Tunnelling Under the Thames

Alan SprayTed Allen

Docklands Light Railway (DLR) Woolwich Extension

• Initially Alluvium, gravels and Bullhead beds

• Water-bearing Upper Chalk• Non-Clastic Carbonate • Cretaceous period• Medium – wide joints• Large flints – non carbonate• Relative strengths

Flint damageWater-bearing chalk

Maintenance – dry refuges

Drilled until cutter broke

Intensive pumping - luck

Repairs to cutter Dig heading Replacements/reinforcements Welding

Stronger cutters

Better investigation More remedial works

Build a bridge