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Grand Island Resources,LLC Page 4 <br /> Idaho Tunnel Portal—Slope Stability Analysis <br /> the 20-ft wide County Road. Starting below the road the slope will be backfilled to 3H:1V using compacted <br /> rock fill. A pair of Connex shipping containers and steel supports will be used to maintain the tunnel <br /> opening through the waste rock. A reinforced concrete retaining structure will be used to create a vertical <br /> face around the portal opening. The surface of the waste rock will be covered with growth media and <br /> revegetated. The previous nature of the cellular concrete, waste rock backfill and presence of the tunnel <br /> will allow groundwater to freely drain from the slope in order to ensure long-term stability. <br /> 3.3.2. Material Properties <br /> The analyses incorporated conservative shear strength parameters for the colluvial soil material, regolith <br /> and blocky rock mass separately. Since the slope height is not great, the shear stresses will be low. For <br /> the low range of stresses present, equivalent linear Mohr-Coulomb shear strength parameters were <br /> assumed. <br /> During excavation the regolith and colluvium was observed to stand near-vertical for up to 28 ft without <br /> ground support. The colluvium material consists of poorly-graded sandy gravel with cobbles, silt and clay <br /> (GP). For the purposes of the stability analysis this material was assigned a friction angle of 38 degrees <br /> and 500 psf (3.47 psi) cohesion with a moist unit weight of 125 pcf. Areas which contain a higher <br /> proportion of coarse rock fragments will exhibit higher shear strength, and the overall average strength is <br /> likely higher, however, if failure were to occur it will tend to pass through the weaker materials which <br /> offer less resistance. <br /> In some areas the underlying bedrock is quite weathered and grades into fully decomposed regolith,while <br /> in other areas it more closely resembles fractured hard rock with little weathering present. <br /> The regolith consists of decomposed gneiss which has been weathered and decomposed in situ, but has <br /> not been disturbed and retains the original rock fabric. The feldspar minerals have been largely altered <br /> to clay and can be readily excavated using the pick point of a geologic hammer. Portions of the rock which <br /> contain a high percentage of quartz require one or more blows of a rock hammer to fracture, but exhibit <br /> a high degree of jointing. The regolith material represents a weak rock mass for which the Hoek-Brown <br /> criterion'was used to estimate the average rock mass strength across this material based on a large body <br /> of empirical data. Conservative rock mass parameters adopted for Decomposed Gneiss: <br /> Intact Rock UCS = 1000-2000 ksf(7,000—14,000 psi) <br /> GSI = 15 (Disintegrated with highly weathered surfaces with soft clay coatings or infilling) <br /> mi = 25 <br /> D=0 <br /> The fractured and weathered blocky gneiss represents highly fractured rock with some weathering and is <br /> quite variable. Conservative rock mass parameters adopted for the Blocky Gneiss: <br /> Intact Rock UCS= 1000-2000 ksf(7,000—14,000 psi) <br /> ' E.Hoek and E.T.Brown, 2018; "The Hoek—Brown Failure Criterion and GSI — 2018 Edition." Journal of Rock Mechanics and <br /> Geotechnical Engineering,Volume 11,Issue 3,June 2019,Pages 445-463 <br /> Applied GeoLogic LLC 5/3/2021 <br />