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Grand Island Resources,LLC Page 2 <br /> Idaho Tunnel Portal—Slope Stability Analysis <br /> at the time. The maximum height at the taller left(south)wing wall excavation is 28 ft,sloping at an angle <br /> of 70-80 degrees from horizontal. <br /> The top of the excavation is approximately 40 ft from County Road 128(Caribou Road)at the closest point <br /> and 20 ft lower in elevation. <br /> 1.1.3. Portal Rehabilitation <br /> Entrance to the Idaho Tunnel at the mine site was in such a state of neglect and disrepair from long-term <br /> gradual deterioration that it was not safe to enter and operate the mine water system per the approved <br /> permit. In particular, the timber ground supports at the portal were tilted dangerously askew and the <br /> ground slopes adjacent to the portal exhibited signs of shallow slope failures and sloughing. <br /> In December 2019 a roof collapse occurred a short distance into the tunnel during initial rehabilitation <br /> efforts. The roof failure occurred in an 11-12 ft section of unsupported ground as the tunnel opening was <br /> being enlarged through a section of mixed soil and decomposed gneiss. The collapse completely blocked <br /> the mine opening, crushed the pipe carrying the flow of mine water, and daylighted in the slope below <br /> County Road 128 (Caribou Road), leaving a large remnant void above the tunnel opening. <br /> As described in TR-7, the remaining void created by the portal collapse was backfilled with pervious <br /> cellular concrete to provide permanent ground support to stabilize the slope and allow drainage. The <br /> cellular concrete backfill is significantly stronger than the soil which originally comprised the slope while <br /> imposing only a fraction of the weight. <br /> Placing the cellular concrete backfill within the initial collapse void was completed on May 19, 2020. This <br /> increased stability of the slope below the county road. Tunnel rehabilitation was resumed approximately <br /> a week later and additional sloughing into the tunnel occurred, daylighting in the slope immediately west <br /> of the previous backfill material. Additional cellular concrete backfill was placed and again more sloughing <br /> occurred when rehabilitation was resumed. This occurred repeatedly as tunnel rehabilitation advanced <br /> for each of the next four steel sets(16 ft). Additionally, high strength grout was used immediately above <br /> the tunnel crown in several areas, and riprap subsequently infilled with cellular concrete was used to <br /> backfill one of the larger voids. The end result is that 447 cubic yards of the disturbed ground overlying <br /> the old adit has now been replaced with substantially stronger cellular concrete, riprap and high strength <br /> grout, a significant amount. Table 1 provides a summary of the final quantity of each of these materials <br /> used. <br /> Table 1—Summary of Backfill Materials <br /> Material Type Quantity(yd3) <br /> Cellular concrete 299 <br /> Riprap 100 <br /> High Strength Grout 48 <br /> The flowable nature of the cellular concrete backfill allowed it to flowed forward within the ground <br /> disturbed above the historic tunnel opening. This served to encapsulate loose blocks of rock and previous <br /> ground supports in a solid mass to provide support during the remaining rehabilitation efforts. <br /> Applied Geologic LLC 5/3/2021 <br />