Transportation Engineering-II

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Transportation Engineering-II

• Principles of Pavement Design

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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

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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.

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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.

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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.

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What is the goal of pavementdesign?

• Provide the most cost-effective structure while
  optimizing the level of service provided to road
  users.

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Pavement Design
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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

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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 roads
  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.

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Fundamental Parameters

• Following are the fundamental parameters to be
  considered

• Subgrade
• Loads
• Environment

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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 values3,000to40,000 psi

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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.
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Loads

• Load characterization
• Tire loads
• Axle and tire configurations
• Load repetition
• Traffic distribution
• Vehicle speed

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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

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

• Temperature extremes
• Frost action
• Frost heave
• Thaw weakening

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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

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Secondary Parameters

• Base and Subbase Courses
• Feasibility
• Grading
• Construction
• Surfaces
• Functions
• Types of materials
• Skid qualities
• Cracking
• Materials Considerations

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Design factors
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General Framework of Pavement Design