Road Design & Construction

Note: The source of the technical material in this volume is the ProfessionalEngineering Development Program (PEDP) of Engineering Services.

Warning: The material contained in this document was developed for SaudiAramco and is intended for the exclusive use of Saudi Aramcosemployees. Any material contained in this document which is notalready in the public domain may not be copied, reproduced, sold, given,or disclosed to third parties, or otherwise used in whole, or in part,without the written permission of the Vice President, EngineeringServices, Saudi Aramco.

Chapter : Civil For additional information on this subject, contactFile Reference: CSE11101 A.M. Al-Khunaini on 8732653

Engineering EncyclopediaSaudi Aramco DeskTop Standards

Road Design And Construction

Engineering Encyclopedia Civil

Road Design and Construction

Saudi Aramco DeskTop Standards

CONTENTS PAGE

Road Terminology, Standards And Materials..................................................1

Material Properties.........................................................................................15

Road Layout And Design...............................................................................36

Drainage.........................................................................................................63

Pavement Design ...........................................................................................83

Road Construction Techniques ....................................................................113

Work Aid 1 ..................................................................................................133

Work Aid 2: Determining Peak Runoff (Discharge)...................................134

Work Aid 3: Ditch Design Nomograph ......................................................136

Work Aid 4 ..................................................................................................137

Work Aid 5 ..................................................................................................138

Glossary .......................................................................................................139



Saudi Aramco DeskTop Standards 1

ROAD TERMINOLOGY, STANDARDS AND MATERIALS

This lesson addresses the common terminology used in road construction, it describes thecomponents of the road, it discusses the pertinent Saudi Aramco standards for roadconstruction, and it reviews some of the common materials encountered in road constructionin Saudi Arabia.

Pavement Types

Rigid

Rigid pavements are seldom used in Saudi Arabia, and therefore their discussion will belimited. A rigid pavement has a portland cement concrete (PCC) surface. Rigid pavement istypically supported by a granular base material that is porous enough to allow water that getsunder the pavement to drain quickly away. The granular base material rests on compactedsoil (subgrade).

Freshly-placed concrete cools quickly and loses a large amount of water in the first hoursafter construction. These events cause concrete to contract, resulting in cracks. Transversecontraction joints are sawed every 4-12 m (12-40 feet) in the rigid pavements soon afterconstruction. This causes cracks where they can be controlled and maintained. The areabetween joints is termed a slab.

Each PCC slab is considered to be "rigid", as the deflection of the slab under the load is verysmall. Concrete pavement is designed thick enough that the traffic loads are almost uniformlydistributed along the top of the granular base. This stress is small enough so that the base andsubgrade are only lightly stressed by the tire loads. The base under a PCC pavement performsprimarily as a drainage layer instead of a structural layer. Figure 1 shows the distribution ofstresses and the typical layers present in a rigid pavement roadway.

Rigid pavements have higher construction costs than asphalt (flexible) pavements. However,rigid pavements may be preferred in the following instances:

For heavily-traveled roads in large cities. Rigid pavements last longer beforemajor maintenance is required (20-30 years). This means fewer maintenancecaused traffic interruptions will occur compared to the shorter life of flexiblepavements (10-20 years).

For pavements in fueling areas and chemical processing areas. PCC pavementsgenerally will not be harmed by spilled fuel or chemicals, but asphalt isdissolved by petrochemicals and will deteriorate.




FIGURE 1

STRESS DISTRIBUTION IN RIGID PAVEMENT

Subgrade (Foundation Soil)

Tire Tire Contact Stress

Subgrade

Tire

Tire Contact Stress

Surface

Base

Subbase

STRESS DISTRIBUTION IN FLEXIBLE PAVEMENT

BASE (SUBBASE)

Uniform Stress DistributionPCC Slab

FIGURE 2




Flexible

A flexible pavement has an asphaltic concrete (AC) surface consisting of aggregate bound byasphalt cement. Below this surface, the pavement structure consists of several AC orunbound granular layers which rest upon the compacted subgrade soil.

Because AC is much more flexible than the PCC (rigid) pavement, the vehicle loads spreadout much more slowly through the AC pavement structure. Thus, the layers beneath the ACsurface may need to be stronger than layers beneath a PCC surface. Figure 2 shows thegeneral distribution of stresses and typical layers present in a flexible pavement.

In a flexible pavement layers typically decrease in strength from surface to subgrade sincethe amount of stress decreases as the depth below the load increases. The pavement structureshouldbe thick enough so that the stress at the top of the subgrade is small and does not affect it.

Asphalt concrete is the most commonly used road building material: it is found in over 75%of pavements. Because of cost factors even PCC pavements are routinely "overlaid" by 2.5-10.0 cm (1-4 inches) of AC when they require major maintenance.

Unpaved

Unpaved roads are often constructed when the expected volume of traffic is low, as in remotelocations. They consist of one or more granular layers resting on compacted subgrade. Loadsare distributed through the layers of an unpaved roadway in much the same manner asflexible pavements. Because none of the layers contain an added binder (such as asphaltcement), the unpaved road depends upon a natural binder (usually clay) to hold the largeraggregate together. The combination of clay and large aggregates give the unpaved structureseveral desirable properties:

Stability: The type and quality of fines (binder clay) should be sufficient tobind the large aggregate but not cause it to lose the aggregate-to-aggregatecontacts which carry the load.

Abrasion resistance: The larger aggregate should provide necessary surfaceroughness so that friction at tire/surface contact points will allow a vehicle tostop and turn curves safely.

Watertightness: Rainfall should drain off the surface quickly and not permeatethe pavement structure.

Water retention: Some moisture must be retained so that air-borne dust causedby traffic will be kept low. This may require application of an admixture, suchas calcium chloride or sodium chloride, in dry regions.




Road Cross-Sections/Components

Once the road project has been designed, a set of plans and specifications are developed toinstruct the project contractor in the details of the project. One important part of these plans isthe typical section. The typical section gives information on pavement layer thicknesses andmaterials, side slopes, side ditch dimensions, and many other important details. Figure 3shows a typical simple cross-section for a roadway with its components. Informationregarding these components is generally given in a set of plans.

Non-Pavement Cross-Sections/Components

The pavement cross-section is different for the three types, but the remaining cross sectioncomponents are similar for all pavement types. Items such as shoulder slope and pavementslope are specified so that the pavement will drain properly. The slopes outside the shoulderin fill areas, the fore and back slopes in cut areas, and the shoulder widths are specified so thatthe roadside will be safe for any errant vehicle that may leave the traveled way. Ditch widthsand types, although set by the drainage needs, must be considered along with the side slopeswhen evaluating roadside safety.

Flexible Pavement Cross-Sections/Components

Flexible pavements have four basic layers, as shown in Figure 4b.

Subgrade

The subgrade is the soil upon which the pavement structure is constructed. It is sometimesreferred to as the foundation soil. It may be material which is brought to the project site andplaced (for fill sections) or material found in place (for cut sections). Subgrade materialsrange from weak clays to strong sands and gravels. These materials affect the pavementdesign thickness, with weaker subgrades requiring a thicker pavement structure than strongersubgrades. The top portion of a weak subgrade may be strengthened by mixing it with betteraggregates or with a stabilizing material, which changes the chemical composition of thesubgrade, and then compacting it to a greater density.




GENERALIZED ROADWAY CROSS SECTION

subb

ase

(if d

esire

d)

base

slop

esl

ope

slop

e

slop

e

slop

e

slop

e

pav

emen

t

trave

led

way

fill

slop

e s

houl

der

sho

ulde

r

fore

slop

e

sid

e

ditc

h

bac

k

slop

e e

xist

ing

grou

nd

slop

e

typi

cal

cut

sub

grad

e

typi

cal

fill

exi

stin

g

grou

nd

( not to scale )

FIGURE 3




FIGURE 4

AC Surface

Base (Granular or AC)

Subbase (Granular or AC)

Subgrade

b) Flexible

Granular Surface with Some Clay Binder

Granular Base

Subgrade

c) Unpaved

PCC Surface

Granular Base (Subbase)

Subgrade

a) Rigid

PAVEMENT LAYER TERMINOLOGY

Note: subgrade can be stabilized if desired.




The subgrade is not designed to carry much load. The layers above the subgrade are designedto spread the load out so that the pressure caused by traffic is very small when it reaches thetop of the subgrade. Very little consolidation or settlement of the subgrade should occurunder these small loads.

