1998 aashto guide - CEProfs

22 Pages·2012·1.02 MB·English

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SUPPLEMENTAL VERSION OF THE AASATO GUIDE, PART I,
SECTION 3.2 RIGID PAVEMENT DESIGN FOR DESIGN
OF PAVEMENT STRUCTURES AND
SECTION 3.3 RIGID PAVEMENT JOINT DESIGN

‘This supplement has heen propared as an slterautcructhod far rigid pavement design, in the form,
‘oF an addonciom ¢o the cument AASHTO Guide. Ic contuins the recommendations from NCHRP
1-20, modified based on the results of the verification stady conducted using the LTE database

3.2 RIGID PAVEMENT DESIGN

‘This section describes the design for Pordand eemest conciete pavements incfuding jointed plain
UPCP), jointed reinforced GRCP), and continuously rciaforoel (CRCP). As inthe design for
exible paveiments, itis wsanmed that these paverneats wll camry tafe levels in excess of 70,000
1-kip 180-N] (rigid pavement) ESALy over the performance period. Examples of usc of this
gid pavement design procedure are presented atthe end of this supplement

Design of Different Types of Concrete Pavement. The JPCP design vonvept iste provides &
sufficient sab thickness and joint spacing lo minimize the development of ransverse cracking.
‘The JRCP and CRCP diesign concepts provide sufficient ab thickness and reinforcement to hold
‘ery tight the transverse cracks that Form so that ageregave imerlock wl be maintained. The
thickness of che desien mode! upon which this puide is hased was developet and validated.
apecifivally for JPCP, for which joint spacing is oue of the important required dcsien inpais,
afcoting theenal curling suesses und, thus, ansverse cracking. «A proper selection af sab
‘hilinoss and join spacing is required to cantrol tbe development of transverse cracking for &
avon climate, base, and subgrade. JRCP har much longer joint spacing and CIRCP tas vo joints,
‘nd the teansverso cracks that eventually farm in these typos of pavements nist be hel tight by
sufficient stel reinforeernent,

‘The uss ofthis design method to determine an approprale lab thickness for TRCP or CRCP
‘equies the sclecLion of unnpat “typotherical” joint spacing, Research asing the LTPP dacabase
Jha shown that the following input values of joint spacing will salen reasomuble design
thicknesses using this design method.

SPCR: Actoal joint spacing, R,

JRCV: Acro joint spacing if less than 20 f [9 ra, or 30 fe eximum (ase Chis value only
16 obtain slab design thickness)

CRCP: 15.4 [4.6 (use this hypocheticl value only to obtain shb design thickaes)
Lond Traasfer at Joints, The AASHTO design procedure is based ou the AASHO Road Test
‘pavement porformance algorithm thet was extended ta include additional design features.
Inherent in the ue of the AASHTO provedure is the use of dowels at tunsverse joints. Joint
‘ruling was nota distress manifestation a the Road Test due co the adequacy of the dowel
design, A fuuiting design check is provided for doweled joints to ensure thatthe dowels sre
sized properly. Ifa significant faulting problem ig expected, an increase in dowel diameter ot
other design change ray'be warranted, The non-dowoled faalting check was developed nsing
‘more recent measurement of field Jata,

the designer wishes to consider undoweled joints,» design check for rulting is provided. if
the faulting check indicates inadequate load tanefer, design modifications such az the use af
dowels or changes in base ype, druinage, and joint spacing may be made.

In addition, ifthe designer wishes to consider undowoled joints, a design check iy also made for
critical suresses due to axle loads applied near the trausverse Joint, along wich u negative thermal
gzadicat, creating a comer loading situation that would load to premature cracking, If this chock:
shows a potential problem, desiga modifications such asthe use of dowels, ineased slab
thickness, or changes in base (ype may be mado,

322. Develop Exfeetive Medulns of Subgrade Reaction (k-Value)

‘The modulus of subgrade reaction (k-value) is defined as that measured or extimated an top of
(he finished roadbed soit or embankment upon which the basc course andlor conerete slab will
eveotually be constructed, The k-velue represents the subgrade (and embankment, if present; ft
does not represent the base coutse, The base course is considered a styctural layer af the
pavement along with the conercie slab, and thus ite hickness and modnlns are important desiga
inputs in determining the required slab thickness in Section 3,

