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Highway Engineering

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The flexible pavement structure consists of three layers, wearing course, base course and subbase. Under subbase laying the subgrade soil. – PowerPoint PPT presentation

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Title: Highway Engineering


1
Highway Engineering
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2
1-Geometric Design Introduction Design
Controls and Criteria for Geometric Design
Cross Section Design Sight Distance
Highway Vertical Alignment Horizontal
Alignment Design of Highway At-Grade
Intersections Grade Separations- and
interchanges Intersections
3
  • 2- STRUCTURE DESIGN
  • 1- Introduction
  • 2-Soil Engineering of Highways
  • 3-Strength and Density of Soils
  • 4-Pavement Components
  •  
  • 5-Highway Materials
  •  
  • 6-Flexible Pavement Design
  • 7-Design of Rigid Pavements
  •  

4
  • Teaching and Learning Methods
  • I- Methods
  • Lectures
  • Laboratory work.
  • Tutorial problem solving
  •  
  • II- Instruments
  • White board presentations
  • Power Point presentations
  • Interactive discussions

5
  • Schedule
  • 1- Drop Quizzes
    Random
  • 2- Solving Assignment Problems
    Every Week
  • 3- Reports Presentations IT applications

  • As per lecturer schedule
  • 4- Practical Works Reports Exam 13th to 15th
    Weeks
  • 5- Mid-term written exams
    9th Week
  • 6- Final written exams
    16th Week

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  • Procedures Used
  • I- Class Works
  • Drop Quizzes.
  • Solving Assignment Problems
  • Reports.
  • Practical Works.
  • II- Written Exams
  • Mid-term written exams.
  • Final written exams.

9
PART II STRUCTURE DESIGN OF HIGHWAYS
10
CHAPTER 1INTRODUCTION
  • The structure design of highway pavements
    comprises studying soil and paving materials
    their behavior under wheel loads, and the design
    of a pavement to carry that load under all
    climatic conditions

11
General Definitions
  • Right-of-way
  • The right-of-way includes the following
  • -The roadway (Traffic lanes and shoulders)
  • -Drainage system (ditches, drains, culverts and
  • bridges).
  • Structures such as guard rails, side slopes,
  • retaining walls, road signs, light signals
    and
  • traffic control devices at intersections.

12
Fig.1 Highway Structure (Right of Way)
13
Pavement Types
  • Two types of pavements are commonly used,
    flexible- and rigid pavements as shown in Figure
    2
  • 1-Flexible Pavement Flexible pavements consist
    of a layered system in which wheel load effects
    are progressively reduced with depth. The
    flexible pavement structure consists of three
    layers, wearing course, base course and subbase.
    Under subbase laying the subgrade soil.

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  • 2.Rigid Pavement Rigid pavements have relatively
    high resistance to bending such as Portland
    cements concrete pavements. The essential
    difference between the two types of pavements, is
    the manner in which they distribute the loads
    over the subgrade. High modules of elasticity
    for rigid pavement tend to distribute the load
    over a relatively wide area of soil. Thus, a
    major portion of the structure capacity is
    supplied by the slab itself

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Structural Components of Pavements
  • 1) Surface course
  • It is the top layer of the pavement directly in
    contact with traffic and has the following
    functions
  • 1. It acts as a wearing surface which resists
    the abrasion and direct traffic effects and
    pressure.
  • 2. It transmits the wheel loads to the base
    and subgrade without cracking or disintegration.
  • 3. It reduces the tractive resistance of
    traffic.
  • 4. It protects the base course from the action
    of water and climatic affect.

18
  • 2-Base Course
  • It is a layer of high quality material below the
    wearing course through which the wheel loads are
    transmitted to the subgrade soil or subbase. The
    main functions of base course are
  • 1.It acts as a foundation to the top surface
    course
  • 2. It distributes the wheel load into a greater
    area
  • 3. It protects the surface course against the
    volume changes of clay subgrades
  • 4. It prevents the capillary rise.

19
  • Base courses are used under rigid pavements for
    various reasons as
  • 1. control of pumping
  • 2. control of frost action
  • 3.drainage
  • 4.control of the subgrade swelling.

20
  • 3- Subbase Course
  • It is a layer of material may be used between
    base course and subgrade. The functions of
    subbase are
  • 1-It drains the water and prevents the rise of
    capillary water, and subsequently protects the
    base course against the volume changes of
    subgrade.

21
  • 2. In soft clay subgrades, a sand or stabilized
    soil subbase must be used to prevent the working
    of clay subgrade into the voids of the crushed
    stone or gravel above it.
  • 3. It transmits the wheel load to subgrade and
    protect it against frost action in freezing
    weather.
  • Subbase are usually from granular materials as
    gravel, sand, crushed stones, and stabilized soil.

22
  • 4- Subgrade
  • The subgrade is the top layer of embankment in
    fill soil or the top portion in the cut over
    which the pavement are placed. It has a depth of
    30-50 cm and acts as the foundation, and must be
    compacted to max. dry density by artificial means
    of compaction.

23
  • 1.The wheel load, W, is transmitted to the
    surface of pavement through the tire as a uniform
    vertical pressure Po . The stresses are spread
    through the pavement structure to produce a
    reduced vertical stress, P1 at the base surface,
    P2 at the subbase surface and P3 at the subgrade
    surface
  • 2.The deflection in pavement structure leads to
    creating compressive and tensile stresses

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1.2. Traffic Loading
  • The primary loading factors in flexible pavement
    design are
  • 1. Amount of axle (and wheel) loads
  • 2. Volume and composition of axle loads
  • 3. Tire pressure and contact area.

27
1.2.1. Wheel Loads
  • 1. single and dual wheels
  • 2. single and tandem axles.

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1.2.2.Volume and Composition of axle loads
  • The asphalt Institute and also the AASHO
    recommend that the effects of traffic on
    structural design of the pavement be expressed in
    terms of the number equivalent single axle loads
    (ESAL).

30
3.Tire Pressure and Contact Area
  • The radius of contact area is as follows
  • a ? P/Pt . ?
  • where
  • a radius of contact area
  • P total tire load,
  • Pt contact pressure.

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