Various mathematical and physical models available, were selected

and tested using the prepared RSD data sets. The discussion of

these models are divided into two subgroups namely; Linear and

non-linear models, based on the procedures of regression analysis

used. In both cases the SPSS Statistical Package for the Social

Sciences (Nie et al., 1975; Robinson, 1984) was used to do linear

and non-linear regression analyses. The reason for the choice of

the SPSS package was the compatibility with the computer system

where the deflection basin data sets are stored. Each of the models

used are briefly discussed in terms of the results.

If a typical set of deflection basin results are plotted on a

logarithmic versus linear scale, like in Figure A.1, some guiding

observations can be made as to what types of models can be used.

There is in general a tendency towards a straight line, althouih

as shown, it is still slightly curved. Based on these obser-

vations. the following models as shown in Table A.1, were used.

The values of the related parameters are also given as derived

from the linear regression model in the SPSS package (Nie et al.,

1975) for a typical data set.

The results of these models for typical data sets are shown in

Figures A.2 and A.3. Before even considering the statistical

evaluation, it can be seen that there are some shortcominis in

some of these models.

Figure A.2 illustrates that models 1 and 2 (as defined in Table

A.1) are only applicable to the area of positive curvature. Model

2 is however able to be accurate over a wider area (10 to 300 mm).

Figure A.3 shows that if model 1 is used over a wider area than

that covered by the positive curvature of the deflection basin, it

can easily lead to an ill fit. For that reason models 1 and 2

~~ ~----..~••• x~ __ ...... ~

•• I~ .~ . .~. ... ... , ....:~~

x FITTED MODEL• MEASURED POINTS101

EEz0~uW...JlL.W0 16

FIGURE A.ITYPICAL LOG VERSUS LINEAR PLOT OF RSD DEFLECTION BASIN MEASUREMENTS

200HORIZONTAL DISTANCE (mm)

FIGURE A.2

TYPICAL PLOTS OF LINEAR REGRESSION MODELS FITTED TO THE POSITIVE CURVATURE

D aa

5 0,200....uW--J

tt 0,150o

FIGURE A.3TYPICAL PLOTS OF LINEAR REGRESSION MODELS FITTED

TO THE WHOLE DEFLECTION BASIN

Parameters for atypical data set

l. Y •••A exp (A1 x2)0

or y •••A 10(A1x2)0

or log y •••log Ao + A1x2

2. y •••A x20

3. y •••exp (a2 x2 •••a1 x + a )0

or y •••10(a2x2+a'1x+ao)

A •••0,2959o

-6A •••0,991 x 10o

A ••• 0,45780

a ••• -0,49900

a1 ••• -0,4513 x 10-3

a2 ••• -0,1330 x 106

a •• 0,44670

a1 •• 0,7818 x 10 -3 0,98

a2 ••• 0,2309 x 10-6-9

a3 ••• -0,1021 x 10

were only applied to the first 200 rom. This is covering an areawider than the normal width of positive curvature (Dehlen 1962)but it does not lead to ill fits of model 1 (see Figure A.2).

A distinctive feature of the deflection basin curves as shown inFigure A.3, is the peakedness of the area of the area of positivecurvature. This area of positive curvature is on average lessthan 10 per cent of the horizontal distance of the wholedeflection basin.

The R-square values of model 1 and 2 are an acceptable 0,99. Thegoodness of fit was also calculated as follows:

n- E (y - Y )2

T i=l i i * 100 %n

- E (y - A)2i=l i

where A = Average of measured valuesY. = Measured data values~Yi = Values from model fitted

The goodness95 per cent.and goodness

of fit for a typical data set for models 1Both therefore have acceptable values of

of fit for the positive curvature region.

and 2 isR-square

Models 3 and 4 are polynomial functions of the order 2 and 3.There is no real advantage gained in accuracy when the order ofthe polynomial is increased above the third order. The computa-tion takes longer and becomes costlier too. The goodness of fitof the second order polynomial (model 3) for a typical set ofmeasurements is 99 per cent. It can be seen in Table A.1 thatthe R-square values for models 3 and 4 are also an acceptablyhigh 0,98. This is very good, but visually it can be seen inFigure A.3 that the deviance from the observed values in thevery small area near the origin (positive curvature) does leadto some concern as to the applicability thereof for the wholedeflection basin. This tendency to give equal weight to alldata points along the linear horizontal distance (x) is typicalof this linear regression model used in the SPSS package. Forthat reason it was decided to investigate the non-linear re-gression analysis with available models that would tend to givea better description of the whole deflection basin.

Another point of interest in the vicinity of maximum deflection(x-a) is the gradient of the tangent at x-a. In Table A.2 the

gradient of the curve described by any of the 4 models is givenas first order differentials.

First order differentials

~ = A (Exp (Alx2» 2Alxdx 0

~ - 2A xdx 0

~ = a .- 2'2x) exp (a xl2+a Xo + a )dx . 1

2. y" A x2o

~ -dx

At the point of maximum deflection (x-O) only models land 2have a horizontal gradient as the first order differentials areequal to zero. The gradient given by Models 3 and 4 aredependent on the values of the constants when x-O. This isanother indication of ill fit of models 3 and 4 at the point ofmaximum deflection.

As indicated earlier, the non-linear model of regressionanalysis used in the SPSS packaie (Robinson, 1984) tends to giveequal weight to each measurement on the deflection basin. Inusing this non-linear regression analysis package the aim isthen to minimize the sum of squares. It is the sum squares ofthe difference between the fitted model and the observedmeasured points. For this reason it is therefore important that

the unnatural "spikes should be smoothed out before curvefitting is done.

There are two options in the non-linear regression analysispackage of SPSS (Robinson, 1984) namely using the Gauss methodor the Marquardt method. The latter was selected as superiordue to its shorter computing time required. In Table A.3 thetwo models tested by the two options are shown with thecalculated constants and sum of squares values.

Sum of squares Parameters fora typicaldata set

3,768*10-3

A ••3,321*10-1A~ ••-9,991*10-1

a ••-1,066 3o -a1 "" -1,134*10_7a2 ••-2,796*10

-18,914 x 10

As can be seen both models had been tested for curve fitting bythe linear regression analysis facility of SPSS before. Model 1was again tested here on an area wider than the positivecurvature by selecting the first 350 mm for curve fitting. Ascould be expected it did lead to a poor fit as reflected in therather high value of sum of squares.

The residuals (difference between prediction and observation)are also plotted. Apart from giving a visual impression of thegoodness of fit, it also serves as a monitor for specificpatterns which indicate poor fitting models. In Figure A.4 theresidual plot of the model 1 fitting is shown. The definitepattern confirms the ill fit. It re-emphasises the fact thatmodel 1 can only be applied to the area of positive curvature «150 rom).

Model 2 (Table A.3) proved to be better suited for the fittingof the whole deflection basin and particularly the large area of

00

15 0

0enL&J 0en<t 0u~

0

a: 0UJ 0lD~ 0::lZ 0

0

5 0

0

0

0

0 10 20 30RESIDUALS (X 16~

FIGURE" AARESIDUAL PLOT OF AN ILL FITTING MODEL

the reverse curvature of the deflection basin. The good fitthereof is reflected by the low value of the sum of squares intable A.3. The plot of residuals in Figure A.S also reflects nospecific patterns indicating a good fit. The lack in fittingthe area of positive curvature in the vicinity of maximumdeflection still persists as was indicated in the linearregression analysis too. It would be possible though to usethese two models of table A.3 and limit the curve fitting of thepositive curvature to that by model 1 and the curve fitting ofthe larger reverse curvature to that of model 2 and achievesatisfactory results.

