Building a station below a station for the Crosstown LRT

Eglinton Crosstown
To complete the required drilling, Crosslinx enlisted three Liebherr LB 36-410 heavy-duty drilling rigs.

Constructing the Crosstown LRT requires building new stations underneath active subway stops

Alongside serving as the largest transit expansion in Toronto’s history, the Eglinton Crosstown is tackling impressive construction feats, including building new stations below existing subway stops, while the trains continue to operate.

The LRT is being built by Crosslinx Transit Solutions, a design and construction consortium comprised of ACS-Dragados, Aecon, EllisDon and SNC-Lavalin.

The Crosstown, a $5.4 billion project, will span 19 km from Weston Road to Kennedy Station and include 25 stations.

About 10 km of the LRT line will be underground, between Keele Street and Laird Drive.

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During the recent Liebherr 2018 Information Tour for International Trade Press, CrossLinx invited media to tour the tunnel and two stations of the Crosstown project.

“This is the largest construction project in Canada at the moment,” said Paul Sandberg, divisional director for Liebherr Canada for drilling rigs, crawler cranes and concrete equipment.

“We have been involved with most of the stations either with cranes or drill rigs.”

Eglinton Station

Eglinton Station will be the largest station on the line, and one of the stops where the LRT station will be built below the subway line.

Construction of the Eglinton Station began in the summer of 2016, with completion scheduled for 2021.

The station will feature six entrances; one at each corner of the Yonge and Eglinton intersection, a new entrance at the former bus bay and a south entrance at Canada Square.

Customers will be able to move to and from the TTC without leaving the fare paid zone.

The station is being built using the cut and cover method, where the excavation is performed, then covered with wooden decking while crews continue to dig and build the station below.

As well, Eglinton Station will require the LRT line to run underneath the existing Yonge subway line and its station. As an interchange station, Eglinton will be one of the busiest.

“In the morning, we have between 50,000 and 75,000 people that exit and use the subway,” said Stanley Hole, project manager of Eglinton Station for Crosslinx Transit Solutions – Constructors.

“So, one of our challenges outside of the work itself is managing the pedestrians and our work.”

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The station’s excavation footprint will span about 130 metres by 20 metres — roughly the size of two hockey rinks — and reach a height of about 20 metres.

“The station itself is a box. We excavate to the side of the box, then dig underneath the subway,” Hole said. “When we dig this, it will be a very big space.”

Crosslinx is constructing 26-metre-deep caissons to facilitate the underpinning of the subway station. In total, building the LRT station will require about 450 micro piles and 500 tiebacks. Concrete strength in the caisson piles is a higher strength capacity at about 30 to 40 MPa concrete. The filler piles are about 4 to 10 MPa concrete.

“Once we get it to a permanent state, we’ll put beams and use the caissons to support the existing subway, then dig down,” Hole said. “So now the subway is held in the air with this structure, then we’ll build a station around that.”

“At some point, it all gets connected.”

eglinton stationLB 36-410

To complete the required drilling, Crosslinx enlisted three Liebherr LB 36-410 heavy-duty drilling rigs.

The LB 36-410 is used for the production of bored piles. Various methods such as Kelly drilling, continuous flight auger drilling, partial and full displacement drilling or double rotary drilling can be applied using the rig.

With an operating weight of 115 tonnes and a maximum torque of 302 foot-pounds, the LB 36-410 has a max Kelly drilling depth of 88 metres and max drilling diameter of 300 cm.

“The method used here is the Kelly drilling method and they’re installing secant pile walls to form the shoring to support the excavation of the tunnel boxes,” Sandberg said.

The drill rig is designed for easy transportation and set-up at the jobsite. Despite its large class, the upper carriage is compact and designed for small working radii. When producing piles with large diameters, the rig may be optionally equipped with an additional equipment package. This includes an extended drilling axle, more ballast weight and a longer leader.

The crane control system offers a multitude of program and control options for various drilling methods. Service and machine data is also provided on colour displays.

The Liebherr D946 A7-04 Tier4 Final engine provides 523 hp at 1,700 rpm. When using attachments like casing oscillators, no additional power pack is needed.

The hydraulic BAT rotary drive — designed by Liebherr — delivers the required torque for a wide range of drilling applications. The automated torque adjustment and the continuous speed optimization react flexibly to changing soil conditions, guaranteeing optimum crowd force.

At other stations on the line, like Mount Pleasant, piles as deep as 44 metres were required for construction. To reach 44 metres, a LB 44-510 drilling rig was used, the most powerful drill in Liebherr’s LB series. Support for the excavation was achieved using bentonite liquid.

“The bentonite is keeping the walls of the excavation open, while the drill rig goes in and out, and excavates the material out, then you just fill it up with additional bentonite,” Sandberg said.

When construction of the Crosstown is complete in 2021, Liebherr will continue to have a presence on the transit line. The trains purchased by Metrolinx are built using Liebherr suspension and air handling components.