The proposed works comprised the installation of Ram-Arch steel mesh as temporary support to the tunnel lining between 61 and 62 chains in order to stabilise heavily spalled and loose brick at the crown and haunches. The mesh comprised welded Grade B500B reinforcing bars, and was fixed to the existing lining using Hilti resin anchors.
A permanent solution, which also remdiates ingress of water through the lining, is planned for the future.
The Ram-Arch mesh was analysed linearly as a steel arch using Strand7 finite element analysis software. An elastic-perfectly plastic model was used to describe material behaviour. The arch was assumed to be pinned at its base, with spring supports applied round the perimeter to model restraint provided by the tunnel lining.
Loading on the mesh was generated by the tunnel lining. It is conservatively assumed that the Ram-Arch was required to support the entire lining from springing level on either side of the tunnel.
The proposed Ram-Arch mesh, when supplied galvanised, has a design life of 120 years. The proposed temporary works scheme has a design life of 10 years as it is anticipated that a permanent solution will be installed within this timescale.