The Danish Pavement Design Guide. Gregers Hildebrand, Danish Road Directorate

Transcription

1 The Danish Pavement Design Guide Gregers Hildebrand, Danish Road Directorate

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3 New Danish design guide Modern tool based on sound scientific principles Designs for roads at all levels Designs in three ways: Pavement catalogue Analytical-empirical method Simulation and optimisation Relative importance of road is considered in the design

4 Pavement design Design provides: Layer thicknesses Expected lifetime Based on: Traffic Climate Natural soils Pavement materials Failure criteria Reliability levels

5 Design traffic (the easy way) Class Trucks/day in both directions ESALS/day day/track Design traffic ESALS/year T0* Only light vehicles - - T1 T2 Less than Up to T3 75 to T4 150 to T5 600 to T to T7 More than

6 Design traffic (the tough one) ESAL = P K F K K K R F SS Σ ( F ESAL L ) Increase in traffic volume P Road width K F Channelised traffic K K Roundabouts K R Road type F SS Type of vehicle and road location ( F ESAL L )

7 Design by catalogue Simple, empirical design for minor roads Often expensive solution Flexible pavements Concrete paving blocks

8 Analytical-empirical model Response model: analytical Failure models: empirical

9 Failure criteria Asphalt: permissible tensile strain at bottom of asphalt layer ( ) 6 N 0,191 Æ10 ε = 0, h Cement stabilized gravel: permissible tensile strain at bottom of layer ε 6 ( N ) 0,125 h = A Æ10 10 Unbound materials: permissible compressive stress at top of layer σ 6 ( N ) 0,25 1,06 z = 0,086 MPa (E 160 MPa) Æ10 10

10 Failure criteria functions The failure criteria limit Cracking in the asphalt layer Deterioration of cement stabilized gravel Unacceptable rutting/roughness

11 Material library Material E-value (MPa) Min. thickness (mm) Cement concrete, non-reinforced Cement stabilzed gravel, intact layer (factory) Gravel macadam (SKM) Singels macadam (SIM) Granular base (SG) Recycled cement concrete A (KGBA) Recycled cement concrete B (KGBB) Recycled cement concrete C (KGBC) Recycled asphalt (KGA) Recycled tile Blast furnace slag Sandy sub-base base (BL)

12 Subgrade type determines total pavement thickness Frost sensitivity Material type Traffic class Safe Questionnable Sensitive Sand and gravel without significant amounts of silt/silty soils. Moraine clay and clay. Silt and very silty soils with possible acccess to water, Slags and fly ash. T0, T1 As determined 400 mm 500 mm T2 by the M-E analysis 500 mm 700 mm T3 600 mm 800 mm T4, T5, T6, T7 700 mm 900 mm

13 Special features Adjustment of E-values for asphalt based on driving speed: E E v 60 = v Material Straight section (v > 60 km/h) Turning lane (v = 10 km/h) Asphalt surface course 35 mm 35 mm Asphalt bound base 108 mm 149 mm Granular base 220 mm 190 mm

14 Design by simulation For 300 mm pavement sections: permanent deformation reduction in E-value for asphalt Models for: Pavement: longitudinal profile, thicknesses, E-values Load: reaction between wheel and pavement Climate: temperature and E-value Pavement response: stress, strain, deflection Asphalt deterioration Permanent deformation Fase 3 Stigende tøjningshastighed Fase 2 Konstant tøjningshastighed Kote 1 E 1 Kote 2 E 2 Kote 3 E 3 Kote 4 E m Anvendt model: Alene Fase 1 & 2 Fase 1 Aftagende tøjningshastighed

15 Failure criteria - simulation Lifetimes based on four failure criteria: Roughness, IRI: Rutting, RD: Average E-value: Minimum E-value: 4 m/km 10 mm 67% of E (new asphalt) 33% of E (new asphalt)

16 Reliability of design Lifetime calculated using several simulations Low safety Likelihood 50% that reliability failure limits are not passed Reliabilty Asphalt 128 mm Gravel 210 mm Important assets should use high Life reliabilty (year) level (>90%) Average less important Std. dev. Average assets down to 50% IRI Thickness of asphalt and granular base layers Standard MMOPP 85% reliability mm 220 mm High safety 95% reliability 158 mm 230 mm Std. dev. Average Std. dev Rutting Cracking Potholes

17 Optimization Determination by simulation of the pavement, which exactly satisfies the specified reliability level

18 The new design guide Easy accessible software obtainable at at no cost Easy to evaluate a high number of alternative design solutions Easy to see how pavement material characteristics, layer thicknesses and traffic influence the design Complete integration between design of new pavements and overlays Varying safety factors makes it possible to design with a view to the relative importance of road sections

19 The design guide at the web