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Grand Island Resources, LLC Page 10 <br />Idaho Tunnel Portal – Slope Stability Analysis <br />Applied GeoLogic LLC 5/7/2020 <br />2.0 PROBLEM DESCRIPTION <br />Figure 2 presents a plan and profile of the Idaho Tunnel based on 10-ft topographic contours of the original <br />ground surface. Superimposed on this figure are the approximate position of the rehabilitated tunnel <br />portal following excavation. <br />The material encountered during portal excavation and currently exposed in the wing walls consisted of <br />regolith and colluvium, with some decomposed rock encountered at depth. The excavated slopes stood <br />unsupported following excavation and were dry at the time (Photograph 7). The maximum height at the <br />taller left (south) wing wall is 28 ft, sloping at an angle of 70-80 degrees from horizontal. The top of the <br />excavation is approximately 40 ft from County Road 128 (Caribou Road) at the closest point and 20 ft <br />lower in elevation. This creates potential long-term concerns for stability of the road. <br />Photograph 7 – Idaho Tunnel Portal following excavation <br />The excavated slope above the portal opening and wing walls were reinforced with 10- and 20-ft soil nails, <br />6-gauge wire mesh, and nominal 6-inches of fiber-reinforced shotcrete. Grouted threadbar spillings were <br />also installed at 12-inch spacing above the portal. These were reportedly 35 ft long, extending into harder <br />ground and grouted. Unfortunately, little as-built documentation is available. <br />As of May 2, 2020, the sink hole above the collapse has grown slightly in size. Otherwise, there are no <br />obvious signs of slope stability issues with the excavation or adjacent slopes, such as cracking or <br />slumping, despite the occurrence of spring thaw and presence of some ground water. Locations which <br />had been seeping water have stopped (Photograph 2) and the ground exposed in the non- <br />shotcrete covered margins of the excavation has dried considerably.