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Grand Island Resources,LLC Page 1L <br /> Idaho Tunnel Portal—Slope Stun iy,,rzr; <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 /> ' <br /> • <br /> • <br /> f ash <br /> ,�. ,.444' «,. <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 crown slightly in size. Otherwise, there are no <br /> obvious signs of slope stability issues with the excavation or adjacent slopes,such as cracking or slumping, <br /> despite the occurrence of spring thaw and presence of some ground water. Locations which had been <br /> seeping water have stopped (Photograph 2) and the ground exposed in the non-shotcrete covered <br /> margins of the excavation has dried considerably. <br />