Welcome to the lecture

1
Welcome to the lecture!

• Unit CE113 Construction Practice
• Roadworks

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Objectives of the lecture

• To introduce the methods and techniques of road
  construction

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Learning outcomes

• By the end of the lecture, the student will
• understand
• The methods and techniques of road construction
• The key considerations in the design and
  construction of roads

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Roadworks - Outline

• Earthworks
• Construction of pavement
• Equipment and plant
• Road geometry
• Conclusions

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History of Highway Construction

• Stem from invention of the wheel - Samaria 3000
  BC.
• Earliest UK road - log raft over the Somerset
  peat bogs to Glastonbury 2500 BC.
•  Romans- built 50,000 miles of road throughout
  Europe
•  - straight from hill top to hill top, less
  chance of ambush, wagons could not easily turn.
•  - constructed above ground level (defence) -
  HIGHWAY.
•  - 3 types depending on usage levelled earth,
  gravel and paved.
•  Post Roman- Britons had no need to travel, roads
  deteriorated, used for building material.
•  1765- John Metcalf road design included surface
  drainage and a good foundation of large stones
  (sub base) supporting finer material.
•  1820- Macadam developed cheaper road with camber.

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Earthworks

• Preparation of the soil to obtain the right
• level
• gradient
• profile
• strength
• Cut and fill
• Concerns
• balance of cut fill quantities
• side slopes
• treatment of compressible soil

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Earthworks

• Side slopes
• Non-cohesive soils
• Natural angle of repose
• Cohesive soils
• Height of bank

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Earthworks

• Treatment of compressible soil
• Removal
• Blasting
• Overloading
• Jetting
• Stabilisation
• Involves mixing the sub-grade with agents
  (cement, lime, bitumen, liquid chemicals)
• The objective is to increase the strength of the
  sub-grade

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Construction of pavements

• Flexible pavements
• Elastic
• Three main layers
• Surfacing
• Wearing course
• Base course
• Road base
• Sub base
• Supported by Sub-grade

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Pavement Sub-grade

• Strength of sub-grade determines thickness of
  pavement needed
• Usually measured by the Californian Bearing Ratio
  (CBR) test
• If CBR of sub-grade is too low then ground
  improvements necessary

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Californian Bearing Ratio (CBR)
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Construction of pavements

• Rigid pavements
• Rigidity does not deform under stress
• Concrete air entrained increases resistance to
  frost damage and de-icing salt corrosion
• Reinforcement may be bars or mesh. Continuous
  rigid pavements have heavy reinforcement
• Joints used in non-continuous pavements to
  allow for thermal movement. Includes a filler
  and surface sealant

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Construction of pavements

• Rigid pavements laid as single layer by
  concrete paver

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Construction of pavements

• Surface water drainage
• Water causes damage and reduced skid resistance
  and should be removed as soon as possible
• Need an adequate surface drainage system
• Key issues
• Intensity of rainfall
• Size of catchment area
• Duration of storm or time of concentration and
• Permeability factor of the surfaces.

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Urban single carriageway
Rural single carriageway
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Road geometry

• Standard size of traffic lane 3.65m

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Equipment and plant

• Excavate only
• Ripper, Grader
• Excavate and load
• Back hoe / Back actorFace shovel/ Forward
  loader DraglineBucket wheel excavator
• Haul and deposit
• Lorries Dump trucks Conveyors
• Excavate, load, haul and deposit
• Bulldozer Scraper Elevated scraper
• Compact
• Smooth wheeled roller Pneumatic roller
  Vibratory roller

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Equipment and plant
Bulldozer
Planer
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Equipment and plant
Wheel loader
Excavator
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Equipment and plant
Dump truck
Grader
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Equipment and plant
Paving machine
Chip spreader
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Equipment and plant
Vibratory roller
Dead weight roller
7 Wheel pneumatic roller
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Conclusions

• Good roadworks ensure
• Strong subgrade
• Strong pavement layers
• Adequate surface water drainage and
• Appropriate road geometry.