‘The k:Value input defined. The elastic kasi ontop ofthe subgrade or embankment i the
required design input. The gost k-vahe incorporated in previous versions ofthe AASHTO
Guide ropeseuts not only eastio dermaton ofthe ibpmade nader a loading lite, bt also
evbstantal permanent deformation. Only the elastic ooupoueat ofthis deformation is eosidered
representative ofthe espante ofthe sbgrade wo trafic load onthe pavement. The elie
‘alu test was the main subgrade test conducted oxensvely atthe AASHO Road Test. Whon the
lati i-vatue was used i strucual analysis ofthe AASHO Road Test pavements, iv was found
tbat slab strees computa wih ¢hreedimensional Fite element mpdsl wore approximately
qual o those measured in the fcld under fill-scal ruck axle loediys at coop speed, providing
farther jutfemion for use ofthe elastic Koval in Ge design,

‘Steps in determining design K-vafue. The k-value input requied for this design method is
determined by the following steps, which are described in ths seston:

1, Seloeta subgrade kevalue foreach season, using any of the three fallowing methods:
@)_Comrelations with soil ¢ype and other soil properties ar teats.
(©) Dedtection testing and backcalculation (most highly recormmended),
(©) Plate bearing tests,
2. Detemmin a seasonally adjusted effective k-vatue,
3, Adjust the seasonal effective k-value for effects of a shallow rigid layer, i[present, andor an
‘cnbantament above the natural subgrade,

‘Note that the AASHTO design methodology requires the mean K-value, not the lowest value
‘measured or some other conservative value, Note also that ao additional adjustment to the k-
‘value is applied for loss of support. Substantial Joss of support existed for many sections at the
AASHO Road Test, which lod to increased slab eracking and loss of eerviceebility. Therefore,
the performance dats, upon which the AASHO Road Test performance madal is based, already
reflet the effoet of considerable loss of support,

Step 1. Select a Subgrade k-Value for Fach Season, A season ia defined as a period af time
‘within a year, such a5 3 months (ie. spring, swmmet, fll, winle), The number of scasons and
the length of each season by which a year is characterized depend on the climate of the
pavement’a feestion,

‘There are several ways to micasure or estimate the subgrade clastic kevaluo, Procedures are
provided for three methods described below—carreletion methods, backcaleulacioa methods, and
plate testing methods.

Correlation Methods. Guidelines are prescatod for selecting an appropriate F-value based on
soil classification, moisture level, density, California Bearing Ratio (CAR), or Dynamic Cone
Penetrometer (DCP) data, The CBR may also be estimated from the R-value, These carrelation
‘methods are nticipated 1 be used routinely foe design, ‘The kevaluce obtained fiom soil iype or
(esis comrelation methods may need to be adjusted for erabaakaent above the subgrade at &
shallow rigid layer beneath the subgrade,

‘Phe hovalues end enrretations fo cohesive soils (A-¢ through AT). The boating capacity

off cohesive soit is strongly infaenced by ther degre of eaturation (8, pow, whi

function of water content (w, percent), dry density Cy, Ib/f), and specific gravity (G,)
(4 -( 2) (2s)

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Recorumended kvalus fo each ie-yined sil peas auton of degre of satiation are

show in Fgure 40. Bac ine eprevats the mid ofa range ofeasoneble ves fork For

aay given sol type and degree of tration, te ang of eacnsble values is ebout +40 pin

[11 €Pafaun]. A reonsble lover limit fr kat 100 percent stration is considered to be 25

pee [7¥Pafmm). Thus, for example, an A- ci ght bo expected ro exhibit valves

‘bctwoen abou 180 and 260 psifin [49 and 70 Pam] at $0 percent satwation, and k-values
‘betwoe about 25 and 85 psi/in [7 and 23 kPa/mm] at 100 percent saturation,

‘Two different types of materiafs can be classified as A-4: predominantly silty materials (at least
75 percent passing the #200 sieve, possibly orgaaic), and mixtores of sil, sand, and gravel (up 10
64 percent retained on #200 sieve). ‘The former may havea density between about 90 and 105

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lve, ps

Subgrade k val

5

50

‘ine mpmsenm mid of gr
aa Brest case, Raat 9 pala
Fo cine Fort owe sd Sep of ssn

fc maa at Atti fy
Sosy ates pt end OR Ge Fac,
pe tua ie td wi ey
nyt espe cucmn sn
Seopa

1 pet = 16018 kgm?
Ips 274 KPadmn

60 65 70 75 80 8 90 95 100
Degree of saturation, percent

‘Figure 40, The kevalue versus degree of saturation for cohesive soils,

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‘Recommended k-value ranges For fine-grained soils, along with (ypicat ranges of dry density aad
‘CBR for each soil typo, ac summarized in Table 11

‘The Kevalnes and correlations for cohesionless soils (Ac1 snd A-8). ‘The bearing capacity
of cohesionless materials is furly insensitive to moisture variation and is predominantly &
function oftheir void ratio and overall sess state. Recommeuded k-value ranges for
ccobosionless soils, along with typical canges of dry density and CBR for each sail type, are
suramarized in Table 11.

