LOW VOLUME ROAD DESIGN EMPIRICAL APPROACH

1. LOW VOLUME ROAD DESIGN EMPIRICAL APPROACH

2. WHAT ARE THE DIFFERENCES ??

3. Roman Road 30060

4. TYPES OF FAILURE • FUNCTIONAL FAILURE • STRUCTURAL FAILURE Do they occur at the same time? How do they differ for low volume roads ? Do all users agree ? How do we combine the different views ?

5. Total or Whole Life Costs • Minimise total costs Need to….. • predict road deterioration • predict the effects of maintenance • calculate road agency costs • predict road user costs • PLUS • calculate social ‘benefits’ Models such as HDM 4 ??

6. What structural design factors does road performance, and therefore design, depend ? • strength of subgrade • traffic loading • wheel loads • number of repetitions of wheels • strength of pavement layers • thickness of pavement layers • ? • but also time dependant • but how?

7. try to For high traffic roads we control as much as we can to reduce risks of failure to a very low value But for low volume roads we cannot afford to do so

8. Pass/fail criteria - no risk Number of samples Specification for trunk road Strength of material

9. BASIC AASHTO METHOD 1 Estimate traffic loading in equivalent standard axles2 Multiply traffic by regional factor3 Estimate subgrade strength (now as an elastic modulus) 4 Select serviceability loss (maximum level of acceptable deterioration) METHOD THEN RECOMMENDS A STRUCTURAL NUMBER, SN

10. STRUCTURAL NUMBER (SN) SN = a1 h1 + a2 h2 + a3 h3 + .... Where a1 , a2 , a3 etc. are strength coefficients for layers 1, 2, 3, etc. and h1 , h2 , h3 , etc. are the thicknesses of layers 1, 2, 3 The strength coefficients are related to normal strength measures such as CBR, unconfined compressive strength, Marshall stability, etc.

11. Strengthcoefficient(a2) a2 = {29.14 (CBR) - 0.1977 (CBR)2+ 0.00045 (CBR)3} x 10-4 0.15 • 0.14 • 0.10 0.08 • 0.05 0 40 50 100 110 150 CBR value STRENGTH COEFFICIENT, a2 FOR GRANULAR BASE MATERIALS

12. Strengthcoefficient(a3) 0.150 • 0.125 • 0.100 0.075 • 0.050 a3 = 0.01 + 0.065 (log10CBR) 0.025 1 5 10 50 100 200 CBR of sub-base STRENGTH COEFFICIENT, a3 FOR SUB-BASE MATERIALS

13. 103 104 105 106 107 108 EQUIVALENT THICKNESS De, INCHES 45 x 40 x x x x x x x 35 x x x x x x x x x x x x x x x 30 x x x x x x x 25 x x x x x x x x x x 20 x 15 x 10 x x 5 0 WEIGHTED EQUIVALENT ESA APPLICATIONS AASHO "DESIGN" EQUATION COMPARED WITH DATA

14. AASHTO EQUATION Traffic Subgrade CBR Structural number Allowable deterioration Reliability

15. Effect of ‘Reliability’ For 250,000 esa and subgrade CBR = 7% 95% Reliability SN = 2.54 85% Reliability SN = 2.29 a difference of 62 mm of sub-base

16. ROAD DETERIORATION STATE OF ROADPSI FROZEN FROZEN SPRING THAW SPRING THAW TIME or TRAFFIC

17. Effect of climateThe ‘regional’ factor Illinois in summer SN = 2.54 Dry SN = 2.14 (-100mm of sub base) Wet SN = 2.97 (+110mm of sub base) But no guidance available from the Road Test

18. ROAD NOTE 31A PAVEMENT DESIGN GUIDE FOR PAVED ROADS IN TROPICAL CLIMATES

19. TAKES ACCOUNT OF….. • Variability in material properties • Uncertainty in traffic estimates • Variability in road performance

20. KEY FACTORS • Influence of tropical climates on the moisture conditions in the subgrade • Influence of tropical climates on the nature of soils and rocks • High axle loads and tyre pressures • Severe conditions imposed on the bituminous surface by tropical climates • Inter relationship between design and maintenance

21. ESTIMATING EQUILIBRIUM MOISTURE CONTENT CATEGORY 3 No permanent water table Arid climate Rainfall < 250mm pa

22. ESTIMATING EQUILIBRIUM MOISTURE CONTENT CATEGORY 2 Deep water table but rainfall sufficient to produce seasonal changes under the road Rainfall >250mm pa. per year and seasonal

23. ESTIMATING EQUILIBRIUM MOISTURE CONTENT CATEGORY 1 Water table sufficiently close to the surface to control the subgrade moisture content (This depends on the type of soil)

