Innovation solves tunnel access challenge in Vancouver

At a depth of 110 meters, accessing the south shaft of the Second Narrows Water Supply Tunnel in Vancouver presented a challenge.

The vital infrastructure project, which will replace three aging water mains installed between 1948 and 1978, required a unique solution to ensure safety and efficiency for workers performing critical welding and backfilling operations.

The 1.1-kilometer tunnel, crossing under the Burrard inlet from north Vancouver to the City of Burnaby, will house new water mains nearly 100 feet (30m) below the inlet. The new mains are designed to carry twice as much water as the existing, seismically vulnerable lines currently operating near full capacity.

After a crane lowered the platform into the tunnel shaft, the top platform was suspended with chains to anchor points on a structural steel frame built at the top of the shaft. (Photo: BrandSafway)

Designing for Deep Access

The Second Narrows project involved the construction of two tunnel shafts, each approximately 52 feet (15.8m) in diameter. The north entry shaft was about 197 feet (60m) deep, while the south exit shaft on the inlet’s south side plunged to an impressive 361 feet (110m). Traylor Aecon General Partnership, the contractor for this segment, tasked Spider by BrandSafway with providing access for personnel to weld the three large-diameter steel water mains and backfill the shaft with shotcrete as they ascended from the bottom. The water mains themselves are composed of 100-foot (30-m) sections of pipe.

Vancouver ‘for the win’! BrandSafway celebrated its SAIA Project of the Year Award for Suspended Access last year at the SAIA’s Annual Convention & Exposition, seen here. (Photo: SAIA) BrandSafway, Spider and AlumaSafway, working in close collaboration with Metro Vancouver, Traylor Aecon General Partnership, Delve Underground and Jewel Holdings, engineered and installed a first-of-its-kind access solution for the Second Narrows Water Supply Tunnel project in Vancouver, Canada, setting a new standard for deep shaft work. The innovative approach saw the company take home the Scaffold & Access Industry Association’s Project of the Year Award – Suspended Access. The Suspended Access Project of the Year Award is presented to a member company where suspended access is utilized to: raise the overall level of safety on a project, contribute to the overall success of the project, or complete a dynamic installation in a new or innovative way. To learn more about the SAIA Project of the Year Awards, visit www.saiaonline.org/awards.

For the shallower 197-foot (60m) north shaft, Traylor Aecon General Partnership had utilized a custom steel platform. This platform was lowered by a crane and then bolted to the shaft walls. Moving it required worker evacuation, crane securing, unbolting, hoisting and re-bolting at the new level, proving to be a time-consuming process.

As planning commenced for the significantly deeper south shaft, Traylor Aecon explored options with Spider, including swing stages, davit arms, and the company’s largest hoists. The contractor sought a solution with 4-ton live load capabilities and the mobility to traverse the shaft efficiently. However, conventional swing stages and davit arms could not provide the required 4:1 safety factor and were not ideal for circumferential work. While supported scaffold was a possibility, it was deemed cost prohibitive.

A crane hoists the dual-tiered motorized platform so it could be lowered into the tunnel shaft. The solution doubled the work area and eliminated the need for a crane to move the bottom platform. (Photo: BrandSafway)

A Ground-Breaking Solution

Recognizing Traylor Aecon’s need for a mobile platform capable of supporting substantial loads, the Spider Vancouver branch assembled a multidisciplinary team. This team custom-engineered a unique solution that combined BrandSafway’s proprietary QuikDeck suspended access system modular rigid platform with Spider hoists.

QuikDeck segments, comprised of plywood and planks supported by a steel truss system, pivot on a central node. These nodes also serve as connection points for suspending the platform with chains or cables. The pivoting design allows for configurations in various shapes – including the specific layout required to fit around the three large water pipes in the Second Narrows shaft. Structural grade one plywood provides a flat, stable, and sturdy work surface, rated for a standard load of 25 pounds per square foot.

