Services between London and Birmingham have been cancelled or delayed after the ground near tracks fell away.
The line is the a major route connecting the capital with the north-west of England.
Mounds of waterlogged earth under the rails in Leighton Buzzard, Bedfordshire, tumbled down the tracks, causing at least a week of disruption.
Commuters were left raging as they crammed into carriages and found their usual services missing in action.
Many said they weren't told about the cancellations - and one complained her train was so full she couldn't squeeze on.
Engineers scrambled to pile up more than 2,200 tonnes of stone to fix the problem - but will take at least a week.
Details of the changes have been published online.
@LondonMidland unacceptable that you've just stopped serving Bushey and Harrow with no poor explanation. Got more info from @LDNOverground
Commuter trains from Birmingham to Euston are picking up the slack by making more stops, causing delays on the lines.
Virgin Trains services are expected to be delayed by up to 20 minutes, although they are making all stops as normal.
A Network Rail spokesman said: "We are aiming to complete this work by Friday and can’t be any more definitive at this point.
“Regrettably this means disruption to passengers for the duration of the week while our teams work hard to make repairs."