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Mr. Raymond Lazuk June 28, 2017 Climax Molybdenum Company, Climax Mine 4 1661214 006 RSP RevO A single integration of the measured acceleration history provides the velocity curve, with the displacement computed by double integrating the velocity.As can be seen in Figure 1,the ground moves in both a positive and negative direction during the earthquake. The maximum displacement, measured approximately 5 seconds after the start of shaking was +8.3 inches. The final displacement at the cessation of shaking was approximately-3 inches. In general, the resistance to sliding for the OSF will be lower in the downslope direction, leading to a net downslope displacement in the event of a large seismic event. Due to the nature of the OSF foundation materials and the high strength mine overburden itself, a liquefaction type failure or a high displacement mobilization of the OSF materials is considered implausible.A better analogue is to consider the OSF as a semi-rigid block,which has the potential to move over the foundation during strong ground motions caused by large earthquakes. There may also be some settlement of overburden within the dump, but this is not considered to be of consequence to any downgradient infrastructure (e.g., Highway 91). Under the semi- rigid block framework,the OSF may move incrementally in the downslope direction with each local peak in ground acceleration. However, the movement will stop (or even reverse direction) between local peaks, and the OSF will come to a complete stop at the end of the earthquake. The OSF will not "break loose" from the foundation and undergo rapid downslope movements in the manner of a debris flow in response to seismic shaking. 1.2 Pseudo-Static Approach As previously noted, the pseudo-static analyses conservatively models seismic events as a force with constant acceleration and direction, i.e.,an infinitely long seismic pulse.As a result,the standard of practice for geotechnical engineers is to take only a fraction of the predicted peak ground acceleration (PGA)when modeling seismic events using a pseudo-static analyses. A pseudo-static factor of safety of 1.0 is considered appropriate for water retention structures,when the structures are evaluated using one-half the PGA generated from the design earthquake (Hynes and Franklin 1984), with a strength reduction of 0.2 (i.e., use 80% of the static strength parameters) applied to materials which may generate excess pore pressure during shaking, and to account for any potential strain softening materials. The Climax OSE earthquake loading conditions were evaluated consistent with the Hynes and Franklin methodology(1984), with the 20% strength reduction applied. As defined by Hynes and Franklin (1984), if the results of a pseudo-static analysis provide a FoS>_ 1.0, any displacement occurring during a seismic event is expected to be within the tolerance of the structure. In the event that the pseudo-static analysis results in a FoS of less than unity, one can estimate the magnitude of displacement using several techniques developed for seismic displacement analyses of embankments, e.g., Newmark (1965); Marchson, et al. (2007); Makdisi and Seed (1979); finite element analysis; etc. For an OSF where the computed FoS >_ 1.0, Golder considers generally accepted seismic induced displacements would be on the order of 1 meter (3.3-ft). The inherent conservatism of pseudo-static analyses and the way in which FoS of 1.0 is defined as acceptable in the literature (e.g., by Hynes and Franklin) is the reason why acceptance of pseudo-static stability results is typically defined as a FoS>_1.0. The fundamental goal of defining a minimum FoS is, essentially, to define the amount of risk or conservatism that is appropriate for a given facility, under a specific potential failure mode. In static stability, higher FoS corresponds with lower risk(higher conservatism).The same is generally true for pseudo-static evaluations, with the caveat that FoS is not the only factor that defines the risk. In addition to the FoS, it is possible to design for different risk levels by defining different design seismic events, different allowable displacements, or by varying the seismic coefficient. Several variations of the pseudo-static method, each with its own recommendations regarding the seismic coefficient, are acceptable FoS, applied strengths, etc. (see Bray 1995, Bray and Travasarou 2007, Bray and Travasarou 2009, Hynes and Franklin 1984, Leps and Jansen 1984, Seed 1979). A FoS of 1.0 indicates acceptable levels of performance, depending on the nuances of the method used. For seismic stability evaluations of dams, the level of conservatism for seismic assessments is typically a function of the level of hazard(high, moderate,or low),seismic response, and reoccurrence interval selected. - G,,older},, 1661214 006 RSP RevO Responses to DRMS Comments 28JUN17 docx oc><r ates