Punched anchors and voids led to shoring wall collapse: WorkSafeBC report

Problems at 500 Foster Ave. dated back more than one year before a dramatic shoring wall collapse in November 2023, according to a WorkSafeBC inspection report.

In October 2022, Amacon development company found their efforts to remove water from the site, “was determined not to be effective,” the report stated.

The company brought in “additional dewatering measures,” however, those methods were also ineffective and soil came loose, leading to “punched anchors and formation of voids behind the shoring walls” in April 2023.

Anchor punching is when the head of the steel anchor pulls through the shotcrete shoring wall.

The company investigated the voids and brought in more dewatering measures, according to the report.

An anchor was reported to have punched through the wall on Nov. 22, 2023. This was likely caused by voids behind the walls, according to the report.

An engineer reviewed the site in November 2023 and recommended more reinforcement at the anchor heads.

“The prime contractor was mobilizing the equipment to be able to install the additional reinforcement at the time of the incident,” according to the report.

The engineer had instructed the contractor that there shouldn’t be any more bulk excavation adjacent to the punched anchor “until the repair was in place.”

An anchor was drilled at the northwest corner of the site at the end of November.

“Significant material loss was reported during anchor installation, which may have propagated to a pre-existing void in the upper fill zone, which subsequently sloughed.”

At 11 a.m. on Nov. 29, the site was evacuated. At about 4:40 p.m. that day the wall partially collapsed.

No one was injured in the collapse.

In a video posted to social media, a horizontal fracture spreads across the wall as soil pours through until the wall bursts amid an avalanche of construction fill.

There were no indications of distress or global stability concerns on the rest of the shoring wall, the report concluded.

The area was immediately backfilled.

The collapse of the site’s north wall led to a traffic closure along Foster between North Road and Whiting Way workers went about securing the site.

“Coquitlam joins Amacon Construction Ltd. in apologizing to neighbours for these inconveniences and appreciate the ongoing patience as we work together to resolve this,” stated Coquitlam building permits manager Doug Vance at the time.

The City of Coquitlam required Amacon development company to hire a third-party geotechnical engineer.

Engineers & Geoscientists British Columbia conducted an investigation into the collapse, according to Coquitlam director of development services Chris Jarvie.

“Third-party oversight of the proposed repairs, which included review of the other temporary shoring systems for the excavation, was requested by the city and undertaken at the developer’s expense,” Jarvie wrote in an email to the Dispatch.

Engineers & Geoscientists British Columbia investigated the matter, Jarvie stated. However, the agency is required to keep all information about ongoing investigations confidential.