Commonwealth of Kentucky Department of Highways

THE APPLICATION OF KENTUCKY FLEXIBLE PAVEMENT DESIGN METHOD TO W ASHO TEST ROAD CONDITIONS

by

W. B. Drake Senior Research Engineer

A Report Pre sen ted at the Kentucky Highway Conference, University of Kentucky, Lexington, March 29, 1956.

Highway Materials Research Laboratory Lexington, Kentucky

March, 1956

INTRODUCTION

In the summer of 1952 the Flexible Pavement Design Committee

of the Highway Research Board began the sponsoring of a comparative

design project. Several state highway departments and other organiza­

tions were invited to submit flexible pavement designs, based upon their

own current practices, for the subgrade, materials, and traffic condi-

tions of the Western Association of State Highway Officials (WASHO) test

road. This road was being constructed in Malad, Idaho, through the parti­

cipation of 13 western states and the Bureau of Public Roads. The Kentucky

Department of Highways was one of the organizations invited to participate

in the comparative design project.

After the organizations invited had indicated their interest and

willingness to participate in the study, they were each furnished with

samples of the subgrade, subbase, and base materials, as well as a

statement of certain specific traffic patterns, s01ne of which would be

used in testing the road. All test vehicles would be of the semi-trailer

type, with two loaded axles. Single-axle loads would be 18,000 and

24,000 lb., while the tandem-axle vehicles would have 32,000 and 40,000-

lb, loads. It was intended that a total of 200,000 passes would be made

by each vehicle.

The surface course of the entire W ASHO roadway was bituminous

concrete with 12-150 penetration asphalt, 4, 8 percent by weight. This

course was placed in compacted thicknesses of two and of four inches.

The base course consisted of graded-crushed gravel, ranging from 100

percent passing the l-in. sieve to seven percent passing the No. 200 sieve,

and placed four inches thick in sections paved with two inches of asphaltic

concrete, and two inches thick in sections with a 4-in. surface course.

The gravel for the subbase was pit run, with 100 percent passing the 2-in.

sieve and five percent passing the No. ZOO sieve.

There were two specific objectives for the design project:

a.) To determine the pavement thickness indicated necessary by

the methods of the various participating organizations for a given type of

subgrade soil, given pavement materials, and for definite patterns of

traffic.

b.) To compare the designs obtained in (a..) with those indicated

to be adequate under the actual traffic imposed upon the WASHO test

pavement by the .four test axle loads.

The Design Problem

The problem of design for the organizations participating in the

study was actually three fold. It consisted of determining, with their own

construction standards but for conditions at the Idaho test site, the

following:

1. Subbase thickness specifications necessary for 200,000 passes

of each test vehicle, for each of the variable surface course and base

thicknesses indicated in the table below:

TABLE l. SUBBASE DESIGN PROBLEM

Axle L~ad (lb.) Pavement Siri~1e Tandem Component 18,000 ~~~400 _?2,000 40,000

Surface (in.) 2 4 2 4 2 4 2 4

Base (in.) 4 2 4 2 4 2 4 2

Subbase (in.) ? ? ? ? ? ? ? ?

Z. The number of trips of vehicles with each of the four axle

loadings required to produce failure for the following designs:

TABLE 2. W ASHO TEST PAVEMENT DESIGNS ..,_,_.,."' __ . --~=~.~~~~--'-.--·~--. --~--

Compon.~t Thickness in ln.ches

Surface 2 2 2 2 2 4 4 4 4 4

Base 4 4 4 4 4 2 2 2 2 2

Subbase 0 4 8 12 16 0 4 8 12 16 .. -· ~---~··-~-~----~.....-.~ - . -- --Total 6 10 14 18 22 6 10 14 18 22 -~, . .., __

'-~~~-~~-·-· __ ,_...~.

3. The pavement thickness necessary for the climatic conditions

where the particular design procedure is normally used (in this depart~

ment's case, for Kentucky) but for certain specified traffic conditions.