The non-linear package of SPSS makes it possible to userelatively complex models in the regression analysis. Thisgives the opportunity to look at physical models which can beadapted to the observed deflection basin. A promising model isthat of beams of unlimited length on elastic foundations withconcentrated loading. This model is described in great detailby Het~nyi (1971) and Fryba (1967). The intention is not togive a detailed description of this theory here, but ratherconcentrate on the use and manipulation of the derived solutionsin the curve fitting exercise. In the analysis of bending ofbeams on an elastic foundation H~tenyi (1971) states that theassumption is that reaction forces of the foundation areproportional at every point to the deflection of the beam atthat point based on the Winkler theory. This theory also statesthat deformation exists only along the portion--d±·ree-t.ly--··underloading and was verified in experiments for a variety of soils.Het~nyi (1971) is quoted as follows; II that the Winklertheory, in spite of its simplicity may often more accuratelyrepresent the actual conditions existing in soil foundationsthan do some of the more complicated analysis •••11

A short description of the model is as follows; Consider aninfinite beam subjected to a single concentrated force P at thea point 0, which is the origin of the axis system as shown infigure A.6. The general solution for the deflection curve of a

••• • •• •• ••.100 •• • • •• • l;j• •• ~• C• ~

• ~•• <:• • i:::• •••••

• G::• • ~70 •• • C• 10 C• • • « ~•• w

~• 0::• •• ::> •••••• e"•• - C• IJ..~•• ••

• • -..J

• §••• ~

• -<t)

• lA,J•• ~

• ••• • •• •

• ••• •• •• • ••• •• •• •

(f) •m • ••••.... ••.•.••. -20 -15 -10 -5 0 5 10IDID RESIDUALS ( x 103)eno;t

I

~

0.;ren

BENDINGMOMENT

PA -AX .Y = 2 k e (cos AX to SIn A X )

DOWNWARDDEFLECTION

M= :A e-AX (cos AX - sin AX)

PAx'Q =-2' e- cos AX

SHEARINGFORCE

FIGURE A.6POINT LOAD ON AN INFINITE BEAM ON AN ELASnC

FOUNDATION

beam subjected to transverse loading is derived by Hetenyi(1971) as;

where y is the deflection taken as positive downwardsx is the horizontal distance from the origin

C1, CZ' C3, C4 are constants~ is the damping factor, and

k is the modulus of the foundation expressed inkg/m2/m

E is the modulus of elasticity in kg/mnI is the second moment of area of the beam

Without even going into further detail of the simplification ofthis model it can be seen in Figure A.6 what the similaritiesbetween the modelled deflection curve and the measureddeflection basin curves are. When the symmetry of thedeflection curve and the equilibrium of the reaction forces areconsidered this general equation reduces to;

p -).xY = Zk e (cOSAX + sin~x), which gives the deflection curvefor the right side (x>o) of the beam. This correlates well withthe data preparations of the deflection basin described in thepreceding sections. The form of the curve suggests that thecase of no dampening can be considered for this part of thecurve analyzed. Fryba (1967) gives the solution as follows forsuch a situation;

-blxle (a cosax + bsina Ixl)

This form is obviously similar to that derived by Hetenyi (1971.In order to simplify the determination process of the constantsin these equations, it was decided to use the following curvefitting model;

In figure A.7 a plot of a typical data set and the curve fittingis shown. Visually it can be seen that this model succeeds indescribing the observed deflection basin accurately. The sum ofsquares value is low (4.15 x 10-3 for this typical data set) andthe plot of the residuals does not indicate any ill fit. Thegoodness of fit for such a typical data set is above 98 percent. It was found that this mode is applicable over a widerange of variances in load. load repetitions and structuralcondition of pavements. It is obvious though that although thismodel gives the best fit of all models tested it still tends togive an ill fit in the positive curvature area. Although thisarea is very small and very peaked in relation to the rest ofthe deflection basin. it was decided to use the parabola of thelinear models in this area of possible curvature in order toarrive at a true representation of the whole deflection basin.

82 X

E 0.2 Y = B 1e (COS B 3X + si n B3X )

EzQI-Uw...JLLWo

LOAD 60 kNNO REPETITIONS

x - PREDICTED• - OBSERVED

FIGURE A.7TYPICAL CURVE FITTING OF PHYSICAL MODEL

SUHHARY ON CONDITION SURVEYS ENHANCING

DEFLECTION BASIN ANALYSIS

A condition survey is an important input in the non-destructivetesting of an analysis procedure. In Figure B.1 it is shown howthis kind of visual survey greatly enhance the understanding ofthe material characterization in a typical analysis procedure foroverlay design. Condition surveys are non-destuctive testingprocedures enhancing the other non-destuctive testing proceduressuch as deflection basin analysis. In Figure 4.1 it was explainedhow in the South African mechanistic rehabilitation designprocedure (Freeme, 1983) it is important to identify the pavementlayer state. The discussion on condition survey will thereforefocus on crack and rut classification related to the deflectionbasin survey (see Figure B.1).

Ullidtz (1982) defines a functional and structural condition inhis model on pavement rehabilitation. He states that; "Thestructural condition is of no immediate interest to the road userbut is is extremely important to the highway agency because thefuture functional condition depends on the present structuralcondition." A visual condition survey can be seen as an aid to aproper structural evaluation.

The standard procedure for conducting a condition survey, asoutlined in Draft TRH12 (NITRR. 1983), should be followed.Normally the visual assessment precede the deflection basin surveybut it is suggested that the deflection basin survey and visualassessment may be done simultaneously on smaller scale projects.The results of both surveys should be plotted on the same scale.By this means the obvious weak spots can be identified when otherrelevant information such as drainage, cut or fill transition andsoil changes is taken into consideration.

Pavement Evaluation and Overlay Design Inputs

Destr uct iv e Testi ng

raff ic DeflectionData Survey

AnalysisSections

In-situ Material Sampling1esting Lab. Testing

Pavement Class Identification

Compute Deflection BasinParameter Function

Compute Distress Determi nants

Fatigue Cracking

Overlay Criteria

Overlay Thickness and System Selection

FIGURE 8.1Mechanistic overlay design flow diagram

B.3Cracks in the existing asphalt concrete layer have a major in-fluence on the overlay design procedure. Normally pavements areclassified as either cracked or not cracked. However, themajority of pavements fall somewhere between these extremes. Theaim of this section is therefore to establish quantitive proce-dures to classify cracked pavements in order to improve therehabilitation design procedure.

Grant and Curtayne (1982) point out that fatigue is not neces-sarily the cause of cracking in asphaltic concrete layers in SouthAfrica. Other factors, not necessarily traffic-related, shouldalso be considered as being possible causes of premature cracking(Grant, et al (1979). Pronk and Buiter (1982) indicate thatwith full depth asphalt pavements, even in the Netherlands,cracking does not necessarily begin at the bottom of the asphaltlayer. Grant and Curtayne (1982) therefore stress that a studyof the past behaviour of the pavements can provide good clues inthis respect. The preceding statements are to indicate thecomplexity of crack mechanisms of asphalt concrete layers.Different reasons for cracking are therefore discussed in order toarrive at a classification for cracked pavements.

The aim of this is purely to simplify the analysis of such apavement by using the deflection basin parameters in the mecha-nistic approach.

First it is suggested that the difference in basic crack mecha-nism, due to the difference in pavement structure be considered.For the South African condition it is suggested that on thegrounds of as-built plans or matericiTsam-pting--procedure (FigureB.1), a flexible pavement under survey be classified according tothe basic TRH4 (NITRR, 1985a) catalogue, i.e.

(a) granular base pavements(b) bitumen base pavements (tar as an alternative)(c) cemented base pavements.

This basic classification is taken a step further by Freeme (1983)by relating the time-dependent behaviour of different pavementtypes to the concept of equivalent material state illustrated inFigure B.2. It is explained in Chapter 3 how the measureddeflection basin parameters can be used to accurately identify anysuch pavement behaviour state.

