thrust system until the gantries were introduced inside the tunnel, leaving enough space behind to assemble the rest of the machine and recommence excavation with the final TBM configuration. The tension between the thrust frame and the steel
Thrust ring top running plate
ring was kept by tightening the inner lock nuts, so the structure could receive part of the reaction of the TBM during the excavation. Then, the external cylinders were decommissioned. This configuration had to be in place during the installation of the following 45 concrete rings.
DISASSEMBLY OF THE PRESSURE RING LAUNCH SYSTEM The configuration of the structures left after the launch had to be maintained to provide enough support so the thrust of the TBM could be absorbed. The theoretical factored friction between the concrete
rings installed within the tunnel and the ground was not sufficient to counteract the force from the TBM rams. This force was increased as the machine advanced
due to an increase of the production rate thus, speed of the machine, and the rise of the earth pressure that had to be achieved in the working chamber of the TBM to minimise any ground movement or settlement. The team had to find a balance between the expected
total thrust force and the friction created in the tunnel for the TBM to stop in a safe haven for intervention. To do this, it was agreed to stop 45 rings built after
Above, figure 9: Bottom of steel ring temporary supported on the thrust frame and auxiliary props
26 | June 2023
the launch; at this location it was expected a maximum total thrust force of 45,000kN that had to be opposed
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