Thicknesses of surface, base, and subbase were to be selected as thought

necessary. The traffic conditions specified included the already detailed

WASHO pattern, with the ZOO, 000 passes of each vehicle; as well as

certain other traffic patterns as indicated in the table below:

TABLE 3. COMPOSITE TRAFFIC PATTERNS --Pattern ---pattern-----pattern Pattern

·~~--"( a=l., _______ Jbl lcl ( d'"-) __

Passenger Cars (No. of Vehicles/Day)

Commercial Vehicles (No, Axles/Day)

10, 000 lb. or less 12,000 lb. 14,000 lb. 16,000 lb. 18,000 lb.

80

10 4 3 2 1

800 3200 1000

100 400 600 40 160 800 30 120 1000 20 80 520 10 40 80

13,587,000 63,734,000

Ke~ky Desig~,

Kentucky Flexible Pavement Design is based on a modification of

the CBR method. Traffic is evaluated by the equivalent 5000~lb. wheel­

load method (EWL). The pavement design curves are based on Kentucky's

experience, having been developed from the results of a comprehensive

study made by the Department of Highways in 1947 and 1948. These curves

have since been extended and modified to provide for the greater volumes

and weights of present and expected traffic. The curves in Fig. 1 show

the combined thickness of high-type macadam base and asphaltic-concrete

pavement required for certain CBR values and various traffic ranges.

Anticipated axle loads of 10,000 lb. and greater are converted to the equi­

valent number of 5000-lb. wheel loads. A 10,000-lb. axle is equal to

one 5000-lb. wheel load, while a 12,000-lb. axle is equivalent to two

5000-lb. wheel loads and an 18, 000-lb. axle equal to sixteen 10, 000-lb.

axles. The table of equivalents was worked up by the California Depart­

ment of Public Works and is generally accepted, Total 20-yr. antici-

pated traffic is calculated in EWL values.

The CBR method for determining bearing values of soil has been

modified for Kentucky use. This value is determined in the laboratory

for subgrade samples from the pt"oject.

Subgrade, subbase, and base !>amples from the WASHO test track

were tested in the Highway Department's testing laboratory by the Divi­

sion of Materials. The sub grade soil was found to have a CBR of 5. 5

percent. The crushed- gravel base was found to be about equal in bearing

value to Kentucky macadam base, while the uncrushed-gravel subbase

had only 80 percent of the bearing value of the crushed material (tested

(J) w ::I:

2

0 4 z

1-.:" 6 z w ~ 8 w > ~ 10

0 z 12 <1:

w (J)

<1: ro I

(J) (J) w z ~

14

i 16

18 I

0 20 ") J: 1-

0 22 w z ro 24 ~ 0 0 26

MINIMUM LABORATORY C 8 R VALUE

3 4 5 6 7 8 9 10 20 ~0 4 o e 0 ,o 70 090 .00

~--~-----

--(,A) ----

v v ~ !---- -~--~ v 1-- f..---' Curve Limiting E WL v v ~ - (million) /

t-

/ v v v v v-- - lA Less than 112

(ii}_ / v v 1-- --- --- I Less than I

~ / / v --- II 1-2 -

L_ v v --- Ill 2-3

/ / ·" -- ---- w 3-6 -- -

~ ~ v / --- v 6-10

/ 1-" - ---- VI 10-20 // / --- VII 20-40 - t-

VL X // _/

/' -- ---- VIII 40-80 /® v/ -v -- IX B0-160 / ./ ---- X 160 -"320 t-

v/ ~ v / / --

/ ----------v v,...._ _/ / --v/ -~ /"

v/ / V...-= /

v/ v~ v"'

"/ . fv\

~---/"

vy

~/ PC' 1~5 ,.

Kentucky Department of Highways Materials Research Lob ora lory

FLEXIBLE PAVEMENT DESIGN CURVES

Fig. l. Kentucky Flexible Pavement Design Curves.

by the CBR method). Because of these evaluations, crushed-gravel

base thickness was determined in the designs on an equal basis with

macadam; while the subbase material, when used, was increased 25 per~

cent in thickness, to compensate fo!' its lower quality. Consideration in

the overall design was given for the 4~in. asphaltic concrete thickness

versus the 2-in. surface. The thickness required was lowered somewhat

for the 4-in. surfaced sections.