Subbase/Base

The subbase is sometimes omitted from the pavement structure. If present, it is placedimmediately above the subgrade. This layer consists primarily of an untreated aggregate(coarse sand or lower quality stone) with a small amount of clay to add stability to the layer.Subbase material should be locally available, strong enough to carry some load, andinexpensive.

The base layer is located between the subbase and surface layers. It is similar to the subbaseexcept that the aggregate particles are stronger than those found in the subbase. Basematerials may have to be shipped from a distant location to the project site. This cansignificantly increase the cost of constructing the base layer. On pavements supporting heavyloads, the base layer may consist of an AC mixture to provide necessary added strength.

Surface

The surface of a flexible pavement is constructed of asphaltic concrete and must be able toresist the high stresses encountered near the roadway surface. The AC consists of a strongaggregate that is held together by asphalt cement to give the aggregate the required stability.It must also provide a safe, smooth riding surface with good skid resistance.

A surface layer is often divided into two layers with two distinctly different purposes. Bothlayers are made of asphaltic concrete. The lower surface layer is called the binder layer. It ismade of relatively large pieces of aggregate held together by asphalt cement, and it providesthe strength necessary to resist the large surface loads. The upper surface layer is the wearingcourse. Its primary function is to provide skid resistance. The aggregate size in the wearingcourse is typically smaller than that found in the binder. It also contains more asphalt cementto help repel water.

Unpaved Road Cross Section Components

Low traffic volume roadways often are not paved. The unpaved surface layer is similar to thebase layer found in a flexible pavement in both its construction and performance. Figure 4cshows the layers found in an unpaved road. Sometimes a granular base of lower-qualitymaterials is placed between the surface and subgrade, but often a thick layer of surfacematerial is placed directly on the subgrade.




The surface must also have the right combination of clay fines and aggregate to achieve thestability, abrasion resistance, watertightness, and water retention properties previouslymentioned in the section describing "Pavement Types."




Rigid Pavement Cross Section Components

Rigid pavements have some of the same layers that are found in flexible pavement. However,the function of the pavement is different. Figure 4a shows the typical cross section of a rigidpavement.

The surface consists of portland cement concrete which carries virtually all of the appliedloads. Little stress is transferred to the base, which serves primarily as a drainage layer forremoving water from under the pavement. The subgrade will carry little additional load,because the pavement structure spreads the load out over a large area at the subgrade surface.

Summary

There are three main types of pavements: rigid, flexible, and unpaved. Flexible pavementsare the type most frequently built by Saudi Aramco. They consist of a top surface of asphaltlaid directly over an aggregate layer called the base. Another aggregate layer of lower qualitymaterial called the subbase is frequently placed beneath the base. The soil on which thepavement layers rest is called the subgrade.

Drainage

The construction of a road across an existing piece of land causes special drainage problems.The roadway, including the pavement, shoulders, and side slopes, must be properly drained.Drainage across the land where the road is built will be disrupted, so flow of water from oneside of the road to the other side must be allowed.

When a road is constructed, one of the primary concerns is to get water off the pavementquickly so that standing water will not create a driving hazard. Some of this water may seepthrough joints or cracks in the pavement and infiltrate the lower pavement layers, which cansoften and weaken the subgrade. Water that falls on the shoulders and cut and fill slopes mustbe drained as well. Figure 5 illustrates some of the typical drainage techniques for roadways:




ROADWAY DRAINAGE COMPONENTS

pave

men

t

exis

ting

grou

nd

(cut

)

inte

rcep

ting

chan

nel

exis

ting

grou

nd

(fill)

toe-

of-s

lope

ch

anne

l

fill s

ectio

n

cut s

ectio

n

road

side

ch

anne

l

(not to scale)

gran

ular

bas

e/su

bbas

e

shou

lder

FIGURE 5




Toe-of-slope channel: Sometimes used at the bottom of fills, this channelcollects water from a fill slope and carries it to the nearest drainage area.

Intercepting channel: Water from the existing ground slope drains into thischannel in a cut at the top of the back slope and is deposited in the nearestchute for transport to a drainage area.

Chutes: Chutes carry water runoff from existing ground at the top of cut,down the side of the hill in the cut area, and into the nearest drainage area.They may be lined with PCC or riprap to prevent erosion.

When a road is built across a strip of land, the natural drainage pattern of the land isinterrupted. The design engineer should insure that water can collect on the uphill side of theroadway, drain from that side to the other, and disperse on the downhill side, withoutnegatively affecting the land on either side of the highway. Depending upon the amount ofwater to be carried, bridges, box culverts, or pipes may be placed so that water may flowproperly without disturbing the roadway traffic or weakening the ground on which theroadway is placed. Additional details will be covered later in the section of this module titled"Drainage".




Saudi Aramco Standards/Design Practices

Saudi Aramco Engineering Standards (SAES) set forth the minimum requirements for design,construction, and testing of various components found on a road or highway project.

Saudi Aramco Design Practices (SADP) expand upon and explain the information provided inthe Saudi Aramco Engineering Standards. When applicable, SADPs provide detailed, step-by-step design procedures or background explanations on computer programs used fordesign.

Several SAES and SADPs are directly applicable to road and highway design, construction,testing, and analysis:

SAES-Q-006 Asphalt Concrete Paving

SAES-Q-006 prescribes the minimum mandatory requirements governing the design andinstallation of asphalt concrete paving. It is based on three well known pavement designdocuments which are listed below. SAES-Q-006 does not contain those documents; instead itlists exceptions and additions to them. Some of those changes will be discussed in themodule.

Document Source Topic

Guide for Design ofPavement Structures

American Association of StateHighway & Transportation Officials(AASHTO)

Structural Design ofPavements

MS-1 Asphalt Institute Traffic Analysis

General Specifications forRoad and BridgeConstruction

Kingdom of Saudi Arabia All roadwayconstruction




SAES-S-030 Storm Water Drainage Systems

This standard establishes the minimum requirements for storm water drainage systems underthe operation and maintenance of Saudi Aramco. Stormwater drainage design is applicable toroads because the road often interrupts natural drainage basins. This necessitates thespecification of box culverts, bridges, and pipe culverts for transporting storm water from theupstream to the downstream side of a drainage basin. Secondly, the road alignment creates anew area with different drainage characteristics. This area must be drained for traffic safetyand to ensure the structural integrity of the pavement.

In the design of storm water drainage systems, determinations must be made of time ofrainfall concentration (using the Kirpich Formula) on the drainage area, frequency of stormreturn used in design of various facilities, rainfall intensity, rainfall quantity (using theRational method), and flow velocity (using Manning's Equation) in both pipes and openchannels. These items can then be used in determining the type and size of the drainagestructure and the type of protection required at the ends of a pipe or culvert.

The standard also specifies minimum pipe sizes, headwall requirements at pipe ends, manholesizes and locations, shape and protection of open channels, and materials from which stormdrains and road crossing culverts shall be constructed.

Installation and testing of pipes and culverts is not covered in detail in this standard. Thefollowing standards are specified for installation and testing:

SAES-S-020 for storm drains that are part of an oily water sewer system.

SAES-S-070 for general storm drains and culvert crossings.

SAES-Q-001 for construction of concrete structures used in the road drainagesystem.

Simple calculations for determining the quantity of flow used in storm water drainage systemdesign will be covered in a later section of this module. Saudi Aramco Design PracticeSADP-S-030 provides a detailed description of and several example problems using theformulas discussed in SAES-S-030. It also describes in some detail the applications andlimitations of these formulas.




MATERIAL PROPERTIES

The materials which comprise the pavement layers are very important in design. Thefollowing paragraphs will describe design properties of the subgrade, aggregate, and asphaltlayers of a pavement.

Subgrade

The subgrade is the supporting soil that the pavement lies on. In cut sections, subgradeconsists of the naturally occurring soil exposed when the topsoil is removed. The surface ofthe material is then compacted. In fill sections, soil is brought in to form the subgrade. It iscompacted in 6" (15 cm) layers.

Subgrade soils are described in descending order of grain size. They are composed of sand,silt, and clays. Sand makes the strongest subgrade, and it is least affected by water. If sandcan be prevented from blowing, it is the preferred subgrade material. Most Saudi Aramcosubgrades are sands. Clay is the least desirable subgrade because it is the weakest and mostaffected by water. Water causes clay to lose strength, and it causes some clays to swell,leading to cracking of the paved surface.

