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1. The 9-month delay in implementing the monitoring plan was unfortunate because we <br />don't have enough pre-failure data to make any assessment on the behavior of the <br />rockmass and whether creep movement since last December was continuous or <br />episodic. <br />2. Weather data for the Colorado Springs area reports a 0.69 inch rainfall event on 9/12/09, <br />which may have been the ultimate trigger for the September 13-14 failure, even though <br />the slope was experiencing creep-type movement prior to the actual failure event. <br />3. In the south block of the rockslide, the September 13-14 slope failure was preceded by <br />displacement in several of the prisms. Following the event, prisms in the failure area <br />continue to show signs of slope creep. While no prism data is yet forthcoming from <br />prisms 20 through 30, visual observations show that reactivation and development of the <br />new landslide scarp within the Precambrian granite also extended behind the north block <br />(figure 4). There is not enough data presently submitted to allow for much analysis <br />beyond these observations. <br />4. It is the opinion of CGS that the entire southern and northern portion of the quarry wall <br />slope (defined by the upper scarp, the uppermost dashed red lines in figure 1) remains <br />unstable, in incipient failure conditions, and rockslide episodes will continue until the <br />quarry wall reaches equilibrium. Both the existing remnants of the south block and the <br />north block will fail over time. As stated in our review of the CTL slope stability report, no <br />analysis of these potential slope failures has been presented. Without detailed slope <br />stability analyses, determination of the exact condition of the slopes is not possible, as <br />well as formulating a realistic mitigation and reclamation plan. The rockslide along the <br />quarry wall remains unstable and unsafe, and should be avoided. We reiterate the <br />precaution we mentioned in our first memo. There should be no personnel allowed <br />within the rubble zone or below the major scarp of the rockslide. <br />5. We 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 5/8-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 <br />and the prism is mounted close to the ground so that the bar remains rigid and not be <br />prone to undesired sway or vibrations. Obscuring vegetation would need to be removed.