The rail company will formally confirm Bam has won the contract at the end of the month. Work is expected to start next May.
Acton freight yard is a significant part of the network but to enter and leave the yard, trains currently need to cross main line passenger tracks.
The rail underpass will be constructed to provide paths for freight trains going to, and from, Acton Yard without disrupting Crossrail trains and other services.
Two goods lines and three depot reception lines will need to be realigned considerably north of their current location to accommodate the rail underpass.
VolkerRail and sister company VolkerFitzpatrick are working on a £15.5m track relaying contract at the Acton freight yard. These advanced works will be completed by early 2013, with the remaining programme of work for Acton, including a dive-under, due for completion in 2016.