CA ERFO KLAMATH NF 17N11(1) Final Pavement Memo signed revJW.pdf
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This memorandum provides pavement structural recommendations for replacing two bridges in the Klamath National Forest in California. A geotechnical investigation found that the subgrade soil at the Upper Doolittle Creek Bridge site is clayey with poor load-bearing capacity, while the subgrade at the Mill Creek Bridge site consists of silty sands and gravels with good load-bearing capacity. The recommended pavement sections comprise 3 inches of asphalt concrete pavement and 9 inches of crushed aggregate base for the Upper Doolittle Creek Bridge approaches, and 3 inches of asphalt concrete pavement and 6 inches of crushed aggregate base for the Mill Creek Bridge approaches. Both bridge decks will have corrugated steel decking filled with two lifts of asphalt. The Central Federal Lands Highway Division is soliciting engineering and construction services to replace the bridges utilizing Emergency Repair for Federally Owned Roads funds from the US Forest Service. Required pay items include roadway aggregate and asphalt concrete pavement.
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Memorandum
Subject: CA ERFO KLAMATH NF 17N11(1) Upper Doolittle & Mill Creek Bridges Final Pavement Recommendations
Date: November 9, 2021
From: Robert Norick
Through:
Pavement & Materials Engineer
Mike Voth Pavement & Materials Team Lead
To: Mike Daigler, PM Paul Aguilar, Lead Designer
Project Description:
This memorandum provides the pavement structural section recommendations for the CA ERFO KLAMATH NF 17N11(1) Upper Doolittle & Mill Creek Bridges in Sisikiyou County, California. The Upper Doolittle Creek Bridge is located approximately 5.9 miles northwest of the Town of Happy Camp along Forest Route 17N11 within the Klamath National Forest and crosses Upper Doolittle Creek. The Mill Creek Bridge is located approximately 15.3 miles northwest of the Town of Happy Camp along Forest Route 18N15 within the Klamath National Forest and crosses Mill Creek. Page 3 includes location maps for both bridges. Both of the previous timber bridges were destroyed by fires in 2020 and will be replaced with prefabricated bridges with rolled steel girders, structural steel decking, and asphalt fill
Geotechnical Investigation:
In June 2021, CFL’s Geotechnical Group conducted a geotechnical investigation for the project consisting of two 30-foot deep geotechnical borings (one at each bridge abutment) for both bridges using a truck mounted hollow stem auger. Standard penetration tests (SPT) and sampling was performed at both borings at 5-foot intervals.
CFL personnel logged the findings including depth of boring and subgrade soils, SPT data, visual soil classification, and aggregate base thicknesses. SPT subgrade samples were collected and submitted to the CFLHD lab for testing to determine the soil classifications. At Upper Doolittle Creek, the investigation found a 9 inch depth of crushed aggregate base over a clayey subgrade, a “poor” quality subgrade. At Mill Creek, the investigation found a subgrade of silty sands and gravels, a “good” quality subgrade. Based upon Exhibits 11.4.2.B and 11.4.2.C of CFLHD’s supplement to the
ROBERT E NORICK Digitally signed by ROBERT E NORICK Date: 2021.11.09 12:09:06 -07'00'
PDDM, the resilient modulus (MR) of “poor” and “good” subgrade soils can be estimated to be 5,000 psi and 8,000 psi, respectively.
Pavement Recommendations:
The two-way average daily traffic (ADT) along the forest routes are estimated to be less than 100 with a minimal number of trucks; i.e. a “low” traffic level. According to PDDM Section 11.2.1.2, a minimum of 50,000 ESALs shall be used for the design of paved roads. Based upon 50,000 ESALs, the subgrade resilient moduli (MR), and the PDDM pavement design criteria, the 1993 AASHTO procedure requires 20-year pavement Structural Numbers (SN) of 2.21 and 1.85 for the Upper Doolittle and Mill Creek bridge approaches, respectively. After evaluating alternatives, the following pavement structural sections are recommended for the project.
Upper Doolittle Creek & Mill Creek Bridge Decks
Corrugated steel decking with asphalt fill in 2 lifts as follows.
First asphalt lift to fill steel decking corrugations.
Second asphalt lift to extend 1.5 inch minimum above steel decking.
Upper Doolittle Creek Bridge Approaches (SN = 2.22)
3 inches of Asphalt Concrete Pavement (SN = 3” x 0.44 = 1.32”) 9 inches of Crushed Aggregate Base (SN = 9” x 0.10 = 0.90”)
Mill Creek Bridge Approaches (SN = 1.92)
3 inches of Asphalt Concrete Pavement (SN = 3” x 0.44 = 1.32”) 6 inches of Crushed Aggregate Base (SN = 6” x 0.10 = 0.60”)
Additional recommendations include a tack coat applied to the steel decking and between asphalt lifts (subsidiary to asphalt).
Recommended Pay Items for this Project:
Item Number Item Description Unit
30202-2000 Roadway Aggregate, Method 2 Ton 40301-0100 Asphalt Concrete Pavement, Type 1 Ton
The pay items above are to be constructed using the FP-14. Any changes to these items should be reflected in an addendum. CFLHD’s standard Special Contract Requirements (SCRs) related to pavements and materials are expected to be used apart from a 403 SCR to incorporate Caltrans 85 gyration asphalt mixes (see attached). Any additional SCRs may be developed as needed.
Upper Doolittle Creek Bridge
Mill Creek Bridge Location
File details come from the government source that posted it. Updated .