Several other terms are used to describe soils. Clay is called a cohesive soil because it stickstogether naturally. Sand and silt are not cohesive. They are called cohesionless soils.

Sand is composed of large particles. It is called a granular material, as are the bases andsubbases above it. Silts and clays are composed of small particles that cannot be individuallyidentified without a microscope. They are called fine-grained soils, or "fines."

Subgrade Classification

In the field, a subgrade soil is not usually composed of only one soil type. It is a mixture ofsand, silt, and clay. Classification systems group together soils which exhibit similarproperties. Once a soil has been classified, the road designer or road builder can predict theperformance of that soil because he knows what to expect from soils in that classification.

Gradation Analysis

Two laboratory tests are used to help classify soils. They are Gradation Analysis andAtterberg Limits. Gradation Analysis gives the particle size percentage breakdown of the soilbeing tested. This is achieved by sifting the soil through sieves with various sized openings.The #200 sieve (75 micron opening size) separates sand particles from silt and clay particles.The lower the sieve number, the larger the particle size.

Figure 6 shows the results of a Gradation Analysis test. The percentages of the soil passingcertain sieve sizes are joined by a smooth curve.




TYPICAL GRAIN SIZE DISTRIBUTION CURVE

100

90

80

70

60

50

40

30

20

10

0

0

19

4.75

2.00

0.85

0

0.42

0

0.15

0

0.07

5

0.01

0

0.00

2

0.00

1

Grain Diameter (mm)

No.

4

No.

10

No.

20

No.

40

No.

100

No.

200

Per

cent

Fin

er

Gravel

Sand

Coarse to medium Fine

Silt Clay

U.S. Standard Sieve Sizes

FIGURE 6




Atterberg Limits

The Atterberg Limits laboratory test is also used in the soil classification process. Water isadded to a mass of dried subgrade soil in small increments. The percentage of moisture atwhich the soil changes from a dry solid to a liquid consistency is noted. Figure 7 shows therelationship of the Atterberg Limits.

For classification, the two most important moisture content points are the plastic limit and theliquid limit. The plastic limit (PL) marks the % water where the soil changes from thesemisolid state to the plastic (easily deformable) state. The liquid limit (LL) marks the %water at which the soil changes from the plastic state to the liquid state. The plasticity index(PI) is defined as LL-PL.

AASHTO Classification System

Several different systems can be used to classify soils. For road-building purposes, AASHTOM-145 is most often used. Figure 8 gives the classification criteria.

There are 12 classification groups: A-1-a through A-7-6. Looking from left to right onFigure 8, the particle sizes of the soils decrease. The soils go from very good (strong) soils atthe left side to poor soils on the right side. The A-1-a is the best soil to build on; the A-7-6 isthe worst to build on. Most Saudi Aramco soils are A-1 and A-2 soils.

Use the following procedure to properly classify subgrade soils:

Assemble Atterberg Limit and Gradation Analysis test data.

Start in either column A-1-a or A-4 to determine if the soil fits the requirementsin that column. Start in column A-4 only if more than 35% of the soil issmaller than (passes) the No. 200 (0.075 mm) sieve.

Move one column to the right if the soil does not satisfy the requirements of thefirst column, then try again.

Stop as soon as the soil meets the requirements given in one of the columns.

In Figure 8, N.P. stands for "non-plastic." That means the soil has a P.I. of 3 or less.




ATTERBERG LIMITS

FIGURE 7

Sol

id

stat

eS

emis

olid

st

ate

Pla

stic

st

ate

Liqu

id

stat

e

Incr

easi

ng

moi

stur

e co

nten

t

Liqu

id

limit

(LL)

Pla

stic

lim

it (P

L)

Shr

inka

ge

limit

(SL)

Pla

stic

ity

Inde

x (P

I)

w =

0




AASHTO SOIL CLASSIFICATION SYSTEMG

ranu

lar M

ater

ials

(35%

or l

ess

pass

ing

No.

200

)

Silt

-Cla

y M

ater

ials

(Mor

e th

an 3

5% p

assi

ng N

o. 2

00)

A-1

A-2

A-7

Gen

eral

Cla

ssifi

catio

n

Gro

up c

lass

ifica

tion

A-2

-6A

-2-7

A-1

-aA

-1-b

A-3

A-2

-4A

-2-5

A-4

A-5

A-6

A-7

-5,

A-7

-6

Sie

ve a

naly

sis,

per

cent

pas

sing

:

No.

10

(2.0

0 m

m)

50 m

ax...

......

......

......

...

m)

30 m

ax50

max

51 m

in...

......

......

......

m15

max

25 m

ax10

max

35 m

ax35

max

35 m

ax35

max

36 m

in36

min

36 m

in36

min

Cha

ract

eris

tics

of fr

actio

n p

assi

ng N

o. 4

0 (4

25m

Liqu

id li

mit

Pla

stic

ity in

dex

40 m

ax

10 m

ax

41 m

in

10 m

ax

40 m

ax

11 m

in

41 m

in

11 m

in

40 m

ax

10 m

ax

41 m

in

10 m

ax

40 m

ax

11 m

in41

min

11 m

in

...

6 m

ax

...

N.P

.A

mm)

No.

40

(425

No.

200

(75

m):

Usu

al ty

pes

of s

igni

fican

t

cons

titue

nt m

ater

ials

Sto

ne fr

agm

ents

,

grav

el a

nd s

and

Fine

San

dS

ilty

or C

laye

y G

rave

l and

San

dS

ilty

Soi

lsC

laye

y S

oils

Gen

eral

ratin

g as

sub

grad

eE

xcel

lent

to g

ood

Fair

to p

oor

AP

last

icity

inde

x of

A-7

-5 s

ubgr

oup

is e

qual

to o

r les

s th

anLL

min

us 3

0. P

last

icity

inde

x of

A-7

-6 s

ubgr

oup

is g

reat

er th

anLL

min

us 3

0.

......

...




EXAMPLE PROBLEM #1AASHTO SOIL CLASSIFICATION SYSTEM

Given: For a given soil, LL = 12, PL = 7, PI = 5

The gradation analysis of the soil follows:

Sieve % Passing

No. 10 60No. 40 40No. 200 20

Find: The soil classification by the AASHTO SoilClassification System.

Solution:

Try A-1-a. More than 50% passes No. 10 sieve, so it does not fitthis classification.

Try A-1-b. It fits this classification

Answer: A-1-b




Strength Characteristics

In general, sand is stronger than silt, and silt is stronger than clay. Stronger subgrade soils willallow a thinner pavement to be designed. The strength of subgrade soils can be measured inthree major ways.

California Bearing Ratio - The California Bearing Ratio (CBR) test rates soil strength on anumbered scale. Zero means no strength; 100 or greater is a high strength rating. The CBR ofmost soils falls in the range of 1 to 30:

The typical CBR range for clay is 1-15. The typical CBR range for silt is 1-15. The typical CBR range for sand is 10-30.

Soil Support Value - SAES-Q-006 specifies soil support value (S) as the soil strengthparameter for designing asphalt concrete pavements. It is a dimensionless number whichranges from 1 to 10. The higher the number, the stronger the soil. Most Saudi Aramco soilswill have S values between 3 and 7.

There is no laboratory or field test for soil support value. It is found by first performinganother test (such as CBR), then correlating the two values. Saudi Aramco correlates CBR andS using Figure 9.

CORRELATION OF S WITH CBR

SOIL SUPPORT VALUE (S)

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0

1 2 3 4 5 10 20 30 40 50 100 200

CALIFORNIA BEARING RATIO (CBR)

FIGURE 9




Modulus of Subgrade Reaction, k - The modulus of subgrade reaction, k, is only used todescribe soil strength when designing a PCC pavement. The typical range of k value is 700-4000 kPa (100-600) psi. The higher the value, the stronger the soil.

Soil Compaction

Road subgrades are compacted for two primary reasons:

Increased density results in increased strength. Increased density leads to less settlement under wheel loads.

There are three main types of compaction equipment called rollers:

Vibratory rollers. Vibration is the best way to compact granular soils such asthose found in most of Saudi Arabia.

Sheepsfoot rollers. Projections (feet) on the rollers allow this type ofcompactor to work especially well in clays or silt-clay mixtures.

Pneumatic tire rollers. Rows of closely-spaced rubber tires roll over thesubgrade. Pneumatic tire rollers are used to compact both granular andcohesive soils.

