WY Red Grade Road Final Pavement Memo Signed.pdf

Memorandum

Subject:

WY FLAP SHE 26(1)

Red Grade Road Final Surfacing Recommendations

Date: August 27, 2024

From: Robert Norick

Through:

Pavement & Materials Engineer

Mike Voth Supervisory Materials Engineer

To: Julia Dietsch, PM Matthew Steiner, Lead Designer

Project Description:

This memorandum provides the pavement structural section recommendations for the WY FLAP SHE 26(1) Red Grade Road (County Road 26 and US Forest Service Route FSR 26) between Mileposts 0.95 and 3.56 (Stations 149+00 to 282+40) in Sheridan County, Wyoming (see attached county map and site map with mileposts and stationing, respectively ). The project is located approximately 15 miles southwest of the City of Sheridan. The road provides access to the Bighorn National Forest and BLM units, as well as, state and private land and is currently a”dirt” road without any gravel surfacing.

This section of the road is 13 to 18 feet wide with tight curves and steep grades (as steep as 19%) and is closed during the winter. With the steep grades, the road has a tendency to erode, ravel (loss of aggregate), and washboard; exposing underlying boulders and rock in the process. The road degrades into a four wheel drive road and vehicles must drive slowly to avoid bottoming out. As such, the road has a very low level of traffic with the only trucks being associated with road maintenance (road graders and dump trucks). The project proposes to widen this section of road by as much as 5 feet, provide the required geometry and site distance, improve the drainage, and add gravel surfacing.

Pavement Investigation:

On May 19, 2022, a pavement investigation was conducted for the project consisting of two test pits along the west edge of the road at Mileposts 1.4 and 2.4. Two bulk subgrade samples were collected and submitted to the CFLHD lab for testing to determine the soil classifications (see attached lab report and photos). Both samples were found to be silty sands with gravel (ASTM SM soils).

On September 19, 2023, a follow-up geotechnical investigation was conducted consisting of eight shallow borings (up to 5 foot deep) using a truck mounted drill rig with a 4-inch hollow stem auger. Eight bulk subgrade samples were collected and submitted to the CFLHD lab for testing to determine the soil classifications (see attached boring log and lab report). The geotechnical investigation found the subgrade soils to consist predominantly of silty and clayey gravels with sand and silty sands with gravel (ASTM GM, GC, and SM soils). The subgrade soils serve as the road surfacing.

The proposed aggregate surfacing is designed in accordance with the South Dakota Catalog Method for a “high” subgrade support condition (CBR >10%) with less than 5 trucks per day (see attached tables). The soil corrosivity was checked for three of the eight subgrade samples (pH, resistivity, sulfates, and chlorides). One of these subgrade samples was found to be corrosive with a low resistivity (511 ohm-cm) and high chlorides.

Surfacing Recommendations:

Based upon the pavement and geotechnical investigations, it is recommended that the road be surfaced with 4 inches of crushed aggregate base (item 30202-2000 Roadway aggregate, method 2). The project is to be constructed using the FP-14 and CFLHD’s standard SCRs related to pavements and materials with the exception of a 602 SCR to specify corrugated steel pipe with either a 12 gage wall thickness or a polymer coating.

Any additional SCRs may be developed as needed.

Attachments:

County Map and Site Map (2 pages) 2022 Lab Report and Photos (3 pages) 2023 Boring Log and Lab Report (3 pages) South Dakota Catalog Method with CBR Values

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WY FLAP SHE 26(1) Red Grade Road

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WY FLAP SHE 26(1) Red Grade Road

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Milepost 2.4 – Looking Ahead at Road Conditions on May 19, 2022

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