REP20218 - Laserfiche WebLink

Home Browse Search

' intended as grading plans for the revised mine plan for the failed east wall of the central pit. Sheets 3 through 9 of l0 are sections through the east wall depicting the proposed slope reconfiguration at seven representative locations. Sheet ]0 is a profile view looking west depicting the change in elevation that will occur along the ridge at the eastern boundary of the central pit when the proposed interim slope reconfiguration described in this report is implemented. The maximum elevation drop resulting from the proposed reconfiguration will be approximately 14 ft. The proposed interim reconfiguration represents the ' minimum slope remediation geometry to achieve stability and safety objectives while at the same time attempting to minimize exceedance of the approved preexisting limits of disturbance. In order to implement the design, Cooley should reconstruct the slope as shown on the drawings ' working from the top down. Excavation of soil and loose landslide debris can be accomplished with conventional excavating equipment such as dozers, backhoes, and loaders. Excavation of bedrock should use equipment and methods which minimize disturbance to rock outside the limits of ' excavation, It is likely that dozers equipped with rippers would he effective for a majority of rock in the cut. Mechanical excavation of the rock would also avoid potential problems with drilling and shooting short holes and utilizing small blasts. If blasting is used, special perimeter control blasting ' techniques will be necessary at the final interim cut surface as described below. Haley & Aldrich has included a general blast design to achieve improved perimeter control and, hence, improved rock quality and strength at the final surface. The recommended perimeter control techniques should be used fur the interim configuration in case this becomes the recommended final slope configuration after subsequent data collection and analysis. In addition to working from the top down, it is important for slope stability that the pit not he deepened any further than the existing pit floor as shown on the drawings. Our stahility analyses and interim reconfiguration design were based on remediating a failing slope under "emergency" ' conditions and undercutting the toe of the slope from the conditions at the time of the survey work would require a re-evaluation of the analyses and design presented herein and would likely result in larger impacts to the limits of disturbance and elevation change at the crest of the ridge. Another general recommendation for remediation of the slope is to perform construction documentation and design verification during construction of the interim slope reconfiguration. To ' :tchieve construction documentation, we propose that a Haley & Aldrich geotechnical engineer make periodic site visits during the course of the work to make construction observations and verify our design. Modifications Co the design and recommendations can be made, if necessary, based on the Observational Method (Peck, et. al.) working in concert with Cooley to avoid possible construction delays that could occur as a result of unanticipated subsurface conditions. ' 5-02. PERIMETER CONTROL BLASTING Our observations lead us to believe that Cooley's existing blasting techniques are highly effective at ' removing the desired quantities of rock in a manner that is compatible with pit excavation and crusher operations. However, it appears that the production blasting at the quarry causes more damage than is necessary to the unexcavated rock at the final pit cut slopes causing reduced rock quality and ' strength in the final slopes. This has evidently not been a source of slope instability elsewhere in the quarry, but likely contributed to instability of the subject failure area. We believe that additional care ' l1 ~ fcT~