The pavement designs and failure estil:nations determined by the

Kentucky Department of Highways for the problems are shown in the

following tables. Table 4 contains the subbase designs for the first por-

tion of the prob tern.

TABLE 4. SUBBASE DESIGNS ~~----= -~-----~~------~.,......._--=--~

Pavement Component Single Axle Tandem Axle

(in.) Ts, ooo lb-.-··-zz,_4oo_!~~_g, ooo lb. 40,000 lb.

Surface 2 4 2 4 2 4 2 4

Base 4 z 4 2 4 2 4 2

Subbase 12 11 17 16 12 11 17 16 " --..

Total 18 17 23 22 18 17 23 22 ___......_,3 ______ _______.,-~~--

Table 5 below, presents the findings for the second portion, list-

ing the number of passes of the various vehicles which each of the pave~

ment designs used in the test track was calculated to withstand adequately.

These values were determined from the Kentucky flexible pavement design

curves. At the bottom of the table are listed the subbase thickness values

- 6 -

that were found to be adequate for 119,000 passes of the various vehicles

at the test track. (It was decided during the running of the tests that the

originally planned 200,000 passes wruld not be feasible, and the traffic

was stopped on May 29, 1954, after all vehicles had made 119,000 trips

over their respective sections.)

TABLE 5. NUMBER OF TRIPS TO PRODUCE FAILURE ' ' ·- :.==.;;:_c.;;;;;:_ ___ _

Thickness 18,000 Single

Z·in. A-:c-:--:;r::in. A.c: 22, 40 0 Single ·-,;--,.,.--

:;r:'in. A.C. 4-in. A.C.

4-in. Base 2.~in. Base 4-in. Base _____ __;:__;:c;;;c:_: ·-~-· ---·----

2-in. Base

0 31,250 46,900 7,810 11,720

4 78,100 93,000 19,550 23,500

8 226,200 312,000 56,600 78,200

12 93:8,000 1,563,000 235,000 391,000

16 1,750,000 5,620,000 938,000 1,420,000

W ASHO FINDINGS

(Subbase Thickness Found Adequate for 119,000 Trips)

10 in. 4 in. 13 in. 4 in,

Table 6, which follows, shows the designs for the third portion

of the design problem, for the WASHO traffic pattern of 200,000 passes

of each vehicle.

TABLE 6', PAVE:MEN'l' l),ESlGNS :Ji'G!l 'I'!li>TAL 'I'HlCKMESS (UI!ins Anr S.el~~>.eted Qogrroplllcl1e:Jlt l?liekael!ll}

Pavem.e:J\t <l:lllmp~neJI,t

(i:J\d

Bas.e

3

4

ll

3

6 4

3

6

13 -18 Zl 19

Fig, Z indic.ates. gr.aph.ically .the deroigas .l!elec.ted by each l'£ .tM

p~.ticipatl.ag agenciel! .£91 this pcn:tiq,a af .the p:e~b!em, i.a which the i:n•

dlyidl!lal thickll.esaea Q! atl cpmpl!lnents were 1e!t till the chc>i<.!,e 111£ the

de.~~:igne:r~ The Kel!.tncky tllltal thiekne.aroe!l wne made '!I.P e£ .tM e.Gm•

ponen~s already ~~~ in Ta'l;illil 6.

Tal:!t!!> 7 1 betQw, El.hows ib.e design$ fQr ~he cempP!iite traffic

patti!! tn!l Ul111ted l.n Table l) fe.r the .ihird porthm .~.J£ tne pl:'C!blem,

TAB:L)l: 7., . PAVEMENT. ~ESIGNS. :11'011. COJ\i!P0$!TE. 'I'ItMFtO PA'l'T.Ell.NS .

:Pave'm.ent QC!Impllflilijl!n~

(J):I,.J Pattel:'n Pa~e:t:n Pat~e:rn

Jci) PaUe:rn

Ia! {!) __ ,d)

z z~s Z,15 3

Bas.e z 4 4 6

5 7 Ul '**"'

11 zt tM.

9 13,5 16.75 zo

":! .... (IQ

N

<:'1:1 (D llJ ::r<: , .... (D 0 ~s AI (D (D ,_,;:; ro " .... 0 ij·O ~0 "' <1> 0 . m ,... 0

(IQ >;:l

0 ,....m <:d .... " en ~i;! 0 & s s or '0 .... r 0 ... I'TI)g ;::l rti (D 0.. -l<i ;J AII'TI ... c-..,.'<!

