Excalibur has the edge 04 September 2020

Excalibur’s PLUS bolts have been designed into the PES support frames at 5 Elizabeth Line tunnel stations after meeting stringent shear and tension capacity, corrosion resistance, and safety specifications.

Full height PESs are a signature feature of the new Elizabeth Line station platforms, and Excalibur studbolts were designed into the PES support structures at the five tunnel bored stations on the line. These include Bond Street, Tottenham Court Road, Farringdon, Liverpool Street and Whitechapel stations. There is over 0.5km of screen at each station, with tunnel bore PES frames extending for over 2.5km in total.

They are designed to improve passenger safety and experience since they almost entirely screen passengers from air movement as trains approach and leave the platform. Because of the large tolerances involved at the sprayed concrete tunnel lining interface, and the different door configurations of trains on the line, the chosen structural design was an adaptable hybrid. This can function in a suspended or propped configuration, giving the PES frame an inherent robustness.

Since the Boston Interstate 90 tunnel ceiling collapse of 2006, caused by creep in chemical fixings, technical standards have prohibited chemical anchors in direct tension in overhead fixings. Excalibur screwbolts are self-tapping through bolts, proven over many years on high profile projects such as the Channel Tunnel Rail Link. On the Elizabeth Line, the bolts offer full shear and tension capacity immediately when screwed into position, without the need for any subsequent operation or curing time. This allowed the PES brackets to be offered up, lined, and levelled with holes drilled using the brackets as templates. Two nuts clamped the PES bracket to be held firmly in position immediately while work is completed.

To test bolt performance and ensure that delamination in the tunnel lining would not occur, Crossrail commissioned testing at Imperial College London to replicate the connection between the PES-frame and sprayed concrete lining. The Excalibur anchors were subjected to a cyclic load, representative of 10 years in service, and demonstrated that the threaded anchors would not fatigue or loosen in service, even under the 24M+ fatigue cycles during the 120 year design life of the tunnel. The Excalibur studbolt’s corrosion protection system provides a minimum maintenance solution with its cost-effective, long-term finish.