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Young worker injured when excavation wall collapses


A young worker was standing on a section of pipe in an unsloped, unshored trench about 6.5 feet deep. He was waiting for another worker to deliver a new section of pipe by excavator. The worker's supervisor noticed water at the bottom of the trench, about 6 to 8 feet from the worker, and told him to get out. The worker stepped off the pipe into the trench to retrieve a laser stick before exiting the trench. At that moment, part of the trench wall collapsed, burying the worker almost up to his chest and causing serious injuries.


Findings as to causes
  • The young worker was injured when the wall of a trench he was standing in collapsed onto him. A WorkSafeBC engineer concluded that the prime cause of the cave-in was a lack of shoring or sloping.
Findings as to underlying factors
  • The water in the soil of the trench added hydrostatic pressure to the soil pressure. In addition, the stresses from the spoil piles dumped next to the trench not only pushed down but also pushed out laterally. The unsupported trench cut was unstable and subject to collapse, as the lateral stresses pushed against the face of the trench wall.
  • Vibration from the two excavators that were being used likely contributed to some ground movement.
  • The spoil piles were more than 2 feet deep and close to the edge of the trench excavation, creating lateral stresses on the soil.
  • The construction of the trench required engineering assessment. Engineering advice wasn't sought out before workers were allowed to enter the excavation.

Publication Date: Oct 2007 File type: PDF (264 KB) Asset type: Incident Investigation Report Summary NI number: 2007157410184