Compaction Requirements - A laboratory "moisture density test" (AASHTO T99 orAASHTO T180) is performed on a soil to determine how well it can be compacted in the field.T99 is usually called the "Proctor Test." T180 is usually called the "Modified Proctor Test."The test gives two results: the maximum dry density and the optimum moisture content.

Maximum dry density is given in kg/m3 (pcf). It represents the density of the dry soil particlesif a good job of compaction is done in the field. The optimum moisture content is given inpercent. It represents the moisture content at which compaction of the soil will be easiest.

The construction crew is usually required to compact the soil to "95% of Modified Proctor."

For example, if the laboratory Modified Proctor test results for a soil are 1,700 kg/m3 (106pcf) dry density and 8.7% optimum moisture content, the soil must be compacted to at least95% of 1700 kg/m3 = 1615 kg/m3. If the actual field compaction is 1650 kg/m3 or 1675 kg/m3or 1725 kg/m3, those results are acceptable; 1610 g/m3 is not acceptable.

The compacted soil does not have to meet a specification for moisture content. The crew triesto reach a moisture content near optimum by spraying water onto the soil, but only because itmakes the compaction work easier. If the crew can achieve the required dry density at a lowmoisture content, that is acceptable.




Dry density and moisture content are checked at the job site by an inspector. He takes a smallsample of the soil and determines the dry density and moisture content according to AASHTOT191.

Bases and Subbases

The next layer above the subgrade is the base or subbase. Bases and subbases are granularmaterials such as sand and gravel which provide support for the asphalt concrete (AC) orPortland Cement concrete (PCC). In some cases, the granular materials also drain rainfallaway from the pavement.

Subbases and bases are made of similar materials, but the quality of the subbase material isusually lower than that of the base. Both layers are not always present in a pavement. Somepavements have only one granular layer. The subbase may not be present if the subgrade soilis firm. SAES-Q-006 states: "Where existing subgrade materials have a CBR of 5 or less, asubbase with a minimum CBR of 15 shall be provided with a minimum thickness of 20 cm (8in)."

The typical thickness range for a layer of base or subbase is 10 cm (4 in.) to 30 cm (12 in.).They are placed in compacted lifts of 15 cm (6 in.) thickness or less.

If the available granular material is of low quality, strength can be improved by addingapproximately 2% asphalt cement. The resulting material is called "asphalt treated base." It islike a low-quality asphalt concrete.

Strength

Any base material with a CBR greater than 40 is a good quality base. Standard SAES-Q-006gives four classes of base materials:

MOC Class A - CBR 100 MOC Class B - CBR 50 MOC Class C - CBR 50 Lime Treated MOC Class C - CBR 50 Portland Cement Treated

Because most treated bases are "asphalt treated base," MOC Class C Lime Treated or PortlandCement Treated will almost never be used.




Aggregate

Sand, gravel, and crushed stone are called aggregates. They are the materials most used inroad construction. Unpaved roads are composed entirely of aggregate (often with anadditional small amount of clay to bind the aggregate together.) Portland cement concrete andasphalt concrete are both more than 85% aggregate.

The aggregates used in granular bases and subbases, unpaved roads, and rigid and flexiblesurfaces share a common characteristic: dense gradation. Dense gradation means that bigaggregate particles and little aggregate particles are both present in sufficient quantity to givethe aggregate mix a high density. The holes between the big particles are filled by littleparticles (see Figure 10). In general, the denser the aggregate mix the stronger the base,subbase, unpaved surface, or asphalt concrete. For those uses, try to employ a densely gradedaggregate. For example, a compacted subbase with a density of 2,200 kg/m

3

(137 pcf) isusually a high density granular material.

In road construction, the maximum size of aggregate rarely exceeds 3.2 cm (1.25 in.). Whenlarger aggregate pieces are used, the aggregate mix is hard to work with. Fines (materialsmaller than a #200 sieve) are usually not desired. However, because it is almost impossible toexclude fines, a small amount (3-5% by weight) of fines is usually acceptable.

AGGREGATE GRADATIONS

FIGURE 10

(a) dense graded (b) open graded (c) excessive fines




Asphalt Concrete

Asphalt concrete is composed of aggregate held together with a black-colored cementing agentcalled bitumen. The proportions of materials in asphalt concrete are approximately 5%bitumen and 95% aggregate. The thicknesses of the asphalt concrete portions of roads varywidely, ranging from approximately 5 cm (2 in.) to 25 cm (10 in.), depending on the expectedtraffic on the roads.

Bituminous Materials

The black material which holds flexible pavements together is called a bitumen or abituminous material. Saudi Aramco uses two kinds of bituminous materials: asphalt cementsand cutbacks.

Asphalt Cement - Asphalt concrete is usually made out of asphalt cement and aggregate.Asphalt cement is a petroleum product which comes directly from the refinery. It is almostsolid at room temperature. Asphalt cement and aggregate are both heated to 250-325 F (120-163 C) then mixed together.

The various types of asphalt cement are graded on the basis of their viscosity. The typicalgrades of asphalt cement are listed below:

AC-5 AC-10 AC-20 AC-30 AC-40

The number associated with the name describes the viscosity. AC-5 has low viscosity; AC-40has high viscosity. The most important characteristic of bituminous materials is that theirviscosity changes as the temperature changes. If the temperature goes up, the asphalt cementbecomes softer. In a hot country such as Saudi Arabia, roads should be built with hard(viscous) asphalt cements so that the road will not become soft and weak at high temperatures.Thus, most roads in this climate will be built using a high viscosity asphalt such as AC-40.

Cutbacks - Asphalt cements must be heated to make them mix with aggregate. Sometimes,there is a need for bituminous materials which do not have to be heated to be useful. Forthese purposes, Saudi Aramco uses cutbacks. Cutbacks are asphalt cements which have beendiluted (cut) with a solvent such as gasoline or kerosene. The resulting material can besprayed onto surfaces or mixed easily with aggregate at relatively low temperatures.




Cutbacks are usually used for two purposes: as prime coats and tack coats. In both uses, thecutback is sprayed onto a surface. In a short time after being sprayed, the solvent evaporates,leaving a thin, sticky layer of asphalt cement. The process of evaporation is called "curing."Curing can take from minutes to days to occur.

A prime coat is sprayed onto the granular base material before the asphalt concrete is added.The prime coat fills voids at the top of the granular base layer and helps the asphalt concretebond to the granular layer. Tack coats are sometime used between layers of asphalt cement.They help one asphalt concrete layer bond to another.

SAES-Q-006 specifies four types of cutbacks. Cutback RC-250 and cutback RC-800 are usedfor tack coats. MC-70 and MC-250 are used for prime coats. The "C" in the designationindicates a cutback. The "R" stands for "rapid curing," that is, the solvent will evaporaterapidly after spraying. The "M" stands for "medium curing." The numbers indicate theviscosity of the cutback, with a higher number indicating higher viscosity.

Cutbacks are much more dangerous than asphalt cements because cutbacks contain explosivesolvents such as kerosene. They must be kept cool, and cigarette smoking near them isprohibited.

Specifications - Bituminous materials used in pavement construction must meet productspecifications. Figure 11 presents typical specifications for a bituminous material, in this caseRC-250. The specifications in Figure 11 are divided into two areas. Tests run on the cutbackitself are shown on the top half of the figure. The bottom half of the figure shows tests run onthe RC-250 after the solvent has been boiled (distilled) away. The asphalt cement that is leftafter the distillation process is called the "residue from distillation." The distillationspecifications ensure that the proper type and amount of solvent has been used in the cutback.

Flashpoint is important. If the cutback is not stored at temperatures below the flashpoint, anyspark can cause its fumes to ignite. (The flashpoint is usually well below the temperaturewhere spontaneous combustion occurs.)

Viscosity is measured at a standard temperature, in this case 140 F. The unit of measure iscentistokes (cST). Note that minimum viscosity for an RC-250 is 250 cST.

Penetration value is another measure of viscosity. The test is performed at a standardtemperature by allowing a sharp needle of known weight to sink vertically into a sample ofbituminous material for five seconds. The depth of penetration is measured in units of 0.1mm. An asphalt cement of low viscosity has a high penetration value.




SAUDI ARAMCO STANDARD A971CUTBACK ASPHALT RC-250

TEST GUARANTEE METHOD

DISTILLATIONDistillate, % by ASTM D-402Volume of TotalDistillate to 680 F

to 437 F 35 Min.to 500 F 60 Min.to 600 F 80 Min.

