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2010-02-02_REVISION - M1977211
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2010-02-02_REVISION - M1977211
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Last modified
8/24/2016 3:59:14 PM
Creation date
2/3/2010 7:19:55 AM
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DRMS Permit Index
Permit No
M1977211
IBM Index Class Name
REVISION
Doc Date
2/2/2010
Doc Name
CGS Assessment
From
CGS
To
DRMS
Type & Sequence
TR14
Email Name
BMK
Media Type
D
Archive
No
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vibration for this blasting method will be minimal. Their confinement factor is considered the <br />upper bound and relatively conservative in this application. "Bombing" rock features with <br />abundant fissures and other dilated rock discontinuities should not be considered a controlled <br />blasting scenario. There are so many unknown variables. Also, in our experience, placing <br />bombs in rock fissures to remove rock features, even small ones, generally does not work very <br />well. Almost all the blast energy escapes into the air and open rockmass discontinuities, which <br />will result in less ground vibration but a louder air blast and higher fly-rock potential. Fly rock is <br />very random so the threat to nearby structures is very difficult to qualify. <br />Recommendations <br />We have no compiling reason to recommend against approval of this technical revision. <br />The quarry's present difficult situation warrants giving it a try. It should be understood by the <br />quarry operator and DRMS that this approach may result in no net effect; or worse, a degraded <br />stability situation where they have further destabilized the rockmass of the upper blocks without <br />the hoped-for failure (i.e., the blocks slide, break apart, and become incorporated into the <br />rockslide rubble zone below). Loading the head scarp fissure with explosives may also result in <br />destabilization and movement of the intact rock above and behind the head scarp. Presently, <br />the sole reliance of determining whether the rockmass above the headscarp will be disturbed is <br />prism 19 (see Fig. 2). <br />We offer the following observations and recommendations with regard to this Technical <br />Revision. <br />1. While the specifics of their blast plans are not stated in their Technical Revision, we are <br />presuming that some form of stemming or mud cap will be poured into the fissures after <br />the explosive has been placed to improve the blast energy confinement at the fissure. <br />2. The blast plan should make some arrangement to mitigate the fly-rock potential. <br />3. We reiterate our recommendation #5 in our last report dated November 2, 2009. We <br />believe that retrogressive movement of the slope above what is now the major scarp <br />remains a good possibility. The granite is weathered and abundant discontinuities in the <br />rockmass (related to the proximity of the Rampart Range fault) has weakened it. With <br />the loss of lateral support, we would expect dilation of the fractured rockmass over time <br />and additional tension cracks to open above the scarp. For this reason we recommend <br />that additional monitoring devices be installed above the upper scarp as soon as <br />possible. There is suitable "line of sight" to the Total Station to safely install additional <br />prisms on the slope above the main scarp of the rockslide. As we discussed with the <br />mine operator, if the rock condition is unsuitable to anchor prism brackets in desired <br />locations, they can also be mounted on 518-inch all-thread bars that can be pounded or <br />nailed into the soil-covered slope. The main criteria is that the bar is at sufficient depth
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