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Helical piles integral for installation of new elevator in iconic Winnipeg building

By Susan Rennie, PCL Canada Inc.

 

The Scotiabank Tower, located at 200 Portage Avenue, sits on the corner of the historic Portage and Main intersection in the heart of Winnipeg’s downtown commercial district. It is one of only four primary office buildings surrounding this significant junction and provides 82,000 square feet of office space to the downtown area.

The building owner recognized the need for upgrades, not only to attract new tenants, but also to maintain existing ones. A new elevator and stairwell between the main floor and concourse level were identified as critical to these improvements to create efficient access to these areas. Scotiabank partnered with Nejmark Architecture and awarded the project to PCL Constructors Canada Inc. (PCL) in August 2018.

 

Attracting new tenants

New office towers like downtown Winnipeg’s True North Square (TNS) have left many landlords scrambling to renovate existing structures to appeal to new tenants and keep existing ones. TNS was the first high-rise office tower constructed in Winnipeg in several decades and quickly attracted corporate clients to relocate their head offices. TNS consists of several hundred thousand square feet of office, retail and residential space, and a plaza for public gatherings, outdoor concerts and movies.

Although the Portage Avenue Scotiabank Tower was sold in 2017, when Scotiabank moved its corporate offices to TNS in 2018, the bank planned to maintain the branch location and update it to meet their needs. Like many downtown property managers/owners, Scotiabank decided a renovation, which included updated accessibility features, was crucial to maintaining and attracting new tenants. This included the demolition and renovation of the existing Scotiabank offices, updates to the vault and upgrades to the mechanical and electrical systems. The renovations began in September 2018.

 

The issue of access

According to the City of Winnipeg’s Public Works department, Portage and Main is the city’s third-busiest intersection, with an average of 81,000 vehicles passing through the intersection on an average weekday. With its location on one of Winnipeg’s busiest intersections, access was the first major hurdle to overcome.

Many factors were considered when creating the construction plan and schedule, including the lack of space for material offloading and staging, building occupancy during construction, the age of the structure and the tower’s proximity to road and foot traffic. To solve the offloading and staging concern, PCL worked with the City of Winnipeg’s permit department to close nearby Main Street between 9 a.m. and 3 p.m., to provide as little disruption to rush hour traffic as possible. Arrangements were also made for the pickup of refuse bins, which were placed on the street each evening and removed by 6 a.m. the following morning.

 

Demolition

Driven by the need for tenant improvements, a new elevator and stairwell would be constructed between the tower’s main floor and concourse level. A challenge for construction, but a win for tenants. To add the elevator, PCL first needed to remove the concrete slabs on the main and concourse levels.

While removing interior sections to make room for the staircase, the aging building required the installation of temporary shoring to support the concourse slab, the support beams underneath and the concrete walls. To achieve the necessary stability, the shoring was installed on temporary mud sills inside the building’s crawlspace. Along the exterior walls, PCL also installed diagonal hollow structural section bracing 15 feet apart, along with a W18 beam running the length of the wall. Diagonal bracing was then installed on a ¾-inch-thick plate with eight ½-inch rods at each pile location. An opening was made on the exterior of the building to allow for the movement of the structural steel bracing and piling equipment directly from the street to the building’s crawlspace.

Concrete cutting and placing were conducted by PCL as a cost-savings measure.

An unexpected challenge

Once the building was stabilized, the PCL project team worked to remove the concourse slab. Original drawings provided by the client showed a concrete tower crane pad leftover from the building’s construction under the concourse slab, which would need to be removed to make room for the new elevator foundations. However, PCL crews discovered the actual tower crane pad was nearly twice the size indicated by the drawings and over five feet thick. It was also so heavy that none of the equipment on site could remove it.

Consideration was given for reducing dust, noise and vibration to ensure the building’s current tenants were not negatively impacted by demolition activities. PCL investigated and chose Ecobust, a controlled expansive demolition agent composed of a biodegradable powder. The powder is mixed with water and poured into pre-drilled cavities, where it then expands with a force of more than 20,000 pounds per square inch.

Ecobust provides controlled breaking to cut or demolish concrete and rock without any noise, vibration or dust, making it ideal for situations like the Scotiabank Tenant Improvement project in which the building was occupied during demolition. It is designed to break reinforced concrete and rock into manageable pieces. It is often used for concrete demolition, rock crushing and cracking, quarry work and mining when conventional methods are not suitable, such as restricted access locations and busy or occupied buildings. The product could be used by PCL’s own forces, which made the solution efficient and cost-effective.

Using Ecobust, the crane pad was demolished and removed in stages over the next four months.

Tenant considerations

Close coordination with the owner and tenants helped minimize additional impacts of construction such as air quality. PCL installed additional ventilation equipment to circulate the air. Exhaust scrubbers were required on all equipment to control the risk of air pollutants during demolition.

In accordance with the project specifications, much of the demolition work early in the project was done in the evenings to minimize the disruption and impact on daytime bank operations. As the project progressed, the work shifted to daytime hours. By working with the City of Winnipeg, Scotiabank and the trade contractors, PCL minimized the disruption to tenants while achieving a successful completion of the upgrades to 200 Portage Avenue.

Due to its location in such a high traffic zone, the piling work for the Scotiabank Tenant Improvement project was done overnight over multiple weekends to minimize the impact to both street and pedestrian traffic.

 

Piling within the basement

VersaPile was contracted to install the new foundation piles. Equipment was hoisted into the excavated crawlspace using a highly technical engineered lift. The scope included the installation of 18 new helical piles, with eight for the elevator pit alone. The piles measured 55 feet in length, with a diameter of 4.5 inches and a 16-inch helix on the end.

Helical piles were used for this project to ensure the load of the structure would be equally distributed. To provide sufficient load transfer for the soil conditions, each pile was made of galvanized steel and concrete to prevent rusting and had helical steel plates, instead of continuous flighting. Using helical piles allowed PCL to achieve adequate foundation support within the confines of the tower’s basement.

The use of helical piles, also known as screw piles, was ideal for this project due to the unpredictable composition of Winnipeg soils. Helical piles are economical, relatively quick to install, provide a tremendous amount of strength and stability and are great for reinforcing existing foundations.

During the installation, a hydraulic drill motor was attached to an excavator boom using a drive attachment and the piles were screwed into the ground to depth, working within the basement level. The piles for the elevator were installed 13 feet deeper than required to avoid any issues with soil moisture fluctuation. To minimize tenant disruption, the pile installation work was done primarily during evenings and weekends.

Once the piles were installed, the elevator pit was formed and placed, as well as the elevator walls to the concourse level. All concrete slabs were installed by PCL. At this stage, PCL had the structural steel infill installed to support the four new automated teller machines at the main floor entrance, which were part of the Scotiabank branch upgrade.

The Scotiabank Tenant Improvement project was driven by a need to provide an updated tenant experience within this iconic structure. While construction provided a unique challenge to PCL and its trade contractors, the new elevator and stairwell not only make the building more attractive to existing users, but also provide much-needed access and accessibility. Updated office finishes, as well as new mechanical and electrical systems, create a winning situation for both current and future tenants. Work on the site was declared substantially completed on July 17, 2019. The updated Scotiabank branch opened to the public a month later, with a grand opening celebration held in December 2019.

 

 

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Piling Canada is the premier national voice for the Canadian deep foundation construction industry. Each issue is dedicated to providing readers with current and informative editorial, including project updates, company profiles, technological advancements, safety news, environmental information, HR advice, pertinent legal issues and more.