CE 315 EC8 – Group #5: Structural Design of Railways and Pavements
STRUCTURAL DESIGN OF RAILWAYS AND PAVEMENTS
RAILWAYS AND RAILWAY STRUCTURES
Railway - a transportation system that utilizes tracks and locomotives to transport passengers from one
place to another. It has various components including tracks, bridges, tunnels, and stations.
Railway Structure - a wide array of construction to support railway operations. In designing railway
structures, various loads must be considered such as live loads, dead loads, and environmental loads.
Bridge Deck - part of a railway that carries the track rails.
Types of Bridge Decks:
➢ Open Bridge Deck - anchored directly to timber bridge ties supported directly on
the floor system. It is less costly but requires additional measures to protect
vehicles from falling objects during the operation.
➢ Ballasted Bridges - anchored directly to timber track ties supported in the ballast
section. Ballasted bridges protect vehicles from dropped ballast and materials.
Track Substructure - the foundation that supports the track and facilitates drainage.
Track Substructure Layers:
➢ Ballast - the free draining granular material placed at the top of the substructure
layer in which the sleepers are embedded.
➢ Capping - well-graded natural or artificially blended gravels/solid which have
sufficient fines to permit compaction to high densities.
➢ Subgrade - the upper part of the earthworks or natural ground upon which the
capping layers and ballast layers are placed.
Railway Structure Design Considerations:
1. Dead Loads
2. Live Load from carried traffic
3. Environmental load (wind, snow, ice, thermal, seismic, and stream flow loads)
Parameters That Determine or Affect the Geometry of the Railway Track
▪ Gradient in the track
▪ Curvature of the track
▪ Alignment of the track
Considerations For Proper Geometric Design of a Railway Track
• Ensure smooth and safe running of trains
• Achieve maximum speed
• Carry heavy loads without failure
• To avoid accidents
• Least maintenance
• Good aesthetics
Gradients - the rise and fall in the level of the railway track. Sometimes it is indicated as percent rise and
fall. Rising gradient is when the track rises in direction while down gradient is when the track loses
elevation.
Objectives of Gradients
● Reach various stations at different elevation
● Follow the natural contours of the ground
● To reduce the cost of earthwork
CE 315 EC8 – Group #5: Structural Design of Railways and Pavements
Grade Compensation on Curves
● For broad gauge (BG) tracks 0.04% per degree of the curve
● For meter gauge (MG) tracks 0.03% per degree of the curve
● For narrow gauge (NG) tracks 0.02% per degree of the curve
PAVEMENTS, PAVEMENT DESIGN AND REHABILITATION
TYPES OF PAVEMENTS
Flexible Pavement - consists of a surface layer of bitumen-bound aggregate (asphalt concrete), several
lower layers of appropriate quality aggregate and the subgrade beneath. The layers enable the pavement
to “bend”, reducing damage and the need for repairs over time.
What are the functions of layers in a flexible pavement?
Flexible pavement consists of a surface layer of bitumen-bound aggregate (asphalt
concrete), several lower layers of appropriate quality aggregate and the subgrade beneath. The
layers enable the pavement to “bend”, reducing damage and the need for repairs over time.
The structure of flexible pavement is typically made up of the following layers:
• Surface Course
• Binder Course
• Base Layer
• Subbase Layer
• Capping Layer
• Subgrade Layer
Rigid Pavements - constructed from Portland cement concrete slabs resting on a prepared subbase of
granular material or directly on a granular subgrade. Load is transmitted through the slabs to the
underlying subgrade by flexure of the slabs.
Types of Rigid Pavements
• Jointed Plain Concrete Pavement (JPCP) - plain cement concrete pavements constructed with
closely spaced contraction joints. (Dowel bars or aggregate interlocks are normally used for
load transfer across joints. They normally have a joint spacing of 5 to 10m.)
• Jointed Reinforced Concrete Pavement (JRCP) - although reinforcements do not improve the
structural capacity significantly, they can drastically increase the joint spacing to 10 to 30m.
• Continuous Reinforced Concrete Pavement (CRCP) - Complete elimination of joints are
achieved by reinforcement.
• Pre-Stressed Concrete Pavement (PCP) - designed and produced to be prestressed to bear
tensile forces caused by external loads by various live objects such as vehicles on the road or
aircraft in the airports.
Composite Pavement - a structure comprising two or more layers that combine different characteristics
and that act as one composite material.
Factors Affecting Pavement Design
1. Wheel Load Influence on Pavements - wheel load on pavement determines the required
pavement thickness to prevent subgrade soil damage. Adequate thickness safeguards against
deformations caused by the wheel load at specific points on the pavement.
2. Axle Configuration - by providing multiple axles, vehicles can carry more load. So, the axle load
also influences the design of pavement.
CE 315 EC8 – Group #5: Structural Design of Railways and Pavements
3. Tire Contact Pressure on Pavement - when a vehicle moves on pavement, pressure develops
between the tire and the pavement.
4. Vehicle Speed - if the vehicle is moving at creep speed, then damage also occurs to the pavement.
If the vehicle speed is gradually increased then it will cause smaller strains in the pavement.
5. Repetition of Loads - the wheel loads are repeated all the time; due to this, some deformation
occurs on the pavement.
