The Application of Kentucky Flexible Pavement Design Method to WASHO Test Road Conditions

Transcription

1 Tanspotation Kentucky Tanspotation Cente Reseach Repot Univesity of Kentucky Yea 1956 The Application of Kentucky Flexible Pavement Design Method to WASHO Test Road Conditions William B. Dake Kentucky Highway Mateials Reseach Laboatoy This pape is posted at UKnowledge. eseachepots/1256

2 Commonwealth of Kentucky Depatment of Highways THE APPLICATION OF KENTUCKY FLEXIBLE PAVEMENT DESIGN METHOD TO W ASHO TEST ROAD CONDITIONS by W. B. Dake Senio Reseach Enginee A Repot Pe sen ted at the Kentucky Highway Confeence, Univesity of Kentucky, Lexington, Mach 29, Highway Mateials Reseach Laboatoy Lexington, Kentucky Mach, 1956

3 INTRODUCTION In the summe of 1952 the Flexible Pavement Design Committee of the Highway Reseach Boad began the sponsoing of a compaative design poject. Seveal state highway depatments and othe oganizations wee invited to submit flexible pavement designs, based upon thei own cuent pactices, fo the subgade, mateials, and taffic conditions of the Westen Association of State Highway Officials (WASHO) test oad. This oad was being constucted in Malad, Idaho, though the paticipation of 13 westen states and the Bueau of Public Roads. The Kentucky Depatment of Highways was one of the oganizations invited to paticipate in the compaative design poject. Afte the oganizations invited had indicated thei inteest and willingness to paticipate in the study, they wee each funished with samples of the subgade, subbase, and base mateials, as well as a statement of cetain specific taffic pattens, s1ne of which would be used in testing the oad. All test vehicles would be of the semi-taile type, with two loaded axles. Single-axle loads would be 18, and 24, lb., while the tandem-axle vehicles would have 32, and 4,- lb, loads. It was intended that a total of 2, passes would be made by each vehicle. The suface couse of the entie W ASHO oadway was bituminous concete with penetation asphalt, 4, 8 pecent by weight. This couse was placed in compacted thicknesses of two and of fou inches. The base couse consisted of gaded-cushed gavel, anging fom 1 pecent passing the l-in. sieve to seven pecent passing the No. 2 sieve, and placed fou inches thick in sections paved with two inches of asphaltic concete, and two inches thick in sections with a 4-in. suface couse.

4 The gavel fo the subbase was pit un, with 1 pecent passing the 2-in. sieve and five pecent passing the No. ZOO sieve. Thee wee two specific objectives fo the design poject: a.) To detemine the pavement thickness indicated necessay by the methods of the vaious paticipating oganizations fo a given type of subgade soil, given pavement mateials, and fo definite pattens of taffic. b.) To compae the designs obtained in (a) with those indicated to be adequate unde the actual taffic imposed upon the WASHO test pavement by the.fou test axle loads. The Design Poblem The poblem of design fo the oganizations paticipating in the study was actually thee fold. It consisted of detemining, with thei own constuction standads but fo conditions at the Idaho test site, the following: 1. Subbase thickness specifications necessay fo 2, passes of each test vehicle, fo each of the vaiable suface couse and base thicknesses indicated in the table below: TABLE l. SUBBASE DESIGN PROBLEM Axle Lad b.) Pavement Sii1e Tandem Component 18, 4 _?2, 4, Suface (in.) Base (in.) Subbase (in.)????????

