Laserfiche WebLink
movements within these rock blocks that now exist below the head scarp and above the <br />rockslide rubble zone. From our observations of the latest monitoring data forwarded to CGS by <br />DRMS it appears that the rates of movement at the South Block have slowed slightly, while the <br />rates at the North Block remain constant. Please consider the following observations and <br />recommendations. <br />The operator's proposed method of removal is to artificially cause the failure of the upper <br />blocks by inserting explosives into the open fissures of the rockmass, including the headwall <br />scarp. We don't consider this Technical Revision to be a blast plan since the proposed <br />locations of the charges, explosive quantities, and delays are not given. The brief discussion in <br />the revision document seems to emphasize the removal of the remaining southern block where <br />prisms 13, 15, 18, and 19 are located. It does not explicitly state that they will also attempt to <br />remove the northern block where prisms 21, 22, 24, and 25 are located, which has also <br />experienced significant and constant rates of movement. See figure 2. <br />We noted some minor factual errors in the Technical Revision. It states that prism 13 <br />has been very stable since the initial slide. It is prism 19 that does not show any movement <br />outside of the inherent error of the tool. While we cannot precisely locate this prism from the <br />prism-location image provided by the mine operator, we are assuming that it has been installed <br />above the rockslide head scarp (See Figure 2). Also, that lack of movement in prism 19 has <br />only been measured since monitoring began, in early September of 2009. Whether movement <br />occurred in the interim 9 months after the initial slide in December 2008 is unknown. The Photo <br />3 image in the Technical Revision, which is labeled as the photo of the quarry immediately after <br />the 2009 slide is incorrect. The photo shown is the quarry immediately after the December <br />2008 rockslide, before the September 2009 event. <br />We consider this Technical Revision to be a "hope for the best" approach to mitigate the <br />dangerous hanging blocks in the quarry. We concur with the mine operator that ground <br />Figure 2. Prism map provided by mine operator showing the December 2008 rockslide. Prisms <br />numbers with red circles presently show landslide movement. Those with black circles were lost in the <br />subsequent rockslide of September 2009 that is not shown in this earlier image.