Electrification of British Railways' East Coast Main Line: Calton South Tunnel, Edinburgh, strengthening works for electrification Available to Purchase

Calton twin tunnels lie just east of Waverley Station Edinburgh. The North Tunnel carries a single line and was repaired in Tunnel was the subject of major strengthening works costing about £1.0 million and is the subject of this Paper. The 150 year old twin track tunnel is driven through a mixture of volcanic rocks and mudstones and has a fault passing through near its east portal. Large accessible voids were recorded above the crown's bricklining and evidence of several serious bulges of the lining were noted using photogrammetry. Distometer monitoring of these bulges revealed the need to support the lining in two locations. Rock bolting, grouting and guniting was used at one weak area whereas at the east end a tunnel-within-a-tunnel was constructed for 120 m using precast concrete segments. Extensive temporary works and careful monitoring of the tunnel structure was necessary to allow the invert rock excavation necessary to build the new ‘tube’ which catered for the operators' needs of an electrified single rail track.