The Second Narrows tunnel shaft is 50m deeper because of the more steeply sloping shoreline. To improve efficiency, a motorized suspended access solution was implemented on the south shaft. (Photo: BrandSafway)

BrandSafway designed two identical suspended platforms, which were fabricated and rigorously tested at the company’s Scotia, New York, facility. After testing, they were disassembled for transport. On the job site, the Spider team installed four motorized Spider UpPro P series hoists, each rated for 2,200 pounds, on the bottom platform. Eight pulleys were strategically placed on the underside of the top platform. This innovative system of hoists, pulleys, and wire rope assemblies provided a total lifting capacity of four tons with a 4:1 safety ratio.

Building the Future

The Second Narrows Water Supply Tunnel project was completed on time and within budget, with BrandSafway completing all work without a single recordable incident. The project duration spanned from April 2023 to December 18, 2023.

A top-down/cross-section view of the Second Narrows tunnel shaft. The suspended access platform fit within the tunnel yet around the three water mains. (Photo: BrandSafway)

BrandSafway’s dual-tiered motorized platform delivered multiple benefits to the contractor:

This is the isometric drawing that showed Traylor Aecon how the double-tiered suspended access platform would fit around the three water mains. Note the four motorized hoists on the bottom platform and pulleys on the top platform. Also note the trap door, which enabled access for a personnel basket to lower workers to the bottom platform. (Photo: BrandSafway)

• Doubled Work Area: The entire structure was rated for four tons, accommodating up to 10 people on each platform along with a deadload for equipment such as concrete pumps and welding equipment.
• Simultaneous Work: Allowed two different skilled trades, such as welders on the top platform and concrete workers on the lower platform, to work concurrently.
• Independent Mobility: The bottom platform featured independent mobility, enabling concrete workers to backfill the tunnel shaft with shotcrete, a process that moves more rapidly than the welding performed on the upper level.
• Fewer Work Interruptions: Up to four workers could remain on the lower platform as it moved up or down, minimizing interruptions.
• Minimized Crane Use: The crane was only necessary to raise the top platform when the next 100-foot section of pipe was installed and welded.
• Reduced Hazard Potential: The rigid QuikDeck platform provided secure footing and excellent mobility for workers and materials. The two-tiered motorized solution also reduced the travel distance for trade workers, inherently lowering the potential for incidents.

The BrandSafway teams are proud of their ability to integrate various access solutions and diverse engineering expertise, demonstrating their value as a partner to contractors like Traylor Aecon General Partnership. This unique double-tier motorized solution is anticipated to be adapted for other projects requiring multiple levels of access in challenging environments.

The QuikDeck pivoting node and truss system enables configuring the platform to accommodate just about any shape while also providing rigidity and multiple suspension points. (Photo: BrandSafway)

Collaborative Efforts

The successful implementation of this complex access solution was a testament to the collaborative efforts of several key players:

• Metro Vancouver (Greater Vancouver Water District): The tunnel owner.
• Traylor Aecon General Partnership: The primary contractor, a consortium of Aecon (40 percent) and Traylor Bros Inc. (60 percent).
• Delve Underground: Tunnel and shafts designer, with Andrew McGlenn serving as engineer of record.
• Jewel Holdings: Pipe welding and coating subcontractor.
• Spider (a BrandSafway company): Designed and manufactured suspended access equipment, known for its powered suspended access innovations.
• AlumaSafway (a BrandSafway company): A leading global provider of access, specialized services, and forming and shoring solutions.
• BrandSafway: Provided comprehensive engineering and fabrication services, including the patented modular QuikDeck suspended access platform.

Using four of these Spider hoists, pulley and wire rope assemblies created four tons of lifting capacity with a 4:1 safety ratio. (Photo: BrandSafway)

Key BrandSafway team members recognized for their outstanding contributions include District Sales Representative Leo Sullivan, who devised the challenging access solution; Regional Suspended Access Manager Mike Hiebert, who diligently worked with the customer throughout the project; and Lead Engineer Jon Burkhart, who successfully and safely designed the double-tier QuikDeck system.

At the job site, the platforms were built one on top of the other. The shoring shown in this photo provided clearance for installing the Spider hoists and pulleys. (Photo: BrandSafway)