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 Inputs 1. Design life (analysis period) 1. Structural Layer Coefficients 2. Traffic (ESAL’s) 2. Drainage Factor 3. Foundation stiffness (M r or 3. Layer Thickness ≤ CBR) 4. Performance criteria ( Δ PSI) 5. Reliability (Z R and S o ) Output Output 1. Required Structural Number 1. Design Structural Number

AASHTO DARWin Method “Required” Structural Number ≤ “Design” Structural Number (structural coefficient) (drainage coefficient)

AASHTO DARWin Method Benefits of Use Drawbacks of Use � Quick calculation � Not calibrated for regional use � Data requirements � Climatic � Universal use � Materials � Traffic � Layer Coefficients � Pass/Fail Empirical design from one test track (Ottawa, IL) in the 1950’s

MEPDG Method Climate Traffic Materials Structure Damage Time Damage Response Distress 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 � Type of Design ◦ New pavement expectancy ◦ Restoration of JPCP � Critical milestones ◦ Overlay (HMA or PCC) � Month of subbase construction � Desired pavement type ◦ Flexible (HMA) � Month of pavement construction ◦ Jointed Plain Concrete Pavement (JPCP) � Month that the road is ◦ Continuously Reinforced opened to traffic Concrete Pavement (CRCP)

Inputs from INDOT - General INDOT Design Life Expectancy INDOT Traffic Groups INDOT Assumed Milestones Base/Subgrade Construction Month: May Pavement Construction Month: July Traffic Open Month: September

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 Bottom Line: Lots of data collection & analysis by INDOT * Based on statewide WIM data

Inputs from Designer - Climate � Project location (latitude, longitude & elevation) � Annual Average Water Table Depth LTPP Weather Stations

Inputs from Designer - Materials Soil Resilient Modulus (M R ) – Modulus of Subgrade Reaction � � (“k” value) NOT CBR � Untreated Subgrade – “Virgin” Material Subgrade Treatment Type � � Treated Subgrade Underdrain Requirement AASHTO Soil Classification � � Initial Pavement Design FWD (Falling Weight � � Deflectometer) Testing if Structural Resurface

Inputs from Designer - Materials � Typical Sections - PCCP Fig. 52-13F: PCCP Section with PCCP Shoulder Fig. 52-13G: PCCP Section with HMA Shoulder

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 Subgrade Treatment as Determined by Geotechnical Engineer Type II � Type I � 8” of chemical soil modification, or � 14” of chemical soil modification, or � 6” of subgrade excavated and � replaced with C.A. #53, or 12” of subgrade excavated and � 12” of soil compacted to density and � replaced with C.A. #53, or moisture requirements 24” of soil compacted to density and � moisture requirements Type IIA � 8” of chemical soil modification, or � 6” of subgrade excavated and Type IA � � replaced with C.A. #53 14” of chemical soil modification, or � 12” of subgrade excavated and � Type III � replaced with C.A. #53 6” of soil compacted to density and � moisture requirements, or 6” of subgrade excavated and � Type IB � replaced with C.A. #53 14” of chemical soil modification � Type IIIA � 6” of subgrade excavated and � Type IC � replaced with C.A. #53 12” of subgrade excavated and � replaced with C.A. #53 Type IV � 9” of subgrade excavated and � replaced with C.A. #53 on geogrid

Inputs from INDOT - Materials In DARWin, the strength value (resilient modulus) of Subgrade � Treatment and Subbase for PCCP were ignored o 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 - 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