roadbed construction

8/12/2019 Roadbed Construction

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Roadbeds underlie highway pavementstructures and the ballast and track on whichtrains move.

Unless there is a bridge, tunnel, or otherspecial structures, this roadbed is constructedof in-situ soils or on earth embankments.


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CONTRACTUAL, MANAGEMENT, AND

QUALITY ASPECTS OF CONSTRUCTION Organizing to Carry Out Construction

Competitive bids

Payments to contractor usually is on a unitprice basis.

Construction contracts are directed and carriedout by the management staff and workers ofcontractors or by subcontractors employed bythem.


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Quality Assurance in Construction

Construction plans and specificationsstipulate many requirements that are tobe met by materials or construction

procedures.Two approaches for obtaining them:

a) Manner and method spell out in detail thematerials to be supplied or the procedures

to be followed.b) Result or End result stipulates the desired

end product and leaves manner and methodto the contractor.


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Weather Effects on Construction Precipitation as rain snow, high winds, and

extremely hot or very cold temperatures canslow or halt certain construction operations.


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CLEARING THE SITES

Site clearing in rural areas

Site clearing in urban areas


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GRADING OPERATIONS Grading an inclusive term to describe

construction operations between site clearingand paving.

Detours are carefully planned, signed, andoperated so that traffic flows freely.


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Excavation Excavation the process of loosening and

removing earth or rock from its originalposition in a cut and transporting it to a fill orto a waste deposit.

Selection of equipment depends on the natureof the material, how far it is to be moved(hauled), and the method of disposal.

Materials are usually described as rock,

loose rock, or common with commonsignifying all materials not otherwiseclassified.


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Where material is moved less than about

200ft of steeply downhill, drifting with a trackor wheel type bulldozer.

For moderate and longer hauls, self loadingscrapers pulled by rubber-tired hauling units

and push-loaded by tractors offer low costs. For hauls of considerable length over the

public highways where axle loads are limited,rear- or bottom-dump trucks loaded by front-

end loaders, power shovels, or belt conveyorsmay be cheapest.


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bulldozer


11/28Pull-type scraper


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rear- or bottom-dump trucks


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Payment for excavation commonly is made at

a bid price per cubic yard measured inplace in the space originally occupied.

This unit price includes payment forloosening and loading the material,

transporting it any distance less than thefree haul limit, and spreading andcompacting it in the fill.

Payment for light clearing and grubbing andfor trimming cut and fill slopes is also includedin the unit price for excavation.


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Slides and Slipouts The side slopes of all cuts are steeper than

the original ground surface and those of highfills commonly are relatively steep in order toreduce the amount of embankment.

Payment for slides on cuts commonly is madeunder the excavation item for the project.


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Overbreak Presplitting Overbreak occurs in rock cuts when material

outside the staked backslopes becomesloosened and falls or is removed along withthe intended excavation.

Presplitting is a drilling and blasting procedurethat may be employed or even specified tocontrol overbreak and give a uniform face tothe backslope of rock cuts.


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EMBANKMENT Embankment describes the fill added above

the low points along the roadway to raise thelevel to bottom of the pavement structure.

Materials for embankment commonly comesfrom roadway cuts or designated borrowareas.


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Free Haul - Overhaul When the material is moved a distance

greater than this free-haul distance, it is usualto pay for the added transportation under abid item called overhaul.

Units for overhaul are commonly the station-yard or cubic yard-mile.


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CONSTRUCTION OF FILLS AND

EMBANKMENTS Principles of Embankment Construction

At one time, fills, weather of rock or earth,were constructed to full height by enddumping from the transporting vehicle.

Today, engineers agree that properembankment construction requires that the soilbe spread in layers, moistened or dried to

something near an optimum moisture content,and compacted.


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Control ofEmbankment Construction Two basically control procedures for assuring

a specified embankment density.

1. State the expected end result which is theminimum acceptable value for relativecompaction, and to make sure, by fielddensity tests, that the specified density isobtained.

2. State the manner and method for constructingthe embankment.


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COMPACTION EQUIPMENT Tamping rollers

Grid rollers

Pneumatic-tired rollers Smooth-tired rollers

Vibratory compactors

Hauling and spreading equipment


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Tamping rollers


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Grid rollers


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Pneumatic-tired rollers


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Vibratory compactor


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Payment for Embankment

Construction Methods of payment for embankment

construction vary.

Some agencies , specify that the price percubic yard of excavation or of borrow shallinclude all charges for compaction, forwater as needed, or for aerating the soil.

Others, pay separately for water. Still others pay for rolling, either at a bid price

per hour of rolling with an acceptable roller orat a bid price per cubic yard of material.


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FINISHING THE ROADBED Finishing describes a number of operations

associated with shaping the roadbed and therest of the cross section.

Surfaces that will underlie the traveled wayand shoulders are compacted and smoothedto close tolerance.

Roadside and other ditches, backslopes in

cuts, sideslopes in embankments, androadside areas will be dressed to therequirements set by the plans andspecifications.


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There is no specific pay item covering thesefinishing operations; rather the contractor isinstructed to include these costs in other bid

items.


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THANK YOU!

roadbed construction

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