5 -,. Z. The numbe of tips of vehicles with each of the fou axle loadings equied to poduce failue fo the following designs: TABLE 2. W ASHO TEST PAVEMENT DESIGNS,_,_.,.. --=.--' Compon.t Thickness in ln.ches Suface Base Subbase Total , '--- -,_ 3. The pavement thickness necessay fo the climatic conditions whee the paticula design pocedue is nomally used (in this depat ment's case, fo Kentucky) but fo cetain specified taffic conditions. Thicknesses of suface, base, and subbase wee to be selected as thought necessay. The taffic conditions specified included the aleady detailed WASHO patten, with the ZOO, passes of each vehicle; as well as cetain othe taffic pattens as indicated in the table below: TABLE 3. COMPOSITE TRAFFIC PATTERNS --Patten ---patten-----patten Patten --"( a=l., Jbl lcl ( d'"-) Passenge Cas (No. of Vehicles/Day) Commecial Vehicles (No, Axles/Day) 1, lb. o less 12, lb. 14, lb. 16, lb. 18, lb ,587, 63,734,

6 Keky Desig, Kentucky Flexible Pavement Design is based on a modification of the CBR method. Taffic is evaluated by the equivalent 5lb. wheelload method (EWL). The pavement design cuves ae based on Kentucky's expeience, having been developed fom the esults of a compehensive study made by the Depatment of Highways in 1947 and These cuves have since been extended and modified to povide fo the geate volumes and weights of pesent and expected taffic. The cuves in Fig. 1 show the combined thickness of high-type macadam base and asphaltic-concete pavement equied fo cetain CBR values and vaious taffic anges. Anticipated axle loads of 1, lb. and geate ae conveted to the equivalent numbe of 5-lb. wheel loads. A 1,-lb. axle is equal to one 5-lb. wheel load, while a 12,-lb. axle is equivalent to two 5-lb. wheel loads and an 18, -lb. axle equal to sixteen 1, -lb. axles. The table of equivalents was woked up by the Califonia Depatment of Public Woks and is geneally accepted, Total 2-y. anticipated taffic is calculated in EWL values. The CBR method fo detemining beaing values of soil has been modified fo Kentucky use. This value is detemined in the laboatoy fo subgade samples fom the pt"oject. Subgade, subbase, and base!>amples fom the WASHO test tack wee tested in the Highway Depatment's testing laboatoy by the Division of Mateials. The sub gade soil was found to have a CBR of 5. 5 pecent. The cushed- gavel base was found to be about equal in beaing value to Kentucky macadam base, while the uncushed-gavel subbase had only 8 pecent of the beaing value of the cushed mateial (tested

7 MINIMUM LABORATORY C 8 R VALUE (J) w 2 ::I: 4 z 1-.:" 6 z w 8 w > 1 z 12 <1: w (J) <1: o I (J) (J) w z i 18 I 2 ") J: 1-22 w z o o e,o v 1-- f---' Cuve Limiting E WL (,A) ---- v v! v v - (million) / v / v v v-- - la Less than 112 (ii}_ / v 1-- I Less than I --- / / v --- II L_ v / / " ---- w v v 6-1 / / 1-" ---- VI 1-2 // / --- VII 2-4 VL X // / v/ - _/ t- VIII 4-8 /' B-16 X 16 -"32 t- -- v ---- IX /./ v/ v -- / / / v v,_ -- _/ / v/ - /" v/ / V.-= / v/ v v "/. fv\ --- /" vy / PC' 15,. Kentucky Depatment of Highways Mateials Reseach Lob oa loy FLEXIBLE PAVEMENT DESIGN CURVES t- Fig. l. Kentucky Flexible Pavement Design Cuves.

8 by the CBR method). Because of these evaluations, cushed-gavel base thickness was detemined in the designs on an equal basis with macadam; while the subbase mateial, when used, was inceased 25 pe cent in thickness, to compensate fo!' its lowe quality. Consideation in the oveall design was given fo the 4in. asphaltic concete thickness vesus the 2-in. suface. The thickness equied was loweed somewhat fo the 4-in. sufaced sections. The pavement designs and failue estil:nations detemined by the Kentucky Depatment of Highways fo the poblems ae shown in the following tables. Table 4 contains the subbase designs fo the fist potion of the pob ten. TABLE 4. SUBBASE DESIGNS ----= ,._--=-- Pavement Component Single Axle Tandem Axle (in.) Ts, ooo lb-.- -zz,_4oo_!_g, ooo lb. 4, lb. Suface Base 4 z Subbase " -- Total ,3.,--- Table 5 below, pesents the findings fo the second potion, listing the numbe of passes of the vaious vehicles which each of the pave ment designs used in the test tack was calculated to withstand adequately. These values wee detemined fom the Kentucky flexible pavement design cuves. At the bottom of the table ae listed the subbase thickness values

