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Author:
Sam Paterson
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2006-05-16 |
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We have a problem where our contractor wants to blast then support with rock bolts and then blast deeper again in an open cut type excavation.
Can anyone help with a rationale for determining the likely effect of the blasting on stability and how we account for that in design.
At present I can only find references for; Seismic type loads - which isn't really applicable due to frequency differences, And references for PPVs vs blast damage to structures.
I have found a reasonable reference from HK GEO report 12 but it doesn't truley consider the presence of support and is I beleive over-conservative.
Any response would be most welcome - especially something with a quick empirical fix :-)
Regards
Sam
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Follow-up:
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Author:
Tom Sklucki
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2007-06-14 |
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hi sam
Similar blasting has been done when benching in large underground caverns. Generally if the blasting is controlled well enough not to make a mess of the rock in the wall above, then there is no problem with regard to damage to rock support. May be useful to consider smooth blasting to get a better finish to the upper bench rock face and less loosening on discontinuities. I presume that rock anchors will be grouted, whether cement or resin - ungrouted mechanical shell anchors would come loose. Rock anchors, tensioned or not, depend on face plate and nut to secure near surface rock possibly aided by mesh and sprayed concrete depending on frequency of joints. Fly rock may damage face plate and nut if blasting is poorly designed. Blast mats e.g. old conveyor belting or tyres and cable) may be used to suppress fly rock.
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Follow-ups:
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Subject:
Accounting for blasting in a rockbolted wall 