‘The k-values and correlations for A-2 sails. Soils in the A-2 class are all granular
amalerials falling between A-I and 4-3. Although itia difficult to predict the behavior af such a
‘wide varity of materials, te avpiluble data indioate that in terms of bearing capacity, A-2
unatcrials behave similarly to cohesionless materiels of comparable density. Recommended k-
‘valuc ranges for A-2 soils, slong with typical namges of dry density and CBR for each soil ype,
are suenmarized is Table 11.

Correlation af k-values to California Bearing Ratio. Figure 4) illustrates the approximate
sange oF k-values that might be expected for a soil with a given Californis Boaring Retio,

Correlation of k-values to penetration rate by Dynamic Cone Penetrommeter. Figure 42
ilhustrates the range of values that might be expectod fora soil with a given penetration rte
(nches per blow) mewsured with a Dynamic Cone Penetrometer. This ia a rapid hand-held
‘esting device that can be used to quickly test dozens of locations along en alignmont. The DCP
‘can also penetrate AC surfaces and surfice weatments to test the foundation below.

Assigament of K-values to seasons, Among the factors that should be considered ix
selecting seasonal K-values are the seasonal movement of the waler ible, seasonal precipitation
levels, winter fost depths, number of fteeze-thaw eycles, and the exteat to which the subgrade
‘will be projected from frost by embanlonent material. "frozen" Ik may nat be appropriate for
‘winter, even in a cold climate, ifthe fiost will not reach und remain ina substantial dhicknese of
‘the subgrade throughout the winter. 111i anticipated thet « substantial depth (e.g, a Few feet) of
‘tho subgrade will be frozen, a k-value of SO0 psitin [135 kPa/mm] would be an appropriate
"frozen? I,

‘Tho seasonol variation ip degree of sofuration is difficult to predict, but in locations where a
‘water table is constanlly present ata depth of less than abour 10 £13 m], itis reasonable to
expect that fine-grained subgrades wil remain at least 70 o 90 percent gaturaied, and may be
‘completely saturated for substantial periods in the spring, County aol reports ean provide data
‘on the position of the high-water table (Le, the typical depth to the watcr table atthe time af the
_your that i isa its highest). Unfortinately, eounty soll ports do not provide data on the
‘variation in depth to the water tle throughout the year.
Table 11. Recommended k-vulue ranges for various soil pes,

“AASHTO ‘Bescon united | Deydniy | car | vate
ass tes] toe) L foapenn | sti 4
Coeme pained site
‘A, well graded ta5-140 | 60-80 | 300-450
evel ow,ar
‘Acta nooely graded zo -130_ | 35-60 | 300-400
Ate ane end sw | 10-130 [20-40 | 200-400
Ad Faosand se] 05-120 | 15.25 | 150-300
2 sols (gra aril wl hih Bos
ADA, gravely sly gavel om | woetas [so-so [300-500
ADs, gvlly ily endy ave
AD sandy shy st sf ios [29-40 | 300-400
AS andy sly grovel sand
126, golly covey grned ec [2010 [20-40 | 200-450
4-7, gravelly layey sandy gravel
Acd6y sandy iyey and
se | 105-130 | 10-20 | 50-350
AD, way aay ervey
ad
ioe yrloed sot
sit go-t0s [ae | 25-1656
MM ML,OL
itera oo-ias | sis [40-2206
gavel
AS poet eraded wi TP po-to0 | 4-8 | assao0e
st
AG lutioely a _| o-ms [seis [ a5-ass*
ATS motrieiystente [cot | vas | asas | a5-ais6
‘adie lay
Ans ighy psi exon | sna [3-5 | ae-z
ito ak

"eval of Sos atand sol Is highly depends om degon of anation. See Fle 0

‘hetoreronttonded value range ply toa homogntnae el aie test 10 RG] Wie fan eabanavont yet,
{est 10 fs ens vera soto subg, te kvaue fr the unyiesi shuld Le when ee ee
tabi and aut fe th ypc and choses of eabankmcnt matri atag Pipe 4 Ta ap of bedock cone ch:
100m oft op of te sel, he chonl be adh ted ul igs,

Vt 16.0.0 | pain 0.271 Krahn
600

gS
3

stic k-value, psi/in

400

300

200

Approximate static ela:

100

Lpsiin= 0271

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23 5 10-20 30-50
California Bearing Ratio, percent

KPa
Figured, Approximaue relationship of kevalue range to CBR.