9 - 6 - that wee found to be adequate fo 119, passes of the vaious vehicles at the test tack. (It was decided duing the unning of the tests that the oiginally planned 2, passes wuld not be feasible, and the taffic was stopped on May 29, 1954, afte all vehicles had made 119, tips ove thei espective sections.) TABLE 5. NUMBER OF TRIPS TO PRODUCE FAILURE Thickness 18, Single Z in. A-:c-:--:;::in. A.c: ' ' - :.==.;;:_c.;;;;;: _ 4-in. Base 2.in. Base 4-in. Base ;: ;:c;;;c:_: , 4 Single -,;--,.,.-- :;:'in. A.C. 4-in. A.C. 2-in. Base 31,25 46,9 7,81 11, ,1 93, 19,55 23, ,2 312, 56,6 78, :8, 1,563, 235, 391, 16 1,75, 5,62, 938, 1,42, W ASHO FINDINGS (Subbase Thickness Found Adequate fo 119, Tips) 1 in. 4 in. 13 in. 4 in, Table 6, which follows, shows the designs fo the thid potion of the design poblem, fo the WASHO taffic patten of 2, passes of each vehicle.

10 TABLE 6', PAVE:MEN'l' l),eslgns :Ji'G!l 'I'!li>TAL 'I'HlCKMESS (UI!ins An S.el>.eted Qogoplllcl1e:Jlt l?liekael!ll} Pavem.e:J\t <l:lllmpneji,t Bas.e (i:j\d 3 4 ll Zl Fig, Z indic.ates. g.aph.ically.the deoigas.l!elec.ted by each l'.tm p.ticipatl.ag agenciel!. 91 this pcn:tiq,a af.the p:eb!em, i.a which the i:n dlyidl!lal thickll.esaea Q! atl cpmpl!lnents wee 1e!t till the chc>i<.!,e 111 the de.:igne: The Kel!.tncky tllltal thiekne.aoe!l wne made '!I.P e.tm e.gm ponens aleady in Ta'l;illil 6. Tal:!t!!> 7 1 betqw, El.hows ib.e design$ fq he cempp!iite taffic patti!! tn!l Ul111ted l.n Table l) fe. the.ihid pothm J tne pl:'c!blem, TAB:L)l: 7.,. PAVEMENT. ESIGNS. :11'11. COJ\i!P$!TE. 'I'ItMFtO :Pave'm.ent QC!Impllflilijl!n (J):I,.J PA'l'T.Ell.NS. Pattel:'n Pae:t:n Pate:n Jci) PaUe:n Ia! {!),d) z zs Z,15 3 Bas.e z Ul '** 11 zt tm. 9 13, zo