Residue from Distillation 65 Min.to 680 F, % volume by difference.

Flashpoint, 80 + Min. ASTM D-3143(Tag Open Cup), F

Viscosity, Kinematic 250 Min. ASTM D-2170@ 140 F, CST 500 Max.

TESTS ON RESIDUE FROM DISTILLATION:

Penetration @ 77 F 80 - 120 ASTM D-5100G, 5 Sec.

Ductility at 77 F, CM 100 Min. ASTM D-113Solubility in Trichloroethylene, % 99.0 Min. ASTM D-2042Water, Vol. % 0.2 Max. ASTM D-95

FIGURE 11




An asphalt cement must be flexible, so its ductility is measured. The ductility test involvesstretching a sample of asphalt cement at a known rate of speed in a tank of water at 77 F. ForRC-250, the residue must stretch at least 100 cm before it breaks.

The test for solubility in trichloroethylene checks for impurities. Pure bitumen dissolves 100%in trichloroethylene. If 1% of the residue from RC-250 does not dissolve, it is 99% pure.

Bitumen is allowed to contain only a very small amount of water. If much water is present,when the bitumen is heated, the water will boil and cause foam. Foaming is unacceptable,therefore only 0.2% water is allowed in RC-250.

Figure 12 gives the test specifications for MC-250 as opposed to the RC-250 of Figure 11. Inmany respects, the two cutbacks are alike. For example, they have the same viscosity (250-500 cS) and ductility. However, the "medium curing" MC-250 is less volatile than the "rapidcuring" RC-250, making its flashpoint higher (150F compared to 80 + F).

Figure 13 presents Saudi Aramco Standard A-970 for penetration grade paving asphaltcement. It includes specifications for ductility, flash point, penetration, and solubility intrichloroethylene. The only item in Figure 13 not previously discussed requires that some ofthe tests are run "after the thin film oven test." The thin film oven test is a procedure designedto simulate the harmful effects of being in the heat and sun for several years. A small sampleis heated in the oven, and then the residue is tested. Exposure in the oven makes asphaltcement harder and more brittle, decreasing ductility and penetration.




SAUDI ARAMCO STANDARD A-974CUTBACK ASPHALT MC-250

TEST GUARANTEE

DISTILLATIONDistillate, % byVolume of TotalDistillate to 680 F Min. Max.

to 437 F -- 10to 500 F 15 55to 600 F 60 87

Residue from Distillation 67 Min.to 680 F, % volume by difference.

Flashpoint, 150 Min.(Tag Open Cup), F

Viscosity, Kinematic 250 Min.@ 140 F, CST 500 Max.

TESTS ON RESIDUE FROM DISTILLATION:

Penetration @ 77 F 120 - 250100G, 5 Sec.

Ductility at 77 F, cm 100 Min.

Solubility in Trichloroethylene, % 99 Min.

Water, Vol. % 0.2 Max.

FIGURE 12




SAUDI ARAMCO STANDARD A-970PENETRATION GRADE PAVING ASPHALT

TEST GUARANTEE

Ductility at 77 F, cm 100 Min.

Ductility after thin 50 Min.film oven test

Flash Point, C.O.C., F 450 Min.

Penetration at 77

F 60 - 70(100 g, 5 sec.)

Retained penetration after 52 Min.Thin Film Oven Test, %

Solubility in trichloroethylene, 99.0 Min.wt. %

FIGURE 13




Geosynthetics

Geosynthetics is a general term for a wide variety of materials being used in road construction.These materials are usually man-made polymers derived from petroleum products.

Geosynthetics are used in several ways in road construction:

To "bridge" a weak subgrade soil so that the soil can support the load appliedby a road embankment.

To reinforce an earth embankment.

To serve as a filter or partition between two dissimilar materials.

In any application, the lifetime of the geosynthetic can be affected by various chemical,biological, or climatic conditions. Prolonged exposure to ultraviolet radiation from the sun canalso reduce the expected life of the material. These conditions should be carefully studiedbefore specifying a geosynthetic for a particular purpose.

Geogrid and geotextile are two primary types of geosynthetics that are commonly used in roadconstruction. The geogrid is a fairly recent innovation which is being used in manyreinforcement applications. The geotextile is the oldest of the geosynthetics and has been usedsuccessfully as both a reinforcing and a filter/separation material.

Geogrids

A geogrid is a flat polymer material with horizontal members that are typically orientatedlongitudinally (in the major stress direction) and transversely (perpendicular to the major stressdirection) within a soil mass. These longitudinal and transverse members enclose openings,called apertures, which aid in the geogrid performance.

Geogrids are used primarily for reinforcement of soil layers; thus, they are applicable for twoof the three common uses for geosynthetics mentioned previously. The soil is reinforced by 1)soil/polymer friction on the horizontal members and 2) soil bearing between soil in theapertures and the transverse members. When the reinforced soil mass moves, the members aretensioned and begin to support the load.




Bridging Weak Subgrade Soils - Often when a weak soil is encountered in the field, it isremoved and replaced to a specified depth, usually at great expense, so that a suitablefoundation can be provided for a proposed highway embankment.

By placing geogrids in several layers throughout the lower portion of an embankment on topof a soft soil, the stresses can be distributed more uniformly through the embankment to thesoft soil instead of being concentrated under the highest (and heaviest) portion of the fill. Asthe embankment begins to settle under the heavy portion of the fill, the geogrid becomestensioned, and stresses are transferred through the geogrid from the embankment center to theembankment edges. The highest stress is significantly reduced so that embankment settlementwill decrease. The weak soil will also then be strong enough to support the distributedembankment stress so that a failure is avoided.

Reinforcing Earth Embankment Slopes - Slipping failure on earth embankment slopes is aconcern on many road projects. Sometimes soil in the embankment is not strong enough tosupport its own weight at the side slopes. Geogrids may be used to anchor the soil so that itwill be unlikely to fail at the embankment edges. Figure 14 shows how the geogrids performin the embankment slope. The geogrid material is placed in layers in the embankment,embedded well past the location of a potential failure plane. If the soil begins to move alongthe failure plane, the geogrid becomes tensioned. The portion of the geogrid buried well intothe embankment will help to support the wedge of soil that has begun to slip. Soil friction (s)along the potential failure plane also helps to support the soil wedge so that the entire load isnot carried by the geogrid.

Geogrids may be used to help achieve a steeper embankment slope where necessary. They canalso be used with concrete or similar panels to provide a vertical face on a fill.

In either case, the geogrid reinforcement decreases the amount of space needed for a roadembankment.




GEOGRID REINFORCED SLOPE

FIGURE 14

Geogrids

Embankment

S

S

S

S

S

S

T1

2

3

4

5

6

7

T

T

T

T

T

T

Potential Failure Surface




Geotextiles

Geotextiles are composed of polymeric fibers which have been bonded either by weaving(woven fabrics) or by heat treatment, chemical treatment, or needle punching (nonwovenfabrics). Unlike the geogrid, geotextiles can be made so that they have only very smallopenings in the fabric. Thus, geotextiles can not only be used for reinforcement of soil layersbut also as a filter or separation material between two dissimilar layers.

One advantage of using geotextiles to bridge weak foundation materials is that they canseparate the poor foundation soil from the good embankment material. As traffic begins to usethe road constructed on the embankment, it can cause the embankment to deflect under load.This repeated deflection can cause finer particles from the poor material to move up into thepores of the good material, causing the good material to be weakened. A tightly wovengeotextile placed between the two layers can act as a filter to prevent this movement andpreserve the integrity of the good embankment.

Geotextiles can generally perform many of the same reinforcement functions as previouslydescribed for geogrids. The primary difference is that geotextiles reinforce the soil using thesoil/geotextile friction to cause tension in the geotextile upon movement of the soil. Theinterlocking component is not very pronounced, so the granular base reinforcement would notlikely be as successful with the geotextiles as with the geogrids. Geotextiles can be usedsuccessfully, however, to bridge weaker materials and to reinforce embankment side slopes.

Summary

Lesson I introduced road terminology, road design standards, and typical roadbuildingmaterials. Pavement layer names and layer construction materials for rigid, flexible, andunpaved roads were emphasized. SAES-Q-006 on asphalt concrete paving and SAES-S-030on storm water drainage were described as important engineering standards. Soil, aggregate,and asphalt concrete were all described in detail as the most important road constructionmaterials for Saudi Aramco.