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160
800

700

ey
3
3

w
3
S

Approximate static elastic k-value, psi/in
6
S

Lt

0 : ; >
O1 0203 05 1 23 = 5
DCP Penetration Rate, in/blow

1 psiin=0.271 kPa
lions 254mm

Figure 42, Approximate relationship of kovalue sange to DCP penctration rate

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Deflection Testing and Backealeulation Methods. Thess methods aro suiluble Cor determining
‘kevalue for design of ovevlays af existing pavements, for design of a reconstructed pavement on,
‘existing alignments or for design of similar pavements in the same general location on the samme
‘ype of subgrade, An agency may alo use backealcalation mettods to develop correlations
‘between nondestructive deflection testing results and subgrade lypes und properties, Cul and fill
sections are likely to yield different kevalues, No embankment or rigid layer adjustment is
required for backcalculated k-values if theso charactoristics aro similar forthe pavement boing
tested and the pavement heing designed, but backcslootated dynamic kevalucs do nod to be
reduced by 4 actor of approximately 2to estimate a static elastic k-value for use in design,

_An appropriate design subgrade kevalue for ure as an inpot to tis design method Is determined
bythe following tps:

“Measure deflections on an in-service concrete or composite (AC-averlaid PCC) pavement
‘with the same or similar subgrade as the pavement being designed.

Compute the apprupriaie AREA of each deflection basin

Compute an intial estivnate (wsurning an infinite slab size) of the radius of relative stitiuess,¢
(Compute an initial caimatc (assuming an infinite slab size) of the subgrade k-value,

‘Compute adjustment factors forthe maximum deflection dana Ube iililly estima # to
saecount for the finite slab size.

‘Adjust tho initially estimated k-valuo to account for tho fini slab size.

‘Compute the mean backealeulated subgrade k-value for all of tho deflection basins considered,
‘Compute te estimated mean static k-value for use in desig.

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‘Those steps ae deseribed below, with the relevant equations for hare conerete and composite
‘pavements given foreach ssp,

‘Measure deflections. Measure slab dofloction basins along tho projoct at an interval sfficfent
toadeguately assess conditions. Intervals of 100 0 1000 f [300.300 mi] ae typical. Measure
deflections with sensors located ar 0, 8, 12, 18, 24,36, and 60 in [0, 203, 305, 457, 610,915, and
1524 mm] frou the centee ofthe load. ‘Measure deflections in te outer wheel path. A heavy-load
deflection device (e.g, Falling Weight Deflectometer) and a Foad magaitude of 9,000 ibf [40 EN]
mrerecommended. ASTM D4694 and D4695 provide additional guidance on doflection testing,

‘Conspute AREA. For a bare concret> pavement, compuir the AREA, of euch deflection
‘bast using the following equation:

fmol) CRAB oe) oo)

‘where dy = deflection in center of loading plat, inches
4, = deflections at 0 8 12, 18,24, 36, and 60 in [0, 208, 305, 457, 620, 915, and 152A mm]
fiom plate center, inches
For a composite pavement, computc the ARBA, of cach deflection hasin using the following
equation:

won oof) )-a[ 8) (2)

ay

Estimate { assuming an infinite slab size. The radius of relative stifines fora bare concrete
‘Pavement (assuming an infinite slab) may be estimated using the following equstion:

60 - anna,) |
mn | SoA
te 2.768 (28)

~0.698

‘The radius of relative sifiness for x composite pavement (assuming an infinive slab) may be,
estimated using the following equation:

te { 27 AREAS) |
15840. 19)

ial 0.476

[gtlonate ic sssuming an lofiulte stab size. For a bate cancrete pavemont, compute an initia
estimate of the k-value using the following equation:

Pay
ate

rs

9}

= backealoulated dynamte K-valu, psivin
load, Ib

deflection measured at venter of load plate, inc

estimated radius of relative stfiness, inches, from previous step

‘ondimenslonal coefficient of deflection a center cf Joad plate:

= 011245 ¢ [-orarer Kees o}] Bu

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