chapter seven structural design of pavement

7/25/2019 Chapter Seven Structural Design of Pavement

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CHAPTER SEVEN

STRUCTURAL DESIGN OFPAVEMENT

R O B E A M . S .

2 0 1 6

r o b e a m 2 0 0 0 ! m a " # . $ o m

Addis Ababa Institute of Technology (AAIT)

HIGHWAY ENGINEERING II (CENG 4!")


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#t$uctu$al design of fle%ible &a'eent

#t$uctu$al design of a &a'eent is fi%ing thicness of&a'eent laye$s

Can be done fo$ both fle%ibleand $igid&a'eent

The$e a$e diffe$ent ethod fo$ design of a &a'eent AA#HT* ethod

*R+,(ERA) ethod


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AA#HT* ethod

This ethod is based on the $esults of the e%tensi'eAA#H* Road Test conducted

-acto$s that a$e conside$ed in the &a'eent design a$e

.a'eent &e$fo$ance T$affic

#ubg$ade ate$ial

/ate$ials of const$uction

En'i$onent 0$ainage

Reliability


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T$affic

Total load a&&lication due to all the i%ed t$affic 1ithin the design &e$ioda$e con'e$ted to E#A2

W18 (traffic load) using the axel load equivalency factor for each axelweight

The total E#A2 a&&lications e%&ected on the high1ay ust be changed to

the design E#A2 a&&lication in the design lane by di$ection dist$ibution andlane dist$ibution facto$s

W,300021,5

6

No of lanes in Each Direction Percent 80KN ESAL in

1 1002 80 - 100

3 60 - 50

4 50 - 75


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Reliability

.$o'ides a &$edete$ined le'el of assu$ance (R7)that &a'eentsection 1ill su$'i'e the &e$iod fo$ 1hich they 1e$e designed

-o$ a gi'en $eliability Ris a function of the o'e$all standa$dde'iation(#!) 1hich accounts fo$ standa$d 'a$iation in

ate$ial and const$uction Chance of 'a$iation in t$affic fo$ecast

Chance of 'a$iation in actual &a'eent &e$fo$ance

Lo!10FR%&'R.S0

Whe$e8 -R 3 Reliability -acto$

9R3 #tanda$d no$al 'a$iance fo$ a gi'en $eliability

#! 3 !64: fo$ fle%ible &a'eent

#!3 !6+: fo$ $igid &a'eent


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Re#"ab"#"() * S(a+,ar, +orma# ,e-"a("o+ 'R

:! ;!6!!!

"! ;!6= ;,6,

>> ;


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.a'eent &e$fo$ance(se$'iceability)

#e$'iceability &e$fo$ance is easu$ed by .#I(&$esentse$'iceability inde%)1ith scale!to:

Initial and te$inal se$'iceability inde%es ust be established toco&ute the change in se$'iceability(D.#I)

I+"("a# er-"$eab"#"()? is a function of &a'eent const$uction@uality

Term"+a# er-"$eab"#"()? is the lo1est that is tole$able fo$ a&a'eent befo$e it $e@ui$es $ehabilitation

6

Item Value Pavement !"e Source

I"I 4.2 #le$i%le &&"'(

I"I 4.5 )i*id &&"'(

+"I 2.5 ,ar 'i*way &&"'+(

+"I 2.0 (ter pa/eenttypes

&&"'+(


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En'i$onental effects

If the effect of s1ell clay and f$ost hea'e of a subg$ade soil on the &e$fo$ance of the &a'eent in as&ecific $egion a$e significant

2oss of se$'iceability o'e$ the design &e$iod

should be estiated and added to that due to t$afficloads


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#ubg$ade soils

The basis fo$ sub g$ade soil &$o&e$ty is Resilient /odulus(/$)

If eithe$ CR o$ R 'alues a$e gi'en8 the follo1ing con'e$sationfo$ula can be used

Mr%1/00CBR

( for fine grain soils with soaked CBR of 1 or less)

Mr% 1000///R&-a#3e4 5or R %20

The effect of te&e$atu$e and $ainfall $educing the le'el ofst$ength of the subg$ade $eflected on the 'alue of $esilientodulus