Next, the degree of cracking should be defined. In the light ofwork done by Kilareski et al. (1982) and Treybig et al. (1978), itis suggested that the AASHO definition of cracking could beapplied. Jordaan and Servas (1983) give a very clear descriptionof three types of cracking and how it should be calculated. Thesetypes are crocodile or map or block cracking, longitudinalcracking and other crack patterns or combinations of the precedingtypes. For these types each 100 m of road length is classified asbeing in a sound, warning or severe condition. This depends onthe percentage of 100 m being cracked and the road category.

Crack conditions can be improved by crack filling and repair ofthe low percentage of severe cracking of the defined categories orcrack types. The decision to repair cracks should be based oneconomic comparisons, but it is obvious that crack repair willimprove possible crack attenuation behaviour in general. Koole(1979) suggests though that an overlay design based on the severecondition of cracking might in some cases be the most economicalin the final analysis owing to the expensive nature of proceduresto upgrade the pavement in regard to the crack condition outlinedabove.

In the final level of crack classification more sophisticatedmethods should be considered. This normally consists of analysisprocedures associated with the overlay design analyses. Variousresearchers, such as Molenaar (1983) and Coetzee and Monismith(1979) suggest the use of fracture mechanics principles and finiteelement computer programs in the analysis stage. In order to usethese procedures though, the previous crack classification wouldhave to be elaborated in order to establish average values ofcrack width too. Molenaar (1983) states the following:

I1940-4 -4760/9 B.D.

STATE .---.. VERY STIFF I STIFF I . FLEXIBLE I VERY FLEXIBLE

APPROXIMATE DEFLECTION 0,2 0,4 0,6LEVEL (mm)

CONCRETE ~

EXAMPLES OF CHANGE CEMENT TREATED BASE PAVEMENT •OF STATE OF DIFFERENT CRUSHED- STONE OR BITUMEN TREATED BASE OVERPAVEMENT TYPES CEMENT TREATED SUBBASE

BITUMEN TREATED BASE OVERGRANULAR SUBBASE

GRANULAR BASE IGRANULARSUBBASE. LOW SUBGRADECBR VALUE

CONCRETE ROAD N2

HOORNSNEK (TVU ; BRONKHORSTSPRUIT P67/1 (TVU; N3 SWINBURNE (OFS)

P157/1 a PI57/2 JAN SMUTS AIRPORT nVU;PARADISE VALLEY (NTUTYPICAL EXAMPLES N3 MARIANNHILL (NTUIN PRACTICE P205/2 GI LLOOL Y (TVU

KOEBERG (CAPE)PI23 MAGALIESBURG nvuP6/1 BABSFONTEIN (TV L)

FIGURE B.2

DIAGRAMMATIC REPRESENTATION OF THE TIME DEPENDENT BEHAVIOUROF DIFFERENT PAVEMENT TYPES (Freeme, /983)

"Although the fracture mechanic's approach has the potential to bean excellent tool in solving the reflection crack problem, it hasnot gained very much popularity. In fact it can be stated thatit is still a research tool and that its practical application islimited to only a few cases."

Recently the monitoring of crack movements, as described by Rust(1984), has become another viable method that may be associatedwith the classifications outlined above. The Crack Activity Meter(CAM) that was developed can measure amongst others the definedtotal crack movement. Crack activity or total crack movementnormally has the typical peaking behaviour with axle repetitionsas shown in Figure B.3. Rust (1985) was able to determine thatfor a flexible pavement with a cemented base and under specificconditions, there is a good correlation between block size andcrack movement. The data indicated that there is a critical blocksize below which the crack movement increases markedly withfurther decrease in block size. Typical results are shown inFigure B.4. These concepts can be used effectively to enhance thecrack classification as given above.

In Appendix E the good correlation between the measured crack-activity and measured deflection basin parameters is illustratedby means of an example. As will be shown there this greatlyenhances the rehabilitation analysis procedure.

One of the major aims of a rut survey is to determine the amountof material needed for the levelling of the existing rut before anoverlay is applied. This is all related to ride comfort (PSIvalues) and, in wet conditions in particular, to rider safety.The extent of rutting is generally used in overlay design as amajor criterion of permanent deformation and the structural stateof the pavement. The general procedure is to limit rutting inoverlay designs by limiting the vertical subgrade strain (e: ).vsThis approach was originally developed by Dorman and Metcalf

• JOINT 132

-x- JOINT 131

WHEEL LOAD: 40 kN

E

-=-I-Z 400llJ::EllJ>0::E:l<::U<ta:u...J<tI- 2000I-

-x .•..•.....•• ...•.••.•x ....... ..•.. ..•..

....•. ..•.. •........•.,•....

"X

oo 200 400

REPETITIONS (x 103)

FIGURE B.3

CHANGE IN TOTAL CRACK MOVEMENT DURING HVSTESTING ON THE N2 CONCRETE ROAD-SECTION 258A2

(Rust I 1984)

olD

If)....If)

If)

~IVIo·v

140-4-5097/2 BS

400 .\\\\\\300 \\

.•..• \ .,E \ ,~J- \ .',zw \ • "-:IE "'- tJ:l200 • .w \ ......... .......-. 00>0 .....•.. -...-:IE \ • • . ------~ \ • • ----0 ----« , • ----0:: --a-_0 , • • --. ---.-, •100 , •• •"........ . •----- •----------------~----

oo 4

BLOCK SIZE (m)

FIGURE 8.4CORRELATION BETWEEN CRACK MOVEMENT AND BLOCK SIZE ON THE MR 27 (Rusf,1985J

(1963) in their analysis of the behaviour of the test sections ofthe AASHO road test.

It is should be noted that rutting is not only related to thesubgrade but that contributions also come from the various layersin the pavement. For this reason Koole (1979) mentions that therut in the asphalt concrete layer should be treated separately.The South African experience also indicates that such a directionshould be followed. Freeme et ale (1982a) indicate that bettercharacterization of the bitumen layer in terms of volumetric andshear properties is necessary to accommodate this deformationphenomenon in the bitumen layer. Maree et ale (1982) show thatfor granular base pavements tested with the Heavy Vehicle Simu-lator (HVS). most of the permanent deformation took place withinthe granular base and subbase. The subgrades never meaningfullycontributed towards the total deformation and were always wellprotected. In the same report Maree et ale (1982) illustrate thestrong correlation between cracking, excessive rain, moistureintrusion and deformation for typical granular base pavements;this is shown Figure B.S.

The preceding statements make it obvious that a more qualitativeclassification of rutting is needed than just a report of theaverage rut. In line with the classification outlined in theprevious section on cracking, it is suggested that the pavementstructure classification as defined be used also. In fact it isre-emphasized that no indicator like rutting or deflection shouldbe used in isolation. The concept is clearly illustrated byFreeme (1983) in Figure B.6 where various indicators of thebehaviour of typical granular layers are shown.

