Pavement Design Where are We? By Dr. Mofreh F. Saleh

Transcription

1 Pavement Design Where are We? By Dr. Mofreh F. Saleh

2 Pavement Design Where are We?? State-of-Practice State-of-the-Art Empirical Mechanistic- Empirical Mechanistic Actual Current Practice??

3 Inputs Structure Materials Traffic Climate To account for Reliability, both mean and standard deviations inputs are required Selection of Trial Design Design Reliability Structural Responses (σ, ε, δ) Performance Prediction Distresses Smoothness Performance Verification Failure criteria Design Requirements Satisfied? Revise trial design No Yes Final Design

4 PERMANENT DEFORMATION IN FLEXIBLE PAVEMENTS

5 LOAD RELATED - Rutting Vertical Displacements Lateral Displacements

6 Rutting - Permanent deformation in all layers. Wide versus narrow rut depths.

7 Shoving & Corrugations

8 Rutting Vertical and/or horizontal permanent deformation of one or more layers in the pavement system.

9 Rutting Mechanisms Densification Vertical movements Compression Consolidation Shear deformation Lateral movements

10 Rutting Mechanisms Potential Primary Causes: Plastic movement of HMA in hot weather Inadequate compaction of HMA during construction Potential Secondary Causes: Plastic movement in other layers Inadequate compaction in other layers

11 Plastic movement - Depression in the Wheel Path with Humps in Either Side Consolidation/Densification -Depression in the Wheel Path Without Any Humps Mechanical Deformation - Subsidence or Densification in the Unbound Base or Subgrade and Accompanied by a Cracking Pattern

12 Permanent or Plastic Deformations R ecoverable and Plastic Strains ε r ε p Stress Under Repeated Loads

13 Rutting Models Subgrade compressive strain models: determine the cover requirements to protect the subgrade or embankment soil. Permanent deformation/strain models: these models accumulate all permanent strain values to estimate the total rutting at the surface of the pavement structure.

14 Subgrade Strain Models N = f ε f 1 ( ) f2 V Austroad Asphalt Institute Shell Transport and Road Research Lab (TRRL) Belgian Road Research Center (BRRC)

15 Organization f 1 f 2 Allowable Rut Depth, mm (in) Asphalt Institute x (0.5) Shell (revised 1985) 50% Reliability 6.15 x % Reliability 1.94 x (0.5) 95% Reliability 1.05 x U.K. Transport and Road Research Laboratory C (85% Reliability) 6.18 x (0.4) Belgian Road Research Center 3.05 x (0.4) AUSTROADS (Old) 1.66* ? AUSTROADS (New) 6.017* ?

16 Material Properties Dictate The Maximum Allowable Permanent Deformation Tertiary Permanent Strain (in/in) Primary Secondary V=0 Shear Failure N FN (Flow Number) Loading Cycles

17 Austroad Rutting Model N = f µε F1 =6.017*10-8, f2= -7

18 Vertical Compressive Strain (µε) Comparison between different compressive strain models Old SHELL (Rut f =13 mm) AUSTROADS (New) A.I. (Rut f =13 mm) TRRL (Rut f =10 mm) E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 Number of Load Repetitions to Failure

19 Subgrade Strain Models Based on: Specific design conditions Material properties Environmental conditions Limitations Can't accurately be extended beyond inference space Models suggest that allowable rut depth will not be exceeded if ε v is limited Assume that all permanent deformations occur in the subgrade. v

20 Permanent Deformations in all Pavement Layers F p = S = t b a * S p p = 0 1 *( σ + σ = σ 1 σ 3 1 σ 3 ) where: a,b = material parameters that are independent of plastic deformation. p t = the hardening parameter that represents the hydrostatic tensile strength of the material. σ 1, σ 2,and σ 3 = major, intermediate and minor principal stresses, respectively.