AA#HT* de'elo&ed a cha$t that hel&s to estiate the effecti'e$oadbed soil $esilient odulus using se$'iceability c$ite$ia


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En'i$onent

Effecti'e $oad base soil $esilient odulus /Ris ane@ui'alent odulus that 1ould $esult in the saedaage if seasonal odulus 'alues 1e$e actuallyused6

The $elati'e daage to fle%ible &a'eent Bfand the&$ocedu$e fo$ co&uting /R a$e


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,6 A yea$ is di'ided into


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/ate$ial of const$uctionCha$ts used to con'e$t the &$o&e$ties of &a'eent const$uction ate$ials to st$uctu$al

nube$ a+8a< and a,

a, 'alue is ostly taen to be !64

a$iation in g$anula$ base laye$ coefficient (a


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a$iation in g$anula$ base laye$ coefficient (a+) 1ith 'a$ious base st$ength

&a$aete$s


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0$ainage @uality

The @uantity of d$ainage is easu$ed bythe length oftie fo$ 1ate$ to be $eo'ed f$o bases and sub bases6

de&ends &$ia$ily on thei$ &e$eability

The &e$centage of tie du$ing 1hich the &a'eentst$uctu$e is e%&osed to oistu$e le'el a&&$oachingsatu$ation de&ends on the a'e$age yea$ly $ainfall andthe &$e'ailing d$ainage condition

Table belo1 sho1s the $ecoended d$ainagecoefficient fo$ unt$eated base and subbase ate$ial infle%ible &a'eent


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#election of &a'eent thicness

-igu$e belo1 $e&$esents the onog$a&h fo$ dete$ining thedesign st$uctu$al nube$ $e@ui$ed fo$ the s&ecific in&ut condition

SN%a1D1a2D2m2a9D9m9

The in&uts $e@ui$ed a$e W,8 R8 #!8 /$and

.#I

6


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Gene$al &$ocedu$e fo$ selection of laye$ thicness

,6 Bsing E< as /R and cha$t8 dete$ine the st$uctu$al nube$ #N,$e@ui$ed to &$otect the base and co&ute the thicness of laye$ ,(0,)

D1 SN1:a1


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E%a&le

E#A23


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Bae, o+ ,e"!+ 5orm3#a

Whe$e?

Wt,3 the nube$ of (!N) sigle a%el load a&&lication to tie t

.t3 is te$inal se$'iceability inde%

#N3 st$uctu$al nube$

/R3 is the $esilient odulus


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*R+,(ERA) ethod

The design of fle%ible &a'eents is based on thecatalog of &a'eent st$uctu$es of TR2 Road Note +,

1ith odification 6

efo$e the catalog is used8t$affic loading $esult

subg$ade CR 'alues

info$ation $ega$ding a'ailability8 costs and &ast

e%&e$ience 1ith ate$ials should be gathe$edThe catalog offe$s8 in se'en diffe$ent cha$ts8

alte$nati'e &a'eent st$uctu$es fo$ cobinations oft$affic and subg$ade classes


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Ue o5 (


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#u$$ary of %aterial Require$ents for the &esign Charts

All the cha$ts &$o'ide alte$nate &a'eent st$uctu$es fo$ all subg$ade classes(#, th$ough #")6 They a$e not ho1e'e$ suitable fo$ all classes of t$affic8 assoe st$uctu$es 1ould !e neither technically a''ro'riate norecono$ically ustified

The choice of cha$t 1ill de&end on a 'a$iety of facto$s but should be basedon iniiing total t$ans&o$t costs6


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-acto$s that 1ill need to be taen into account in a full e'aluationinclude? the liely le'el and tiing of aintenance the &$obable beha'io$ of the st$uctu$e the e%&e$ience and sill of cont$acto$s and the a'ailability of suitable

e@ui&ent the cost of the diffe$ent ate$ials that ight be used othe$ $is facto$s

The cha$ts ha'e been de'elo&ed on the basis of $easonableassu&tions conce$ning the fi$st th$ee of these and the$efo$e initialchoice should be based on local costs of feasible o&tions