A further practical classification is needed to discriminatebetween various mechanisms of permanent deformation. Molenaar(1983) classifies two types of rutting (see Figure B.7). Thefirst type is that without lateral displacement due to densifica-tion. The second type is that with lateral displacement due toPrandtl type of shear deformation. This ties in with the prev-ious discussion on the South African experience. Grant and

zQti~ 10Q:

~Wo

INGRESS OF WATER

\ \ \HIGH QUALITYGI STANDARD

FIGURE 8.5

SCHEMATIC DIAGRAM OF THE RELATIVE BEHAVIOUR OFGRANULAR MATERIAL OF DIFFERENT QUALITIES

(Moree, of 01., 1982)

.......

owr--~I

~Io~lI'L _

EE 15

Zo~ 10

~0::~ 51LIo

IDENSIFICATION I

IIIII

PHASE 2STABLE STATE

PHASE 3IEFFECT OF INGRESS OF WATER

III

WATER AND WATER-ISUSCEPTIBLEMATERIAL

tv<1:-~

~'i" RATE OF INCREASE OF0'< DEFORMATION CAN REDUCEe, AGAIN IF WATER IS REMOVED

<lot/;~(j

"

RATE OF INCREASE DEPENDENT ONQUALITY OF MATERIAL AND STA BLEMOISTURE· CONDITIONS

ESOs OR TRAFFIC ••(a) PERMANENT DEFORMATION

~I-Ua:lLIlL1-I)-L&.<t1LI-1o

Z1--zJ:1LI!::::::;~(f)lLI0::

INGRESSWATER

IF WATER IS REMOVEDDEFLECTIONS CAN

~

REDUCE BECAUSE OFINCREASE IN RESILIENTMODULUS OF LAYER- ....•. -----

DEFLECTION REMAINS LOWIF LAY ER NOT SUSCEPTIBLE TO WATERe.g. CRUSHED- STONE BASE OR WATER-BOUND MACADAM

ESOs OR TRAFFIC ••(b) RESILIENT BEHAVIOU R

05000..~(f)

:3:>o~ 250

I-ZlLI-I(f)lLI0:: 0

/

MATERIAL NOT SIGNIFICANTLYSUSCEPTIBLE TO THE INGRESSOF WATER---I

III

I NGRESS OF WATERAND WATER-SUSCEPTIBLEMATERIAL

-----,..,. --~WATER

REMOVED

ESOs(c) CHANGE IN MODULUS OF

~gm........

z0..2u~00::

I-lLIZlLI0..

OR TRAFFICCEMENTED LAYER

I INGRESS OF WATER

I AND WATER-SUSCEPTIBLEI MATERIAL

III

.,.,....---...WATER~""" -_REMOVED

MATERIAL NOT SIGNIFICANTLYSUSCEPTIBLE TO THE INGRESS

ESOs OR TRAFFIC ••(d) STRENGTt-l BEHAVIOUR

FIGURE 8.6INDICATORS OF THE BEHAVIOUR OF GRANULAR LAYERS

.. IE reeme. / !lE31

r LORIGINAL SURFAr PROFILE

~-~·

r·

~ ~ 1· ·I ......•.....•.•

~ IType A

Rutting without lateral displacement of the material. Thistype of rutting is due to densification of the material .

t~~·I·r

._I

I·~-------.;I

Type 8

Rutting with lateral displacement of the material.Rutting can be judged to be a Prandtl type of sheardeformation.

FIGURE 8.7TYPES OF RUTTI NG WHICH CAN 8E DISCERNED

( Molenaar, 1983)

Curtayne (1982) note that shear in the subgrade is characterizedby wide rutting. Shear in the base layer is characterized bynarrow ruts with displaced material appearing like a moundadjacent to the rut.

From the visual survey therefore a classification of the type ofrutting that exists may be made. which will strongly influence theoverlay design analysis. The Draft TRH12 (NITRR. 1983) give clearindications for rut criteria related to pavement class andpavement type. It is suggested that those criteria and thosesuggested by Jordaan and Servas(1983) be followed.

At any specific moment, an existing pavement has a certain amount ofaccumulated damage done to it by repeated traffic loading. Thereis normally also a certain amount of remaining damage which theexisting pavement can undergo before failure. The severity of thedamage caused by each repeated traffic loading depends on thestructural strength of the existing pavement. This is usuallyexpressed in terms of the equivalent number of standard axles(E80s). If the magnitude of the critical strains is reduced, thenthe existing pavement can carry a larger number of standard axleloads (E80s). The function of an overlay is therefore to reducethe magnitude of these critical load-induced strains or stresses,depending on the distress determinants being used.

Remaining life has two meanings. Without an overlay a pavementnormally has remaining life and with an overlay a pavement has aremaining life, that is usually lengthened or prolonged. For thisreason "remaining life" will refer to the remaining life of apavement without an overlay.

In the literature remaining life is usually analysed on the basis ofthe phenomenological theory of cumulative damage. Attempts torelate the structural condition, based on deflection basin measure-ments, in a different way to the life of the pavement, will also bediscussed.

The phenomenological theory of cumulative damage is also referred toas the linear summation of cycle ratios. This was advanced byMiner (1945) to predict the fatigue life of metals subjected tofluctuating stress amplitudes. Monismith et ale (1966, 1969) usedit to estimate fatigue life of bituminous layers in pavement struct-ures and established it as an acceptable and useful relationship.

Let n. ••number of applications at stress or strain level1

N. ••number of applications to failure at stress or strain1

levelD. ••damage due to N. number of applications at stress1 1

or strain level

Then the damage, Di, is defined as the stress or strain cycleratio, i.e.

D = n1·.1 N.

1

Failure will occur when D. = 1.1

Let r = number of different stress or strain levels involvedD = cumulative damage due to number of applications at

different stress or strain levels

Then the cumulative damage, D, is stated as the linear summation ofcycle ratios, i.e.

r rE D = E ni

i=l i i=l N.1

rE n. 1or 2- =

i=l N.1

Snaith et al. (1980) use the distress determinants vertical subgradestrain (€vs)' and maximum horizontal aspahlt strain (ERA)' asdiscussed in chapter 4 and 6 , to determine damage due to ruttingdeformation and fatigue cracking respectively. For both forms ofdamage the strain-life relationship is given by the generalequation:

It is therefore possible to apply the cumulative damage theory toboth forms of damage. The accumulation of damage from repeatedapplications at various strain levels is illustrated diagram-matically in Figure C.1. In Figure C.1(a) the strain-lifediagram is shown with a typical strain-life curve, l-k. On thiscurve a strain level E1, for example, corresponds to a life N1.Lines a-b, c-d, etc., represent n1 applications at strain levelEl, and nZ applications at strain level EZ' etc. These lines,represented by arrows, are called damage paths. The dashedlines, b-c, d-e etc. are called iso-damage lines. If the amountsof damage at band c are the same, then

This is represented more simply in a damage-life diagram (seeFigure C.1(b». The damage scale ranges from 0 to 1. Thedamage paths can be plotted continuously as shown in FigureC.1(c). In this way, the cumulative damage arising from repeatedapplications is determined in diagrammatic form.

In practice the number of repeated applications (n.) is expressed1

in terms of the equivalent number of standard axles (E80s). Thisreduces the analysis to only one strain level to determine re-maining life. In Figure C.1(a), therefore, at strain level E1the damaged or consumed life is nl and total life is N1.Remaining life at this strain level is equal to:

Alternatively, damage (D1) is often expressed as previouslydefined and remaining life (R1) is then:

'c,

-.. DAMAGE PATH--- ISO-DAMAGE LINEE', a b

d.,'" "' ••.._e _

nlll N4 N--"I

n4N4 N-....

h

~ DAMAGE PATH- ISO-STRAIN LINE

(c) DAMAGE-PATHDIAGRAM

FIGURE C.I

GRAPHICAL PRESENTATION OF CUMULATIVEDAMAGE THEORY (Snaith , et a I., 1980 )

R = 1-D1 1

1n1= -N1

Using the same distress criteria, vertical subgrade strain (e ) dvs an

maximum horizontal asphalt strain and (eRA)' Anderson (1977) alsoused this theory to determine remaining life. It is pointed out,though, that future environmental or traffic changes cannot usuallybe foreseen and therefore such a procedure should be seen as a guideonly. In considering the remaining life of a pavement with ruttingdue to permanent deformation, Anderson (1977) reasons that thedamaged life or consumed life will be nullified when the surfacedeformation is removed by an overlay. Koole (1979) supports thisview by Anderson (1977) in his description of the Shell overlaydesign method. The remaining life of a pavement with fatiguecracking is determined in accordance with the description by Snaithet ale (1980).

