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Geotechnical Evaluation of Mine-Induced Earthquakes on Bruce Park Dam <br />Bowie Resources, Limited <br />June 2002 <br />• Section 5- Conclusions <br />Based on the results of the evaluations performed and documented in this report, we <br />conclude the following: <br />1. Bruce Park Dam and Bruce Park Saddle Dam should not be adversely impacted <br />from mine-induced seismicity generated from long wall mining at the Bowie <br />Resources mine for the following reasons: <br />a. The dams and foundations consist of clays soils that are not susceptible to <br />liquefaction during seismic loading. <br />b. Permanent deformations of the dam and saddle dam during seismic loading <br />should be insignificant because the expected ground motions (accelerations) at <br />the dam and saddle dam sites are less than the computed yield acceleration. The <br />applied acceleration needs to be greater than the yield acceleration for significant <br />deformations to occur'. <br />c. The dam and saddle dam are generally homogeneous earthen structures without <br />distinct internal zones of materials having significantly different properties and <br />without an inlet tower or other type of structure that would behave independently <br />during seismic loading <br />• 2. The computed static factor of safety for the existing landslide depends on the pore <br />water conditions in the slope and would range from about 1.1 to 2.0 for phreatic <br />surfaces ranging from the ground surface to the top of bedrock, respectively. <br />3. A permanent deformation of about 9 inches may occur in the existing landslide if a <br />rare magnitude 4.2 mine-induced seismic event occurs under conditions where the <br />phreatic surface in the landslide is at the ground surface. If the phreatic surface is at <br />mid-depth or at the bottom of the landslide, a rare magnitude 4.2 event would <br />generate permanent deformations of 1.5 and 0.3 inches, respectively. <br />4. No cumulative deformation of the landslide is expected if the phreatic surface is at or <br />below the mid-depth of the landslide and mining activities over a 2-year period <br />generate a total of 100 magnitude 1.75 events, 20 magnitude 2.0 events, and 5 <br />magnitude 2.5 events. <br />5. Cumulative deformation of the landslide is expected to be about 11 inches if the <br />phreatic surface remains at the ground surface and mining activities over a 2-year <br />02-05-22 Geotechincal Evaluation of Mine-Induced Earthquakes <br />• ' Item 1 b amended (applied and yield reversed) by J. E. Stover 12/22/06 with authority from BRL. <br />19 12/22/06 <br />ri2-16 <br />A PPROVO <br />I1Z 4/a 8