NM FS 220(1) Romero Creek Bridge - Pavement and Materials Final Tech Memo-V2.pdf

Subject: Pavement & Materials Recommendations NM FS 220(1) Romero Creek Bridge

From: Mike Voth Pavement & Materials Team Leader, CFLHD

To: Mike Daigler, Project Manager, CFLHD Jake Keithley, Highway Designer, CFLHD

INTRODUCTION

This memorandum provides final pavement and material recommendations for the approaches, diversion, and other items for the Romero Creek Bridge. The existing bridge will be replaced as a part of this project. A temporary diversion will need to be constructed as the route cannot be closed during construction. The length of new asphalt pavement is 200 feet, which includes two 100 foot paved approaches, but due to some grade changes the reconstruction limits will be beyond the 100 foot paved approaches and will require the addition of gravel surfacing. The project is in the Gila National Forest in southwestern New Mexico.

This memorandum also documents the assumptions used to develop the recommendations. No pavement investigation was completed but data from the geotechnical borings for foundations and earthwork were used to estimate the subgrade conditions. The geotechnical field investigation was completed in September 2020. Lab testing was completed in December 2020.

Traffic data was estimated from discussions with staff from Gila 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 at the bridge approaches. They also photographed, reviewed, and collected grab samples from multiple potential borrow sources. This information along with data from the Forest Service and scoping documents were used to develop the final 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 3 feet of subgrade is expected to be of good quality. It consisted of silty sands, clayey sands, and

Technical Memorandum

Date: November 9, 2022 gravel. An R-Value of 40 and resilient modulus of 9500 psi can be conservatively assumed.

The existing thickness of the surface gravel at the approaches was reported to be 4 to 8 inches. Test results from a grab sample of the existing gravel surfacing indicated a relatively clean and non-plastic gravel with a maximum aggregate size of 1-1/2 inches.

No defects or deficiencies in the roadway gravel at the approaches was reported. Staff indicated that the performance and function of the gravel roadway was adequate.

Based on feedback from the Forest Service, the ADT is less than 100. The Forest Service is expecting a short-term influx of several thousand haul trucks due to an upcoming restoration project.

Geotechnical staff reviewed two borrow sources that were close to the project site and previously cleared by Forest Service from a compliance basis. At least one of these borrow sources appears viable from an access and material quality standpoint.

DESIGN RECOMMENDATIONS

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

3 inches ACP (403 asphalt, type 1, pay item 40301-0100, placed in two lifts) 6 inches of aggregate base (302 roadway aggregate, method 2, pay item 30202-2000)

For the graveling surfacing beyond the paved approaches the following is recommended:

9 inches of aggregate base (302 roadway aggregate, method 2, pay item 30202-2000) 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.

For the diversion, the recommendations are as follows:

6 inches of aggregate base (302 roadway aggregate, method 2, pay item 30202-2000)

Note that the contractor is required to maintain the diversion at a good serviceability level throughout the duration of use.

The following borrow sources were investigated:

Erin Lake Pit (109.044, 33.979): No recent activity in pit. Relatively difficult access.

Material appears to meet unclassified borrow requirements.

Badger Pit (109.04, 33.958): Recent activity (stockpiles). Easy access. A surface grab sample from a stockpile was collected and tested. The material classified as A-1-a according to AASHTO M 145. See attached lab report for additional information.

Material appears to meet unclassified borrow requirements.

Recommend targeting the Badger Pit as a potential government-listed source. At 95% review meeting, CFT should discuss potential issues such as source development, quantity limits, and restoration requirements from the Forest Service, if any. If CFT concurs with use of this borrow source, an SCR for Section 105.02 would be provided.

Additional material recommendations:

Provide tack coat (pay item 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

Our standard 403 SCR will be adjusted to allow for multiple NM DOT asphalt mixes to be used (with expectation for reduced bid risk and lower costs). If the borrow source is incorporated in the project, an SCR for Section 105.02 will be provided. Numerous SCR examples from similar projects are available.

With the expected prefabricated steel superstructure bridge, quantities for concrete will be relatively small. Haul distances for concrete are expected to be one to two hours with material possibly coming from the Springerville, AZ or Show Low, AZ. If a concrete or timber deck is not selected as deck wearing surface, support for asphalt deck surfacing will be provided, as needed. A gravel surfaced diversion will be constructed and carry traffic for the duration of the project.