11 ! ":! (IQ N <:'1:1 (D llj, ::<: (D s AI (D (D,_,;:; " o ij O. <1> m,. (IQ >;:l,m <:d " en i;! s s o & '. I'TI)g ;::l ti (D -l<i ;J AII'TI. c- _s:,.'<! ""tji'ti :: ::. CJ)2 :e-l (D ;:l ('") --I (D -l:::t: Ol I :I:- Ol <1> J>2 == :!! " CJ)I'TI (D :::t:ul " (D ;J oul Ol(IQ (D > 3:,(IQ l> <1> (D -1 ;:l I'TI Cll () AI <1> l> '<! "" H>,.o Ul ::". (D N o.,o oo a (IQO ;::l (D " Thickness in Inches Thickness in Inches o o (JJ o o (JI (JI (JI (JI (JI MoTland T I T hla:vvand I 1 1 Alabama I CJd Noth Cao inq I Coloado o Washinaltm - (JI Woslunof> n i Coloado!» i Pvefo Ri o Alabama g Oelawae Kentucky 1. Colif"onio Califonia l Kenfuckv 1'-,,-1 Oe/oWQe I CA:l, /Vol"hCa Jina 1 l> Pvtl"fo Ric'p R Ul NewMex/cb I (1) Ne":Mexic 2 AizOntll I I'TI Atzono I I Wyom,;;;; T 3: W_yoming I I'TI west v/iain Ia T l> l> West Vi.oi T I l> TeJ<as _I. I Te_xos.,8 X MISS u/1 a I'TI MISS OUT/ CD m CD m w. N Mq_y/and I Mayland I Aloham<t I Wqshmgta I Nofh Cal> tina I Noth Coe 1/n.q I Wa.shinof< n I Kentuckv - o Kentucky!<, o Aizona II o.!'l Delawae I J,o Alabama -.!!> Pueto R i o 1'\1 Callfol'lla g Aizona b; Coloqda Califonia NewMeicl:o I New MexiCio i;! Pvefo Ri(jt> I :. Ul Coloado T 2 f)elawae 1 h z WyomiiiQ I IJ West v, gi iq I l> Wesf Vio1 ia I l> " Wvomin<t I ;ii I'TI < eus. l l> Tuqs. 1,g l> MisstJvNi I X MIS.Soun I CD X CD fl1!j) I'TI w - b - = (JJ

12 W ASHO FINDINGS Duing the peiod fom Novembe, 195Z, though May, 1954, the test tack was subjected to 119,() tips of the test vehicles on atl t;>st sections, The minimum total thicknesses that wee found to withstand adequately the 119, vehicle passe; in the oute wheel path, fo the 2-in. sufacing of asphaltic concete, wee 16 in. fo the 18, lb. single axle, 19 in, fo the 22,4 lb. single axle, 17 in. fo the 32, lb. tandem; and ZO in. fo the 4, lb. tandem, In the inne wheel path, the 1-in thick pavement sections wee undamaged by any of the fou loading. Compaable values found fo the 4-in. asphaltic concete pavement, oute wheel path, H) in fo the fist thee loadings and 14 in. fo the 4, lb. tandem.axle load. Fo the inne path they wee 6 in. fo the two single axle loading and 1 in. fo the two tandem axle loads. In the section of this epot w}lich J'ollows, gaphs ae used to pesent a compaison between the findings of the WASHO test and the designs submitted by the paticipatin$ oganizations. The Kentucky designs ae indicated on each of the gaphs

13 2 5- IB,OOOLB SINGLE AXLE - 22,4LB SINGLE AXLE II" 1--' " Aveage 12.3" J.-Aveage 1" --.!!f--. " " " I I - I- ' Q: " ",. 5-f >!e 1--, -.. I l ", lj '!:',j'., li " ' s: til " 8. Q li\ 'I( u? Cl.., 1! , <: 1 :E 1-- E 32,LB TANDEM AXLE " -. ".e 1} _ LJ '.,'>I- - 4,LB TANDEM AXLE f " J. #Aveae 13.4" f- [Aveage 1.6" - f1 -Ei ".s 1-- Q; - 1.? (.,J bt" -.l( 5,$!%2.: 3 h 1 i :.i " ". ' -:: ' -»1. " Q fo - I) IJ I 1-- " :s: -. -2" <:: J " "5. < '1:- l:. : UNCRUSHED-GRAVEL SUBBASE THICKNESS FOR 2, VEHICLE TRIPS 4" A.C. + 2" CRUSHED GRAVEL BASE FIGURE 3 This chat shows the subbase thicknesses that each of the coopeating agencies submitted fo 2, tips of each test vehicle, with a 4-in. asphaltic concete suface and a 2-in. base couse. Note the aveage subbase thickness submitted and the Kentucky design fo each taffic loading

