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Grand Island Resources,LLC ?a: 3 <br /> Idaho Tunnel Portal—Slope Stability Analysis <br /> r. <br /> , , , . 4.,.._ <br /> . .. <br /> .. <br /> s <br /> ,. , ..._ <br /> . ,. ,_:. , <br /> _ . <br /> ..,..,.. : <br /> 0_, . . <br /> ,, <br /> ,.. <br /> ,. . . <br /> ... , ... <br /> . .., , <br /> .,: ,,.,,,,, , _ <br /> .„.„,,,.. , <br /> s , ,‘_.-,,v,. <br /> 1`J <br /> Photograph 2—Current Condition of the Idaho Tunnel Portal. The three safety cones and caution tape <br /> at the top of the slope mark the edge of Country Road 126(Caribou Road). The crown hole over the <br /> void is visible between the two small trees above the portal. <br /> 1.1.3. Collapse Repair <br /> In late February 2020,two additional new steel sets were installed in the area of the tunnel portal beneath <br /> the collapse and lined with lagging on the ribs and back. As with the initial two steel sets,these consisted <br /> of W6 x20 wide flange steel beams and posts installed on 4-ft center-to-center spacing. Lagging consisted <br /> of 3-in. x 8-in. treated Douglas Fir planks. This design and installation were inspected and approved by <br /> Mr. David Hallman, a geological engineer with 37 years of experience and registered as Colorado <br /> Professional Engineer No. 26076. <br /> The narrow gap between the new ground supports and the existing ground was been closed using pieces <br /> of lagging, plywood, polyurethane foam, and caulk to create a tight seal. The remaining void created by <br /> the portal collapse will be backfilled with pervious cellular concrete to provide permanent ground support <br /> that will stabilize the slope and allow drainage. <br /> The completed cellular concrete backfill will be significantly stronger than the soil which originally <br /> comprised the slope while imposing only a fraction of the weight. This will serve to increase stability of <br /> the slope below the county road. The flowable nature of the backfill will allow it to completely <br /> encapsulate the tunnel lining system in a solid mass to create robust permanent support for the mine <br /> entrance. The previous nature of the backfill will allow groundwater to freely drain from the slope in <br /> order to ensure long-term stability. <br />