WY FLAP SHE 26(1) Red Grade Road.Addendum Memo FINAL.December 2025.pdf
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- WY FLAP SHE 26(1), Red Grade Road, Phase 1
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This is a Technical Memorandum serving as a geotechnical addendum to the Final Geotechnical Report for the Red Grade Road project in Sheridan County, Wyoming (WY FLAP SHE 26(1)), dated December 17, 2025. The memorandum, prepared by Brendan McGarity, Geotechnical Engineer at CFLHD, and reviewed/approved by James M. Arthurs, Senior Geotechnical Engineer, addresses changes to Table 4.2 in subsection 4.1.4 of the original May 2025 Final Geotechnical Report. Following the 100% Preliminary Supplemental Engineering (PS&E) deliverable, alignment modifications were made at two property locations to remain within existing right-of-way boundaries, requiring station equation adjustments that affect only local stationing, not overall project stationing.
The updated Table 4.2 provides revised earthwork and shrink/swell recommendations for cut slope and rockfall catchment measures across the project corridor, with stationing ranges from 149+00 to 282+40. Key modifications include changes to station endpoints at three locations: 203+63 to 209+70/1001+70, with subsequent cascading adjustments affecting the GC section from 209+70/1001+70 to 211+00/1003+00, the Dolomite section from 211+00/1003+00 to 216+30/1008+30, and associated material type designations. The table specifies material types, maximum slope ratios ranging from 1:1 to 4:1 (vertical:horizontal), minimum catchment ditch widths of 4 feet where applicable, and shrink/swell factors ranging from 0.9 to 1.4. The addendum confirms that all other recommendations in the original Final Geotechnical Report remain in effect unless specifically superseded herein, and the disclaimer and limitations clause from the original report applies to these revisions.
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To: Steven Davis, P.E., Project Manager, CFLHD, Lakewood CO
From: Brendan McGarity, Geotechnical Engineer, CFLHD, Lakewood CO
Through: James M. Arthurs, P.E., P.G., PhD., Senior Geotechnical Engineer, CFLHD, Lakewood CO for Devin T. Dixon, P.E., Geotechnical Team Leader, CFLHD, Lakewood CO
Subject: Geotechnical Addendum for the Red Grade Road Final Geotechnical Report, Sheridan
County, Wyoming, WY FLAP SHE 26(1)
This memorandum serves as an addendum to the final geotechnical report for the Red Grade Road project, titled “Red Grade Road, Sheridan County, WY, WY FLAP SHE 26(1), FINAL
Geotechnical Report”, dated May 2025. This addendum addresses changes to Table 4.2 in subsection 4.1.4 of the Final Geotechnical Report.
Following the 100% PS&E deliverable, changes to the alignment were made to stay within the existing right of way (ROW) at two property locations. Station equations were added at both locations to only change local stationing and not the overall project stationing. Any recommendations not specifically superseded in this memorandum remain in effect.
1 EARTHWORK AND SHRINK/SWELL RECOMMENDATIONS
The following table replaces Table 4.2 of the final geotechnical report to reflect station changes described above. Changes from the original table are shown with strikethroughs and red text.
Technical Memorandum
Date: December 17, 2025
Table 4.2:- Summary of Cut Slope and Rockfall Catchment Recommendations
BEGIN STA END STA
MATERIAL
TYPE1
MAX SLOPE
RATIO (V:H)
MIN.
CATCHMENT
DITCH
WIDTH (FT)
SHRINK/SWELL
149+00 173+40 SC to CL 1:1.5 (1:1 if < 5
ft) or match existing
- 0.9
173+40 177+30 Decomposed
Rock (25R/75S to 50R/70S)
1:1 - 0.95
177+30 186+80 GC 1:1 - 0.9
186+80 193+30 Decomposed
Rock (25R/75S)
N/A (Rockery &
Embankment area)
- 0.9
193+30 196+50 GC 1:1.5 - 0.9
196+50 197+50 Decomposed
Rock (75R/25S)
1:1 - 1.1
197+50 199+58 Dolomite 2:1 4 1.4
199+58 202+89 Decomposed
Rock (75R/25S)
1:1 or match existing
- 1.1
202+89 203+63 Dolomite 2:1 4 1.4
203+63 209+70 1001+70 Dolomite 2:1 4 1.4
209+70 1001+70 211+00 1003+00 GC 1:1 - 0.9
211+00 1003+00 216+30 1008+30 Dolomite 2:1 4 1.4
216+30 1008+30 217+10 Dolomite 4:1 4 1.4
217+10 220+65 Decomposed
Rock (50R/50S)
1:1 - 0.95
BEGIN STA END STA
MATERIAL
TYPE1
MAX SLOPE
RATIO (V:H)
MIN.
CATCHMENT
DITCH
WIDTH (FT)
SHRINK/SWELL
220+65 221+65 Dolomite 2:1 4 1.4
221+65 222+40 Decomposed
Rock (50R/50S)
1:1 - 0.95
222+40 223+90 SM to SC 1:1 - 0.9
223+90 224+15 Decomposed
Rock (25R/75S)
1:1 - 0.9
224+15 228+40 Decomposed
(50R/50S)
1:1 - 0.95
228+40 232+90 Decomposed
Rock (25R/75S)
1:1.5 or match existing
- 0.9
232+90 239+90 Sandstone 1:1.5 4 1.35
239+90 252+20 2006+80 SM to SC 1:1 or match existing
- 0.9
252+20 2006+80 253+00 2007+65 Decomposed
Rock (75R/25S)
1:1 or match existing
- 1.1
253+00 2007+65 260+50 2015+15 SM to SC 1:1 or match existing
- 0.9
260+50 2015+15 261+50 2016+15 Sandstone 1:1.5 4 1.35
261+50 2016+15 282+40 SM to SC 1:1 or match existing
- 0.9
1Percent composition of soil and rock denoted by S and R, respectively.
2 DISCLAIMER/LIMITATIONS CLAUSE
This memorandum presents updated slope recommendations based on revised project stationing.
The disclaimer and limitations clause presented in the Final Geotechnical Report applies to these revisions.
Prepared by:
Brendan McGarity
Geotechnical Engineer, CFLHD
Reviewed by:
James M. Arthurs, P.E., P.G., PhD.
Senior Geotechnical Engineer, CFLHD
Approved by:
James M. Arthurs, P.E., P.G., PhD.
Senior Geotechnical Engineer, CFLHD for Devin T. Dixon, P.E.
Geotechnical Team Leader, CFLHD
| 2025-12-17T06:56:05-0700 | |
| BRENDAN LEE MCGARITY |
| 2025-12-17T07:34:17-0700 | |
| JAMES M ARTHURS |
| 2025-12-17T07:34:42-0700 | |
| JAMES M ARTHURS |
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