How do you construct an underpass below a busy rail line? Build a bridge

To a non-engineer, looking at the construction of the city's new underpass on 78th Avenue in Ogden is a bit mystifying.

But there's plenty of method to what's going on. It's just that most people can't see what's happening or how it fits with the final vision.

The underpass is needed for a few reasons.

First, CPKC plans to close the level rail crossing at 69th Avenue southeast.

Second, the underpass will provide vehicle and pedestrian access to the Ogden shop/CPKC campus from the west, once the 69th Avenuerail crossing closes.

Third, building the new access point now will make it easier for the Green Line LRT to come through the area next to the CPKC line. The Green Line also will pass over 78th Avenue on a new bridge.

The project manager, Colin Stang, said there is a lot of co-ordination with CPKC to ensure this work is done safely.

"We are diverting a main line track that sees upwards of 20 trains every day. There's a lot of train movement in this area. So the co-ordination is the biggest challenge on this project. Other than that, it is a fairly typical bridge structure."

So what are the steps to getting this project built?

Earlier this year, freight trains on the busy CPKC line were diverted onto new tracks laid down on the top of a temporary embankment that was built on the west side of the existing embankment.

Stang said a lot of care went into that. "The hardest part was building the diversion embankment because we were right up beside their main line track when we were doing this."

Once the trains were running on the temporary track, work crews cut into the original CPKC embankment and removed the portion where 78th Avenue will eventually go through the site.

Then workers built a concrete support wall to shore up the temporary embankment.

Support piles were driven into the ground on the east side of the underpass site. These piles will help support a new rail bridge that will be going up in the coming months.

Completing that bridge will allow the CPKC line to be restored to its original alignment.

Once that's done, the underpass beneath the bridge will begin taking shape and it will be extended westward to link up with the existing 78thAvenue.

The CEO of the Green Line, Darshpreet Bhatti, said getting this project done before the city's next LRT line is under construction helps make that process easier. Essentially, he said it reduces risk.

"It's just certain types of works require more time and more planning to ensure that they're done correctly and 78th Avenue is one of those because we're working on a live rail corridor," said Bhatti.

For that reason, he said their contractor has been working closely with CPKC to ensure the rail line remains in operation throughout this project.

"The diversion track that we created needed to be stable enough, needed to meet their requirements, not just ours, to make sure that they're happy," said Bhatti.

"We have lots of live traffic and people working in that same corridor. So lots of co-ordination in making sure that as trains come through, we're fully aware of the schedules and our staff is providing the appropriate distances and buffers as needed."

He said the Green Line budget is paying for this project which is estimated at more than $50 million. However, that figure does not include a future Green Line bridge which will be built to the west of the rail line.

So the City of Calgary is going to be spending millions more at 78th Avenue in the future.

The area's city councillor, Gian-Carlo Carra, said this all goes back to a Green Line-related deal struck years ago between the city and CPKC.

Essentially the deal was: if the city could build its LRT line next to the CPKC line, then it would build a road connection to its headquarters and campus to replace the 69th Avenue crossing, which will be closed.

"We couldn't build the Green Line without the use of CPKC right of way. And we're using that right of way and they're getting this (underpass) in return," said Carra.

"Is it the deal we would have struck today given the cost implications of where we're at? Probably not. But it's a very good thing for the city. It's a good thing for CPKC. It's a great thing for Ogden and the Ogden shops and it enables the Green Line to run smoothly."

For its part, CPKC said in a statement that it's a satisfactory arrangement for the railway.

"The issue of importance to us was the ability to maintain our operation throughout the lengthy construction for the Green Line. The embankment and temporary track realignment have been done to accommodate the construction of transit, road and pedestrian infrastructure for the City of Calgary's Green Line and Ogden station project."

The bridge for the CPKC line is expected to be done by the end of this year but then the road construction and a new road on the east side of the underpass, which will link up with Ogdendale Road, must be completed.

Construction on the underpass project is expected to be done in the summer of 2025.

After years of preliminary works,formal construction on the Green Line is expected to begin later this year.