By American Structurepoint, Inc. Cash Canfield, PE - - PowerPoint PPT Presentation

By American Structurepoint, Inc. Cash Canfield, PE ccanfield@structurepoint.com Jason Koch, PE jkoch@structurepoint.com 614-901-2235

What is MEPDG?

Mechanistic-Empirical Pavement Design

Guide by AASHTO

Pavement analysis tool that uses project

specific traffic, climate, and materials data for estimating damage accumulation over a specified pavement service life

Design process based on predictive

performance of a pavement section designed to predefined parameters identified as failing

Why use MEPDG?

FHWA considers implementation of MEPDG a high

priority as a critical element in improving the National Highway System

Existing design procedures based upon 1950’s

AASHO Road Test and use empirical relationships

Current pavement designs often exceed the data

limits and conditions used in the AASHO Road Test

MEPDG provides a more realistic characterization of

in-service pavements and provides uniform guidelines for designing in-common features of all pavement types

AASHTO DARWin Method

“Required” Structural Number ≤ “Design” Structural Number

≤

Inputs

• 1. Design life (analysis period)
• 2. Traffic (ESAL’s)
• 3. Foundation stiffness (Mr or

CBR)

• 4. Performance criteria (ΔPSI)
• 5. Reliability (ZR and So)

Output

• 1. Required Structural Number

Inputs

• 1. Structural Layer Coefficients
• 2. Drainage Factor
• 3. Layer Thickness

Output

• 1. Design Structural Number

AASHTO DARWin Method

“Required” Structural Number ≤ “Design” Structural Number

(structural coefficient) (drainage coefficient)

AASHTO DARWin Method

Benefits of Use

Quick calculation Data requirements Universal use

Drawbacks of Use

Not calibrated for

regional use

Climatic Materials Traffic

Layer Coefficients Pass/Fail

Empirical design from one test track (Ottawa, IL) in the 1950’s

MEPDG Method

Climate Traffic Materials Structure Distress Response Time Damage Damage Accumulation

MEPDG Overview

Mechanistic design – finite element analysis Research grade software Local calibration is the key Does not “output” a design – your design is an

“input” for analysis

Expandable to new materials Narrowing down design life deviations

MEPDG Overview

• User Interface
• General Inputs
• Requirements from Designers
• Inputs provided by INDOT
• Traffic Inputs
• Requirements from Designers
• Inputs provided by INDOT
• Climatic Inputs
• Material Inputs
• Requirements from Designers
• Inputs provided by INDOT
• Performance Criteria
• Requirements from Designers
• Inputs provided by INDOT
• Outputs

MEPDG “Dashboard”

Inputs from Designer - General

Design life

expectancy

Critical milestones

Month of subbase

construction

Month of pavement

construction

Month that the road is

• pened to traffic

Type of Design

• New pavement
• Restoration of JPCP
• Overlay (HMA or PCC)

Desired pavement type

• Flexible (HMA)
• Jointed Plain Concrete

Pavement (JPCP)

• Continuously Reinforced

Concrete Pavement (CRCP)

Inputs from INDOT - General

Base/Subgrade Construction Month: May Pavement Construction Month: July Traffic Open Month: September

INDOT Traffic Groups INDOT Assumed Milestones INDOT Design Life Expectancy

Inputs from Designer - Traffic

Roadway classification Truck traffic data – AADTT (current, future, & growth rate)

Determination of Traffic Group (A, B, C, or D)

Traffic direction (north/south or east/west)

• No. of lanes in design direction

Determination of % trucks in design direction Determination of % trucks in design lane

Posted Speed (not design speed)

INDOT Inputs - Traffic

% Trucks in Design Lane % Trucks in Design Direction

* Based on statewide WIM data

Bottom Line: Lots of data collection & analysis by INDOT

Inputs from Designer - Climate

Project location (latitude, longitude & elevation) Annual Average Water Table Depth

LTPP Weather Stations

Inputs from Designer - Materials

• Soil Resilient Modulus (MR) –

NOT CBR

Untreated Subgrade – “Virgin”

Material

Treated Subgrade

• AASHTO Soil Classification
• FWD (Falling Weight

Deflectometer) Testing if Structural Resurface

• Modulus of Subgrade Reaction

(“k” value)

• Subgrade Treatment Type
• Underdrain Requirement
• Initial Pavement Design

Inputs from Designer - Materials

• Fig. 52-13F: PCCP Section with PCCP Shoulder
• Fig. 52-13G: PCCP Section with HMA Shoulder

Typical Sections - PCCP

Inputs from Designer - Materials

Typical Sections - HMA

• Fig. 52-13A: Full Depth HMA with Full Depth Shoulder
• Fig. 52-13B: Full Depth HMA with Composite Shoulder

Inputs from INDOT - Materials

• Type I
• 14” of chemical soil modification, or
• 12” of subgrade excavated and

replaced with C.A. #53, or

• 24” of soil compacted to density and

moisture requirements

• Type IA
• 14” of chemical soil modification, or
• 12” of subgrade excavated and

replaced with C.A. #53

• Type IB
• 14” of chemical soil modification
• Type IC
• 12” of subgrade excavated and

replaced with C.A. #53

• Type II
• 8” of chemical soil modification, or
• 6” of subgrade excavated and

replaced with C.A. #53, or

• 12” of soil compacted to density and

moisture requirements

• Type IIA
• 8” of chemical soil modification, or
• 6” of subgrade excavated and

replaced with C.A. #53

• Type III
• 6” of soil compacted to density and

moisture requirements, or

• 6” of subgrade excavated and

replaced with C.A. #53

• Type IIIA
• 6” of subgrade excavated and

replaced with C.A. #53

• Type IV
• 9” of subgrade excavated and

replaced with C.A. #53 on geogrid

Subgrade Treatment as Determined by Geotechnical Engineer

• In DARWin, the strength value (resilient modulus) of Subgrade

Treatment and Subbase for PCCP were ignored

• Only CBR of “virgin soil” used

In MEPDG, subgrade & subbase are assigned strength values

• Chemical soil modification
• Compacted soil
• C.A. #53
• Virgin soil
• Subbase for PCCP

Subbase for PCCP

• 3” of #8’s for Drainage Layer (25,000 psi)
• 6” of #53’s for Separation Layer (30,000 psi)

Inputs from INDOT - Materials

Inputs from INDOT - Performance

HMA Criteria PCCP Criteria

HMA Performance Criteria

INDOT Criteria

Terminal Roughness (IRI) Bottom-up Cracking / Alligator Cracking (Fig. 1) Permanent Deformation – Rutting (Fig. 2) Thermal Fracture (Fig. 3)

Dependant on Classification & Reliability

• Fig. 1: Alligator Cracking
• Fig. 2: Rutting
• Fig. 3: Thermal Fracture

PCCP Performance Criteria

INDOT Criteria

Terminal Roughness (IRI) Transverse Slab Cracking (Fig. 4) Mean Joint Faulting (Fig. 5)

Dependant on Classification & Reliability

• Fig. 4: Transverse Slab Cracking
• Fig. 5: Mean Joint Faulting

MEPDG Output