ROAD LAYOUT AND DESIGN

This section contains basic information on factors that affect the layout of a roadway, aparking lot, or a loading area. It will emphasize design elements such as sight distance,horizontal and vertical alignment, roadway cross section, and design controls such as designvehicles, driver performance, and highway capacity. Designing safety into a facilities will bestressed in each of these areas.

Geometric Design and the Roadway Cross Section

Stations

Stations are fundamental units used in designing and constructing a roadway. One station is aunit of length equal to 1000 m or 1 km. A project that is 10.8 stations long is 10,800 m or10.8 km long.

Distances between exact station numbers are noted by adding "+xxx" or "+xxx.xxx" to thelower station number. For example, the station exactly halfway between station 5 and station6 on a project is 500 m from both station 5 and station 6. The correct notation for this stationis 5 + 500. As an additional example, if a point between stations 5 and 6 is to be located740.30 m "up-station" from station 5, then the station number would be 5 + 740.30. (Notethat this same point could be found if it was defined as the point 250.62 m "down-station"from Station 6.)

When it is necessary to find the distance between two stations, simply subtract the lowerstation number from the upper station number after dropping the "+" sign. For example, if acurve begins at station 219 + 018.13 and ends at Station 225 + 078.32, the length of the curveis:

225078.32 - 219018.13 = 6060.19 m

On highway projects, stationing is generally labeled along the centerline of the project. Oneast/west roads, stations increase from west to east; on north/south roads, stations increasefrom south to north.

Often the position of an object that is off the centerline must be addressed. This is done bygiving the station or range of stations for the object and then the perpendicular distance left orright of the centerline to the object. To establish "left" and "right", face in the up-stationdirection. For example, on the roadway plan view shown in Figure 15, a 300 mm diameterconcrete pipe is placed under a driveway for drainage. The pipe happens to be parallel to thecenterline of the roadway, making it the same distance from the centerline at all points.The notation shown in the figure is typical and can be interpreted as "There is a 300 mmdiameter concrete pipe running from station 5 + 023 to station 5 + 041 that is 35 m to the rightof the centerline."




Stations are affected by the horizontal distances along the roadway. Vertical changes inelevation do not affect the stationing on a project.




LOCATING POINTS OFF THE CENTERLINE

5 6

35 m driveway

edge of pavement

centerline

+ 023 to +041, 35m Rt.300 mm concrete pipe

FIGURE 15

Plan and Profile Views

In a standard set of highway plans, plan and profile views of a roadway section are shown onthe plan and profile sheets. Each sheet shows plan and profile details for a portion of theroadway. Stations are used to match the sheets and provide continuity. The plan view showsthe roadway and all related elements as if the observer was above the roadway looking down.The horizontal dimensions of a project can be easily observed. Items such as direction of thecenterline, horizontal curves, drainage culvert lengths and locations, work limits, right-of-waylimits, and many other features can be defined.

The profile view shows the roadway and all related elements as if the observer was looking ata vertical slice taken out of the roadway at the centerline. The vertical dimensions of a projectcan be easily observed. Items such as the slope of the centerline, vertical curves, areas wheresoil is removed (cut) or added (fill) to obtain the desired elevation, elevations of variousroadway elements, and many other features can be defined.




Horizontal Curves

Horizontal curves on a roadway are used to allow vehicles to smoothly change horizontaldirections from a straight line (tangent) in one direction to a tangent in another direction.Generally, the horizontal curve is circular--the curve has a constant radius--and it begins andends at points tangent to the tangent lines. These curves are shown on the plan views.

Figures 16 and 17 show the basic components of a horizontal curve.

P.I. = Point of intersection. The P.I. is the point (station) where the two tangents oneither side of the curve intersect. The P.I. is s point on a line that bisects he arcof the curve.

P.C. = Point of curvature. The P.C. is the point (station) where the roadway changesfrom a straight-line section to a curve section. Also sometimes calledbeginning of curve (B.C.)

P.T. = Point of tangency. The P.T. is the point (station) where the roadway changesfrom a curve section to a straight section. Also sometimes called end of curve(E.C.)

T = Tangent length. For a circular curve, T is either the length along the backtangent from the P.C. to the P.I. or the length along the ahead tangent fromfrom the P.I. to the P.T.

R = Curve radius. R is the radius of the circular curve. A smaller value of Rindicates a sharper curve. Most curves are designed with integer values of R.

D = Degree of curvature. D is a very common way to refer to the sharpness of acurve. If a 100 m length of curve is drawn and if a radius is placed througheach end of and extended to the origin of the circular curve, the angle formed atthe intersection of these radii is called the degree of curvature (Figure 17). Thisnomenclature is losing favor with modern highway design.

L = Curve length. L is the distance along the curve from the P.C. to the P.T.

D = Interior angle. This angle is formed by the P.C., the centerpoint O, and theP.T. (Figure 17 and Figure 16).




HORIZONTAL CURVE NOTATION

T T

P. C. P. T.

R R Ahead tangentBack tangent

Circular curve

P. I.

FIGURE 16




HORIZONTAL CURVE NOTATION (CONT'D)

L

R

if L = 100 m then = D

O

FIGURE 17




When a circular curve is encountered on a roadway, the P.C. marks the beginning of twotypes of stationing (Figure 18). Curve stationing measures stations of the curve along thecenterline of the project. This is the standard used throughout the design and construction ofa roadway to identify points on the roadway.

CURVE AND TANGENT STATIONING

FIGURE 18

P.C. P.T.

Curve stationing

tangent station

curve station

stationing curve = tangent

P.I.tangent

stationingtangent

stationing

Tangent stationing is often used by location surveying crews in intially laying out theroadway, since straight lines are easier to plot than curves. The tangent stations are measuredalong the tangents from the P.C. to the P.T. This technique allows survey crews to locate theproposed line of the roadway as quickly as possible near the completion of the design stage.The P.T. station is always defined using the curve stationing method.




Superelevation

Superelevation involves tilting the roadway toward the inside of a horizontal curve. It issometimes required to allow a vehicle to safely negotiate the curve at the design speed of thehighway. As the vehicle enters a horizontal curve, its tendency is to keep going in a straightline. However, the friction between the tires and the pavement will resist this tendency andkeep the car on the pavement. If the maximum friction between the tires and pavement isexceeded, the driver will lose control of the vehicle, and it will leave the road.

Figure 19 shows a normally crowned pavement (which is sufficient for drainage) and asuperelevated pavement. Superelevation tilts the car so that gravity works with friction tohold the vehicle on the road. Superelevation should be great enough so that the driver feelscomfortable going around the curve at the design speed.

Superelevation must be limited so that a slow-moving or stopped vehicle does not slide to theinside of the curve. Typically, the maximum superelevation is 0.1 foot (meter) of vertical risefor every foot (meter) of horizontal distance across the pavement. Because of this limit in theamount of superelevation, the allowable degree of curvature must also be limited for eachdesign speed.

Usually, the pavement is rotated gradually around either the pavement centerline or pavementedge on the tangent approach to a curve so that full superelevation is obtained on the curveitself.




SUPERELEVATION

FIGURE 19

Normal section

Cross slopeCL

Lanes

Origin

CL

Superelevated section

Lanes




Grades

Because roadways are sometimes constructed in hilly terrain, they must rise and fall togenerally conform to the terrain. Usually, the rate of change in elevation remains constant forsome length of roadway before a vertical curve is needed to allow a vehicle to go over the topof a hill or to change from one slope to another. This constant rate of change in elevation iscalled the roadway grade.

Grades are usually expressed in percent. The grade is defined as the vertical rise in theroadway divided by the horizontal distance over which this rise occurs. This quotient is thenmultiplied by 100 to obtain the percent grade. For example, if a highway rises 3 m (9.84 ft)over a horizontal distance of 100 m (328 ft), the grade is calculated as (3/100 x 100) = 3%(see Figure 20). The grade is positive if it is uphill and negative if it is downhill looking upstation.

Because heavy vehicles tend to slow down on a grade, a maximum allowable grade must beset so that the roadway can continue to carry a certain number of vehicles per hour past agiven point. For example, the maximum allowable grade would be lower on a freeway thanon a two-lane service road at an oil refinery because the speeds are expected to be muchhigher on the freeway. Figure 21 shows maximum allowable grades for a) local streets and b)freeways.

