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Grand Island Resources, LLC Page 15 <br />Idaho Tunnel Portal – Slope Stability Analysis <br />Applied GeoLogic LLC 5/7/2020 <br />4.0 ANALYSIS RESULTS <br />Analysis of the slope under drained conditions indicates a minimum Factor of Safety (FoS) failure surface <br />of 1.36 for a non-circular failure of the excavation slope. The minimum FoS for a failure surface which <br />intersects the County Road was only slightly higher at 1.37. Figure 4 presents a summary of these stability <br />analysis results and includes the critical failure surface as well as a summary plot of all trial failure surfaces <br />color-coded by FoS. These analyses demonstrate that the lower FoS failure surfaces pass entirely through <br />the colluvium and regolith soil materials due to the slope geometry. The position of the weak hard rock <br />and decomposed rock beneath the slope has little to no effect on the overall stability. <br />During spring thaw, several areas of seepage were observed coming through the shotcrete <br />facing (Photograph 2). This seepage indicates that portions of the slope may become saturated during <br />snow melt, and soil saturation. The seepage is not present everywhere and does not discharge <br />uniformly from the slope which suggests isolated areas of seepage flow rather than complete <br />saturation. Table 1 presents a summary of perched water depth with the Alluvial Rock unit versus <br />FoS. As indicated in this table, a perched water depth of 15 ft, or about half the thickness of the <br />material, results in a FoS of 1.0. Figure 5 depicts the stability section with the assumed perched water <br />table and critical failure surface from this analysis. <br />Including the open collapse void in the stability section reduces the minimum FoS to 0.74 for a non-circular <br />and 0.90 for a circular failure surface respectively, indicating a condition of instability. Since the slope was <br />observed to be stable despite the presence of the tunnel and open void, these results serve to <br />demonstrate that the shear strength adopted for the regolith and colluvial soils is conservatively low. <br />These results are presented in the summary included in Table 1. <br />Including the 200 psi cellular concrete void fill within the stability section increases the FoS considerably. <br />The minimum FoS for all trial failure surfaces passing through the cellular void fill is above 4.0. <br />Table 1 – Stability Analysis Summary <br />Model Case Water Depth <br />(ft) <br />Minimum FoS <br />Janbu, <br />non-circular <br />Bishop, <br />circular <br />Fully Drained 0 1.36 1.46 <br />Perched Water 5 1.32 1.46 <br />Perched Water 10 1.12 1.40 <br />Perched Water 15 1.00 1.24 <br />Open Void 0 0.74 0.90 <br />Cellular Concrete 0 > 4.0 > 4.0