14 v 25 18,LB SINGLE AXLE 22,4LB SIN.GLE AXLE 1- WASHO 4" 15 I" f-1 I,, l"! f--e-.1 J\, - v vv I '. 1'-' I ;:: I 11 1:!: IG f- -16" WASHO 4" I.. V.25 f- 32,LS TANDEM AXLE 4,LB TANDEM AXLE 2v_ "=--:!ge J2.'- - WASHO 4" -f-_j WASHO.8" 1.5- LAve.pge.1$.4" 1 '- 11" c- I, - -tau,("""'uv 1.8 -, _d I a: 1- ':' F!1. li l:: <:I >I I UNCRUSHED-GRAVEL SUBBASE THICKNESS FOR 2, V.EHI.CLE :!"RIP$ 4" A. C.+ 2" CRUSHED GRAVEL BASE FIGURE 4 W ASHO adequate thicknesses fo 119, vehicle tips plotted on chat showing designs submitted by the agencies fo ZOO,OOO vehicle tips. A 3-in. band 1-1/Z in. above and below the detemined value is shown. 1 -

15 '1:1 ;:I. ;:I :;;. N. '1:1..,.,,.. m.,.,,,. t=. >1>-, 1 ;:I t=. OQ <:T :: s I» ; '1:1,.. 5" OQ,., OQ "., g 8'.,. ;:I :;; s; N ;:I 1 ;:!!. :::. n n g.,. OQ., ::T., s;.,.,. I. S"!l i "1. C'l c:: ::>;; t'l \J1 c :z 11! 9 G> ;;lll 1\) m J> (I> +C 1 ow 11!!{!-I.,. 11!;!; G>:Z ::11'1 )>(I> <VJ PI! 1 )> II) I\) PIO iii i Thickness In Inches - - 1\) 1\) 1 (J1 1 Alahamo Delawae IVofh Co!iohnc Maylon( AFizona ltloho II "" I 1\) b I til z 3: )> X PI til z PI 3: )> X PI ' (.pi Thickness in Inches - - 1\) 1\) UIO(JIUI Nolh CDJ Alo!:J:!.and NewMexiC4 Califonia Coloado Kentuc!q_ Idaho Alabama De/a woe.:uei1rim TII!)(OS Wash. W.Va. 1//no _j _j 1J,. I l ;;; h 11 Nolh Caf-olina Aizono Idaho Alabam11 Texas I _j -.I lj. 1 1!!.! z G> ITl )> )( _j ITI 1\) 1\) til U>! )> X ITI (jl i!. Mayland!, J l Ken tu clc:y I I 1-. l West V!Yq1 io Washin.qto. I Delawt:u e Noih CoJ;Jint: _j Puet-o Rico _j Mayland _j NewMexi(Jc j Califonia _j Coloado ;;; = NewMexko :---T Pueto R " I I K enfvcky! I J +.;;.,--+,.-,J I --

16 j.e I 1-25 IS,OOOLB SINGLE AXLE WASHO 1" ,4LB SINGLE AXLE it WASHO 13" 1 12" :1. Aveage II - I - : 11. ] ; I. Iii I I v ,LB TANDEM AXLE 4,LB TANDEM AXLE v 1-t--t - v ov I(' ' 14' 1 12" 1-' ' 1!l li -::-- I ti? " 5 ll I _lj 11 li I 111 v 'I( 14.6":J UNCRUSHED-GRAVEL SUBBASE THICKNESS FOR 2, VEHICLE TRIPS 2" A.C.+ 4" CRUSHED-GRAVEL BASE FIGURE 6 WASHO adequate thickness fo 119, vehicle tips is plotted hee on the chat which shows de signs fo 2, tips. The aveage thickness submitted and the WASHO findings ae each shown by a hoizontal line, and the shaded aea epesents a band of 1-1/2 in. on each side of the test-detemined thickness

17 The Kentucky Depatment of Highways welcomed the oppotunity to paticipate in the design coelation study and to evaluate itei design method in the light of the contolled taffic and pefomance data. The esults of the oad test and o the companion studies have been most helpful in evaluating Kentucky pocedues and will undoubtedly aid in futue Kentucky flexible pavement designs.