Bolted lining segments are normally designed in accordance with the Water Industry Specification, with a strength of 40 N/mm2 and sulfate resisting cement. They are reinforced to withstand normal handling and erection stresses. Rebates for seals are cast into the joint faces of all segments, along with grout holes. The units are connected with mild steel or galvanised bolts as appropriate.
Standard bolted linings can be used in shafts constructed by underpinning, caisson or bottom up methods. Depths of between 20 and 40 metres can usually be accommodated, depending on the shaft diameter. Special linings can be produced to meet additional loading or specific service conditions. In addition special units may be incorporated to support intermediate landings in shafts.
Standard bolted linings can also be used in hand-built or shield-driven tunnels to a maximum depth of approximately 40 metres and are suitable for most ground conditions including those requiring compressed air. Special linings can be produced to meet additional loading or specific service conditions.
Tapered rings or packings are used for tunnels constructed with curves. Due to the requirement for a secondary lining to achieve a smooth finish, bolted linings are generally used for temporary works and for structures not requiring a smooth internal finish.