Nucor Skyline adds strength to Canal de l’Aqueduc with new bulkhead wall

By Janet Himstead, Technical Writer, Nucor Skyline

Built in 1853, the Canal de l’Aqueduc on the Island of Montreal in Québec, Canada, is an open-air aqueduct. The canal serves as part of the drinking water supply for the city of Montreal and draws water from the Saint Lawrence River. It runs through the city of LaSalle and the boroughs of Verdun and Le Sud-Ouest, where it ends at an underground reservoir and pumping station in the City of Montreal.

While the canal itself is closed off with fences, it is lined with wetlands, a bicycle path, and a park along its southern banks for pedestrians and bicyclists to enjoy the beauty surrounding it. The canal runs approximately 8,100 metres in length and varies between 30 and 50 metres in width.

Canals, waterways, and wetlands are exposed continuously to erosion and flooding from rainfall and runoff. One way to keep the earthen sides of a canal from eroding is to build a retaining wall. A retaining wall helps keep the earth in place and protects the surrounding areas from runoff and flooding. Preventing the runoff also increases the water quality in the canal by keeping the turbidity low. A retaining wall that retains soil on the backside and water on the front side is called a seawall or a bulkhead. These walls come in many forms, such as concrete, interlocking steel sheet piles, or steel combi-wall systems.

At Canal de l’Aqueduc, there was an additional reason for the bulkhead wall, as a new highway was being built alongside the canal, and the bulkhead would also add support for the roadway. The existing elevated highway near the canal will be demolished and the new highway will be built at ground level.

The joint venture of KPH-Turcot/WSP/

ETPO, located in Québec, reached out to Nucor Skyline Canada for their engineering expertise in steel retaining and bulkhead walls. Steel sheet pile bulkhead walls are often used in soft soil and tight spaces. The site at Canal de l’Aqueduc consisted of approximately one to two metres of soft, shallow soils over the rock layer and did not permit driving the sheet piling deep enough to develop toe support. Nucor Skyline’s engineering team proposed various solutions to toe pin and anchor the sheet piling wall into the bedrock and stabilize the wall. Because of the soft soil conditions and the slope of the soil toward the centre of the canal, the design team from WSP opted for a toe-pin wall system to obtain maximum stability. Project drawings were prepared by Nucor Skyline’s engineering team.

The optimal solution for the bulkhead wall at Canal de l’Aqueduc consisted of using approximately 1,300 net tons of AZ 36700N and AZ 46-700N sheet pile sections with casing welded to the sheet pile for driving to bedrock. The sheet piles ranged in length from six to 15.24 metres. Because the sheet piles will be in a corrosive, marine environment, the piles were coated with a coal tar epoxy to enhance their life. Using a vibratory hammer, Groupe ETPO, the general contractor on the job, was able to drive the sheets without incident to bedrock. A drilling rig was then utilized to drill into the bedrock through the casing. Steel toe-pins were inserted into the casing and ultimately, the rock. Once the toe-pins were in place deep in the bedrock, grout was injected into the casing and rock layer to solidify the system. Walers were installed on the back side of the bulkhead wall for additional stability and to set up the tieback system.

A deadman wall was installed on the other side of the proposed roadbed in order to utilize a tieback system from the bulkhead wall. Anchoring the sheets near the top of the wall will limit wall deflection and prevent settlements on the future highway. The top of the wall is supported by the tie rod and the bottom of the wall is anchored by the toe-pin. The sheet pile acts as a supported beam between the two reaction points.

The project was completed successfully, and the new highway is in use at the Canal de l’Aqueduc.

For more information on bulkhead walls and other project using steel sheet piling, please visit www.nucorskyline.com. l