Transcript Transportation Engineering

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
• It consists of all structural elements or
layers, including shoulders
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.
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.
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.
What is the goal of pavement
design?
• Provide the most cost-effective
structure while optimizing the level of
service provided to road users.
Pavement Design
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
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.
Fundamental Parameters
Following are the fundamental
parameters to be considered:
• Subgrade
• Loads
• Environment
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
Subgrade
Some Typical Values
Classification
Good
Fair
Poor
CBR
≥ 10
5–9
3–5
MR (psi)
Typical Description
20,000
Gravels, crushed stone and
sandy soils. GW, GP, GM, SW,
SP, SM soils falls in this
category.
10,000
Clayey gravel and clayey
sand, fine silt soils. GM, GC,
SM, SC soils falls in this
category.
5,000
Fine silty sands, clays, silts,
organic soils. CL, CH, ML,
MH, CM, OL, OH soils falls in
this category.
Loads
Load characterization
•
•
•
•
•
Tire loads
Axle and tire configurations
Load repetition
Traffic distribution
Vehicle speed
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
4
 load 

  relativedamage factor
 18,000lb. 
Typical LEFs
6
ESALs per Vehicle
5.11
5
4
3
1.85
2
1.35
1
0.0007
0.10
Car
Delivery Truck
0
Loaded 18-Wheeler
Loaded 40' Bus
Notice that cars are insignificant and thus usually
ignored in pavement design.
Loaded 60'
Articulated Bus
LEF Example
The standard axle weights for a standing-room-only loaded Metro
articulated bus (60 ft. Flyer) are:
Axle
Steering
Middle
Rear
Empty
13,000 lb.
15,000 lb.
9,000 lb.
Full
17,000 lb.
20,000 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?
Environment
• Temperature extremes
• Frost action
• Frost heave
• Thaw weakening
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
Secondary Parameters
• Base and Subbase Courses
• Feasibility
• Grading
• Construction
• Surfaces
•
•
•
•
Functions
Types of materials
Skid qualities
Cracking
• Materials Considerations
Design factors
General Framework of
Pavement Design