Treybig et ale (1978) also use the theory of cumulative damage inorder to determine remaining life for a pavement with fatiguecracking and rutting due to permanent deformation. As mentioned inAppendix B, however, the cracked state of the existing pavement istaken into consideration in determining the material parameters (E

asphalt). Chapter 4 described how these material parameters areused to determine the distress determinants. In a pavement withfatigue cracking the maximum horizontal asphalt strain (ERA) iscalculated and used to determine the remaining life in terms ofstandard axle (E80) repetitions, as described by Snaith et ale(1980). It was shown in Chapter 6, Treybig et ale (1978) considerthe contribution of all the structural layers to rutting due topermanent deformation by determining the various stresses andstrains of each layer.

It is obvious that Kilareski et ale (1982) only considered fatiguecracking when determining remaining life. The strain (eRA) neednot necessarily be determined, but as shown in Figure C.2 the

deflection basin parameter. surface curvature index (SCI). isrelated to the number of equivalent single-axle loads (EAL). Inthis case the structural number has also been determined. based onthe AASHO Design Procedure (for the various test sections). The 10per cent fatigue cracking line is the same form as described abovefor the general relationship. N = A(l)b. The equation fore:remaining life is as described above. namely (N1 - n1). Kilareskiet al. (1982) advance this one step further by relating remaininglife (in terms of equivalent axle loads) to the SCI for variousstructural numbers (pavement strengths). as shown in Figure C.3.

Residual life determined from deflection measurements alone does notlead to satisfactory results. Koole (1979) states: "It is notpossible to determine the residual life of a pavement solely fromdeflection measurements". The reasoq lies in the fact that thechange in a structural parameter. for example elastic modulus (E).with an increase in load repetitions shows a sharp decrease in valueinitially but thereafter there is a long period during whichvirtually no change occurs and only at the end of the structurallife is there a definite sharp decrease to distress. Deflectionmeasurements also reflect this typical behaviour. However. it ispossible to relate early life deflections empirically to thecritical life of particular types of pavement structures. as shownin Figure C.4 using work done by Lister and Kennedy (1977). Koole(1979) also mentions that original design life can be determinedfrom FWD deflections. A "crude" test on consumed life is to takeFWD deflections between the wheel tracks. If the deflectionsmeasured in the wheel tracks. are significantly greater than thosemeasured between the wheel tracks the pavement is approaching theend of its service life.

Pronk and Buiter (1982) mention the procedure in which the declinein effective layer thickness is related to the structural strength.This forms the basis of the structural performance model developedby Molenaar (1983). This principle is shown schematically inFigure C.5 where equivalent layer thickness (H ) decreases ine

c: 1000

10I

0700 Section No. Structural No.~ • •-C,) H (2.70)

(J) 500 10% Fatigue Crocking Line)( 400 ~

8 (:3.14) 9(3.58 )Q)

14(3.65)~300c:-Q) 200 ~,..,...•...

::s 1d (3.72 ).-#/1, ,........- ___ .• I

C Ic (3.94) __ .•, ">•...2 (4.38) "::s

C,)7 (4.74)-- ••.•

Q) 100(,)

c 80-•...::s(J) 60

I x 10s 2 3 4 6 8 Ix 106 2 3 4 6

18-kip (80-kN) Equivalent Single-Axle Loads

FIGURE C.2VARIATION OF SURFACE CURVATURE

lNOEX-WITH EAL. (Kiloreski, et 01.,1982)

--l~ 3.0

~ 2.0

WlL.--l 1.0~z 0.7w~w

~(,!)zz 0.2<t~wa::

O. I

0.07

0.05

STRUCTURAL NUMBER, SN5.0' 4.5 4.0 3.5 3.0

50 100 150 200 250 300SURFACE CURVATURE INDEX, SCI<l66IN.)

FIGURE C.3REMAINING PAVEMENT LIFE BASED ONFATIGUE CRACKING FOR BITUMINOUSCONCRETE PAVEMENTS WITH SUBBASE.

(Kilareski, et aI., 1982)

140-4-4760/38

ROAD BASE& Hot rolled asphalt

200 • Dense bitumen macadam

• Dense tarmacadam150 " Medium textured tarmacadam

N • Open textured tarmacadamI x0

100 AO Readings still sound)(

E •E 80 • A

.yAyZ 60 • A n0

~

.-0- 50 y.-u 0 0

w 40 A-ILLW

300

0,2 0,3 0,4 0,6 0,8 1,0 1,5 2 3 4 5 6 8 10 15 20CUMULATIVE STANDARD AXLES (x 106)

FIGURE C.4RELATION BETWEEN DEFLECTION AND CRITICAL LIFE OFPAVEMENTS WITH BITUMINOUS AND TAR BOUND BASES

(Lister and Kennedy, 1978 )

(f)(f)wz:::c:u:cI-~0::-W Q)>-:c<X:-...J

I-ZW-J<X:>~oW

LOAD REPETITIONS n

FIGURE C.5HYPOTHESIZED DECREASE OF THE EQUIVALENTLAYER THICKNESS (He) WITH RESPECT TO THENUMBER OF LOAD APPLICATIONS (n).

relation to the number of load applications(n). The structuralcondition of the pavement can be characterized by means of thestructural condition index p. which is defined as:

P = H /Hecn eco

where H = equivalent layer thickness after n loadecnapplications corrected for temperature andenvironmental fluctuations

H = equivalent layer thickness just afterecoconstruction corrected for temperature andenvironmental fluctuations

In order to determine H • deflection values between the wheelecopaths are measured as described above. Molenaar (1983) defines Hecovalues determined in this way as "candidate" H values since theyecowould have been subjected to some loading between the wheel paths.The amount of future deterioration depends on the expected number ofload applications. the structural condition index P and the shape ofthe deterioration function characterized by Sl N.

og

Values for Sl N should also be determined by means of deflectionogmeasurements. Sl N can be calculated as follows:og

2 2 2 S2= a1 b1 S log He + l.o.f(l N 1 )og - oge:

where a1 = slope of fatigue relation

b1 = slope of H versus log e:relation (=2)e

S2 = lack of fit of the equation used to describe1.o.f.the fatigue relation (=0,16)

In Figure 4.10 the typical relationship between H and surfaceecurvature index (SeI) is shown from results of deflection basin

- 1,0a..-xw0zz0I-

0,80z0U...J<r0:: f3:::>I- --- S\OgNu 0,6:::>0::I-en

0,2 0,4REPETITION RAT\ ° n / N

FIGURE C.6COMPARISON OF THE THEORETICALLYDERIVED STRUCTURAL PERFORMANCEMODEL AND THE EQUIVALENT LAYERTHICKNESS DETERIORATION MODEL

(Molenaar, 1983)

plotted in relation to deterioration (n/N) and the influence ofSl N can also be seen.og

Molenaar (1983) takes this even further by calculating P and SlogNdirectly from deflection basin parameter values such as surfacecurvature index (SCI) as follows:

P = (SCI /SCI )do n

S2 N = d2 2 2 2log 1 c1 S 10gSCI+ Sl.o.f (log N-log €)

where SCI = SCI at time of constructiono

SCI = SCI after n load applicationsn

d1 = absolute value of the slope of the SCI versus He

relation (a reasonable value is 0,53)

c1 = slope of the 10g(SCI)-in relation to log N (=0,943)

All other variables have been defined before. However. Molenaar(1983) warns as follows:

"Although the procedure to calculate P seems very simple, one shouldbe aware of the fact that in a number of cases the ratios H /Hecn ecoand SCI /SCI might be larger than one.o n

Remaining life is determined by this procedure as illustrated inFigure C.7.

Molenaar (1983) modified the work done by the Belgian Road ResearchCentre. He uses the following equation for permanent deformationmodel:

where u· permanent deformation (m)p

ZoI-oZ-o~~ [j 0.9<:toa:Z::>-I-U::> 0.8a:I-en 0.75

-¢......oCD~¢I

~I

o~ ...

