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G. THE HIGHWAY CROSS SECTIONAL ELEMENTS

1. Carriageway and Lane Width

Carriageway is the portion of the road on which the vehicles are expected to travel. The four

basic types of road layout are Two-lane carriageways, Three-lane carriageways, Dual two-lanecarriageways and Dual three-lane carriageways.

Lane width has an iportant bearing on highway capacity, and the standard recoended

for classified roads is !."# wide lanes. $%ee &igures below'

(. %houlders

) shoulder is the portion of the roadway contiguous with the travelled way for

accoodation of stopped vehicles, for eergency use, and for lateral support of base and surface

courses. Well-designed and properly aintained shoulders are necessary on rural highways with

any appreciable volue of traffic.

The standard width of shoulder is (.*#. %houlders are sloped to drain away fro the

travelled way. The slope adopted for shoulders is usually 1 in (+ or #.

With bituinous paveents, shoulders should be constructed of gravel to offer good

contrast to the paveent. )s such, the through traffic lanes should be clearly defined at all ties,

particularly at night or in incleent weather.

The advantages of shoulder are as follows

a' %pace is provided for stopping free of the traffic lane due to otor trouble, flat tyre, or other

eergency. ehicles stopped upon the paved surface of the highway introduce a high

accident potential.

b' %pace is provided for the occasional otorist who desires to stop to consult road aps,

to rest, or for any other purpose.

c' %pace is provided to escape potential accidents or reduce their severity.

d' %oe types of shoulders contribute uch to the appearance of the highway.

e' The capacity of the highway is iproved. /nifor speed is encouraged.

f' %pace is provided for aintenance operations.

g' Lateral clearance is provided for signs and guardrails.

h' %tructural support is given to the paveent.

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!. Caber and crossfall

0rovision ust be ade for the run-off of surface water fro the carriageway, shoulders,

etc., by sloping the carriageway into the sideearth drain or concrete drains.

&or a cabered carriageway, the slope is usually 1 in 2+ or (.#. while for a shoulder, the

slope is usually 1(+ or #.

2. 3erbs

3erbs are used for various purposes including4

a' to control drainage,

b' to act as deterrents to vehicles leaving the paveent at ha5ardous points,

c' to delineate the edge of paveent,

d' to present a ore finished appearance, and

e' to assist in the orderly developent of the roadside.

6ften, a 7erb serves two or ore of these purposes. To be considered a 7erb, soe raised

aspect or vertical eleent is re8uired. 3erbs are needed ostly on highways in urban areas.

There are two general classes of 7erbs 9:arrier; and 9n urban areas, roadside drains are usually reinforced concrete rectangular or trape5oidal

open or covered channels.

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H. THE ROAD PAVEMENT

The odern road paveent is usually coposed of several layers of aterial of differing

8uality4 the strongest aterial being placed upperost and foring the actual running surface.

There are basically two types of paveents &lexible paveent and =igid paveent.

1. &lexible 0aveent

) flexible paveent can be defined as a structure that aintains intiate contact with and

distributes loads to the subgrade and depends on aggregate interloc7, particle friction, and cohesion

for stability. ) flexible paveent is usually coposed of the subgrade, sub-base, base, and

surfacing. $see &ig. 1'.

a. The %ubgrade

This is the foundation layer that eventually supports all the loads that coe onto the

paveent. >n soe cases, the subgrade will siply be the natural earth surface. >n other

and ore usual instances, it will be copacted soil existing in a cut section or the upper

layer of an eban7ent section.

b. The %ub-base

This is a layer of granular or stabili5ed aterial that ay or ay not be included as part of

the flexible paveent. >t will be necessary to use sub-base layer in cases where

- the subgrade soil is extreely wea74

- frost action in the area is severe4 and

- suitable sub-base aterials are cheaper than base aterials of higher 8uality.

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c. The :ase

The base is a layer $or layers' of very high stability and density. >ts principal purpose is to

distribute or 9spread; the stresses created by wheel loads acting on the wearing surface so

that the stresses transitted to the subgrade will not be sufficiently great to result in

excessive deforation or displaceent of that foundation layer.

d. The %urfacing

>t is desirable that the wearing surface should possess the following characteristics

i. ust be capable of withstanding the wear and abrasive effects of oving vehicles,

ii. ust possess sufficient stability to prevent it fro shoving and rutting under traffic

loads,

iii. ust prevent the entrance of excessive 8uantities of surface water into the base and

subgrade fro directly above.

The wearing surface ay be bituinous surface treatent used for low-cost, light-traffic roads

with thic7ness less than (# $1 inch'. &or heavily travelled routes, the wearing surface is asphalt

concrete with thic7ness of up to 1#+ $" in.' or ore.

(. =igid 0aveent

Concrete surfaces and bases are fre8uently classed as rigid paveents. The ter 9rigid; iplies

that paveents constructed of this aterial possess a certain degree of 9bea strength; that perits

the to span or 9bridge over; soe inor irregularities in the subgrade or sub-base on which they

rest.

