The "dig down" is one of the initial and most significant stages of the revitalization. This stage involves excavating several metres below Union Station's existing floor level to create space for two new transit concourses and a new, lower-level pedestrian retail concourse.
The underground excavation stretches east to west from Bay St. to York St. and north to south from Front St. to the Air Canada Centre. A large section is happening immediately below the tracks while the trains operate above ground.
This stage of construction also involves the replacement of 447 concrete columns, 185 of which directly support the train tracks.
Column replacement on this scale is unique. This complex procedure has been employed only in special cases throughout the world and seldom on structures this size that remain fully operational throughout construction.
Nearly 45 truckloads — between 600 and 900 tonnes — of excavated material is removed from the construction site nightly. The excavators and support equipment being used are the same kinds as those used in underground mining operations.
- Around 600 to 900 tonnes - the equivalent of 45 truckloads - of excavated materials are removed from the site nightly.
- There are six columns in one grouping
- 10 excavators and support equipment are being used, all running on diesel fuel. The equipment is similar to those used in underground mining operations.