__ I_-_n I_N_.....•••._1-

0.5REPETITION RATIO n/N

FIGURE C.7PROCEDURE TO ASSESS THE REMAINING

LIFE (Molenaar,1983)

u = elastic deformation (m)e

By means of regression analyses of a typical three-layered pavementsystem Molenaar (1983) used the BISAR computer program to arrive atvalues of bo' b1 and n for the various interfaces between thelayers. The elastic deformation at the pavement surface must beknown in order to be able to determine the elastic deformation ofthe top layer. This deformation due to dual wheel loading can beestimated from the maximum deflection (6 ) value of the fallingoweight deflectometer (FWD) by using the following equation:

log Ue surface = 0,09+0,948 log 60FWD

The elastic deformation of each layer can be calculated by sub-tracting the deformation at the lower interface from the deformationat the upper interface. The permanent deformation can then becalculated by means of the permanent deformation model withconstants shown in Table C.1.

A correction factor is applied to relate observed rut depth to thesecalculated values. By these means rut depth can be related to loadapplications (n), and consumed rut life can be determined bydefining a terminal rut depth of for example 20 mm.

In chapter 4 and 6 it was concluded that the current mechanisticdesign procedure in South Africa using distress determinantsvertical subgrade strain (€ ) and horizontal asphalt strain (€h )vs ais a sound one. Proper fatigue relationships have been establishedfor these parameters. This makes the use of the linear summationof cyclecracking= (l)b),

€

ratios applicable to bothand deformation rutting.described by Snaith et al.

distress criteria: fatigueThe generalized relationship, (N(1980) can thus be used to

TABLE C.1. Values forob and1b to be used in the calculationof the permanent deformation (Molenaar. 1983)

b= U *b n 1e 0

Bituminouslayers U *4.49nO.25 5 000 (summer)e

U *2nO.3 if n<0.12 me 500U *2nO.2 if n<0.12 me

Stonebase

Leanconcrete base 1 500

GranularU *2nO.3subbase 200e

Subgrade U *(1+0.7 logn) 5. 1O. 20. 40e

determine remaining life for both distress criteria. The morecritical value can then be used in the selection of an overlay, asdescribed in Appendix D. Although Freeme et al. (1982a) give afundamental basis to rehabilitation design in their description ofthe mechanistic design procedure. it is felt that. particularly inthe case of establishing criteria to determine consumed life due torutting, some advances can be made. This would again be possiblewith the information available from HVS tests and observed fielddata. In this regard the approach by Treybig et al. (1978), wherethe deformation contributions of each layer is better rep~e$ented by~_the computed stresses and strains of each layer, should be pursuedwith the available data.

It is clear too that the approach to relate the remaining life ofthe pavement to other structural indicators such as the equivalentlayer approach shows much promise. The structural performancemodel suggested by Molenaar (1983) was developed specifically for athree-layered pavement structure and therefore it is obvious that itwould not be possible to use this approach in all cases. Insteadit is suggested that, with the previously mentioned informationavailable on pavement performance in South Africa, the performancemodel be established with values determined from regressionanalyses. This approach would then take into consideration factors

such as the deflection basin measuring device, deflection basinparameter selected and pavement structure classification describedpreviously.

The model relating permanent deformation and elastic deformation tothe number of load applications seems a sound approach. It wouldalso be possible to establish these relationships with theregression analysis of the information available for the SouthAfrican condition.

This section is a logical continuation of the discussion in AppendixC. In general, the decision to overlay a pavement under analysiswill be based on criteria related to the remaining life or consumedlife. The distress criteria, fatigue cracking and permanentdeformation rutting, are considered separately to determine theremaining life of the pavement. The decision to overlay thepavement is based on the more conservative of the two criteria, butboth criteria are checked again to ensure that the prolonged life(remaining life after the overlay) would indeed be achieved. As inany situation where various possible alternatives are generated,sound engineering judgement is influenced by economicconsiderations. The latter type of decision strongly indicates thetypical considerations of a maintenance or pavement managementprogramme and should be viewed against that broader backgroundalthough the focus here is on a project level based on deflectionbasin related criteria.

Snaith et al. (1980) describe how on the basis of the theory ofcumulative damage, the remaining life can be determined. Ingeneral this remaining life, as described in Appendix C, would beexpressed as: R1 = N1-n1 or R1 = 1-n1/N1. Snaith et al. (1980) donot mention any specific criteria related to this remaining life fordecisions to overlay or not. Anderson (1977) bases the decision tooverlay or not on the length of the remaining life. If theanticipated or estimated future traffic is more than the remaininglife, an overlay is needed. If the remaining life is more than theanticipated traffic over the functional life of the pavement,no overlay is needed. An overlay may be required for otherfunctional reasons such as improving the skid resistance of theriding surface. It is in this regard that Anderson (1977) statesthat even a nominal thickness of asphalt concrete placed on anexisting pavement gives the pavement a new "life" by removing thesurface deformation. "There is no theoretical or practical

evidence which suggests that the permanent deformation which existedbefore rehabilitation will affect the future performance of thepavement."

In general Anderson (1977) does support the analysis proceduredescribed by Snaith et al. (1980). For the generalized fatiguerelationship (N_(l)b) the aim of an overlay would be to reduce thee:strain level (e: ) to the level where the anticipated traffic would

vsmeet the prolonged life or remaining life after overlay. Thisprocess is shown in Figure 0.1 and in a more general form in Figure0.2. The formulation of the fatigue relationship considered byTreybig et al. (1978) (as discussed in chapter 6 and Appendix C) isobViously more complicated. Although no specific mention is madeof any criteria for overlays related to remaining life the reasoningabove was evidently followed.

Molenaar (1983) does not use his permanent deformation model (seeAppendix C) in his proposed overlay design. It is obvious thoughthat this model, if properly calibrated to field performances, wouldalso be able to provide the same criteria based on remaining life asdescribed in Appendix C. If an overlay is needed, the aim would beto reduce the elastic deformation (U ) and resulting permanente .deformation (U ) of each layer in order to meet the requiredp .prolonged life.

Remaining life (N1-n1) compared with the anticipated or futuretraffic is the general criterion for overlays, based on analysisusing the cumulative damage (linear summation ratio) theory. Thishas already been briefly described on the basis of the discussion bySnaith et al. (1980) (see Appendix C and sections 2).

In considering the previously defined rema1n1ng life, Anderson(1977) also considers the cracked state of the existing asphaltconcrete layer and whether the pavement has an asphalt concretelayer when establishing criteria for considering an overlay. Theremaining life is automatically zero if the pavement is cracked

_0_

:tI~:'4.0-- -

FIGURE 0.1CHANGES IN STRAIN LEVELS DUE TO OVERLAY.

"':_0_0_

2 ","""","' .••..,

tDOl

I.-I

4r>- O·

ISO-STRAIN LINE €2

(b) Damage- Life Diagram

(c) Domage - Path Diagram

N~.••..oU)•.....~.I

~I

o~

NOTE: B.O. - BEFORE OVERLAY A.O. - AFTER OVERLAY

FIGURE 0.2DAMAGE PROCESS IN A PAVEMENTSTRUCTURE WITH A SINGLE OVERLAY.

( Snaith, et 01., 1980)

and warrants consideration for an overlay, or if there is noasphalt concrete layer yet. If the remaining life is less thanthe anticipated traffic an overlay may be considered. If theremaining life is more than the anticipated traffic no overlay isneeded. When an overlay is considered as was discussed insection 2 (referring to Figures D.1 and D.2), the aim would againbe to reduce the strain level (ERA) to accommodate a prolongedlife or remaining life after the overlay, which would meet therequired anticipated traffic life. Analysing various pavementsin this way, Anderson (1977) arrived at characteristic curves asshown in Figure D.3. In this figure remaining life is expressedas a percentage of the overlay thickness. The latter value ofoverlay thickness corresponds to the reduction in strain level(ERA)' Comparing these results with those of a fully crackedasphalt concrete layer with no remaining life, Anderson (1977)concludes that it will always be more economical to neglect anyexisting asphalt when the remaining life is below 75 per cent. Inthis overlay design procedure, a "critical" remaining life of 50 percent was adopted, this being the point at which the existing life isdisregarded in designing an overlay. This approach, based on thefatigue relationships described in chapter 6, was also followed byMonismith and Markevich (1983).

