1. Transportation Engineering-II
Principles of Pavement Design

2. Pavement Design What is a Pavement?
Pavement is the upper part of roadway, airport or parking area structure
It includes all layers resting on the original ground
It consists of all structural elements or layers, including shoulders

3. Pavement Design What is Design? What is a pavement design?
Conceived/developed plan for something to serve a specific function.
What is a pavement design?
It is the process by which the structural components of a road segment are determined, taking into account the nature of the subgrade, density and traffic composition.

4. Pavement Design
‘OR’
It is the process of developing the most economical combination of pavement layers (in relation to both thickness & type of materials) to suit the soil foundation and the traffic to be carried, during the design life.

5. Pavement Design
‘OR’
It is a process of selection of appropriate pavement and surfacing materials to ensure that, the pavement performs adequately and requires minimal maintenance under the anticipated traffic loading for the design period adopted. This selection process involves adoption of material types, thicknesses and configurations of the pavement layers to meet the design objectives.

6. What is the goal of pavement design?
Provide the most cost-effective structure while optimizing the level of service provided to road users.

7. Pavement Design

8. Pavement Design Phases
Highway design consists of three stages
Geometric design
(route selection or alignment design)
Capacity design
(number of lanes to meet traffic demand)
Structural design
(to withstand loads and environment)
Structural design consists of 3 steps
Selection of materials (types of pavement)
Proportioning of materials
Layer thickness design

9. Pavement Design Principles
Design objectives are to:
Provide safe and comfortable riding conditions to all road users, being motor vehicles, cyclists and pedestrians, optimized for the road’s intended functions and the level of use.
Provide low cost of ownership (i.e. minimum whole of life cost) to the Government.
Comply with the Standards and relevant State Road Authorities’ Guidelines and/or Standards.

10. Fundamental Parameters
Following are the fundamental parameters to be considered:
Subgrade
Loads
Environment

11. Subgrade Characterized by strength and/or stiffness
California Bearing Ratio (CBR)
Measures shearing resistance
Units: percent
Typical values: 0 to 20
Resilient Modulus (MR)
Measures stress-strain relationship
Units: psi or MPa
Typical values:3,000to40,000 psi

12. Subgrade Some Typical Values Classification CBR MR (psi)
Typical Description
Good
≥ 10
20,000
Gravels, crushed stone and sandy soils. GW, GP, GM, SW, SP, SM soils falls in this category.
Fair
5 – 9
10,000
Clayey gravel and clayey sand, fine silt soils.  GM, GC, SM, SC soils falls in this category.
Poor
3 – 5
5,000
Fine silty sands, clays, silts, organic soils.  CL, CH, ML, MH, CM, OL, OH soils falls in this category.

13. Loads Load characterization Tire loads Axle and tire configurations
Load repetition
Traffic distribution
Vehicle speed

14. Load Quantification Equivalent Single Axle Load (ESAL)
Converts wheel loads of various magnitudes and repetitions ("mixed traffic") to an equivalent number of "standard" or "equivalent" loads
Based on the amount of damage they do to the pavement
Commonly used standard load is the 18,000 lb. equivalent single axle load
Load Equivalency
Generalized fourth power approximation

15. Typical LEFs
Notice that cars are insignificant and thus usually ignored in pavement design.

16. LEF Example
The standard axle weights for a standing-room-only loaded Metro articulated bus (60 ft. Flyer) are:
Axle Empty Full Steering 13,000 lb. 17,000 lb. Middle 15,000 lb. 20,000 lb. Rear 9,000 lb. 14,000 lb.
Using the 4th power approximation, determine the total equivalent damage caused by this bus in terms of ESALs when it is empty. How about when it is full?
Empty
(13,000/18,000)4 = 0.272
(15,000/18,000)4 = 0.482
(9,000/18,000)4 = 0.063
Total = ESALs
Full
(17,000/18,000)4 = 0.795
(20,000/18,000)4 = 1.524
(14,000/18,000)4 = 0.366
Total = ESALs
Increase in total weight = 14,000 lb. (about 80 people) or 39%
Increase in ESALs is (229%)

17. Environment Temperature extremes Frost action Frost heave
Thaw weakening

18. Secondary Parameters
Following are the secondary parameters for pavement design;
Soil Classification
Soil horizons
Parent materials
Moisture-solid relationship
Material Characterization
Soil and Base Stabilization
Sub-grades Strength Studies
Compaction
Strength-Density-Moisture Considerations

19. Secondary Parameters Base and Subbase Courses Surfaces
Feasibility
Grading
Construction
Surfaces
Functions
Types of materials
Skid qualities
Cracking
Materials Considerations

20. Design factors

21. General Framework of Pavement Design