Pavement Design

Pavement Design - Pavement Design Approximately 3.0 million...

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Pavement Design Approximately 3.0 million miles of highways in U.S. (45% fully paved). Basic Functions of Pavements: Visual guidance to drivers Support vehicle load and distribute the traffic-load stresses to the soil (subgrade) at a magnitude that will not shear or distort the soil. - soil bearing capacity 2 to 50 psi - 3500 lb auto tire pressures 35 psi - 80,000 lb trucks (5-axles) tire pressure 100 psi or higher (used for design) Pavement Types : Flexible Pavements: asphaltic cement and aggregates 2-4 inches Wearing Surface asphaltic cement and aggregates 4-10 inches Base crushed aggregates (high quality) 4-10 inches Subbase crushed aggregates (rock) Soil Subgrade 6-8 inches of it is blended and compacted to maximum density NOTE: - Base is usually stabilized with Portland cement, lime, fly ash, or asphaltic cement. - Wearing surface protects the base layer from wheel abrasion and waterproof the entire pavement structure. It also provides a skid-resistant surface. - Thickness of Layers = f(type of axle load, available material, and expected pavement life). Rigid Pavements: Portland Cement Concrete (PCC) and aggregates “dowels” are load Joint transfer device 8-12 inches PCC Slab PCC Slab 10 to 13 ft wide to 40 ft or more long 4-8 inches Base Layer (optional) depending on the properties of subgrade Soil Subgrade 6-8 inches of it is scarified, blended, and compacted to maximize density Other Variations of Flexible and Rigid Pavements: - Composite Pavements (Rigid and Flexible) - Continuously Reinforced - Post-tensioned - etc. 1
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Principles of Flexible Pavement Design: Load distribution on a flexible pavement: Wheel Load Wearing Base Subbase Subgrade Stresses and deflections: - Boussinesq theory: assumes that the pavement is one layer thick and the material is elastic, homogeneous, and isotrophic. P point load x y one layer of pavement depth z stress at a point in the system is 2 z z P K = σ E Q . 4 . 1 σ z = stress at point z in the system, lb/in 2 P = wheel load, lb z = depth of the point in question, inches and 2 / 5 2 z r 1 1 2 3 K + π = EQ. 4.2 where, r = radial distance in inches from the centerline of the point load to the point in question. 2
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A more realistic approach is to expand the point load to an elliptical area that represents a tire footprint. The tire footprint can be defined by an equivalent circular area with a radius calculated by π = p P a E Q . 4 . 3 P = tire load in lb p = tire pressure in lb/in 2 a = equivalent load radius of the tire footprint, inches The integration of the load from a point to a circular area can be used to determine the stresses and deflections in a one-layer pavement system. Influence charts, graphical solutions, and other equations are developed by researchers to calculate stresses and deflections.
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This note was uploaded on 02/09/2011 for the course ECON 2250 taught by Professor Schultz during the Spring '11 term at UNO.

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Pavement Design - Pavement Design Approximately 3.0 million...

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