_s: ::r ...

""tJI'TI .... ::r CJ)2

~(D :e-l ;:l ('") (D 0

--I Ol I

-l:::t: Ol 0

:I:-

"'0 ==~ .. <1>

:!! " J>2

(D ~ CJ)I'TI

" .... :::t:Ul (D ;J oUl Ol(IQ

(D > 3: ,....(IQ l> <1> (D

~;:l -1

Cll () I'TI

0.. .... AI <1>

"""' l>

'<! H> r ..,.o Ul ::r" (D N o.,O roo ... .... a (IQO ;::l 0 (D

" ..

0 (JI

Thickness in Inches

0 (JI ro 0

ro (JI

(JJ

0 0 (JI

Thickness in Inches

0 (JI ro 0

ro (JI

MorTland T I T hlar:vVand I 11

Alabama I CJd North Caro inq I Colorado ro Washinaltm -

(JJ 0

Woslunof> n i 0 Colorado !» i

Pverfo Ri o 0 Alabama g Oelaware ~ Kentucky 1... 0 Colif"ornio Ill California l r Kenfuckv 1'-, ,..-1 Oe/oWQre I CA:l, Ill /Vorl"hCar Jina 1 ..!.. l> Pvt~l"fo Ric'p R Ul NewMex/cb I ~ (1)0 ~ Ne":Mexic 2 ArizOntll I I'TI Artzono I ~

I Wyom,;;;; T 3: W_yoming I ~ I'TI west v/iain Ia T l> l> West Vir.oi ~T I ~ l> TeJ<as _I . I~ ~ Te_xos . ,8 X MISS 0 ur/1 a I'TI MISS OUT/ CD ~

~ m CD N m • w.

Mqr_y/and I Maryland I Aloham<t I Wqshmgta I Norfh Carl> tina I North Core 1/n.q I Wa.shinof< n I ~ Kentuckv ~- ro Kentucky !<, o Arizona II ro.!'l Delaware I rJ,o Alabama - • .!!> Puerto R i o 1'\1 0 Callforl'lla g Arizona b; Colorqda r California NewMe~ricl:o I Ill New MexiCio i;! Pverfo Ri(jt> I :... Ul Colorado T 2 f)elaware 1 h z WyomiiiQ I IJ ~ West v,·rgi iq I l> ~ Wesf Vi~o1 ia I l> ""' Wvomin<t I ;ii I'TI < ~ ~

reurs . l ~ l> Tuqs . 1 ,g l> MisstJvNi I 0 X MIS.Soun I CD X

~ r r CD fl1 !J) I'TI

w -b -=

W ASHO FINDINGS

During the period from November, 195Z, through May, 1954,

the test track was subjected to 119,0()0 trips of the test vehicles on

atl t~;>st sections,

The minimum total thicknesses that were found to withstand

adequately the 119,000 vehicle passe~; in the outer wheel path, for the

2-in. surfacing of asphaltic concrete, were 16 in. for the 18,000 lb.

single axle, 19 in, for the 22,400 lb. single axle, 17 in. for the 32,000

lb. tandem; and ZO in. for the 40,000 lb. tandem,

In the inner wheel path, the 1~-in thick pavement sections were

undamaged by any of the four loading~. Comparable values found for

the 4-in. asphaltic concrete pavement, outer wheel path, H) in .. for

the first three loadings and 14 in. for the 40,000 lb. tandem .axle load.

For the inner path they were 6 in. for the two single axle loading and

10 in. for the two tandem axle loads.

In the section of this report w}lich J'ollows, graphs are used to

present a comparison between the findings of the WASHO test and the

designs submitted by the participatin$ organizations. The Kentucky

designs are indicated on each of the graphs.

