Helical Piles for Port Credit Library Foundation Stabilization

Built in 1961 and opened in 1962, the Port Credit Library is located at the eastern shore of the Credit River just north of Lake Ontario in Mississauga, Ontario. In 2011, as part of the Mississauga Public Libraries Project, the Port Credit Library in particular was one of three Mississauga public libraries to undergo major renovations and additions, which was part of a larger retrofitting and revitalizing initiative for their distinct mid-century modernist structures for a 21^st century audience.

In 2016, it was discovered that the concrete foundation of the Port Credit Library needed significant repairs. The contractor for the project proposed an original solution that called for the repair of the existing concrete caissons. This solution would have required significant excavation on either side of the caissons to replace the concrete pad that supported the existing grade beam. This work would have to be done before the actual caisson repairs could be completed, which would have required significant time and expense. A major challenge with this solution was the library was originally built on top of a historic landfill that had a high-water table. This meant that the original concrete repair solution proposed for the project was no longer an option. They needed to find a way to stabilize the structure with minimum subsurface disturbance. At this point in the project, Techno Metal Post Hamilton-Durham (TMPHD) was contacted and a helical pier solution was proposed.

Once TMPHD was contracted to complete the work, we received all the necessary information and completed pier tests around the perimeter of the property. This was done to make sure we could drill through the buried garbage in the landfill and achieve the required bearing capacities. Working with the Techno Metal Post Engineering Department, we developed several solutions to keep the integrity of the building intact without any major modifications to the library. All proposed options were discussed with the City of Mississauga engineer team, and the final solution was agreed to and TMPHD started the work.

The helical pier solution required stabilization of the library building foundation using piers on either side of the existing caissons to support the existing concrete beams under the building.

A steel I-beam was then installed between the piers running under the building to the outside.

Once the beams were in place, the leveling cap plates were installed to ensure the concrete beams were well-fitted to the steel beams. To hide the piers and the steel beams on the outside of the library, custom boxes were designed to cover them up to keep the original architectural structure and design of the building intact.

In the end, a cost-effective and safe solution was carried out without changing the look of the Port Credit Library and allowing for it to remain open to the public while the work was being done. A major success for this project was that little to no subsurface soils needed to be disturbed during the restoration work.

Year: 2016

Dealer: Derek Hofrichter and Roger Lauzon TMP Hamilton-Durham

Client: Port Credit Library, City of Mississauga

Location address: 20 Lakeshore Road East, Mississauga, ON.

Engineering firm: AMEC Foster Wheeler, Environment and Infrastructure

General contractor: JASS Construction

Project objectives: To find a cost-effective solution to stabilize the library foundation due to deteriorated concrete. All to be completed without closing the library or changing the architectural look of the structure.

Specific challenges:

• Reduced headroom
• Working underneath the building while it was still open to the public
• Ensuring no vibration and little noise
• Installing piers in a high-water table
• Installing piers in a historic landfill

Advantages over other methods:

• Cost
• No excavation required (high water table level and landfill site)
• Access under the building with compact versatile equipment
• Faster installation time, reducing the renovations by weeks

Soil type: Earth fill, and landfill contents, silty clay till

Installation time: 3 weeks

Number of people on site: 3

Materials used:

• P3 pier model (22 units; black steel with welded extensions), with single helix 10” diameter
• Customized leveling cap plates

Equipment used:

• R2D (interior installations under building)
• ET1 (exterior installations along building foundation)

Bearing capacity: 70 kN (15 750 lb) per pier (load mentioned on plan realized by Brook and Banz, Architects, June 27, 1961)

Engineer’s specific requirements: Drill piers until native soil reached and required bearing capacity achieved.

Average depth of piers: piers installed and drilled into the ground on an average depth of 40 feet

Specific details of the structure on piers: Mid-20^th Century public library on concrete beams