2017-01-09_REVISION - M1973007SG (4)

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Transit Mix 12/30/16 Page 5 As summarized in the above table the calculated factors of safety of the proposed wash fines embankment dam exceed the required factors of safety for slope stability for the evaluated loading conditions. Liquefaction Evaluation Brierley evaluated the liquefaction potential of the engineered embankment and embankment foundation. Liquefaction is a prevalent concern where materials utilized for embankment construction consist of loose, saturated sands or sensitive silts and if seismic potential exists at the site. Earthquakes cause ground motions that can cause structures to fail either through structural collapse or loss of ground support. The nearest fault to the property according the US Geological Survey Earthquake Hazards Program is the Ute Pass fault zone (age <750,000 years) approximately 5 miles to the west. According to Widmann (1998), a long term slip rate of <0.2 mm/year was estimated for this fault based on the small size of the scarps and the fact that the fault apparently has not ruptured since the initial deposition of the alluvium about 130,000 years ago. Brierley anticipates a minimal seismic risk potential for the proposed embankment within the design life of the pond. According to the literature, liquefiable sands often correlate to very loose soils with extremely low(less than 10) N-values. The average blow counts for the embankment foundation is 23 blows per foot which indicates a medium dense material. Based on medium dense blow counts and the material classifications in the foundation there is a minimal risk of liquefaction for in- place undisturbed materials at the site. The design report for the new embankment recommends that borrow material is obtained from the existing mine floor within the footprint of the new impoundment. Each lift in the embankment will be compacted to at least 95 percent relative compaction. The borrow material should consists of the eolian soils with USCS classifications of SM, SC or CL. The coarse alluvium should not be used as borrow. The eolian deposits should be borrowed somewhat uniformly over the pit floor footprint such that the depth of excavation in any single location is not more than about 4 ft. The laboratory results for the eolian deposits are presented in the table below. Table 3. Summary of Laboratory Results for the Eolian Deposits Sample Location Atterberg Gravel Sand -200 Limits Boring Sample Depth M M N LL (%) pl (%) USCS No. No. feet BA-1 S-1 4 0.3 69.9 1 29.8 -- -- SM BA-2 S-4 19 5.6 66.5 27.9 -- -- SM BA-3 S-2 9 -- -- 71.1 32 1 15 CL BA-4 S-3 14 -- -- 69.8 28 1 12 CL Loose saturated granular soils such as sand, silty sand or clayey sand; and non-plastic silts within 50 feet of the surface and below the water table can be susceptible to liquefaction during cyclic loading such as exhibited during seismic events. Several methods were used to characterize the liquefaction susceptibility of the soils. The criteria are as follows: BRIERLEY ASSOCIATES Creating Space Underground