Pavement_Materials Final Recommendations January 12 2021.pdf

Subject: Pavement & Materials Final Recommendations AZ FS 24(1) Buffalo Crossing Bridge

From: Mike Voth Pavement & Materials Team Leader, CFLHD

To: Mike Daigler, Project Manager, CFLHD Erin Jessee, Highway Designer, CFLHD

INTRODUCTION

This memorandum provides the final pavement and material recommendations for the bridge approaches and other material items for the Buffalo Creek Bridge project which is on FS Road

24. The existing bridge will be replaced as a part of this project. The existing approaches have a paved asphalt surface for a short distance. The new bridge will have a grade raise and the length of the reconstructed roadway will be over 700 feet. About a 400-foot section of an adjacent approach road is also planned to be reconstructed. The bridge approaches will have an asphalt paved surface for at least the first 100 feet. The surfacing material for the approach road and FS Road 24 (beyond the paved bridge approaches) is planned to gravel. The project is in the Apache-Sitgreaves National Forest in east-central Arizona.

This memorandum also documents the assumptions used to develop the preliminary recommendations. No pavement investigation was completed but preliminary data from the geotechnical borings for foundations and earthwork will be used to estimate the subgrade conditions. The geotechnical field investigation was completed in September 2020. Lab testing was completed at the end of December 2020. Traffic data was estimated from discussions with staff from Apache-Sitgreaves National Forest.

FIELD INVESTIGATIONS

The geotechnical investigations, as mentioned above, took place during the week of September 21, 2020. In addition to completing borings for foundation analysis, geotechnical staff measured surface gravel thickness adjacent to the paved approaches. This information along with data from the Forest Service and scoping documents were used to develop the recommendations. The following is a bullet list of key results from the field investigation and other data sources:

• Based on the borings from the geotechnical investigation, the upper 2 to 4 feet of subgrade consisted of clayey sands (A-2-6) and silty gravels (A-1-b). An R-Value of 40 and resilient modulus of 9,500 psi can be conservatively assumed.

Technical Memorandum

Date: January 12, 2021

• Test results from a grab sample of the existing gravel surfacing indicated a relatively clean, coarse, and non-plastic gravel with a nominal maximum aggregate size of 1-1/2 inches.

• The existing thickness of the paved asphalt approaches is unknown. The surface gravel thickness outside of the approaches was reported to be 4 to 8 inches.

• No defects or deficiencies in the roadway gravel or paved approaches were reported.

Staff indicated that the performance and function of the gravel roadway was adequate.

• The Forest Service indicated that the ADT is 82, and that large trucks use the route for on-going logging operations.

DESIGN RECOMMENDATIONS

The Apache-Sitgreaves National Forest indicated concerns for sediment run-off into the stream from gravel approaches to the bridge. As a result, asphalt pavement surfacing will be provided.

The pavement structural section recommendation for the bridge approaches is as follows:

3 inches ACP (40301-0100, asphalt concrete pavement, type 1, placed in two lifts) 6 inches of aggregate base (30202-2000, roadway aggregate, method 2)

For the graveling surfacing on the approach road and beyond the paved approaches on FS Road 24, the structural section recommendation is as follows:

9 inches of aggregate surface course (30202-2000, roadway aggregate, method 2)

The 9-inch thickness matches the pavement structural section and would provide ease of grading and finishing of subgrade.

Note: Given very small quantities and length, no minimum plasticity index requirements will be specified.

Additional material recommendations:

• Provide tack coat (41201-0000) applied between asphalt pavement lifts.

• Given very small paving scope and limited risk, recommend not including fog seal and prime coat on this project.

CONSTRUCTION CONSIDERATIONS & SPECIAL CONTRACT PROVISIONS

The plasticity index requirement of our standard 703 SCR will be adjusted as discussed above (with expectation for reduced bid risk and lower costs).

Local asphalt mix availability has been reviewed to assure our standard 403 SCR is adequate to allow for an Arizona or New Mexico DOT mix to be used (with expectation for reduced bid risk and lower costs).

Haul distances for concrete are expected to be one hour or less. Springerville, AZ is the nearest source for ready mix concrete. Depending on selection of bridge structure (precast concrete box or prefabricated steel structure), material design support for the wearing surface type will be provided, as needed.

