Above: Aerial view of Kidbrooke intermediate shaft


3. A timber block was wedged between the ring and the vertical soldier, and an anti-roll bracket was positioned beneath the timber block, securely placed against the extrados of the ring and the concrete plinth; and,


4. This procedure was systematically applied to each ring constructed within the shaft.


SCREW CONVEYOR REMOVAL To facilitate the removal of the screw conveyor, the two crown segments had to be removed. The following sequence was followed: ● The operatives working in the tunnel were briefed at New Cross, and the lifting team was briefed at Kidbrooke. Effective radio communication between these teams was crucial;


● The lifting beam, designed by OTB Engineering to match the tunnel curvature, was lowered into the shaft, and rested on the segments of the ring that needed to be removed. Anchors were bolted into the beam to secure it to the segments, with resin injection used to reinforce the fixing;


● The radial spear bolts were removed from the crown and shoulder segments;


● Removing the first two segments proved challenging as they did not dislodge easily. A miner inside the TBM used a hydraulic jack to push the segments from within, while a crane pulled from above;


● The segments, along with the lifting beam, were extracted from the shaft and marked for reinstallation; and,


● These steps were repeated to remove the segments from the remaining five rings in the shaft.


Once the crown segments were removed, the screw removal process commenced: ● The screw was fully retracted, and all mechanical and electrical components were disconnected;


● A winching point was installed at the entry portal, and a pneumatic chain hoist was connected to the screw auger;


● The screw, composed of two sections, was split into halves to facilitate removal;


● Inbye section was secured to prevent it falling within the casing once the outbye half was removed;


● The outbye half was lifted out of the shaft using the crane at the top of the shaft at Kidbrooke; and,


● The inbye half was subsequently removed in the same manner.


SCREW REPLACEMENT ● A refurbished screw was prepared and ready for installation at Kidbrooke;


● The screw was split into two halves and installed in the same sequence as the removal process. The angle of the auger was adjusted to facilitate insertion into the casing;


● The connection point of the split screw was positioned outside the casing, and the two halves were welded together; and,


● The joined augers were slid into the casing, and the main motor was lowered into the shaft and secured to the screw.


REINSTALLING RINGS AND BRIDGE BEAM INSTALLATION Weekly meetings were held with OTB Engineering to align with the design brief. We discussed our requirements, and they provided options to ensure we built the right solution. One option involved installing bridge beams across the entire shaft due to concerns about reinstalling segments, but as they were placed effortlessly, a more efficient approach was chosen. Instead, we left out two rings to install ventilation


from Kidbrooke to Eltham, doubling as a critical emergency exit. Given the tunnel length, this was a key safety measure. Dräger stations and a staircase were also installed to provide a safe escape route in case of an incident. ● After screw replacement, the removed segments were reinstalled. A bridge beam was installed to enable the thrust cylinders to apply load to the tunnel lining;


● The segments stored on the surface at Kidbrooke were reinstalled into the crown of the rings. The segments were strapped, and radial spear bolts were installed. This process was repeated for three additional rings;


● An opening of two rings was required to facilitate the installation of the ventilation booster fan, which would enhance ventilation from Kidbrooke to Eltham;


July 2025 | 13


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