2010-12-09 Tailhold Pulls Away from Bedrock

Coast Region-South Island District-Port Alberni
Date of Incident / Close Call: 
Company Name: 
Alternative Forest
Details of Incident / Close Call: 


Back-end of skyline road for Madill 071 yarder had been drilled and grouted for the tail hold lines the previous day.  Rigging crew started yarding using the skyline and carriage. On the second turn the back-end spotter yelled down to the rigging crew to stop yarding. Inspection of the back-end showed that the rock slab into which the tailblock line had been grouted had pulled away from bedrock. The slab measured 3meters x 3meters x1meter thick, The grouted tail hold line was still firmly in place in the drilled hole.
Inspection of the site where the slab pulled away from the bedrock revealed several seams within the rock that would have not been visible to the drilling crew.


Learnings and Suggestions: 


Given that the “competency” of the rock to be drilled is not always easy to assess, it is recommended the rigging crew does a “test turn” prior to commencing production yarding. This will allow the strength of the tailhold to be tested without putting the rigging / landing crew at undue risk. 
When grouting, drillers should observe if an unexpected amount of grout is being required, as this may indicate the grout is “leaking” into surrounding cracks/seams.


For more information on this submitted alert: 

Sig Kemmler 250-701-1889

File attachments
2010-12-09 Tailhold Pulls Away from Bedrock Coast Region-South Island District-Port Alberni.doc
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