- 8 -

5- IB,OOOLB SINGLE AXLE - 22,400LB SINGLE AXLE 2

0 1--

r-16"

0

5-~ .--II" 1--' rAverage 12.3"

1--1-- - 0 J .-Average 10" --·"' ·~ .!!f-r-"' 0 ~ " I~ 0

I~ -~ ·~ 0 ~ •I-·~ "·- ~ 0 ~ .~ ~" .e • ~1}1--1-. " " ~ "' ~ ~ 0 ' ~ ~ ~

Q: " " ~ ~ 0 ·- £ 5-f >!e "' 0 ~~ 1-- ~~

, ~

,. 0 ·~ " ~ ~ ~~ ~"§ .., 0 ~~ lj ~~ ' !:',j' ... .., ~li ... .~....~ • ~~ ~ I~ l~ ~ •' ~s: til~ " ~ ~~ 8~ ~ ~~ ~ 0 ~ ... ~Q "'li\ ~ ~~ 'I( u "' ?~~~~ Cl. ~~

3 0

E~ 32,000LB TANDEM AXLE - 40,000LB TANDEM AXLE 2 ., 1! ~ 2 01--

f--1-- ..-16 .5

"' .. ., 1-_

51-r-11" J.

#Avera~e 13.4"

<:

~ 10 :E 1--

f- [Average 10.6" -• LJ 0

'.,'>I-~ 0 Q; • ·- 0 ° ~ 1.?

(.,J bt~" -.l(

5,~~~~~$!~~~%2~~~ f1 -Ei~ 0 0 ~ ~ 0 " .s ~ 1--~

~.: ~ 3 ~ ~ ~ ~ h 1i :.i ~ ~ ~ ~ 0

0

·~ ~ 0

~ " ~. "~ ' 0 0 -»1~ ... " -:: ~ '"' •• ~~ ~Q

fo ·-~ ··~ I) IJ I~ 1--~ ~ 0

" ~ 0 :s: ~ -2" ·~ ~<:: ·- "' ·~~ ... ~~ ~ ~ J " ~ "5~ ~ ... ~ • • < "'"' '1:- l: ... :

UNCRUSHED-GRAVEL SUBBASE THICKNESS FOR 200,000 VEHICLE TRIPS 4" A.C. + 2" CRUSHED GRAVEL BASE

FIGURE 3

This chart shows the subbase thicknesses that each of the coopera-

ting agencies submitted for 200, 000 trips of each test vehicle, with

a 4-in. asphaltic concrete surface and a 2-in. base course. Note

the average subbase thickness submitted and the Kentucky design for

each traffic loading.

- 9 -

v~

25 18,000LB SINGLE AXLE 22,400LB SIN.GLE AXL..E

f-1- WASHO 4" r-16" WASHO 4"

15 I" f-1 "r=--~r:!ge J2.~'-f--e-~.1 J\, 0 ..

I -~•v •vv I ,, ~~~~ l"! I ~~~ '"' ~·. 1'-' ~ I~ ;:: I"' ~~ 1~1 1:!: IG

~ . . V

.25 f- 32,000LS TANDEM AXLE 40,000LB TANDEM AXLE r-

2v_ -tau

- WASHO 4" -f-_j WASHO .8" 1.5-

'- 11" ___LAver.pge .1$.4" c- I , ,(""""''u~v 10.8 - ,- --.-.--

10 ~ _d I~

a: ·~ 1-':' F ..

!1 0 ~ ~~~ ~ ~· .~ li~ l:: <:I >I§ I "' UNCRUSHED-GRAVEL SUBBASE THICKNESS FOR 200,000 V.EHI.CL..E :!"RIP$

4" A. C.+ 2" CRUSHED GRAVEL BASE

FIGURE 4

W ASHO adequate thicknesses for 119, 000 vehicle trips plotted on

chart showing designs submitted by the agencies for ZOO,OOO vehicle

trips. A 3-in. band 1-1/Z in. above and below the determined value

is shown.

~ 10 -

--

'1:1 0 ;:I

"' ;:I ... :;; Ill

"' N 0 0 . 0 0 0

..... .... .... '1:1

"' 0 .....

"' Ill (l .,. ,..,. "' m ... ~ .,. .... (l ,.... "'

(l .... "' ,..,. "' "' t= .... ~ (l

"' ~ 0.

Ill

>1>-1 ,.... ;:I

(l .... t= "' ~ 0.