If any info$ation is a'ailable conce$ning the liely beha'io$ ofst$uctu$es unde$ the local conditions8 then a si&le $is analysis can

also be ca$$ied out to select the ost a&&$o&$iate st$uctu$e6


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De"!+ E8am=#eAn e%a&le of t$affic calculations 1as gi'en in Cha&te$ + fo$ a

&a$ticula$ section of a t$un $oad6 In thee%a&le(E#A23


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C1

C2

D

ituinous (H/A) 1ea$ing cou$se and binde$ cou$se



G$anula$ $oadbase G< and +

G$anula$ $oadbase G< and +

G$anula$ sub base

Ceent o$ lie stabilied $oad base

G$anula$ ca&&ing laye$ GC

ituinous $oad base

G$anula$ sub base G#

G$anula$ ca&&ing laye$ GC


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The follo1ing &$eliina$y info$ation has been de$i'edf$o the in'estigations and si&le cost co&a$ison? The ate$ials 1hich ay be conside$ed fo$ ceent; o$ lie;

stabiliation ha'e $elati'ely low 'ercentages of fines and low

'lasticity8 thus aing $eme+( (ab"#">a("o+ o$e &$oising6 *ranular su!!aseate$ials ay not be a'ailable in sufficient

@uantities and ceent stabiliation of the subbase isuneconoical 1hen co&a$ed to ban;$un ate$ials6

#ta!ili+ation of su!!ase $aterials will not !e further

considered6 All othe$ ate$ials ente$ing the co&osition of the &ossible

&a'eent st$uctu$es a$e a'ailable8 albeit in 'a$ious @uantitiesand associated t$ans&o$tFconst$uction costs6


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ased on the abo'e8 and 1ith the TF#+ cobination of t$affic andsubg$ade st$ength classes8 the design cha$ts C,8C< and 0 indicate the&ossible alte$nate &a'eent st$uctu$es as?

,a!le- &esign .xa$'le- /ossi!le /ave$ent #tructures

6


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-u$the$ analyses of $ecent cont$acts8 &$oductioncosts hauling distances and associated costs ha'eestablished $elati'e costs fo$ the 'a$ious alte$nate&a'eent laye$s (all costs &e$ < and e%&$essed as a$atio to the highest cost eleent) as sho1n in Table

ased on the abo'e8 the alte$nate st$uctu$e ceentstabilied laye$ ( st$uctu$e


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,a!le - &esign .xa$'le- Relative 0nit Costs of %aterials


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Table : Relative Costs of the Possible Alternate Pavement Structures

.

DESIGN OF GRAVEL AND LO? STANDARD


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DESIGN OF GRAVEL AND LO? STANDARDROADS

/uch of the info$ation &$esented he$e is based on theJ.a'eent and /ate$ials 0esign /anualJ &$e&a$ed by theBnited Re&ublic of Tanania /inist$y of Wo$s ,>>>8 andon $ele'ant ERA and TR2 &ublications6

A'ailable info$ation has been odified to &$o'ide asi&le &$ocedu$e to design g$a'el 1ea$ing cou$ses and lo1standa$d $oads8 1hich is a&&$o&$iate to Ethio&ian

conditions6

G$a'el $oad &a'eents a$e gene$ally utilied fo$ $oads1he$e design t$affic flo1AA0T is less than


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De"!+ Pr"+$"=#e

Steps To Be Considered In The Design Process

,6 T$affic(aseline flo1 and fo$ecast)


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All-weather Access

An essential conside$ation in the design of g$a'el$oads is to ensure allweather access6

This $e@ui$eent &laces &a$ticula$ e&hasis on theneed fo$ sufficient bea$ing ca&acity of the &a'eent st$uctu$e and &$o'ision of d$ainage and sufficient ea$th1o$s in flood

o$ &$oble soil a$eas (e6g6 blac cotton)6


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Surface PerformanceThe &e$fo$ance of the g$a'el su$face ainly de&ends on ate$ial @uality8 the location of the $oad8 and The 'olue of t$affic using the $oad6

G$a'el $oads &assing th$ough &o&ulated a$eas in &a$ticula$ $e@ui$eate$ials that do not gene$ate e%cessi'e dust in d$y 1eathe$6

