Lecture 1. Mechanistic Empirical Pavement Design Guide (MEPDG): Overview MEPDG 1

Transcription

1 Lecture 1 Mechanistic Empirical Pavement Design Guide (MEPDG): Overview MEPDG 1

2 Overview of Lecture Pavement design guides AASHTO Design Guide o History o Philosophy o Key notes o AASHO Road Test 1958 o Limitations MEPDG o Philosophy o History MEPDG 2

3 Overview of Lecture Why MEPDG important? AASHTO Design Guide vs. MEPDG Why we are moving from AASHTO Design Guide to MEPDG States MEPDG Implementation Plan Improvements of MEPDG Users of MEPDG Benefits of MEPDG Future work Pavement Design State of the Art MEPDG 3

4 Pavement design guides For Concrete Pavement American Association of State Highway and Transport Officials (AASHTO) Design Guide Portland Cement Association (PCA) Design Guide MEPDG For Flexible Pavement Asphalt Institute Guide AASHTO Design Guide MEPDG MEPDG 4

5 AASHTO Design Guide: History Empirical design came about the result of the AASHO Road Test in Several Editions: o 1961 Interim Guide o 1972 o 1986 Resilient modulus, rehabilitation, reliability o 1993 Improved rehabilitation Current version MEPDG 5

6 AASHTO Design Guide: Philosophy Philosophy: This is based on the service performance concept, which provides a means of designing a pavement based on a specific total traffic volume and a minimum level of serviceability desired at the end of the performance period. MEPDG 6

7 AASHTO Design Guide: key notes Based on empirical methodology Empirical design came about the result of the AASHO Road Test in Since design guide based on AASHTO Road Test, limitations include one climate, one sub-grade, two years duration, limited cross sections, and 1950 s materials, traffic volumes, specifications and construction methods. MEPDG 7

8 AASHTO Design Guide: AASHO Road Test 1958 Location: Ottawa, Illinois MEPDG 8

9 AASHTO Design Guide: AASHO Road Test 1958, cont. Construction methods 1950s vehicle loads Single location Single climate condition MEPDG 9

10 AASHTO Design Guide: Limitations Specific set of pavement materials and one type of roadbed soil. Single environment An accelerated procedure for accumulating traffic (a 2-year testing period extrapolated to 10 or 20-year design) Accumulating traffic on each test section by operating vehicles with identical axle loads and axle configurations as opposed to mixed traffic MEPDG 10

11 MEPDG: Philosophy MEPDG: This is based on the Mechanistic- Empirical approach which uses computations of pavement responses such as stresses, strains, and deformations and then adjusts accordingly based on the performance models from the empirical approach. * The ultimate goal for the future is to have pavement designed on a mechanistic approach only MEPDG 11

12 MEPDG: History Process initiated by Joint Task Force on Pavements o Irvine, California: March 1996 Development of the Guide o NCHRP 1-37A o Awarded to ARA: February 1998 o Product Submitted: February 2004 o Cost $7 million Source: MEPDG 12

13 Why MEPDG important? Several pavement distresses such as fatigue, rutting, cracking reduce pavement life. These distresses are analyzed in MEPDG Optimize design and materials to minimize these distresses. MEPDG 13

14 Why MEPDG important?, cont. Design rehabilitation projects Direct considerations of major factors o Traffic-Direct consideration of overweight trucks o Climate o Material-Different HMA, PCC, and Aggregate materials o Support-Foundation and existing pavement MEPDG 14

15 Why MEPDG important?, cont. Compatible with superpave system Most comprehensive approach for structural design Provides link between structural design and material properties Will include method for local calibration MEPDG 15

16 AASHTO Design Guide vs. MEPDG AASHTO Design Guide MEPDG 1. Empirical Methodology 1. Empirical and Mechanistic Methodology 2. Contains 5 inputs for flexible pavements and 10 inputs for rigid pavements, single environment 3. Depends on extrapolation of empirical relationships 4. Uses identical axle loads and axle configurations. 2. More then 100 total inputs with 35 or more for flexible pavements and 25 or more for PCC, more than 800 weather sites. 3. No longer be dependence on extrapolation of empirical relationships. 4. uses mixed traffic. MEPDG 16

17 Why we are moving from AASHTO Design Guide to MEPDG Legislative Mandate Site specific climate and material properties considerations o Material properties affected by climate o PCC joint openings, Curl/Warping In AASHTO Design Guide, pavement performances are predicted by extrapolating pavement performance from Ottawa, IL whereas in MEPDG pavement performances are predicted from 800 weather sites. MEPDG 17

18 Why we are moving from AASHTO Design Guide to MEPDG, cont. The use of updated AASHTO Design Guide produces conservative designs that are not optimally cost effective. MEPDG incorporates mechanistic methodology along with empirical whereas AASHTO is based on only empirical methodology AASOTO Design Guide does not provide performance of prediction of pavements (Coree, 2005) MEPDG 18

19 Why we are moving from AASHTO Design Guide to MEPDG, cont. AASHTO Guide cannot handle rehabilitation adequately AASHTO Guide annot adequately consider all modern design features, materials, loadings AASHTO Guide is thickness-centric MEPDG 19

20 States MEPDG Implementation Plan LEGEND V & D V, Plan, R No Data Available Source: MEPDG 20

21 Improvements of MEPDG Predicts transverse cracking, faulting and smoothness for jointed plain concrete pavements, the addition of climate inputs, better characterization of traffic loading inputs, more sophisticated structural modeling capabilities, and the ability to model real-world changes in material properties. MEPDG 21

22 Improvements of MEPDG, cont. Modular system that allows for incremental enhancement Produces a more reliable design No longer dependent on the extrapolation of empirical relationships Excellent for forensic analysis Calibrate to local materials, traffic, climate.. MEPDG 22

23 Improvements of MEPDG, cont. Provide more information about the development of pavement distresses during design life of the pavement. Utilizes a user friendly software interface. MEPDG 23

24 MEPDG Users State DOT s main user o Pavement Designers o Upper management Academia Industry Consultant Designers Designers MEPDG 24

25 Future work on MEPDG Maintain calibration-validation database along with input libraries Periodically monitor test sections and input parameters and update database Verify local calibration or agency specific factors for future DARWin-ME versions. Source: wford-mepdg.pdf MEPDG 25

26 Pavement Design State of the Art AASHTO 93 MEPDG Future Design Guide Empirical Mechanistic MEPDG 26

27 Questions? MEPDG 27