6. Subgrade Type - testing subgrade soil is crucial for pavement construction.
7. Temperature - in high temperatures, it makes the asphalts less stiff; while in low temperatures, it
makes the asphalt brittle.
8. Precipitation - moisture from rain affects groundwater depth.
Pavement Maintenance and Rehabilitation
Over time, roads and pavements deteriorate due to traffic loads, weather conditions, and other
environmental factors. To ensure the smooth and safe operation of transportation networks, regular
maintenance and occasional rehabilitation are necessary.
Maintenance strategies are employed to combat deterioration. They include:
➢ Crack Sealing
➢ Joint Sealing
➢ Fog Seals
➢ Patching
Maintenance goals target specific deficiencies to slow overall deterioration.
Rehabilitation involves repairing pavement repairs to reset deterioration.
Common Maintenance Technique for Pavements
A relatively inexpensive preventive maintenance treatment earlier in the pavement’s life cycle,
while it may only bring a slight improvement in the condition of the pavement, still makes a tremendous
difference if you consider that it may postpone or avoid the need for a much more expensive treatment
later.
Categories of Pavement Maintenance
▪ Pavement Preservation - programs and activities employing a network level, long term strategy
that enhances pavement performance by using an integrated, cost-effective set of practices that
extend pavement life, improve safety, and meet road user expectations.
▪ Pavement Rehabilitation - structural enhancements that extend the service life of an existing
pavement and/or improve its load-carrying capacity.
▪ Pavement reconstruction - replacement of the entire existing pavement structure by the
placement of the equivalent or increased pavement structure.
TYPES OF CRACKS
Name: Alligator cracks
Definition: It is an interconnected cracks resembling an alligator's skin.
Cause: Heavy traffic or aging.
Solution: Prompt maintenance is needed.
Name: Longitudinal cracks
Definition: Run parallel or perpendicular to the pavement.
Cause: Due to temperature changes or traffic loads.
Solution: Timely repairs prevent further damage.
CE 315 EC8 – Group #5: Structural Design of Railways and Pavements
Name: Transverse crack
Definition: It is a type of pavement distress where cracks form at right angles to the road. These cracks are
typically straight and can span the entire width of the pavement surface.
Cause: various factors like temperature changes or poor pavement design.
Solution: Timely repairs are necessary to prevent their spread and maintain a safe pavement surface.
Name: Block cracking
Definition: It is a pavement issue where interconnected rectangular or block-shaped cracks form on the
road surface.
Cause: It happens due to aging, traffic loads, or inflexible pavement.
Solution: Timely maintenance is crucial to prevent further damage.
Name: Reflection cracks
Definition: Existing cracks in lower layers reflect onto the surface during overlays.
Cause: the existence of fractures in the older pavement layers that spread into the new pavement layer as
traffic loads pass over the cracks and because of temperature changes.
Solution: Proper techniques like crack sealing or milling are needed.
Name: Edge crack
Definition: Travels along the inside edge of a pavement surface within one or two feet.
Cause: The most common cause for this type of crack is poor drainage conditions and lack of support at
the pavement edge.
Solution: As a result, underlying base materials settle and become weakened.
Name: Slippage crack
Definition: Crescent or half-moon-shaped cracks having two ends pointed away from the direction of
traffic.
Caused: They are produced when braking or turning wheels cause the pavement surface to slide and
deform.
Solution: It is necessary to remove the surface course and replace it. The failed area should be taken up to
the point where a good bond is found between the old and new pavement courses.
PAVEMENT MAINTENANCE
Crack Sealing and Filling - prevents the intrusion of water and incompressible materials into cracks. The
methods vary in the amount of crack preparation required and the types of sealant materials that are
used.
Crack Sealing - is the placement of materials into working cracks. Crack sealing requires thorough crack
preparation and often requires the use of specialized high-quality materials placed either into or over
working cracks to prevent the intrusion of water and incompressible materials.
Crack Filling - places materials into non-working or low movement cracks to reduce water and
incompressible material infiltration. it requires less crack preparation than sealing, and the filler materials
may have lower performance requirements.
CE 315 EC8 – Group #5: Structural Design of Railways and Pavements
Patching - patching material can be just about any Hot Mix Asphalt (HMA) or cold mix asphalt material as
well as certain types of slurries. Typically, some form of HMA is used for permanent patches, while cold
mix is often used for temporary emergency repairs.
Pothole Repair - potholes are formed due to water's expansion and contraction under the pavement,
weakening the road's surface. The weight of vehicles further breaks down the pavement, creating
potholes.
Resurfacing And Overlay - involves the application of approximately 2 inches of asphalt concrete to the
existing surface or pavement of the road to help prolong the life of the road. Overlay or resurface treated
roads might undergo repairs to fix cracks and potholes. these repairs are performed before the overlay or
resurface and won't be visible after.
Asphalt Overlay - used for minor surface issues in asphalt like cracks and starting potholes. If subgrade
and asphalt integrity are intact, overlay suffices, requiring no milling for a simpler and faster process. prior
maintenance may include hole filling, crack smoothing, and cleaning.
Asphalt Resurfacing - this process involves removing some surface layer, addressing damaged areas
without excavation. after cleaning, a new surface layer is added. asphalt contractors inspect to determine
the needed depth for structural and visual improvement. Although involved, it remains a more affordable
option than complete asphalt replacement.