avement Structural Evaluation: here we are and where we are oing Prof. Lynne H Irwin Cornell Local Roads Program

Transcription

1 avement Structural Evaluation: here we are and where we are oing Prof. Lynne H Irwin Cornell Local Roads Program

2 Points for discussion How did we get where we are? Where are we? Where do we need to go?

3 Does E = 1500 x CBR? If so, why are we here?

4 How good is "good enough?"

5 Once Upon a Time Visual evaluation was the main tool Test pits helped to gather information at a point We had no reliable method to predict how long an overlay would last

6 Field Test Methods 1955: Benkelman beam. WASHO Road Test. 1955: Hveem, Pavement deflections and fatigue failures. HRB Bulletin 114.

7 Buffalo, NY

8 Field Test Methods : Falling weight deflectometer 1990: Seismic pavement tester Dubai, 1978

9 Laboratory Test Methods 1966: Repeated-load triaxial test for unbound materials 1980: Indirect tensile test for asphalt concrete

10 Analytical Tools 1885: Boussinesq. One-layer theory 1934: Miner. Cumulative damage theory here --- k D i 1 N n i allow, i D = cumulative damage due to all loads k = number of load levels considered 1.0 ni = number of load repetitions at load level i

11 Analytical Tools 1945: Burmister. General theory of stresses and displacements in layered systems. Jour. of Applied Physics 1962: Hveem, Zube, Bridges, and Forsyth. The effect of resiliencedeflection relationship on the structural design of asphaltic pavements. Proc. 1 st Ann Arbor Conference

12 Analytical Tools 1963: AASHTO interim guide (empirical) : Layered elastic computer programs (BISTRO, BISAR, CHEVLAY) 1977: Irwin. Determination of pavement layer moduli from surface deflection data for pavement performance evaluation. Proc. 3 rd Ann Arbor Conference

13 Analytical Tools : Backcalculation computer programs (MODCOMP, EVERCALC) 1988: 1 st conf. on nondestructive testing of pavements and backcalculation of moduli. ASTM STP : Mechanistic-empirical pavement design guide. NCHRP 1-37a.

14 Interest Groups 1980 Today: TRB committees 1992: FWD users group 1993: RPUG 2009: GPR team

15 Where Are We? Multitude of pulse loading devices Portable computers that get faster and more capable every day Software that enables us to analyze the capabilities and limitations of existing pavements Interest groups, conferences, and smart people

16 Where Are We? Mechanistic-empirical design methods are advancing rapidly We know how to backcalculate layer moduli (with some difficulty) We know how to estimate depth to hard bottom We know how to use mechanisticempirical methods to design pavements

17 Basic Assumptions of Elastic Layer Theory (Quick Review) Surface load - uniformly distributed over a circular area Vertical stress continuity at interfaces Horizontal strain continuity at layer interfaces (no slip) Layers extend horizontally to infinity Bottom layer is a semi-infinite half-space Materials - homogenous, isotropic, and

18 Additional Tools Available Finite element analysis methods Neural network analysis methods Seismic analysis of surface waves Ground penetrating radar Cross-anisotropic test methods for unbound materials Dynamic test methods for asphalt concrete

19 "We measure with a micrometer, mark with a grease pencil, and cut with a chainsaw" (Marshall Thompson)

20 Where Are We Deficient? Field testing protocols ASTM and AASHTO offer guidance, but most agencies do their own thing Lab testing methods Stress-dependency of unbound materials Constitutive models Visco-elastic properties of asphalt concrete Seasonal variation of materials Spatial variability of materials

21 Considering seasonality The various regions of the county belong to one of four climatological zones Wet-freeze (Wisconsin) Wet-no freeze (Georgia) Dry-freeze (Montana) Dry-no freeze (Arizona) Pavement materials properties (i.e.,

22 Effect of seasonality he modulus of asphalt concrete is emperature sensitive Not greatly affected by moisture he moduli of unbound base and upper ubgrade materials are moisture sensitive Not greatly affected by temperatures above freezing eeper subgrade is not seasonally affected

23 Helena, MT Airport Weather Averages 30-year monthly normals, Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month Precipitation (in.) Mean Max. Temperature (F) Mean Min. Temperature (F) Mean Temperature (F) Mean Precipitation (in.)

24 Precipitation Minus Evaporation Helena, MT Airport Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Month

25 % Asphalt Concrete in a Hot Summer - Cool Winter Area dulus % J F M A M J J A S O N D

26 ranular Base in a Wet-Freeze Area dulus % % J F M A M J J A S O N D

27 nular Base in a Wet-No Freeze Area Modulus 00% 60% J F M A M J J A S O N D

28 Where Do We Need To Go? Work on our understanding of Seasonality Spatial variability Use of probabilistic methods in design Stress-dependency of materials More accurate constitutive models The role of visco-elasticity in pavement evaluation and design

29 Where Do We Need To Go? Improve field testing protocols Test early in the life of a road Seasonal testing for project level design Improve lab testing methods Combine FWD, SASW and GPR testing into a single pass Head toward real-time backcalculation in the field

30 Too Good to Test?

31 Where Do We Need To Go? Data screening in the field and in the office Utilize the SLIC transform Account for the weather-affected upper subgrade layer Avoid wasting time analyzing bad data Avoid "black box" methods that no one can understand

32 We Have Come a Long Way In 30 Years

33 How Good Is Good Enough? Let's talk about it