RamArch – Springs Tunnel Refurbishment

PROJECT: Springs Tunnel Refurbishment
OWNER: Network Rail
DESIGNER: Donaldson Associates (now COWI UK)
CONTRACTOR: AMCO
PURPOSE: Stabilisation of a masonry & brick-lined railway tunnel lining crown arch.
RAMARCH TYPE: Plain steel 8mm RAMARCH mesh, manufactured to BS standard
RAMARCH FINISH: Galvanised.
DATE: 2017/18

Tunnel is driven through shale and extending on a slight curve for just 77 yards. It was constructed in the early 1860s for the Otley & Ilkley Extension Line on the Midland Railway to the North of Leeds.
Under its civils framework contract, a minor works team from AMCO was dispatched to carry out routine stitching close to the north portal, responding to an examination report which identified hollow and spalled brickwork, ring separation and open joints.
Network Rail asked AMCO to develop plans for a partial reconstruction encompassing the northernmost 12 metres of arch. The work was to be undertaken during night-time possessions and a planned holiday blockade.
Site investigations and historical drawings suggested the arch was formed of at least seven rings of brickwork, sufficient for the designer, COWI, to propose the replacement of the inner three rings with 250mm of sprayed concrete reinforced with RAMARCH. This brought with it the welcome side effect of a 50mm improvement in structure gauge. However, during construction it was found that only four rings of brick were present, which presented a serious problem for the contractor and designer and placed much more reliance on the RAMARCH system to provide the needed temporary support.
The RAMARCH was sprung from the tunnel haunches as the brick lining was progressively removed using a new specially designed mobile milling machine supplied by Foulstone Forge, giving a 300mm wide cut, 125mm deep and was expanded into the soffit to provide immediate temporary support together with shotcrete to what little or no brickwork that remained. Additional fixing anchors supplied by Minova were then installed to secure the arch in place prior to final shotcreting.