#tee& g$adients &lace &a$ticula$ deands on g$a'el 1ea$ing cou$seate$ials81hich ust not becoe sli&&e$y in 1et 1eathe$ o$ e$odeeasily6

Conside$ation should the$efo$e be gi'en to the ty&e of g$a'el 1ea$ingcou$se ate$ial to be used in to1ns o$ stee& sections6

G$a'el loss $ates of about


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MaintenanceThe ate$ial $e@ui$eents fo$ the g$a'el 1ea$ing cou$se

include &$o'ision of a g$a'el su$face that is effecti'elyaintainable6

Adhe$ence to the liits on o'e$sie &a$ticles in the ate$ialis of &a$ticula$ i&o$tance in this $ega$d and 1ill no$allynecessitate the use of c$ushing o$ sc$eening e@ui&entdu$ing ate$ial &$oduction acti'ities6


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De"!+ Me(


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minimum thickness requiredIt is necessa$y to liit the co&$essi'e st$ain in the

subg$ade to &$e'ent e%cessi'e &e$anent defo$ation atthe su$face of the $oad6

-igu$e , and < gi'es the iniu g$a'el thicness $e@ui$edfo$ each t$affic catego$y 1ith the $e@ui$ed thicness ofi&$o'ed subg$ade ate$ials fo$ u&&e$ and lo1e$ subg$adelaye$s6


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!ra-e# #oAcco$ding to TR2 2abo$ato$y Re&o$t "=+8 an estiate of the

annual g$a'el loss is gi'en by the follo1ing e@uation?

GL % 5 T2: T2 /04 @.2 0.02 T 9./0 R2 1.77V4

Whe$eG2 3 the annual g$a'el loss easu$ed in

T 3 the total t$affic 'olue in the fi$st yea$ in both di$ections8 easu$ed inthousands of 'ehicles

R 3 the a'e$age annual $ainfall easu$ed in

3 the total ($ise K fall ) as a &e$centage of the length of the $oadf 3 !6>4 to ,6 fo$ late$itic g$a'els

3 ,6, to ,6:, fo$ @ua$tiitic g$a'els

3 !6= to !6>" fo$ 'olcanic g$a'els (1eathe$ed la'a o$ tuff)

3 ,6: fo$ co$al g$a'els

3 ,6+ fo$ sandstone g$a'els


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total thickness requiredThe 1ea$ing cou$se of a ne1 g$a'el $oad shall ha'e a

thicness 0 calculated f$o?

D % D1 N. GLWhe$e

0,3is the iniu thicness f$o -igu$e 6+

N 3is the &e$iod bet1een $e g$a'elling o&e$ations in yea$s

G2 3is the annual g$a'el loss ne'e$ falls belo1 the iniu thicness 0,6


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Pa-eme+( a+, Ma(er"a#0e&ending on the CRdesignof the subg$ade8 i&$o'ed subg$ade

laye$s shall be const$ucted as $e@ui$ed8 on 1hich the g$a'el1ea$ing cou$se is &laced6

Cro 5a## a+, Dra"+a!e

The c$oss fall of ca$$iage1ay and shoulde$s fo$ g$a'el $oads shallbe L47M as indicated in ERA5s *eo$etric &esign %anual 226

This is to ensu$e that &otholes do not de'elo& by $a&idly $eo'ing su$face 1ate$ e%cessi'e c$oss fall does not cause e$osion of the su$face6

/rovision of drainage is extre$ely i$'ortant for the'erfor$ance of gravel roads


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3igure .x'ected /erfor$ance of *ravel Wearing Course %aterials


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Impro"ed su#grade la$erIn Gene$al the use of i&$o'ed subg$ade laye$s has the follo1ing

ad'antages? .$o'ision of e%t$a &$otection unde$ hea'y a%le loadsO .$otection of unde$lying ea$th1o$sO .$o'ides $unning su$face fo$ const$uction t$afficO Assists co&action of u&&e$ &a'eent laye$sO .$o'ides hoogenous subg$ade st$engthO Acts as a d$ainage filte$ laye$O /o$e econoical use of a'ailable ate$ials6

