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Grand Island Resources, LLC Page 11 <br />Idaho Tunnel Portal – Slope Stability Analysis <br />Applied GeoLogic LLC 5/7/2020 <br />3.0 STABILITY ANALYSIS <br />3.1 Approach <br />The stability analyses were conducted as two-dimensional limit-equilibrium analysis using commercially <br />available software. Three cases were considered at which the slope was observed to be stable and <br />therefore must exhibit a Factor of Safety (FoS) greater than unity; at the end of excavation, during spring <br />thaw, and with an open void present. For the end of excavation scenario, the slope reinforcement was <br />neglected in the analysis and the slope was assumed to be fully drained. For the spring thaw scenario, <br />the presence of groundwater in the slope was considered in the analysis. The open collapse void and <br />backfilled void were considered separately. <br />The actual FoS should be higher than the results presented for 2D analyses section due to the concaved <br />slope orientation and 3D edge effects. Studies have shown that these 3D effects can become significant, <br />often increasing the FoS by 10-20 percent, or even more2. This effect tends to become more significant <br />as the amount of slope curvature increases, particularly as the ratio of the slope width to slope height <br />drops below 3. In the case of the Idaho Tunnel Portal, the excavation has a relatively narrow open width <br />of approximately 30 ft at the base of the mouth of the excavation relative to a height ranging from 15 to <br />28 ft. These effects have been considered qualitatively in the results discussion. <br />3.2 Software <br />The stability analyses were conducted using the RocScience SLIDE2 software, a 2D slope stability program <br />for evaluating the safety factor or probability of failure, of circular and non-circular failure surfaces in soil <br />or rock slopes. Slide2 analyzes the stability of slip surfaces using vertical slice or non-vertical slice limit <br />equilibrium methods like Bishop, Janbu, Spencer, and Sarma, among others. Search methods can be <br />applied to locate the critical slip surface for a given slope. The Bishop method of slices for circular failures <br />surfaces while the Janbu method of slices for satisfying both moment and force equilibrium was adopted <br />for non-circular surfaces. <br />The Slide2 software also allows the effects of slope reinforcement to be included in the analyses. <br />3.3 Model Input <br />3.3.1. Slope Geometry <br />An idealized representative two-dimensional cross-section was considered for analysis. This section <br />consisted of the profile along the axis of the tunnel included on Figure 2, at the maximum cut slope on <br />the left (south) side of the portal excavation. The idealized slope consisted of a 28-ft high excavation at <br />an angle of 75-degrees then natural ground sloping at approximately 40 ft to the edge of the 20 -ft wide <br />County Road. Figure 3 presents the idealized slope stability cross-section superimposed on the tunnel <br />profile section. <br />Included on this figure is the assumed material distributions as described in the following section. <br />2 Zhang, Y., Chen, G., Zheng, L., Li, Y., and Zhuang, X,. 2013; “Effects of geometries on three-dimensional slope stability.” Canadian <br />Geotechnical Journal. Vol. 50, No. 3, pp. 233 – 249.