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below. <br />Hstddlsst omBesry <br />r,.Mnt ra-Deny <br />The results of the analyses are included in Appendix A and are summarized <br />• Gob Pile #2 without Gob Drying Area Circular — minimum FS = 1.530 <br />• Gob Pile #2 without Gob Drying Area Block — minimum FS = 1.559 <br />• Gob Pile #2 with Gob Drying Area Circular — minimum FS = 1.530 <br />• Gob Pile #2 with Gob Drying Area Block — minimum FS = 1.557 <br />• Uncompacted Gob Only Circular — minimum FS = 1.019 <br />3.5 Discussion — Gob Pile #2 <br />As indicated above, the results of the analyses yielded factors -of- safety for the <br />existing slopes along gob pile #2 slightly above 1.5. The analyses also indicate that the <br />gob drying area will have a negligible impact on the stability of gob pile #2. <br />It is important to note that the observed factors -of- safety are heavily dependent <br />upon the presence of the piezometric surface modeled based upon the pore pressure data. <br />In order to evaluate the impacts of changes in the piezometric surface on the stability, <br />HBET conducted sensitivity analyses. In general, the available data suggests that the <br />pore pressures are not increasing near the toe of gob pile #2. As a result, the piezometric <br />surface near the toe was not changed as part of the sensitivity analyses. The piezometric <br />surface was changed by adjusting the pore pressures in the two `active' piezometers near <br />the top of the existing gob pile, VWP -06 and VWP -08. <br />The results of the sensitivity analyses indicate that the stability of gob pile #2 is <br />currently most sensitive to changes in the pore water pressures in VWP -08. An increase <br />in the pore pressure in VWP -08 of 3 psi (equivalent to approximately 7 feet of head) <br />would result in a factor -of- safety of less than 1.5. However, changing the pore pressure <br />in VWP -06 as much as 9 psi (equivalent to approximately 21 feet of head) did not <br />significantly reduce the factor -of- safety of gob pile #2. The results of the sensitivity <br />analyses are included in Appendix B. <br />In addition to the sensitivity with regard to the piezometric surface, HBET <br />evaluated sensitivity analyses with regard to the shear strength of the gob. As indicated <br />in the referenced documents, previous sensitivity analyses completed by Buckhorn <br />included friction angles (fl of 30° and 32 °. However, the triaxial shear testing <br />completed in 2005 showed fully drained friction angles of between 33.6° and 34.3°. In <br />addition, triaxial shear testing completed in October 2013 showed a drained friction angle <br />of 34.5 °. <br />None of the shear strength testing shows a drained friction angle as low as 30 °. <br />HBET does not believe that this value is representative of the gob and as a result, <br />sensitivity analyses using this value is not warranted. However, for conservatism, HBET <br />conducted sensitivity analyses considering a drained friction angle of 32 °. The results <br />indicate that Gob Pile #2 will still have a factor -of- safety above 1.5. The results of the <br />analyses are included in Appendix B. <br />X%2003 ALL PROJECTS-00489- JE Sto.er Associates Jnc OWS9.000J Bowie Jlinet200 - C/eWW4S9.000J R032114R1 doe <br />