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~~ <br />C~ <br />L J <br />6.0 Discussion of Stability for Existing Conditions <br />Based upon the analyses and the monitoring information, the existing landslide is stable from <br />catastrophic movement. As shown on Figure 6, the factor of safety with the pins is about 1.16 or <br />higher. If the dewatering trenches are installed, the factor of safety will increase further, but it is <br />not likely that the water table will decrease the full 30 feet of the trench depth. Dewatering by <br />the stone columns and pond lining, however, will further increase this factor of safety. Therefore, <br />the actual factor of safety is expected to be between 1.2 and 1.3, if the dewatering trenches are <br />installed. A factor of safety less then 1.3 is a reasonable value with aback-calculation of an <br />already failed surface and the observational approach to landslide stabilization. Based upon the <br />FLAC analysis, the landslide is stable. <br />The stability analyses, however, only addresses the overall stability of a massive landslide. It does <br />not address the localized sloughing that will occur as a result of groundwater from the bedrock- <br />wlluvium interface. Further stabilization of these sloughs may be necessary and may include <br />soldier piles or buttressing. <br />oszsoza~ssssi•UABM 13 <br />