Serious Incident: Fill slope failure topples excavator on road building job

Safety Alert Type: 
Road Building/Deactivation
Location: 
near Terrace, BC
Date of Incident / Close Call: 
2014-05-24
Company Name: 
Brinkman Forest Ltd. / Coast Tsimshian Resources
Details of Incident / Close Call: 

It was mid-morning as a very experienced excavator operator was building a section of bush road through a steep side slope area of timber to be harvested. The weather at the time of the incident was clear and warm. However, this particular work site was in a high elevation area where the snow had recently receded. Adjacent creeks had significant water flowing from melting snow in the higher alpine areas.

The excavator was approximately 40 metres past a section of road where a wood box culvert had just been installed across a small but steep gullied creek. The machine was pioneering through hard pan clay and till, laying down puncheon, when the operator heard the “snap” of a tree. He instantly spun the machine around to see a patch of treed ground shooting down the gully between the box culvert and his machine.

With quick thinking, the operator was able to dig his bucket into the ground where the road surface once was. This action prevented the excavator from flipping over the embankment. The machine came to rest perched at about a 45 degree angle, just below the road surface location (see photos in attached pdf).

Immediate Cause: Spring road building in an area with a substantial amount of moisture, as evidenced from adjacent creeks with high runoff flows from alpine snow melt. Road building material, however, was a mixture of hard dry clay and rocky till and showed no evidence of saturation. The weight of adjacent right-of-way log decks could have been a contributing factor.

Root Cause: Upon closer investigation of the slide area it was discovered that there was an exposed plain of smooth rock at least 4 metres beneath the original road surface, pointing at a downward angle of approximately 45 degrees. A significant flow of sub-surface water was running over top of this rock, thereby creating a “slip face” failure plane between the rock and the road material above it.

It is worth noting at this point that the site was assessed for terrain stability issues using a reputable Professional Geoscientist. No significant areas of concern were noted. The completion of this project was ultimately abandoned based on the risk factors involved.

Learnings and Suggestions: 

Recommended Preventative Actions: N/A

This event occurred despite reasonable due diligence measures put in place to prevent it from happening. One might conclude that timing of operations was a contributing cause. However, based on the root cause it is not known if this event would have been prevented, even if road construction activities had occurred during optimal summer months. A post-terrain assessment concluded that this could not have been foreseen.

For more information on this submitted alert: 

Benjamin R. Korving, RPF Operations Forester, Brinkman Forest Ltd. / Coast Tsimshian Resources Terrace, BC (250) 922-4853 Ben_Korving@brinkman.ca 

File attachments
Safety_Alert_Brinkman Forest-Coast Tsimshian_2014-5-24.pdf
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