A tunnel boring machine (TBM) has been suspended following problems with machinery.
The incident happened on Crossrail; the new high frequency railway for London and the South East.
Crossrail bosses halted two TBMs last week following an incident in which a waste hopper fell against a rail wagon at the Westbourne Park site serving the Western Tunnel Drive.
Both machines eventually started again over the weekend, but one has now been halted entirely for the remainder of this week.
Investigations by Crossrail and the main contractor BFK – Bam/Ferrovial/Kier are underway.
A Crossrail spokesman told the Enquirer: "During the transportation of excavated material from the tunnels to the freight trains, the hopper, which feeds excavated material into wagons at Westbourne Park, tilted into an individual wagon. No injuries resulted.
- - - - - - Advertisement - - - - - -
"Network Rail closed the adjacent track to our site as a precaution to enable further investigations to be undertaken.
"As is standard procedure, the Health and Safety Executive was advised."
As a result of the failure, not all tunnel waste can be loaded directly from a conveyor belt and transported off the site.
The conveyor system is located along the inside of the western tunnels and exits at the tunnel portal at Royal Oak. It then continues through to Westbourne Park where excavated material is loaded directly onto freight trains.
This location is where the waste hopper tilted over, rendering direct loading from the conveyor into freight wagons impossible.
The rest of the conveyor system is unaffected, however, and so excavated material from the western tunnels can still be removed through transfer by excavator to freight wagons.