Construction & Contractors/drill blast excavation


excavation by drill blast for D shaped tunnel, 3.2m size has been completed for 131m is complete with slope of 1:150. Now, further the slope needs to be modified to 1:60 for next 40m length, followed by cavern excavation, D shaped,5m width, 22m deep.
contractor had quoted for D shaped, 3.2m excavation with 1:150 slope. Mucking to be done all the way backwards.
what addition in rate may be considered for modified slope and following cavern excavation.

I assume we are talking about a profile slope change here.  I can't give you an incremental cost for the change because I don't have enough specifics on the equipment and methods being used.  However, I don't think the grade change by itself is very substantial.  If it results in a different geological condition because some stratum now appears in the face that would not have otherwise, then maybe, but let's face it, 40 m of 1:60 slope only results in an elevation difference of 0.4 m at the end, so it is unlikely that a significantly different geological picture would result in the tunnel or cavern as the result of the grade change.  Assuming the grade is upward in the direction of drive, the steeper floor grade would have no adverse effect on face water control and would only assist him in his muck haulage.  It would have a slight effect on the muck movement from blasting but not more than would be controlled by other blasting parameters.  There might be some claim that drilling the lifters is more difficult where the steepening starts because of interference between the drill boom and the flatter grade, but that also seems minor.  So I am not sure what, if any, cost adjustment is justified.

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Robert Cummings, P.E.


I can answer questions related to rock blasting, rock and soil excavation (such as tunnels and highway cuts), stability of such excavations, and foundations in rock and soil. I can also answer questions related to geology and mining.


30+ years as a geotechnical engineer and minerals engineer. Active consulting practice in rock blasting, geotechnical engineering, and rock mechanics for mining and heavy construction.

Society of Mining Engineers, Deep Foundations Institute, Association of Engineering Geologists, and International Society of Explosives Engineers.

Mining Engineering, AEG Bulletin.

BS and MS Geological Engineering

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