Calgary’s New Central Library will soon be a welcome addition to the East Village, helping to re-connect this vibrant new community with the downtown core. It will certainly stand as a landmark building – an unusual geometric oval shape with a soaring, four-storey atrium – but it will also stand as a testament to innovative design, engineering – and piling.
An unusual site
The reason the New Central Library will be one of the city’s more prominent architectural feats lies with the fact that it is being built on a piece of land bisected by an existing LRT line. This necessitated the architects lift the ground plane up and over the LRT tracks and create a raised foundation in the process. No simple task.
But fortunately, Calgary Municipal Land Corporation (CMLC) was able to tap into some well-honed experience.
“CMLC hired us to do a study that showed it was possible to build over a live LRT track,” states Ian Washbrook, associate, Entuitive, the structural engineering firm on the project. “We had the unique experience of designing and building the Manhattan West platform at Penn Station in New York, the busiest commuter rail line in North America, on a site that was dissected by many active rail lines. Our solution for that project demonstrated that it was economically feasible to build over the existing LRT tracks on the Calgary site.”
Next up was the architectural team, which was comprised of Snohetta and DIALOG.
“We viewed the site as a ‘probatunity’, which is a combination of problem and opportunity,” explains Rob Adamson, partner, DIALOG. “The geometry of the curving train tracks meant that the building was sort of separated in two. There was no budget in the project to re-align the tracks so we had to sit back and think of how we could leverage the situation to be an opportunity. We ended up designing a curving, structural system to the building. The fact that we had to go up and over the LRT tracks enabled us to make an amazing outdoor public plaza where people in the community can congregate.”
Building up and over the LRT tracks meant that the tracks had to be encapsulated – the first time in Calgary’s history that an active LRT line is being encapsulated to allow for above-grade development. The project will cover 135 metres of LRT track and is covered within the New Central Library’s total $245-million budget.
The other twist in the project was that the LRT had to remain operational.
“We had very limited opportunity to work with the LRT corridor shut down,” states Washbrook. “The window of time was between 2:00 a.m. and 4:00 a.m. each morning. That, and the very rare times when the tracks were shut down for regular maintenance, were the only incidents of the power being shut down. During operational hours construction cannot take place within the right of way. Innovative construction solutions were needed to limit and mostly eliminate work within this zone.”
Entuitive started on the project in January 2014. The design encapsulation and construction documents were completed in August. The structural engineering firm did, however, begin sequential tendering in September to advance the pile work.
The piling work started on the east side of the site.
“Our solution to encapsulate the tunnel prior to building the library involved the use of very, very deep piles that ranged between 18 and 25-metres long and with diameters of four to six feet,” says Washbrook. “The piles were rock-socketed in 10 metres or more of bedrock. We then installed the grade beams and steel posts in the pre-formed wall panels before pouring the tunnel walls.”
The pre-cast double-tee roof structure is scheduled for installation on top of the pre-formed walls in August 2015.
The existing LRT communications and power lines on the north end of the east side of the site posed a bit of a challenge in the encapsulation process.
“There was one area, in particular, where the communications and power lines were right in the way of our piles,” states Washbrook, who adds that the piles were spaced 10 to 12 metres apart. “We didn’t want to increase the width of the tunnel in that particular area as it would increase costs significantly and increase the depth of the tunnel structure required, resulting in an architectural impact of the library. We had to build a temporary cantilevered frame to support the rerouting of permanent communication and power lines before the new permanent piles could be advanced through the abandoned existing communication and power lines. This took some planning and sequencing. There was a four-month period where no piling took place while this rerouting was taking place.”
Eighteen piles were driven in the southern end of the east side of the encapsulation project in September 2014. The remaining three piles on the east side went in after the rerouting of the communications lines.
Work in progress
“This project is very challenging,” states Rodrigo Fragachan, project manager, Bauer Foundations Canada Inc., the company charged with doing the piling for the LRT encapsulation component of the project. “The piling work occurred right beside the high-voltage LRT lines so it meant for very, very tight conditions. We used a Bauer BG28 rig, which barely fit in some areas.”
Fragachan adds that the tightest corner on the site was about eight metres wide.
The encapsulation piling project was divided into two phases. A temporary working platform had to be installed in order to ensure that the rig was stable and would not affect the active LRT.
“The majority of piles used tremmie concrete methods due to the presence of groundwater in the pile bore,” says Fragachan. “We installed mesh and barricades as additional safety measures to ensure that nothing got on the tracks. All the groundwater had to be pumped, treated and then disposed of.”
According to Fragachan, the company had an average crew size of between five and seven on site during the piling work on the east side.
“One of the biggest challenges we had was the use square dowel cage inside the centre of the pile’s reinforcement cage in order to accommodate the grade beams,” he says. “The dowels had to be installed in a particular orientation and extra caution was exercised while extracting the casing in order to reduce the rotation of the cage.”
Fragachan and his team completed the piling work on the west side in May of this year. They then had to disassemble the rig and move it to the east side before re-assembling it for work to begin anew. This alone will take three days.
West side story
The piling rig was moved to the west side of the site in April 2015. This second phase of the encapsulation piling will involve 20 piles in total. Due to the tracks bisecting the site, the piling rig needs to demobilize and remobilize as if the two sites are on opposite sides of town. The rig cannot drive overtop of the LRT tracks.
“The work on the west side will involve several large diameter piles,” states Washbrook, who adds that the larger diameter piles will range between five and six feet. “The larger diameters are needed here because some of the library columns share the encapsulation piles. There are four instances where we have four very large loads that will require large transfer pilecaps measuring more than 14 feet deep consisting of two, five-foot diameter piles.”
The library itself will require approximately 90 piles measuring between four and five feet in diameter. Washbrook anticipates that mobilization for the library work will begin this summer.
A library like no other
The New Central Library is scheduled to open in 2018. When finished, it will have been several years in the making and will have drawn upon the expertise of almost all involved in the project. But it will be a bold and striking embodiment of being able to accomplish the unthinkable – of bringing together two separate physical sites to create a unified whole and, in so doing, connecting two disparate communities to create a stronger city core.