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Transportation Engineering-II

Transportation Engineering-II. Principles of Pavement Design. 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

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Transportation Engineering-II

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  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? • 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 pavementdesign? • 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

  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: AxleEmptyFull 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?

  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 • Feasibility • Grading • Construction • Surfaces • Functions • Types of materials • Skid qualities • Cracking • Materials Considerations

  20. Design factors

  21. General Framework of Pavement Design

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