24. An example of coping with risk 100 80 60 Cumulative percentage 40 20 0 4 8 12 CBR (DCP) per cent

25. CBR at equilibrium moisture content Soaked CBR Required pavement thickness Soil A 5% 15% 300mm Common to area where designs developed 8% 300mm ? Soil B 5% Rare

26. Consideration of the Road Design Environment for LVSR’s AVAILABLE MATERIALS OPTIMUM OR APPROPRIATE PAVEMENT DESIGN

27. THE ROAD DESIGN OR “RISK” ENVIRONMENT • AVAILABLE MATERIALS • Alternative & thin bituminous • surfacings • Pavement materials • Marginal materials • Standards • Subgrade & road formation • Problem soils • Moisture sensitivity • Stabilisation options and treatments OPTIMUM OR APPROPRIATE PAVEMENT DESIGN METHODOLOGY

28. Pass/fail criteria Number of samples Specification for trunk road Strength of material

29. Consideration of the Road Design Environment for LVSR’s PREVAILING CLIMATE DRAINAGE AND HYDROLOGY AVAILABLE MATERIALS OPTIMUM OR APPROPRIATE PAVEMENT DESIGN

30. THE ROAD DESIGN OR “RISK” ENVIRONMENT PREVAILING CLIMATE Rainfall (intensity, distribution) Temperature (evaporation & diurnal change) Future change or unpredictability • AVAILABLE MATERIALS • Alternative & thin bituminous • surfacings • Pavement materials • Marginal materials • Standards • Subgrade & road formation • Problem soils • Moisture sensitivity • Stabilisation options and treatments DRAINAGE AND HYDROLOGY Ground & surface water flow Hydro-genesis Demand of terrain Modifying influences OPTIMUM OR APPROPRIATE PAVEMENT DESIGN METHODOLOGY

31. Consideration of the Road Design Environment for LVSR’s PREVAILING CLIMATE DRAINAGE AND HYDROLOGY AVAILABLE MATERIALS OPTIMUM OR APPROPRIATE PAVEMENT DESIGN CONSTRUCTION

32. THE ROAD DESIGN OR “RISK” ENVIRONMENT • AVAILABLE MATERIALS • Alternative & thin bituminous • surfacings • Pavement materials • Marginal materials • Standards • Subgrade & road formation • Problem soils • Moisture sensitivity • Stabilisation options and treatments PREVAILING CLIMATE Rainfall (intensity, distribution) Temperature (evaporation & diurnal change) Future change or unpredictability DRAINAGE AND HYDROLOGY Ground & surface water flow Hydro-genesis Demand of terrain Modifying influences OPTIMUM OR APPROPRIATE PAVEMENT DESIGN METHODOLOGY CONSTRUCTION Quality control Capacity, training & experience Selection and use of plant Influence of construction traffic

33. Consideration of the Road Design Environment for LVSR’s PREVAILING CLIMATE DRAINAGE AND HYDROLOGY AVAILABLE MATERIALS GEOMETRICS AND CROSS-SECTIONPROFILES OPTIMUM OR APPROPRIATE PAVEMENT DESIGN TRAFFICCHARACTERISTICS OTHERS MAINTENANCE CONSTRUCTION CONSTRAINTS OF THE “GREEN” ENVIRONMENT

34. THE ROAD DESIGN OR “RISK” ENVIRONMENT TRAFFICCHARACTERISTICS Axle loading Tyre pressures Seasonality Position Growth projections PREVAILING CLIMATE Rainfall (intensity, distribution) Temperature (evaporation & diurnal change) Future change or unpredictability DRAINAGE AND HYDROLOGY Ground & surface water flow Hydro-genesis Demand of terrain Modifying influences MAINTENANCE Capacity & skills Funding Programming GEOMETRICS AND CROSS-SECTION PROFILES Road width Crown height Demand of terrain Sealed shoulders CONSTRAINTS OF THE “GREEN” ENVIRONMENT Constrained alignments Access to materials Depletion of resources Terrain stability OPTIMUM OR APPROPRIATE PAVEMENT DESIGN METHODOLOGY • OTHER • Technology solution • labour based • Intermediate equip • Safety • Institutional environment capacity • Financing • Political pressure • Design period • Road side activity • AVAILABLE MATERIALS • Alternative & thin bituminous • surfacings • Pavement materials • Marginal materials • Standards • Subgrade & road formation • Problem soils • Moisture sensitivity • Stabilisation options and treatments CONSTRUCTION Quality control Capacity, training & experience Selection and use of plant Influence of construction traffic