The approach by Molenaar (1983), using the structural performancemodel, obviously differs from the one described above. Molenaar(1983) is quoted as follows:

"Although Miner's law is applicable to the development of one crack,further extension of cracks is dependent on the redistribution ofthe stresses, and in this case Miner's law may not be fullyapplicable. Furthermore Miner's law defines a clear failurecondition which occurs at e.g. the fracture of a test specimen.Such a failure point does not exist in the case of pavements. A100 per cent cracked pavement surface can still be used as areasonable driving surface unless large deformations and/orpot-holes occur. Therefore a straightforward use of Miner's law inthe estimation of overlay thicknesses is not considered to be aproper approach, since this will result in an unrealistic overlaydesign especially in those cases where Miner's ratio comes close to

12

II

10

9-f/)Q)

8.J::(,)

C-f/) 7f/)Q)C.¥.

6(,)

.J::.I-~ 50~Q)> 40

3

2

t*t Case 3

*~ Case 2

*~ Case 6t~t Case 1t ,t Case 5

t* Case 4t1000/025% 500/0 750/0

Remaining Life

FIGURE 0.3EFFECT OF REMAINING LIFE ON OVERLAY

THICKNESS(Anderson, 1977)

This supports the reasoning of Anderson (1977), but also points tothe possibility of the structural performance model being used togive a more realistic estimate of the structural life of a bitumenpavement. Molenaar (1983) does not give any specific indicationof criteria for decisions on overlays. It is evident from thereasoning, however, that the remaining life determined in thisway, would also be used, but with different preconditions.

The two distress criteria, fatigue cracking and permanent deforma-tion rutting have deliberately been considered separately. Thereasoning behind this is explained by Koole (1979):

"In determining the thickness required for an overlay, thesubgrade-strain and asphalt-strain criteria should be considered.separately; it is quite possible that the design criterion thatdid not govern the original pavement design will become limitingfor the overlay thickness."

In this section an overlay thickness is thus decided upon by meansof the limiting life of the two defined criteria described insection 2 and 3. The resulting lower distress criteria parameters(ERA and E ) are usually calculated for the possible thicknessesvsconsidered. Anderson (1977) calculates these relationships for thevarious thicknesses of overlays by means of the techniques describedin chapter 4. This is shown in Figures D.4 and D.5 for reductionin subgrade strain (E ) and asphalt tensile strain (ERA)' InvsFigure D.3 only pavements with more than 50 mm of asphalt concreteprior to overlaying are considered. The reason was discussed inchapter 6 and in Figure 6.2 what the effect of relatively thinasphalt concrete layers (50 to 75 mm) on tensile strain in asphaltconcrete was shown. From the quotation by Koole (1979) above it isobvious that an overlay of for example 25 mm on the existing 25 to40 mm of asphalt for rut requirements, could in fact shorten theremaining life of the fatigue cracking requirements. The desired

'"TV "".- "" , ""V', '"T ""

I

8

Thickness of OVerIOY-f..- 7 5vI0)( 6c

..•..•...

c- 5c0~-en 4Q)

"0 t:l0 .~ '-I

en.03:Jen

cc

20-0:J"0

Q)

0::

2 4 6 8 10Subgrade Strain Prior to Overlay (in lin x 10- 4 )

FIGURE 0.4REDUCTION IN SUBGRADE STRAIN DUE TO OVERLAY (Anderson, 1977)

fO- 4-4 760/45i

VIo 2.5)(

C"'-.S 20- .

Thickness of Overlay (inches)

c:0•.. 1.5-en- t:'.0 00.s:::.Q.en 1.00

-o::J 0.5'04)0::

234Asphalt strain prior to overlay (in/in x 104)

FIGURE 0.5REDUCTION IN ASPHALT TENSILE STRAIN DUE TO OVERLAY( Pavements with more than 2" of asphalt concre~e prior to overlaying)

( Anderson 1 1977 )

reduction in strain level can also be expressed in terms of theselected deflection basin parameters, as shown in Figure D.6,according to Anderson (1977). Similarly the desired lowerdeflection basin parameter such as surface curvature index (SCl)can be related to a higher equivalent layer thickness (H ) (seeeFigure 4.10) according to the analyses of Molenaar (1983).

Treybig et al. (1978) established the most comprehensive procedurefor considering the effect of fatigue cracking and rutting simul-taneously. This is shown in Figure D.7 where the existing asphaltconcrete layer is regarded as uncracked. The overlay thicknessrequired, is determined by selecting the thicker of the two thick-nesses related to the various criteria for the desired loadrepetitions.

Koole (1979) also describes how three separate overlay thicknessesare determined. This includes the previously discussed criteriafor fatigue cracking and rutting, and also a method of determiningthickness based on the assumption that the existing pavement hasdeteriorated to such an extent that the asphalt concrete layer istreated as a granular layer and the overlay as a "new" asphaltconcrete layer.

The latter approach is also suggested by Thompson and Hoffman (1983)when the asphalt concrete layer displays interconnected Class 2cracking.

Remaining life in relation to the distress criteria, rutting andfatigue cracking, is the main criterion in the consideration ofoverlays. The remaining life determined by methods described inchapter 6 was determined for each of the distress criteria sepa-rately. For the rutting criterion the views on remaining life varyconsiderably. The view that remaining life is completely restoredby an overlay removing the deformations is Widely accepted inoverlay design. Using the various models discussed in Appendix Cit is possible to determine the prolonged life by lowering the

- 120:cu OVERLAYz THICKNESS- 110>-<!....J 1000:::W> 9000I- 80w::>

700N

0 60 t1I .-0 00

50z-z 400-I-u 30::>0w 200:::

o 10 20 30 40·50 60 70 80 90 100 110 120 130 140 150DO - 012 PRIOR TO OVERLAY (INCH)

FIGURE 0.6REDUCTION IN 00- 012 DUE TO OVERLAY

(Anderson, 1977)

--;;;8Cl).J::.oc:•.....••en6(J)Cl)c~o.J::. 4I-:>;o~Cl)> 2o

Fatigue---

o10 100 1,000 10,000 100,000

Allowable 18- Kip Equivalent Load Applications, N x 103

FIGURE 0.7SAMPLE OVERLAY THICKNESS DESIGN CURVES

vertical subgrade strain (€ ) for example. The more comprehensivevsmodel proposed by Treybig et al. (1978) warrants a closer look if itwere to be related to the South African situation as were the otherproposals and recommendations mentioned before. This may all beincorporated in a proposed catalogue of overlay designs, which wouldbe similar to the existing TRH4 (NITRR, 1985a).

In consideration of remaining life as a criterion for fatiguecracking, the consideration of cracking only leads to some un-economical overlay proposals. Anderson (1977) indicates that a 50per cent remaining life for fatigue cracking should be a criticalvalue. The structural performance model by Molenaar (1983)attempts to be more economical by considering the structural valueof the cracked asphalt layer. It also offers better considerationof the use of other new materials like bitumen-rubber.

In the final selection of the thickness of the proposed overlay forthe critical strain parameter, the emphasis is on checking the otherparameter again in order to ensure that the overlay does not shortenremaining life after overlay for the previously non-criticalparameter value. From Anderson's (1977) work it is obvious thatthis would be of particular importance with thin overlays on thinasphalt concrete layers. The approach by Treybig et al. (1978) toplot overlay thickness for both criteria simultaneously in relationto remaining life gives a good graphical indication of such trends.

