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.hinuurt• 1 5. 2008 Page 38 <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />v <br />r -Apr <br /> <br /> <br /> <br /> <br /> <br /> <br />• . ??- ? <br /> 1 a <br /> <br /> <br />Figure 24. HighAall Slope Stability Failure at GStrike Pit After September 2005 Failure <br />By October 2006, suflicient mining had been performed in the newG-Dip Pit cut that the <br />hillside had been opened on two sides: on the east from G-Dip mining and on the north from <br />previous (I-Strike mining. The downdip face had been buttressed with spoils to stabilize the <br />failed region. Global instability ol'the hillside was not anticipated because local lailures had <br />never occurred on that scale and the monitoring data was not indicating global instability. <br />After excessive rain in late September, the entire hillside above the old G-Strike Pit <br />became unstable and slid. A view of' the landslide is shown in Figure 20. Characterization <br />activities have shown that the landslide had slid on a single, continuous, thin, weak saturated <br />layer which as discussed previously is referred to as the L-Roof mudstone layer. <br />The slide plane mechanism leading to global slope failure has been simulated using three- <br />dimensional (31)) slope stability analyses.a Complex combinations of groundwater, mining <br />geometry, and rock behavior were simulated in these analyses in order to get the hillside to be <br />unstable. The model, illustrated in Figure 26, accounted for the following key features. <br />Agapito Associates, Inc.