28 pavement design
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Transcript of 28 pavement design
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Pavement Design
CE 453 Lecture 28
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Objectives
Understand and complete ESAL calculation
Know variables involved in and be able to calculate required thickness of rigid and flexible pavements
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AASHTO Pavement Design Method Considerations
Pavement Performance Traffic Roadbed Soil Materials of Construction Environment Drainage Reliability Life-Cycle Costs Shoulder Design
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Two Categories of Roadway Pavements
Rigid Pavement Flexible Pavement
Rigid Pavement Typical Applications High volume traffic lanes Freeway to freeway connections Exit ramps with heavy traffic
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Advantages of Rigid Pavement
Good durability Long service life Withstand repeated flooding and
subsurface water without deterioration
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Disadvantages of Rigid Pavement
May lose non-skid surface with time Needs even sub-grade with uniform
settling May fault at transverse joints Requires frequent joint maintenance
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Flexible Pavement Typical Applications
Traffic lanes Auxiliary lanes Ramps Parking areas Frontage roads Shoulders
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Advantages to Flexible Pavement
Adjusts to limited differential settlement
Easily repaired Additional thickness added any time Non-skid properties do not deteriorate Quieter and smoother Tolerates a greater range of
temperatures
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Disadvantages of Flexible Pavement
Loses some flexibility and cohesion with time
Needs resurfacing sooner than PC concrete
Not normally chosen where water is expected
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Basic AASHTO Flexible Pavement Design Method
Determine the desired terminal serviceability, pt
Convert traffic volumes to number of equivalent 18-kip single axle loads (ESAL)
Determine the structural number, SN
Determine the layer coefficients, ai Solve layer thickness equations for
individual layer thickness
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Basic AASHTO Rigid Pavement Design Method
Select terminal serviceability Determine number of ESALs Determine the modulus of sub-
grade reaction Determine the slab thickness
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Variables included in Nomographs
Reliability, R• Incorporates a degree of certainty
into design process• Ensures various design alternatives
will last the analysis period Resilient Modulus for Roadbed
Soil, MR• Generally obtained from laboratory
testing
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Variables included in Nomographs
Effective Modulus of Sub-Grade Reaction, k• Considers:
1. Sub-base type2. Sub-base thickness3. Loss of support4. Depth to rigid foundation
Drainage Coefficient, mi• Use in layer thickness determination• Applies only to base and sub-base• See Tables 20.15 (flexible) and 21.9 (rigid)
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Other Growth Rates
Multiple payment compound amount factor, with i = growth rate
G = [(1+i)n-1]/i
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Flexible Pavement Design
Pavement structure is a multi-layered elastic system, material is characterized by certain properties Modulus of elasticity Resilient modulus Poisson ratio
Wheel load causes stress distribution (fig 20.2) Horizontal: tensile or compressive Vertical: maximum are compressive, decrease with
depth Temperature distribution: affects magnitude of
stresses
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Components
Sub-grade (roadbed) course: natural material that serves as the foundation of the pavement structure
Sub-base course: above the sub-grade, superior to sub-grade course
Base course: above the sub base, granular materials such as crushed stone, crushed or uncrushed slag, gravel, and sand
Surface course: upper course of the road pavement, should withstand tire pressures, resistant to abrasive forces of traffic, provide skid-resistant driving surface, prevent penetration of surface water
3 inches to > 6 inches
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Economic Analysis
• Different treatments results in different designs
• Evaluate cost of different alternatives
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Sensitivity Analysis
• Input different values of traffic volume
• Compare resulting differences in pavement
• Fairly significant differences in ADT do not yield equally significant differences in pavement thickness
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OTHER ISSUES
Drainage Joints Grooving (noise vs. hydroplaning) Rumble strips Climate Level and type of usage
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FAILURE EXAMPLES
Primarily related to design or life-cycle, not construction
All images from Distress Identification Manual for the Long-Term Pavement Performance Program, Publication No. FHWA-RD-03-031, June 2003
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FATIGUE CRACKING
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RUTTING
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SHOVING
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PUMPING
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EXAMPLES
http://training.ce.washington.edu/wsdot/modules/09_pavement_evaluation/09-7_body.htm
http://training.ce.washington.edu/wsdot/modules/09_pavement_evaluation/09-8_body.htm