ATTACHMENTS

Attachment #1 – Lab Reports Attachment #2 – Pavement and Gravel Surfacing Design Analysis Attachment #3 – 703 SCR

Michael.Voth Text Box Attachment #1

Attachment #1

Attachment #2

ADT 82 Annual Growth Rate0.02 Design Years 20

Directional Distribution

0.6

Lane Distribution

Classification Percent Truck Factor

Growth Factor ADT Yr 1 Design Lane ESALs ADT at N

Autos 71.0% 0.0006 58 0 87 Values Pickups, Vans 12.0% 0.004 24.29737 10 209 15

122 (calculated) Class 4 buses 0.0% 1.5 24.29737 0 0 0 82 Class 5 trucks/RVs 5.0% 0.5 24.29737 4 10908 6

2022 Class 6 0.0% 1 24.29737 0 0 0 2042 Class 8 2.0% 1.5 24.29737 2 13090 2

2 Class 9 10.0% 2 24.29737 8 87266 12 100.00% 111474 122

(refer to Exhibit 11.2-A in the PDDM for additional guidance on truck factors)

Traffic Analysis

Comments logging traffic expected some commercial activity logging traffic expected GR = Growth Rate (%)

Future ADT Calculation ADTf = ADTi (1 + GR)(F-I)

ADTf = Average daily traffic for future year ADTi = Average daily traffic for initial year

I = Initial year for ADT F = Future year for ADT

Michael.Voth

AASHTO FLEXIBLE PAVEMENT DESIGN

Layer Thickness Determination Using Layered Analysis Approach

1 Enter applicable information in cells C15 through F22

2 For the first layer, use the E of the next lower layer as the MR in the Inputs Box below this table and enter the resulting layer SN.

3 The minimum layer thickness is calculated in column H. Enter the "practical" layer thickness in column I.

4 Repeat steps 2 and 3 for each layer, always using the E of the next lower layer as the MR in the Inputs Box spreadsheet below this table.

5 Check to ensure resulting SN meets or exceeds required SN

6 Note that this procedure is not valid if any layer beneath layer 1 has an E greater than 40,000 psi.

SN Using E of next Min. Layer Practical Layer

Layer Drainage Elastic lower layer in Thickness, D, Thickness, D, Associated

Layer No. Description Coefficient, ai Coefficient, mi Modulus, psi inputs box below inches inches SN

(topmost) Layer 1 AC Layer 0.44 1.00 400,000 1.15 2.61 3.00 1.32 Layer 2 Coarse Agg Base 0.14 1.00 35,000 1.94 4.43 6.00 0.84 Layer 3 Gran. Subbase 20,000 0.00 0.00 0.00 Layer 4 Select Borrow 15,000 0.00 0.00 0.00 Layer 5 0.00 0.00 0.00 Layer 6 0.00 0.00 0.00 Layer 7 0.00 0.00 0.00

(bottommost) Layer 8 0.00 0.00 0.00 Subgrade Subgrade N/A N/A 9,500 N/A N/A N/A N/A AC Layer 401 = 0.44 Total Pavement 2.16 Calculated SN

403 = 0.40 Thickness, inches, 7.04 9.00 1.98 SN to Match CAB 301 = 0.14 Design is sufficient

Subbase/Minor agg 302 = 0.12

FDR 304 = 0.12

Select borrow 204 = 0.06 to 0.08

(Refer to Exhibit 11.2-C in Chapter 11 of PDDM for additional guidance on coefficients)

Inputs Box

W18 = 112,000 ESALs Applications Over Design Period

R = 75 % Reliability

So = 0.49 Standard Deviation

MR = 9,500 psi Subgrade Resilient Modulus

Pi = 4.2 Initial Serviceability

Pt = 2 Terminal Serviceability

SN on top of layer = 1.98

Michael.Voth

Section 703. — AGGREGATE

703.01 Add the following:

703.01 Fine Aggregate for Concrete.

(c) Sand equivalent value, AASHTO T 176, 75 min.

Alternate Method No. 2

703.06 Crushed Aggregate. Add the following to the end of the paragraph:

When aggregate is used as a surface course, furnish an aggregate with a gradation and Plasticity index (AASHTO T 90) conforming to Table 703-3a.

Table 703-3a Surface Course Gradation and Plasticity Index

Sieve Size Percent by Mass Passing

Designated Sieve (AASHTO T 27 and T 11)

¾ inch (19 mm) 100 No. 4 (4.75 mm) 41-71 No. 40 (425 µm) 12-28 No. 200 (75 µm) 5-20

Plasticity Index (PI) 0-12

Attachment #3