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2024-12-16_REVISION - M1977410 (17)
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2024-12-16_REVISION - M1977410 (17)
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Last modified
12/17/2024 10:24:26 AM
Creation date
12/17/2024 7:55:05 AM
Metadata
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Template:
DRMS Permit Index
Permit No
M1977410
IBM Index Class Name
Revision
Doc Date
12/16/2024
Doc Name Note
Exhibit 6.5 Geotechnical Stability Idaho Tunnel
Doc Name
Request For Conversion
From
Grand Island Resources LLC
To
DRMS
Type & Sequence
CN1
Email Name
JPL
JLE
EL1
LJW
THM
Media Type
D
Archive
No
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Grand Island Resources, LLC Page 14 <br />Idaho Tunnel Portal – Slope Stability Analysis <br />Applied GeoLogic LLC 5/7/2020 <br />The “Weak Hard Rock” unit represents highly fractured rock with some weathering and is quite variable. <br />In some areas the material is quite weathered and grades into fully decomposed rock, while in other areas <br />it more closely resembles fractured hard rock with little weathering present. Assumed rock mass <br />parameters for Weak Hard Rock: <br />Intact Rock UCS = 1000 -2000 ksf (7,000 – 14,000 psi) <br />GSI = 45 (Blocky/Disturbed/Seamy with rough, slightly weathered, iron stained surfaces -or- Very <br />Blocky with smooth, moderately weathered and altered surfaces) <br />mi = 25 <br />D = 0 <br />3.3.4. Ground Support Elements <br />Due to their relatively short length and irregular pattern of placement, the soil anchors were neglected in <br />the analyses. The shotcrete will have little overall effect on global stability of the slope and was also <br />neglected in the analyses for conservatism. The primary purpose of the shotcrete is to control shallow <br />surface sloughing and raveling. <br />3.3.5. Idaho Tunnel <br />Due to the ground support elements that will be employed and its small size relative to the scale of the <br />slope, the tunnel opening was not included in the stability section. Spillings installed above the top of the <br />tunnel opening will become integrated with the cellular concrete void fill to help stabilize the opening and <br />face of the excavation below the County Road. Its is anticipated that additional spillings and possibly <br />forepolling will be required when tunnel rehabilitation resumes. These measures as well as the timely <br />installation of steel sets or shotcrete and mesh as ground support for the tunnel will be employed to <br />prevent additional collapse beneath the road. <br />3.3.6. Groundwater Conditions <br />The slope was initially modeled as drained, without groundwater to calibrate the model to conditions <br />which existed as the excavation was completed. <br />Subsequently, a parametric study was conducted to evaluate the sensitivity to water levels to reflect <br />conditions which may exist during spring thaw. This was conducted by progressively raising a perched <br />water table within the Alluvial Rock unit in 5 ft increments to evaluate the effect this had on the Factor of <br />Safety. <br />3.3.7. Collapse Void <br />The open collapse void was neglected in the base case analyses since it is not present everywhere within <br />the slope. However, its inclusion is useful for back analysis to provide constraint on the shear strength of <br />the material comprising the slope. <br />The 200 psi cellular concrete void fill is much stronger than the soil and rock colluvium material it replaces. <br />Additional runs were made to assess the amount of beneficial effect this mass of stronger material has on <br />stability of the slope in the sections where it will be present.
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