Grades are shown on the profile portion of the plans.

DEFINITION OF "GRADE"

3 m

100 m

B

A

3 % Grade

FIGURE 20




MAXIMUM ALLOWABLE GRADE__________________________________________________________

Design Speed (mph)____________

Type of Terrain 20 30 40 50 60 Grades (percent)

_____________________________________________________________________________________________

Level 8 7 7 6 5Rolling 11 10 9 8 6Mountainous 16 14 12 10 --_____________________________________________________________________________________________

a) Local Streets

_________________________________________________________

Design Speed (mph)____________

50 60 70____

Type of Terrain Grades (percent)

Level 4 3 3Rolling 5 4 4Mountainous 6 6 5

b) Freeways

FIGURE 21




Vertical Curves

Vertical curves are used for transition when the roadway grade changes. These transitionsoccur in three situations:

At the top of a hill, where the grade changes from positive to negative. Theseare called crest vertical curves.

At the bottom of a valley, where the grade changes from negative to positive.These are called sag vertical curves.

At a change in steepness of the grade, either uphill or downhill.

The vertical curve is generally a parabola, which simplifies the calculations and layoutprocedure for the construction surveyor. Half the curve is on one side of the P.V.I. and halfon the other. The details are shown on the profile views of the plans.

Figure 22 shows the basic components necessary for understanding roadway design andconstruction of a vertical curve. Note that although a crest vertical curve is shown, thenotation is the same for other vertical curves.

P.V.I. = Point of vertical intersection. The P.V.I. is the point (station) where the twogrades on either side of the curve intersect.

P.V.C. = Point of vertical curvature. The P.V.C. is the point (station) where the roadwaychanges from a constant grade to a vertical curve.

P.V.T. = Point of vertical tangency. The P.V.T. is the point (station) where the roadwaychanges from a vertical curve to a constant grade.

L = Length of curve. The length of the vertical curve is the horizontal distancefrom the P.V.C. to the P.V.I. Stationing on the curve length is also based uponthe horizontal distance.

The elevation of the P.V.I. is usually shown on the plans, so any other point on the curve orgrade may be calculated from that value.




VERTICAL CURVES

grade

P.V.I.

P.V.C. P.V.T.

L

grade

( 1/2 ) L ( 1/2 ) L

FIGURE 22

Earthwork

Earthwork calculations are used to determine the amount of embankment, or fill, materialrequired to build up the road to the required grade, and to determine the amount ofexcavation, or cut, needed to cut the road to the necessary grade.

Fill can be obtained from either embankment locations on the site or from a nearby borrowpit. Cut may have to be hauled away from the site if it is not required at some location on theproject. An economic analysis is required to determine how the earthwork quantities shouldbe handled.

Locations of cut and fill can be easily recognized on the centerline profile sheets. Usually, theexisting ground lines are shown as dashed lines and the required highway grade lines areshown as solid lines. Elevations of each are often shown every 50 m. When the existingground is higher than the proposed, then the area will likely be cut. When the oppositeoccurs, the area will likely be fill.

"Built-in" Safety

When designing a facility, the safety of roadway users should be kept foremost in theengineer's mind. The geometric design, traffic engineering, cross section elements, and actualfacility construction all should allow for the safety of vehicles and their occupants.

The safety techniques that are used are too numerous to mention in their entirety, but severalhave proven to be quite effective.




Clear Zone Concept - The clear zone is the area from the edge of the pavement to theclosest obstruction or hazard. The farther the distance from the pavement edge to the hazard,the better chance the driver of an errant vehicle has to recover.

Flat Side Slopes - When possible, the side slopes should be 6:1 (6 length units horizontally to1 vertically) or flatter to allow the driver a chance to recover.

Coordination of Horizontal and Vertical Curves - These two curve types should becoordinated so that unexpected geometrics do not occur. For example, a horizontal curveshould never be placed just over a sharp crest vertical curve because vehicles may be unableto negotiate the curve and will run off the road.

Cross Slope on Pavement - Water is not only a hazard to the pavement structure but also tovehicles if it is allowed to stand on the pavement. The vehicle could hydroplane, or losecontact with the pavement, if it is going at a high rate of speed when it hits this water. Properpavement cross slope helps to rid the pavement of water. The shoulders must also be wellmaintained so that water can run off the pavement, onto the shoulders, and away from theroadway.

Intersections

An intersection is an area where two or more roads or streets cross, with vehicles on eachstreet or road competing for movement through the intersection area. Since many of thesemovements tend to cross, traffic control devices are often used if traffic volumes are highenough so that these crossing conflicts regularly occur.

There are two types of intersections from a traffic control viewpoint. The first is theunsignalized intersection. Control methods for unsignalized intersections may vary from nocontrol at locations with extremely low traffic volumes to a stop control on all approaches tothe intersection for higher volumes of traffic.

The signalized intersection is typically one which has volumes that are high enough to meetsome minimum standard of traffic volume. An intersection may also require a signal becauseof pedestrian volume, accident experience, or excessive delays to the user. The signal is usedto force the sharing of movement time by all vehicles on all approaches to the intersection andto serve all vehicles whose drivers desire to go through the intersection.

In intersection analysis, the intersecting streets are divided into the major and the minormovements. The major movement occurs on the street with the highest traffic volume.




Capacity

The capacity of an intersection is the maximum hourly rate of vehicles which can bereasonably expected to proceed through the intersection. The capacity varies depending upona number of factors:

Number of lanes. The number of lanes for each movement affects the numberof vehicles which can pass through the intersection. For example, if onemovement has one lane, then a maximum of X cars can make that movement inone hour. If another lane is added, then a maximum of 2X cars might beexpected to make the movement in the same hour.

Clearance from the edge of the pavement. If a concrete wall or a line of parkedcars isextremely close to the traffic lane, drivers will move more slowlybecause of the perceived hazard. Thus, capacity is reduced.

Grades. Starting from a stopped position on an uphill grade affects bothpassenger cars and big trucks. Because it takes longer to start and establish aconstant flow of vehicles through the intersection, capacity is decreased incomparison to a level grade. Conversely, capacity increases slightly if vehiclesstart on a downhill grade.

Heavy vehicles. Because heavy vehicles (semi-trucks, buses, and recreationalvehicles) take longer to accelerate, the capacity decreases as a greaterpercentage of the total traffic consists of heavy vehicles.

Traffic control devices. Highway sections with flow that is interrupted becauseof some external control such as a stop sign or a traffic signal, has lowercapacity than highway sections with uninterrupted flow. This is because timeis lost during the starting and stopping movements.

Right turning and left turning traffic. Turning traffic will often block a lanethat might otherwise be used by vehicles that have movements which are freeto flow. Right turning vehicles may have to wait for pedestrians to cross beforethe turn can be completed. Left turning traffic also may have to wait forpedestrians, but, more importantly, will have to wait on the opposing throughand right-turn traffic.

Highway capacity on a facility with uninterrupted flow is generally 2,000 passenger cars perhour per lane (pcphl). At signalized intersections under ideal conditions, capacity will bearound 1,800 passenger cars per hour of green per lane (pcphgpl). However, traffic flow atcapacity is very slow and congested, so the design engineer generally prefers that anintersection operates at some volume less than capacity.




Unsignalized Intersections

The capacity analysis at an unsignalized intersection depends on the concept of how thedriver reacts to traffic gaps that allow him to make his desired movement. There are fourmovements that drivers may have some difficulty in making at an unsignalized intersection.They are listed below from easiest to most difficult. The order of difficulty was basedprimarily on the number of gaps available to make each movement. Figure 23 lists thesemovements and illustrates the traffic conflicts for each.

Right turn from the minor street. Conflicting movements are one through andone right turn movement on the major street approach.

Left turn from the major street. Conflicting movements are all movements onthe opposite major street approach to the intersection.

Through movement from the minor street. Conflicting movements are all themovements on both approaches to the intersection of the major street.

Left turn from the minor street. Conflicting movements are all throughmovements on the major street and the through and right turn movements onthe opposing minor street approach to the intersection.

As traffic becomes heavier on the approaches to the intersection, the delays experienced bydrivers making these movements will increase because of the decrease in available gaps in thetraffic. Intersection capacity will decrease. Once the delay reaches a certain level, and oncecapacity is reached or exceeded by the traffic demand, signalization will become necessary.