Su#grade CB%All subg$ade ate$ials shall be b$ought to st$ength of at least

iniu CR of =7 fo$ ino$ g$a'el $oads

iniu CR


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Material Characteristics#oils used fo$ i&$o'ed subg$ade laye$s shall be non;e%&ansi'e8

non;dis&e$si'eand f$ee f$o any delete$ious atte$6

,hey shall co$'ly with the require$ents shown


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&%A'( )A%I*& C+,%SThe ate$ials fo$ g$a'el 1ea$ing cou$se should satisfy the follo1ing

$e@ui$eents that a$e often soe1hatconflicting? They should ha'e sufficient cohesion to &$e'ent $a'eling and co$$ugating (es&ecially

in d$y conditions) The aount of fines (&a$ticula$ly &lastic fines) should be liited to a'oid a sli&&e$y

su$face unde$ 1et conditions6

E%cessi'e o'e$sie ate$ialin g$a'el 1ea$ing cou$se affects $iding @uality in se$'ice and

aes effecti'e sha&ing of the su$face difficult

Ty&e , g$a'el 1ea$ing cou$se 1hich is one of the best ate$ial alte$nati'es

1hich shall be used on all $oads 1hich ha'eAA0Tdesigng$eate$ than :!6Ty&e , ate$ial shall also be used fo$ all $outine and &e$iodic aintenance

acti'ities fo$ both ao$ and ino$ g$a'el $oads6

Ty&e , o$ Ty&e 4 g$a'el 1ea$ing cou$se ate$ial ay be used on ne1const$uction of $oads ha'ing AA0Tdesign less than :!6


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Maor &ra"el %oads .AADTDSI&*/01 To 0112/ao$ g$a'el $oads a$e $oads 1hich ha'e a design AA0T

g$eate$ than

3all within the design category of to (.R5

*eo$etric &esign %anual 22)It is $ecoended to use g$a'el 1ea$ing cou$se ate$ial of

g$ading Ty&e , in the ne1 const$uction of $oads ha'ing anAA0T g$eate$ than :! and fo$ all $outine and &e$iodic

aintenance acti'ities6Ty&e 4 ate$ials ay be used in the ne1 const$uction of

$oads ha'ing an AA0T less than :!6


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Minor &ra"el %oads .AADTDSI&*3012/ino$ g$a'el $oads a$e $oads 1hich ha'e a design AA0Tdesignless than

They a$e no$ally counity $oads and a$e unsu$faced (ea$th $oads)6Ho1e'e$8 fo$ subg$ade CR 'alues less than :7 and longitudinalg$adients of g$eate$ than "78 a g$a'el 1ea$ing cou$se is $ecoended6

/ate$ials fo$ g$a'el 1ea$ing cou$se shall co&ly 1ith the $e@ui$eentsfo$ Ty&e 4 ate$ial fo$ ne1 const$uction and Ty&e , fo$ aintenanceacti'ities6

The CR $e@ui$eents ay be $educed to

subg$ade st$ength is classified into #:8 #4 o$ #< fo$ the &u$&ose of&a'eent design6


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6a!oratory testingEach CR 'alue shall be dete$ined in labo$ato$y ca$$ied out fo$

a iniu of + density 'alues to gi'e a CR ; 0ensity$elationshi& at the no$al field density s&ecified fo$ the$es&ecti'e o&e$ation6


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Im=ro-e, S3b!ra,e a+, Pa-eme+( De"!+%aor *ravel Roads .a'eent and i&$o'ed subg$ade fo$ ao$ g$a'el $oads shall

be const$ucted based on figu$e,

This includes all design catego$ies 0#:8 0#"8 0#= and 0# asdefined in ERA *eo$etric &esign %anual 226

%inor *ravel Roads .a'eent and i&$o'ed subg$ade fo$ ino$ g$a'el $oads shall

be const$ucted based on figu$e and 0#,!6

The CR ay be $educed to


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3igure 2- /ave$ent and 7$'roved #u!grade for $inor *ravel Roads


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C#"ma("$ 'o+e9ones -o$ the &u$&oses of g$a'el 1ea$ing cou$se design8 Ethio&ia is di'ided into

t1o cliatic ones6 All &laces 1ith ele'ations o'e$

chapter seven structural design of pavement

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