OQ .... Ill

~ .... <:T Ill .. Ill

~

~ ::r I» s (l

(l

;

'1:1 Ill .., ... .... (l .... "' Ill ... 5"

OQ

0 ,., OQ

~ .... " Ill ... ,.... g .. 8' .... .. "' (l ... ,... 0 ;:I .. :;; .... s; Ill N • .... ;:I

10 .. "' ;:r !!. :::. n n g •

~ .,. "' OQ .... ~ .,. .... 5. .... (l

10 ... Ill

"' ... ::T

"' "' ~ Ill ., Ill

s; .... ~ "' .. ., 0.

"' .. ,... I§ .. "' ~ .... ... S" !l..

~ i

"1 ..... C'l c:: ::>;; t'l \J1

c :z £ ~ 11!

9 G> ;;lll

1\)~ •m

J>r ~(I> +C ~01

·~ ow ~11! !{!-I 11!;!; 00 .,. G>:Z ::011'1 )>(I> <VJ PI r"'!

01£ )> II) I\) PIO

~ 0 0

iii ~ Ill

i

Thickness In Inches - - 1\) 1\)

0 010 (J1 0 01 Norih CorJ;Jint:~ _j Puert-o Rico _j Maryland _j NewMexi(Jc __j California _j Colorado ~ Alahamo Delaware

;;; =

IVorfh Co!iohnc Marylon( NewMexko :---T Puerto R ~" I I K enfvckY! I J..

AFizona ltloho

~+.;~;.,--+,.-,J I

II "" I~

'

"' 1\)

b 0 0 r til

~ z ~ 3:

I

)> X r PI

~ 0 0 0 0 r til

~ z 0 PI 3: )> X r PI

(.pi

0

Thickness in Inches - - 1\) 1\)

0UIO(JI0UI Norlh CDJ Alo!:J:!.and NewMexiC4 California Colorado Kentuc!q_ Idaho Alabama De/a wore

r.:uei10Rim TII!)(OS

Wash. W.Va.

1//no

_j _j

1J,. l ;;;

I

h i !. I

11

•

Norlh Caf-olina

lJ _j

Maryland! , J l Ken tu clc:y I I 1-.

l -.I

Arizono Idaho

West V!Yq1£io Washin.qto. I Alabam11 Texas Delawt:u·e ~

~~~ ~ ~

01 . 0 0 0 r 01

!!.! z G> r ITl

)> )( r ITI

_j

1\) 1\)

~ 0 0 r til

U>

! )> X r ITI

(jl 0

j .E .. I 1-

25~ IS,OOOLB SINGLE AXLE r- 22,400LB SINGLE AXLE

r-1- WASHO 10" riT

WASHO 13" 15

1 12" 1- 13.5~

1-r-r-.:1. Average II~ - ~ 10

I~ r-

·~ :~ 11 I~

I~ 5

.~ ] ; I~ ~. ~~· Iii 0

~v

25 3 2,000LB TANDEM AXLE 40,000LB TANDEM AXLE -~v r

1-t--t ·•~v• ov I(' -~--- r-17' 14'

14.6":J 1 12" 1-' 15r~ 11.9'~

~ 10 !l

~~~~

li -::-r- I~ ti? ·"

5~ ~ll I~ _lj

11~ li ·~ I~ 1~11 ~ 'I( ~ v

UNCRUSHED-GRAVEL SUBBASE THICKNESS FOR 200,000 VEHICLE TRIPS 2" A.C.+ 4" CRUSHED-GRAVEL BASE

FIGURE 6

WASHO adequate thickness for 119,000 vehicle trips is plotted here

on the chart which shows de signs for 200, 000 trips. The average

thickness submitted and the WASHO findings are each shown by a

horizontal line,· and the shaded area represents a band of 1-1/2 in.

on each side of the test-determined thickness.

- 12 -

- 13 -

The Kentucky Department of Highways welcomed the oppor­

tunity to participate in the design correlation study and to evaluate itEI

design method in the light of the controlled traffic and performance

data. The results of the road test and o£ the companion studies have

been most helpful in evaluating Kentucky procedures and will un­

doubtedly aid in future Kentucky flexible pavement designs.