MOVEMENT HIERARCHY AT UNSIGNALIZED INTERSECTIONS

FIGURE 23

a) right turn from minor street b) left turn from major street

c) through movement from minor street d) left turn from minor street

conflicting mvt.

desired mvt.




Signalized Intersections

The saturation flow rate (S), or the number of vehicles that can get through a signal during allavailable green time, determines what the capacity of that intersection will be. Saturationflow rate is affected by heavy vehicles, grades, and all other factors listed previously.

The ideal saturated flow rate is 1,800 vphgpl, as mentioned earlier in this section. This rate isadjusted for each factor which is different from the ideal. For example, for heavy vehicles,the ideal situation is 0% heavy vehicles. No adjustment to the ideal saturation flow ratewould be required if no heavy vehicles were present at an intersection. For 4% heavyvehicles, the correction factor is 0.98 (multiply the ideal saturation flow rate by 0.98 to get theequivalent vehicles per hour of green per lane); for 10% the adjustment is 0.95.

Tables of adjustment factors have been developed from experience over the years. The idealsaturation flow rate is adjusted by all factors that are different from ideal. For example,assume all conditions at an intersection are ideal except for heavy vehicles and grade. Theadjustment factor for 4% heavy vehicles (f

HV) is 0.98. The adjustment factor for a 2%

downhill grade at the intersection (fg) is 1.01. The actual saturation flow rate (S) is calculatedby

S = 1800 x fg x fHV

= 1800 x 1.01 x 0.98S = 1782 vphgpl

This value is the capacity of the intersection. As long as the sum of the major volumes whichmust pass through the intersection during signal green times does not exceed this totalvolume, the intersection should function properly. Generally, the traffic design engineerwants the per lane traffic to be substantially less than this saturation value so the signal willfunction without major congestion.

The traffic engineer develops critical lane volumes. This is the heaviest lane volume for aparticular traffic movement. It helps to determine how long the traffic signal should be greenfor each approach. Each time the light turns green for a traffic movement, the length of thatgreen time will have been determined by the critical lane volume. In this way, all traffic thatneeds to pass through the signal will be able to get through the signal.




Intersection Geometrics

The size of an intersection and the turning radii required at an intersection are controlled bythe design vehicle. The design vehicle is the largest vehicle that is expected to regularly usean intersection. Typical design vehicles can range from a passenger car (type P vehicle) to asemi-truck pulling two trailers (type WB-60 vehicle).

Figure 24 shows turning dimensions of a WB-50 vehicle, the standard 18-wheel single trailersemi-truck. Other figures are available for additional design vehicles, such as a passenger car,a bus, a recreational vehicle, a single unit truck, and two other design trucks. The designengineer is responsible for making the appropriate selection before the design process begins.

The vehicle turning radii affect two aspects of intersection design. First, the minimum truckturning radius affects the radius of the pavement edge or curb found at the intersectioncorners. When a truck turns right, it should be able to complete the turn in the proper lanes ifthis minimum radius is used. It is not desirable for the truck to swing into another lane whenmaking a wide turn or to "jump" the curb with its tires. From Figure 24, the minimum radiusat the intersection corners should be 19.8 feet (6.0 m) to accommodate a WB-50 truck as thedesign vehicle.

Second, the maximum turning radius is used in setting the width of the intersection. If twodesign vehicles make opposing left turns at the same time, both should be able to turn withseveral feet of clearance between them as they pass in the intersection. If the design vehicle isthe WB-50 shown in Figure 24, the maximum turning radius of 46.2 feet (14.1 m) for all leftturn movements will allow two vehicles making opposing left turns to complete the turns byjust touching. By using a design radius of, say, 50 feet (15.2 m), there will be about 7.5 feet(2.3 m) of clearance between the two trucks.

Summary: Geometric Design and Roadway Cross Section

This section has introduced the terminology and concepts for geometric design and roadwaycross section. Knowledge of such items as stationing and vertical and horizontal curveterminology will be useful when reading road construction plans. Knowing how roads andintersections are planned to ensure they will carry adequate traffic volumes aids inunderstanding the design process. However, the treatment of these subjects has not been insufficient depth for the participant to design such facilities himself.




WB-50 TRUCK TURNING RADII

FIGURE 24

19.8 Ft. minimum

46.2 Ft.

WB-50 Semitrailer




Parking and Loading

Parking and loading areas are associated with almost every Saudi Aramco facility. Carefuldesign of these facilities may be overlooked when attention is focused on other areas. Thefollowing sections describe the basic design of these facilities, with emphasis on parking.

Thickness Design

SAES-Q-006 provides excellent guidelines for the thickness design of parking and loadingfacilities. Unless a special design has been performed, use the thickness design informationprovided in Figure 25.

DESIGN FOR PARKING LOTS AND LOADING FACILITIES

Minimum Maximum Thickness of Thickness of Combined Binder and

Base Course Surface CoursePavement Category __________________ ____________________________

With Class B or C With Class Abase material base material

cm (in) cm (in) cm (in)

Parking and Storage Lots Sedans and Small Trucks 15 (6.0) 9 (3.5) 6 (2.5)

Parking and Storage Lots Heavy Traffic (Truck Terminals, etc.) 23 (9.0) 14 (5.5) 12 (5.0)

FIGURE 25




Drainage

Most roads are built with a 0.5% longitudinal slope to keep rainfall from standing in the road.The minimum slope for parking and loading areas increases to 1.0 or 1.5%. This slope willprevent large accumulations of water.

Parking Lot Layout

There are four important criteria to remember when laying out a parking area:

Use rectangular areas if possible. Make the long sides of the parking area parallel. Place parking spaces (not traffic lanes) along the perimeter. Place traffic lanes so that they serve two rows of parking spaces.

The number of parking spaces in the parking lot will be maximized if you use those fourrules.




Traffic Lanes in parking lots should be a minimum of 24 feet (7.2 m) wide for two-waytraffic. Large circulation lanes that lead from one part of the parking lot to another should bea minimum of 30 feet (9m) wide.

The minimum entrance for two-way traffic into a parking lot should be 25 feet (7.6 m)wide.The minimum radius of the entrance curb is approximately 10 feet (3 m). See Figure 26 for apicture of these typical facilities.

Parking Spaces - A typical minimum parking space size is 19 feet long by 9 feet wide (5.7 mby 2.7 m).

There are three main ways to arrange parking spaces: at a 90 angle, at a 60 angle, and at a45 angle. Figure 27 shows those parking arrangements. The 90 arrangement is the mostefficient use of space; it places more parking spaces in a given area of land. However, the 90arrangement is hardest for the driver to use; it requires a sharper turn to drive the car into thespace. Thus, the 90o arrangement is used when the people who park there will usually staythe entire day.

If many people enter and leave each parking space every day, the 60 arrangement is the mostoften used because it is easier for people to park their cars. However, this arrangement has alower car capacity than the 90 arrangement. The 45 arrangement is not often used. Its carcapacity is the lowest.

Figure 28 shows the required dimensions for lots using any of the three parking angles. The"single unit" parking lot has one-way traffic, and there are no other rows of additional parkingspaces on both sides. The "overlapping units" parking lot has rows of other parked cars oneither side of the row shown.

Figure 28 is extremely helpful in laying out a parking lot on a given area of land. The value'M' can help you determine how many rows of parked cars can fit into the given area. Thevalue 'a' tells the smallest width for a one-way traffic lane that can be used in the facility. Thevalue 'c' allows you to calculate the number of parking spaces that can be put into each row ofthe parking lot.




PARKING PLAN--90 PARKING

2'-0"

19'-0"

62'-0" Wall to Wall

19'-0"24'-0"

9'-0

" Ty

pica

l

6" Raised curb line

90

Wall or property line

Painted parking lines

.. ..

Entrance

.

25'-0"

.

R = 10'-0" min.

StreetcurbStreet

FIGURE 26




PARKING ANGLES

FIGURE 27

60 45 90

Traffic




PARKING LAYOUT DIMENSIONS

as s

M

a's' s'

M'

n

c

Single unit Overlapping units

n s a c M s' M' a'

90 19'0" 24'0" 9'0" 62'0" 19' 62'0" 24'

60 21'0" 18'0" 10'5" 60'0" 18'9" 55'6" 18'

45 19'10" 13'0" 12'9" 52'8" 16'7" 46'2" 13'

FIGURE 28



Saudi Aramco

Road Design & Construction

Documents

Transcript of Road Design & Construction