Road Works

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Welcome to the lecture!

Roadworks

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Objectives of the lecture

To introduce the methods and techniques of road

construction

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Learning outcomesBy the end of the lecture, the student willunderstand:

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 goodfoundation 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 quantitiesside 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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EarthworksTreatment 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 layersSurfacing

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 BearingRatio (CBR) test

If CBR of sub-grade is too low then ground

improvements necessary

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Californian Bearing Ratio (CBR)CBR (%)

Depth of water table from formationlevel

Type of soil PlasticityIndex(%)

More than 600mm 600 mm or less

Heavy clay 70605040

22

2.53

11.522

Silty clay 30 5 3Sandy clay 20

10 67 45Silt

2

1

Sand (poorlygraded) Non-plastic 20 10Sand (well graded) Non-plastic 40 15Well graded sandgravel Non-plastic 60 20

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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 toallow for thermal movement. Includes a filler andsurface sealant

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Rigid pavements laid as single layer byconcrete paver

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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 onlyRipper, Grader

Excavate and loadBack hoe / Back actor;Face shovel/ Forward loader; Dragline;Bucket

wheel excavator

Haul and depositLorries; Dump trucks; Conveyors

Excavate, load, haul and depositBulldozer; 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 loaderExcavator

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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 rollerDead 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.

Documents

Road Works