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2019-11-12_REVISION - M2004044 (13)
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2019-11-12_REVISION - M2004044 (13)
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Last modified
1/6/2025 6:22:11 AM
Creation date
11/12/2019 1:01:01 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
M2004044
IBM Index Class Name
REVISION
Doc Date
11/12/2019
Doc Name
Adequacy Review Response #3
From
Aggregate Industries
To
DRMS
Type & Sequence
AM1
Email Name
JLE
ERR
Media Type
D
Archive
No
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O TETRA TECH Updated Tucson South Proposed Gravel Mine Slope Stability Analysis <br /> November 8 2019 <br /> PREVIOUS3.0 <br /> A slope stability evaluation was performed by Tetra Tech for the Tucson South mine in November 20043. The <br /> evaluation used the (previously required) required minimum factor of safety value of 1.0 and analyzed sections for <br /> a total of 14 critical structures surrounding the Tucson South mine. A seismic analysis was not required by the <br /> DRMS as part of the slope stability analysis in 2004. The 2004 evaluation was used as the basis for an updated <br /> slope stability analysis performed by Tetra Tech in 2018. <br /> In preparation of an amendment to the Tucson South permit application in 2018 Tetra Tech performed an updated <br /> slope stability analysis. Critical structures within 200 feet of the mine in 2018 were reevaluated and seven <br /> manmade structures were identified as requiring slope stability analysis. A memorandum dated November 9, <br /> 20184 describes the results of the analysis that was prepared and submitted to Aggregate Industries for their use. <br /> A slope stability analysis preformed in February of 2019 to determine required minimum setbacks from permanent <br /> manmade structures around the Tucson South Mine if mine highwalls were excavated at a slope of 0.5HAV and <br /> not reclamation slopes were not constructed concurrently. <br /> 4.0 STABILITY ANALYSIS JUNE 2019 <br /> This updated stability analysis was performed using GeoStudio 2018 (Slope/W Define) computer software5. The <br /> software is capable of computing factors of safety for a range of materials using finite element analysis. Spencer's <br /> method of slices6 was used to calculate the safety factor for the individual failure surfaces. <br /> Several assumptions were made for the models including: <br /> • Surficial geology was modeled based on stability models and borehole data from 2004. <br /> • Geologic layers are generally horizontal in the subsurface. <br /> • The highwall will be concurrently reclaimed, or mined only at 3H:1V slopes <br /> • The West and East pits will be mined after the slurry wall is installed and will be dewatered as needed. <br /> • The slurry wall (designed by others) will be keyed into bedrock. <br /> • No excess pore pressure build up will occur within the soil strata. <br /> • No slurry wall will be constructed around the South pit. <br /> • The South pit will be wet mined. <br /> • The slurry wall is setback a minimum of 20 feet from the crest of the mine slope/reclamation slope. <br /> • The slurry wall will be constructed a minimum of 15 feet from any structure or easement. <br /> Both a reclamation slope and a mine slope were considered during this stability analysis for each section <br /> analyzed in February 2018. A reclamation slope is a slope built of fill material, typically overburden found at the <br /> site, used to stabilize the mine highwall. A mine slope is a slope cut at a stable grade leaving the native material <br /> in place. The grade modeled for both the reclamation slope and the mine slope was a 3HAV. The highwall, from <br /> the February study, is assumed to be 0.5HAV. <br /> 3 Goss, C. (2004, November 22). RE: Revised Tucson South Proposed Gravel Mine Slope Stability Analysis; <br /> Tetra Tech RMC Job No. 19-3919.019.00. (T. M. Refer, Ed.) Longmont, CO: Tetra Tech. <br /> 4 Franke, M. (2018, November 9). RE: Updated Tucson South Proposed Gravel Mine Slope Stability Analysis; <br /> Tetra Tech Job No. 200-23514-18004. (Bolduc, J, Ed.) Longmont, CO: Tetra Tech. <br /> 5 GEO-SLOPE International, Ltd. (2014). SLOPEM 2012. December 2014 Release. <br /> 6 Spencer, E., 1967. A Method of Analysis of the Stability of Embankments Assuming Parallel Inter-Slice Forces." <br /> Geotechnique, Vol. XVII, No. 1, pp. 11-26. <br /> Page 2 <br />
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