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)s a result of rigid nature, inor defects or irregularities in the supporting foundation layer ay

not be reflected in the surface course. Eaturally, defects of this type are certainly not desirable, as

they ay lead to failure of the paveent through crac7ing, brea7ing, or siilar distress.

=igid paveents are usually ade of 0ortland ceent concrete and this ay be defined as a

plastic and wor7able ixture coposed of ineral aggregate such as sand, gravel, crushed stone, orslag, interspersed in a binding ediu of ceent and water.

When first cobined, the aterials listed for a plastic wor7able ass that ay be easily

handled and shaped into any desired for. ) short tie after ixing, the concrete begins to stiffen

or 9set; because of cheical reaction between the ceent and water in the ixture, and in a

relatively short tie it fors a dense, hard ass that possesses considerable copressive and

flexural strength.

When properly designed and constructed, concrete roads and streets give any advantages

i. They are capable of carrying alost unliited aounts of any type of traffic with ease,

cofort, and safety.

ii. %urfaces of this type are sooth, dust-free, and s7id-resistant.

iii. %urfaces of this type have a high degree of visibility for both day and night driving.

iv. They are econoical in any locations because of their low aintenance costs and

relative peranence.

The principal use of concrete paveents has been in the construction of heavily travelled roads

and city streets, including those in residential, business, and industrial areas.

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I. EARTHWORK QUANTITIES

>n the geoetric design of a highway, it is alost always certain that the final grade line will

definitely not follow the existing ground level in order to satisfy certain design controls and criteria.

Thus, there will alost always be areas of cutting away portion of the existing ground and areas of

filling up soe portions. The process of cutting and filling portions of the existing ground is calledearthwor7 operations in highway.

%ince earthwor7 operations for a substantial part of any rural highway proBect and

probably represent the largest variable factor in constructional costs, detailed attention ust be paid

it.

There are basically two standard ethods of calculating earthwor7 8uantities naely

)verage ?nd )reas $)vgendarea' ethod and the 0risodial ethod.

?nd )reas

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J. MASS HAUL DIAGRAM

1. :ul7ing and shrin7age of aterial

%oe aterials such as roc7 and chal7 increase in volue when excavated and subse8uently

copacted to for an eban7ent and this phenoenon is tered bulking. 6ther aterials suchas gravel, sandy soils, and clays show a decrease in volue as a result of ore thorough copaction

and this is teredshrinkage.

The shrin7age factor is the ter used to describe the relationship between the excavated

volue and the volue of fill. ?xcavated 8uantities can therefore be converted to volue of

copacted fill by the use of this shrin7age factor, which could be ta7en as 1.(, thus

excv. G 1.( fill

(. Haulage of n road schees, the earthwor7s are usually planned so that, where suitable, aterial

excavated fro a cutting can be used to for an eban7ent further along the road. )s this ay

entail carting $or hauling' the aterial over a considerable distance, the cost of haulage is ta7en into

account by the contractors a7ing allowance for haulage in the rates 8uoted for the ite$s' covering

excavation in cutting and foring of eban7ents.

!. The

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d. The vertical distance between any two points on the diagra is easure of the net

volue of earthwor7s between these sections.

e. )ny hori5ontal line on the diagra, including the base line, cuts the diagra at sections

between which earthwor7s are balanced.

f. The length of any such balance line represents the axiu haulage distance between

the sections.

2. ?arthwor7 Terinologies

a' HaulI This is the volue of aterial ultiplied by the distance through which it is

oved. >t is usually expressed in station etre. $Haul G olue J Distance'

b' Freehaul a! O"erhaulI 6n certain road contracts, the :ill of Kuantities ay be

drawn up so that the ites relating to general excavation and copaction of aterial

include haulage only within a specified distance, called the freehaul distance. Haulage

over and above this distance is paid for under an additional ite, and the extra distance

is tered the overhaul distance. The aounts of aterial involved under these ites are

tered the freehauland overhaulrespectively, and these volues can be ascertained by

reference to the ass haul diagra.

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c' E#$$% HaulI When the contractor is faced with large haul distances, it is ore

econoical for hi to waste aterial within the entire area of construction and borrow

aterial fro nearby areas than to pay for the expensive overhauling. 6n any given

schee, the econoic haul distance will vary considerably as it depends both on the

availability of suitable borrow aterial and of nearby sites where excavated aterial canbe wasted.

The econoic distance of haulage is tered the Economic Hauland can be deterined

by e8uating the cost of roadway excavation plus overhaul and tipping in eban7ents

with the cost of borrow pit aterial $include original cost as well as cost of excavation,

hauling and tipping borrow in eban7ent' plus excavation, haul and wasting of

roadway aterial within the freehaul distance.

d' Wa'(e a! )$rr$*I