Date of incident: February 2023
Notice of incident number: 2023167730002
Employers: Excavation firm; general contracting firm; concrete supply firm

Incident summary
At a site that had been excavated for highrise construction, workers in the excavation were spraying concrete (shotcrete) on a form wall approximately 2.4 m (8 ft.) high and 29 m (95 ft.) long. The wall suddenly cracked and fell toward the workers, who scrambled out of the way to avoid it. One of the workers was trapped under the wall. He sustained serious injuries as a result of the incident.

Investigation conclusions

Cause

• Inadequately supported wall collapsed. The bracing and support for the single-sided wall (several struts and a row of soil anchors) was inadequate for the weight of the shotcrete being applied to it, and the wall collapsed.

Contributing factors

• Inadequate planning and construction.
  • The general contractor and the concrete forming firm did not engage in planning for the construction of the wall other than sketching out rough drawings and discussing ideas verbally. The bracing system that was used for the wall was inadequate to support the weight of the shotcrete being applied.
  • The general contractor, the excavation firm, and the concrete forming firm did not ensure that the wall was supported to safely withstand the load imposed on it by the shotcrete. None of the employers completed a risk assessment before the shotcrete was applied to the wall.
• Lack of hazard identification, risk assessment, and safe work procedures. The general contractor and the excavation firm did not identify the hazard of the inadequately constructed wall or assess the related risks. Thus, the hazard of the wall falling over was not considered and no controls were put in place to eliminate or reduce workers’ exposure to the related risks. The wall was constructed without engineered drawings; safe work procedures were not developed; and the potential for weather conditions to affect the stability of the temporary wall was not identified. The investigation found that rain, freezing temperatures, and snow over the two weeks leading up to the incident undermined the wall’s stability and likely contributed to its collapse.
• Inadequate supervision. Neither the general contractor nor the concrete forming firm provided any supervision for the construction of the wall to ensure that it was built to withstand the stresses and the weight of the shotcrete that would be imposed on it. Once the excavation firm’s workers started applying the shotcrete, they stood in close proximity to the wall, thus exposing them to the risks associated with the wall collapsing.
• Inadequate prime contractor coordination. The general contractor, the prime contractor for the site, did not coordinate wall-construction activities with its subcontractors so as to ensure the health and safety of workers at the site. The general contractor should have established a system to verify (among other things) that the wall was built to support the weight of the shotcrete application. As prime contractor, the general contractor was ultimately responsible for ensuring that an effective system for this purpose was in place.

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