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Approach to Estimating Shaft Costs

Hi Everyone...I posted this in the Shaft Sinking Group but thought it might get a lot more exposure and potential input here.

I work for a group that conducts mine cost estimating and we would like to begin updating an article that we publish regarding the costs to sink shafts. Currently, we provide pre-feasibility level estimated costs for a number of diameters (or rectangular dimensions) based on low, medium and hard Uniaxial Compressive Strengths.  This association and usage of UCS comes down to our need to estimate the time to drill a hole, which in turn opens up myriad other parameters that we can use to associate costs...i.e. labor, supply consumption, equipment operating costs, etc.

After speaking with a couple of friends and colleagues, we are considering changing our associated parameter from UCS to RQD.  Equipment selections can partially compensate for any particular UCS and we know RQD can have a significant impact on the drill-ability of rock, but would this switch to RQD make sense given that drill runs are short?  That is, we are dealing with single-pass production holes and not deep, exploration holes where loss of circulation and other issues are more critical and time consuming.  (Incidentally, we do understand that in a round about way, RQD can also provide some indication of how easily/quickly the material will be mucked...although I do not know of any studies that relate the two.)

If we choose to make the switch from UCS to RQD, I will need some simple data from which we can make the association to penetration rate.  That is a bridge that I'll cross if we choose a new route for estimating the costs.

Thoughts?

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Comments

  • I have a couple of comments: is there a reason you are estimating rectangular shafts?  Concrete lined circular shafts are now the industry standard.

    Qualitative I agree with your assumption the RQD will not have a significant impact on your blast holes since they are typically short small diameter hole, unless you are drilling sand the holes should stay open long enough to load.  What RQD should give you is an indication of your expected blast fragmentation but you also need to consider that rock that is easily fragmented can be too easily fragmented and will present ground support challenges.   

    I am not an expert on this type of analysis but my understanding is that UCS will provide an indication of drill penetration rate and perhaps long term structural stability but RQD would be better for blast design and temporary ground support design. 

  • all I can suggest is an anonymous survey whereby shaft sinking contractors indicate costs against the RQD and UCS records from a particular project. Quite a challenge to obtain meaningful data that can be compared. 

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