ATTACHMENTS

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

Michael.Voth Text Box Attachment #1

Attachment #1

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 1.73 2.93 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, 5.54 9.00 1.73 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 = 50,000 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 = 1.73

Michael.Voth

Attachment #2

ADT 100 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 75.0% 0.0006 75 0 111 Values Pickups, Vans 20.0% 0.004 24.29737 20 426 30

149 (calculated) Class 4 buses 0.0% 1.5 24.29737 0 0 0 100 Class 5 trucks/RVs 3.0% 0.5 24.29737 3 7982 4

2023 Class 6 0.0% 1 24.29737 0 0 0 2043 Class 8 0.0% 1.5 24.29737 0 0 0

2 Class 9 2.0% 2 24.29737 2 21284 3 100.00% 29692 149

Use 50,000 mininum (refer to Exhibit 11.2-A in the PDDM for additional guidance on truck factors)

Traffic Analysis

Comments sporadic forest restoration work recreation/commercial activity

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

Aggregate Surfacing Design Standards and Guidance November 2010

CFLHD Supplement 11.4.2-1 1 of 5

CFLHD SUPPLEMENT 11.4.2-1

11.4.2 Design Standards and Guidance

Add the following:

This Supplement describes guidelines on the use of the catalog method for aggregate surfacing thickness design. This method can be applied on all CFLHD projects employing aggregate surfacing.

Exhibit 11.4.2-A presents a design catalog of recommended surface aggregate layer thicknesses. This catalog may be used to determine the aggregate layer thickness required for a project when more detailed information about the project is not available. The thicknesses shown are based on specific ranges of 18-kip ESAL applications at traffic levels:

High 60,000 to 100,000 Medium 30,000 to 60,000 Low 10,000 to 30,000

Two other assumptions inherent in this thickness design are that the effective resilient modulus of the aggregate material is 30,000 psi, regardless of the quality of the roadbed soil; and there is a 0.5 inch aggregate loss per year. Exhibit 11.4.2-A is from the AGDPS.

Determine the in situ soil properties and then use Exhibit 11.4.2-B and 11.4.2-C to determine the Relative Quality of Roadbed Soil.

For Soil Classification, use: ASTM Classification of Soils for Engineering Purposes (ASTM D 2487), or AASHTO Classification of Soils and Soil-Aggregate Mixtures for Highway Construction Purposes (AASHTO M 145)

For Strength of Roadbed Soil, use: Resistance Value (AASHTO T 190); California Bearing Ratio (AASHTO T 193); and/or the Resilient Modulus (AASHTO T 307)

When test results from subgrade soil are not available, visually estimate the Unified Soil Classification using ASTM D 2488 or other means. Then use the AASHTO and ASTM Soil Classification chart in Exhibit 11.4.2-B and Roadbed Soil Strength chart in Exhibit 11.4.2-C to determine the Relative Quality of Roadbed Soil.

Determine the U.S. climatic region designation from Exhibit 11.4.2-D. This exhibit is from the AGDPS.

Using Exhibit 11.4.2-A with the appropriate Relative Quality of Roadbed Soil, traffic level, and U.S. climatic region designation, determine the minimum thickness of aggregate surfacing in inches. When a higher type of pavement design is recommended from Exhibit 11.4.2-A, contact the Division Pavement Engineer.

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CFLHD Supplement 11.4.2-1 2 of 5

Exhibit 11.4.2.-A Aggregate surfaced thickness design catalog:

Recommended aggregate thickness (in inches) for the six U.S. climatic regions, five relative qualities of roadbed soil and three levels of traffic.

U.S. Climatic Region

Relative Quality of Roadbed Soil

Traffic Level

I

II

III

IV

V

VI

Very Good

High

8*

Medium 6 8 11 5 7 11 Low 4 4 6 4 4 6

Good High 11 12 17 10 11 17 Medium 8 9 12 7 9 12 Low 4 5 7 4 5 7

Fair High 13 14 17 12 13 17 Medium 11 11 12 10 10 12 Low 6 6 7 5 5 7

Poor High ** ** ** ** ** ** Medium ** ** ** 15 15 ** Low 9 10 9 8 8 9

Very Poor High ** ** ** ** ** ** Medium ** ** ** ** ** ** Low 11 11 10 8 8 9

* T h i c k n e s s e s of aggregate required (in inches).

** Higher type pavement design recommended.

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CFLHD Supplement 11.4.2-1 3 of 5

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CFLHD Supplement 11.4.2-1 4 of 5

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Exhibit 11.4.2-D The six climatic regions in the United States.

REGION CHARACTERISTICS

I Wet, no freeze II Wet, freeze – thaw cycling III Wet, hard-freeze, spring thaw IV Dry, no freeze V Dry, freeze – thaw cycling VI Dry, hard freeze, spring thaw

Michael.Voth