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Geotechnical Evaluation of Mine-Induced Earthquakes on Bruce Park Dam <br />Bowie Resources, Limited <br />June 2002 <br />Section 3 - Main Dam Analysis <br />3.1 General <br />We evaluated potential impacts to Bruce Park Dam and Reservoir from mine-induced ground <br />motions by computing probable permanent deformations of the main dam and landslide. <br />Permanent deformations of the saddle dam were not performed because the saddle dam is <br />constructed of and founded on materials similar to those at the main dam and it is about half <br />as high as the main dam, and thus less critical. <br />The yield acceleration, which is the acceleration that results in a pseudo-static slope stability <br />factor of safety of 1.0 was computed at various locations along the height of the dam. For the <br />yield acceleration computations, the vertical acceleration was considered to be zero. We used <br />the computer program STABL 6, developed by Purdue University and the modified Bishop <br />method for circular failure surfaces to perform the pseudo-static stability analysis. <br />The applied acceleration to the dam and foundation from a mine-induced seismic event was <br />estimated based on one-dimensional shear wave propagation analysis using the computer <br />• program PROSHAKE (SHAKE). We computed the average acceleration time history of the <br />soil mass above particular locations in the dam by dividing the shear stress time history at <br />that particular location computed by SHAKE by the overburden vertical stress at that <br />particular location. Where the computed time history at any location contains accelerations <br />that are greater than the yield acceleration computed for that location, permanent <br />deformations are anticipated. <br />Permanent deformations were estimated using Newmark's sliding block analysis (Newmark, <br />1965), which is implemented in the computer program NMARM, developed by GEI (1986). <br />3.2 Liquefaction <br />Because all soils encountered in the subsurface investigations are cohesive with fines content <br />greater than 70 percent, the embankment and foundation soils are considered non-liquefiable. <br />3.3 Representative Cross Section for Yield Acceleration Analysis <br />We developed a representative cross section at the maximum section of the main dam for <br />two-dimensional pseudo-static slope stability analysis based on information presented in the <br />Geotechnical Data Report (GEI, 2001). The cross section consists of four material types <br />02-05--:2 Geotechnical Evaluation of Mine-Induced Earthquakes <br />GEI Consultants, Inc.