21 . X-Section of FEM Boundary Conditions.. 10 Elements each (2000-X)/10 mm X Plane of Symmetry 8 Elements each mm 8 elements each 75 mm 1250 mm. FIGURE 5 Cross Section of the Finite Element Model

22 . Longitudinal Section in the FEM 2000-X X Unbound Base Course 8 Elements each 75 mm Subgrade Layer Plane of Symmetry 8 Elements each mm 3000 mm FIGURE 4 Elevation View of the Finite Element Model

23 Drucker-Prager Model σ 3 Yield Surface Hydrostatic or spherical axis σ 1 =σ 2 =σ 3 Deviatoric Plane σ 2 π-plane or deviatoric plane at σ 1 +σ 2 +σ 3 =0 σ 1

24 Permanent Vertical Strain& Rutting Calculations Principal Permanent Strain (Microstrain) P= 50kN, q= 750 kpa Interface betw een base course and subgrade P=40 kn, q=750 kpa P=40 kn, q=650 kpa Base course Subgrade Layer 37% Rutting 63% Rutting Depth (mm)

25 Permanent Deformation Prediction Models Considers permanent deformation of each layer individually General form of models: Logε = a + p b( LogN ) Deformation (rutting) is calculated: Total Rutting = n i= 1 (ε p ) i * h i

26 Ohio State Model Permanent Strain Accumulation Model (rutting rate) ε N p -m = A (N) "A" and "m" are constants based on material type and stress state

27 Typical values of A and m in the Ohio State model (Barenberg and Thompson, 1990). Moisture Unconfined Strength, kpa (psi) Optimum 159 (23) 34 (5) 69 (10) 103 (15) Optimum + 4% 90 (13) 34 (5) 69 (10) 103 (15) Repeated Deviator Stress, kpa (psi) m A x

28 Asphalt Institute Model ( ε ) ( ) p Log = * Log N * Log( T) * Log( σ ) * Log( V ) * Log( P ) * Log( Vv) d ε p = Permanent strain (axial). N = Number of load repetitions to failure. T = Temperature, of. σ d = Deviator stress, psi. V = Viscosity at 21 o C (70 o F), Ps x Pbe = Percent by volume of effective bitument. Vv = Percent volume of air voids. be

29 Kaloush-Witczak Model Log ε ε p r = ( LogT ) ( LogN )

30 Logε Allen and Dean Model [ ( )] [ ( )] 2 Log N + C Log N C [ Log( )] 3 p = Co + C N εp = Permanent strain (axial). N = Number of stress or wheel load repetitions. C0-3 = Regression coefficients that are factors of the temperature and the deviator stress, as shown in Table below.

31 Coefficient HMA C o T T ( T) * log 1 Dense-Graded Aggregate Base ( w) * 1 - ( w) * 3 Subgrade w (log 3 ) (log 1 ) C ( w) C (log w) w C (log w) w where, T = Temperature, F. σ 1 = Deviator stress, lbf/in2. w = Moisture content, percent. σ 1 = Deviator stress, lbf/in2. σ 3 = Confining pressure, lbf/in2

32 Fatigue Criteria N f = K 1 ( ) K 2 ( ) K ε E 3 t University of Canterbury Fatigue Models for AC-10 N f = 2. 35* 10 * ε R = N = * 10 * ε * M R = f r

33 Predicted Repetitions N R f 2 = 2.35*10 = * ε HMA, AC Measured Repetitions

34 N R f 2 = 6.64*10 = * ε *M r Predicted Repetitions HMA, AC Measured Repetitions

35 Fatigue Constants Fatigue Equation Response Parameter HMA Response Modulus Other Parameters in Definition of Failure, % Coefficient, K 1 Exponent, K 2 Exponent, K 3 Equation Cracking Dynamic Modulus ε Percent Air Voids 50 Asphalt Institute Percent Asphalt by Volume Shell ε Dynamic Modulus 20 ε 6.601x Flexure Modulus Lab, Crack Initiation ε 8.851x Flexure Modulus 10 PDMAP ε 1.219x Flexure Modulus 45 TRRL ε 1.66x Belgian ε 4.92x Ontario ε 8.86x Dynamic Modulus 20 Canterbury ε 2.35* Lab Model ε 6.64* Resilient Modulus Lab Model

36 Fatigue Criteria AUSTROADS TRRL UC-Model PDMAP BRRC Number of Load Repetitions Strain Level (mm/mm)

37 Factors to be considered Definitions of Failure (10%, 20% or 50%) Developing a set of models relevant to the different mix (AC-10, AC-14, or AC-20) and bitumen types (conventional bitumen versus polymer modified bitumen)