NM FLAP 152(1) - Pavement Tech Memo.pdf

Subject: Pavement & Materials Recommendations NM FLAP 152(1) NM 152 Bridges

From: Mike Voth Pavement & Materials Team Leader, CFLHD

To: Brent Nagen, Project Manager, CFLHD Bianca Smith, Highway Designer, CFLHD

INTRODUCTION

This memorandum provides pavement and material recommendations for the approaches and diversion for NM Bridge #1520 and #1521. Both bridges will be replaced as a part of this project. The length of new pavement, which includes the four approaches to the two bridges, will be approximately 0.39 miles. The project is located on NM Route 152 and is adjacent to the Gila National Forest in southwestern New Mexico. The purpose of the project includes the replacement of the two functionally obsolete bridges, safety enhancements, and roadway reconstruction.

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. Traffic data was supplied by the NM DOT. Photos from the scoping trip and geotechnical work were also reviewed.

FIELD INVESTIGATIONS

As mentioned above, no pavement investigation was completed, but adequate information from the NM DOT, scoping documents, and geotechnical investigations was used to determine needed inputs and parameters. The following list includes the key parameters and data used to support the pavement and materials recommendations:

• Using data from the NM DOT, an ADT of 315 with 14% trucks (commercial) was estimated for the year 2021. A 2% growth rate was assumed per PDDM. 240,000 ESALs was estimated for design.

• Based on information from the geotechnical investigation, the subgrade is generally good quality in the upper 5 feet. It typically consisted of cobbles, gravelly soil, and rock.

Based on this information, an R-Value of 40 and resilient modulus of 10,000 psi was used for the subgrade.

• The one boring that was completed within the paved surface of the road (STA 15+70) indicated a 6-inch asphalt pavement.

Technical Memorandum

Date: March 2, 2018

• The surface of the pavement appears to have been chip sealed. Based on photos the pavement is in fair to poor condition with some edge cracking, rutting, and flushing.

DESIGN RECOMMENDATIONS

The pavement structural section recommendation for the approaches to both bridges is as follows:

4 inches ACP (403 asphalt, type 1, placed in two lifts, less than 5000 tons) 6 inches of aggregate base (302 minor aggregate, method 2, less than 5000 tons) See attachments for more information.

For the diversion, a minimum pavement structural section of 3 inches ACP over 6 inches aggregate base should be included in the Section 650 SCR. The pavement structural section for the diversion should be constructed in general conformance with Sections 302 and 403. Because the contractor will be required to maintain the pavement structural section at a good serviceability level throughout the duration of the project, the contractor may elect to increase the structural and/or functional parameters as they deem necessary.

Additional material recommendations:

• Fog seal (40601-0000) applied to pavement surface, tack coat (41201-0000) applied between asphalt pavement lifts, and prime coat (41102-1000) applied on aggregate base prior to paving should all be included in the contract.

CONSTRUCTION CONSIDERATIONS & SPECIAL CONTRACT PROVISIONS

For the most part, our standard SCRs as related to pavements & materials will be used. No significant unique or special features are being incorporated. The pavement reconstruction should be relatively straightforward. A diversion designed and maintained by the contractor will carry traffic for the duration of the project.

Attachments

NM FLAP 152(1) Pavement Design

Traffic:

AASHTO FLEXIBLE PAVEMENT DESIGN

SN Determination

Design Inputs W18 = 240,000 ESALs Applications Over Design Period Typ. Range 0.1 to 10 million

R = 75 % Reliability Typ. Range 75 to 95%

So = 0.49 Standard Deviation Typ. Range 0.3 to 0.5

MR = 10,000 psi Subgrade Resilient Modulus Typ. Range 3000 to 15000 psi

Pi = 4.2 Initial Serviceability Typ. Range 4.2 to 4.4

Pt = 2 Terminal Serviceability Typ. Range 2.0 to 3.0

DESIGN SN = 2.20

AASHTO FLEXIBLE PAVEMENT DESIGN

Layer Thickness Determination Using Trial and Error

Layer Drainage Layer Layer No. Description Coefficient, ai Coefficient, mi Thickness, in SN

Layer 1 AC Wearing 0.40 1.00 4.00 1.60 Layer 2 Gran. Base A 0.12 1.00 6.00 0.72 Layer 3 Gran. Base B 0.14 0.80 0.00 0.00 Layer 4 Gran. Subbase 0.11 0.80 0.00 0.00 Layer 5 0.00 Layer 6 0.00 Layer 7 0.00 Layer 8 0.00 Subgrade Subgrade N/A N/A N/A N/A

Trial SN 2.32

Design SN to Match 2.20

Design is sufficient

ADT 315 Annual Growth Rate 0.02 Design Years 20 Directional Distribution 0.6

Lane Distribution 1

Classification Percent Truck Factor Growth Factor ADT Yr 1 Design Lane ESALs ADT at N

Motorcycles 5.0% 0 16 0 23 Autos 70.0% 0.0006 24.29737 221 704 328

d) Pickups, Vans 11.0% 0.004 24.29737 35 738 51 Trucks 14.0% 1 24.29737 44 234662 66

100.00% 236103 468

Designer Note Per PDDM 8.6.1.6 Year ADT Seasonal ADT Note Design Hour Factor (K - Factor) Collected: 2015 279 0 Year ADT was collected Typically the 30th highest hourly volume experienced in a year 2018 297 0 PS&E Delivery Year If no specific information is provided use: Current: 2021 315 0 Program Fiscal Year (Construction) K for rural facility is between 12% - 15% Design: 2041 467 0 Design Year K for urban facility is between 10% - 12%

Directional Split Factor (D - Factor) Generally range from 0.54 - 0.59 For one way streets D-factor is 1.0 If unknown and cannot be easily determined use:

55% (expressed as 0.55)

Heavy Vehicle Factor (T - Factor) If unknown and cannot be easily determined use:

T for rural facility is between 10% T for urban facility is between 5%

Designer Note Per PDDM 8.6.1.3 Design Hourly Volume DHV = AADT x K AADT is average annualy daily traffic in the design year K is Design Hour Factor

Calculations for Traffic Data used in Highway Design Standards Form

Designer Note:

NMDOT traffic count data from 2011-2015 does not indicate a growth rate.

There is no significant development in the area that may indicate traffic growth. Based on PDDM 8.6.1.4, minimal growth rate of 2% assumed.

Growth Rate: 2.00%

DHV = 70.1

Factors

14% Heavy Commercial data provided by NMDOT, collected in 2013

K =

D = 0.55

15.00%

T =

Facility is in a very rural setting with no anticipated future development

Use PDDM Default

14.00%

Technical Memorandum