Crossrail Ltd has used eight tunnel boring machines in order to complete ten tunnel drives to create the 21km (42km in total) of twin bored tunnel through which the Crossrail trains will operate.
Crossrail Ltd are using two different types of tunnel boring machine on their tunnel drives. Six of the machines are known as earth pressure balance machines to drive through clay to the west of the River Thames and riverbed deposits to the east. The other two machines are known as slurry machines and have driven through chalk and flint beneath the River Thames.
The average run rate per day of the earth pressure balance machines is 16.9 metres and the average run rate per day for the slurry machines is 7.9 metres.
The progress of each machine differs based on a number of variables including the ground and soil conditions, the sequencing of the project, the drive length, the depth of the tunnel, the maintenance of the machines and production rates.