It has been stated that the selection of an overlay must be seenagainst the background of maintenance or rehabilitation managementsystems. The models discussed for analysis are not alwaysapplicable to the South African situation. It is thereforesuggested that the recommendations in regard to pavement per-formance and structure were made in previous sections be extended .to this area of overlay design in order to make the whole designprocedure mechanistically sound. This could easily be incor-porated in the suggested catalogue of overlay designs, mentionedabove.

In Appendix B it was mentioned that there exists a good correlationbetween the measurements of the Crack-Activity-Meter (CAM) anddeflection basin parameters as measured with the Road SurfaceDeflectometer (RSD). The normal procedure of initial assessmentaccording to the draft TRH12 (1983) guidelines are carried out on atypical cemented base pavement. In the detailed assessment stagethe question whether the cracks recorded on specific sections areactive or not must then be addressed with confidence. The newservice of the NITRR where the CAM and the RSD are combined can thengive the required information to make a sound decision in regards to .the rehabilitation option. Various cracks with related block sizesand degrees of severity are selected on such a section under invest-igation. At the same point (crack) the CAM and RSD are set up andmeasurements are taken with the Benkelmanbeam truck travelling overthe crack following the WASHO procedure. The crack activitymeasurements are then ·correlated with various other parameters suchas block size and deflection basin parameters (Rust, 1984). Thisappendix therefore describes how such an analysis on the N4/3 wasused to verify the rehabilitation option selected in terms of itscrack attenuation.

The cemented base of N4/3 is cracked and urgently needs rehabilita-tion. Crack movement measurements were taken in October (Rust,1986). It was found that there exists sections of road where thecrack movements are very high. The block sizes were found to berelatively large. This means that the crack movements are likely toincrease as the block sizes break down to a smaller size. Therehabilitation option that was selected is to overlay the existingpavement with a 100 mm G1 crushed stone base and 40 mm asphaltsurfacing. The analysis described in this technical note is todetermine what the effectiveness of the overlay is to reduce crackmovement. In the analysis use was made of measured deflectionbasins and the correlation thereof with crack movement measurements.This was followed with a mechanistic analysis of the rehabilitation

option to calculate the deflection basin and predicted crack move-ments.

On each of the measuring points of the CAM the deflection basin wasalso measured with the RSD. The measurement of the wnole deflectionbasin with the RSD makes it possible to determine various deflectionbasin parameters. The most common deflection basin parameters(Rust. 1986) that can be calculated from RSD measurements are listedin Table 1.1 with their respective formula. The maximum horizontalcrack movements (HMAX) and the maximum vertical crack movements(VETOT) in micro-meters were correlated with various deflectionbasin parameters. The results were as follows:

904,271* (MAX. DEFL)2,6 - 9,483E-6*(SCI915)2,5 +

3,086E-3*(SCI610)I,5 - 2,538E-2*(Dl1)l,3 +9,81*(SCI305)l,4 + 71.765

4931.765*(MAX. DEFL)5.2 - l,813E-12*(SCI915)5.1 +4.312E-8*(SCI610)3.6 + 1;65E-3*(Dl1)1.9 -

1.887E-3*(SCI305)1.9 + 49.713

Where: SCI = Surface curvature index with the subscripts indicatingthe offset for deflection in mm.

Dl1 = Deflection Index which is the difference in deflectionat 127 mm and 305 mm.

MAX. DEFL = Maximum deflection in mm.VETOT = Total vertical movement in micrometer.

The regression analysis indicate that VETOT correlated better withthe deflection basin parameters than HMAX. The reason for that canclearly be related to the relatively large block sizes (Rust, 1986).

The pavement structures as shown in Figure E.1 for the existingpavement and the rehabilitated pavement were analysed mechanistic-ally with the computer program ELSYM5. The input values are asindicated in the figure. The stress directly on top of the cementedbase was calculated before and after the G1 crushed stone baseoverlay. The calculated vertical stress was 374 kPa and after theoverlay it was reduced to 111 kPa. This is a drastic reduction inthe calculated stress values and clearly indicates that the overlaydid indirectly reduce the possible crack movements.

During the mechanistic analysis the deflection basin was calculatedfor the two pavement structures. In Table E.1 the relevant de-flection basin parameters are indicated. The deflection basinparameters on top of the old cemented base (now sub-base) and on topof the overlayed pavement are shown.

Deflection basin parameters (mm)MAX. DEFL SCI915 SCI610 SCI305

0,253

0,230

When comparing the deflection basin parameters calculated on thesurface directly it is shown in Table E.1 that the overlay reducesthe deflection basin parameters values drastically. This reductionin the respective deflection basin parameter values are even morewhen the values calculated on top of the cemented base are compared.

i EXISTING PAVEMENT

2,4m 3,7 m I 3,7m 3,7 m rIIEXISTING

EXISTING 150 CI

<t. EXISTING PAVEMENT

I50 AC

150 C I

FIGURE E.!REHABILITATION OPTION ON N4 /3

The regression analysis described earlier were also used to calcu-late the respective predicted crack movements. These results areshown in Table E.2.

The results in Table E.2 show that there is a drastic reduction inthe vertical and the horizontal crack movements. In the case of thevertical crack movements the reduction was more. This verticalmovement was the more severe case for crack movement due to therelatively large block sizes.

(a) The crack movements (HMAX and VETOT) were correlated withvarious deflection basin parameters as measured with the CAMand the RSD.

(b) The vertical stress calculated on top of the cemented baseshow a drastic reduction in values when compared with thevertical stress values calculated on top of the cementedsub-base of the overlayed pavement. This reduction indicatesthat there should be a reduction in crack movements too.

(c) The deflection basin parameters were calculated for theexisting pavement and the overlayed pavement. These calcu-lated deflection basin parameters were used in the correlationrelationships to determine the calculated crack movements.There is a drastic reduction in the crack movements on top ofthe cemented base due to the overlay.

Odemark IS (1949) equivalent layer thickness concept is used as asimple method of approximation. It enables the transformation of amulti-layered system into a single layer with equivalent thickness.The principle is that the equivalent layer has the same stiffness asthe original layer, so as to give the same pressure distributionunderneath the layer. This concept of classifying a pavement withone number that represents more or less the bearing capacity of thatpavement is clearly illustrated by Molenaar and Van Gurp (1980) andMolenaar (1983). The typical South African pavement structures thatwere analysed in chapter 7 were also converted to the equivalentlayer thickness. The equivqlent layer thickness values calculatedwere then rlated to various distress determinants and fatigue lifein order to evaluate this concept as a possible aid in themechanistic rehabilitation design procedure.

2L-l E.(l-v) II= aE h. I]. ~ I 3

]. E (I-v.)s ].

wherea = 0,9 for flexible pavementsh. = thickness of layer i in m].

E. = elastic modulus of layer i in N/m2]. 2

E = elastic modulus of subgrade in Nlmsv. = Poisson ratio of layer i].

Vs = Poisson ratio of subgradelayer with value equal to 0,35

L = Number of layers

Molenaar (1983) and Molenaar and Van Gurp (1980) analysed a typicalthree-layered pavement structure. The typical flexible pavement

structures referred to in this Appendix differ from this three-layered system in the sense that the pavement structures are eitherfour layered or five-layered systems with a different standard wheelload and tyre pressure. The bitumen base pavements analysedresemble these three-layered pavements most closely in terms ofthickness of the bitumen bases. Most of the typical flexiblepavement structures analysed. though, have thin asphalt surfacings(S 40 mm).

In Figures F.l and F.2 typical relationships of H versus deflectionebasin parameters, shape factor (Fl) and slope of deflection (SO) areshown as calculated for bituminous base pavements. The purpose isto show that some deflection basin parameters like SO, R. SCI, BCIand BOI can discern between the various subgrade elastic moduliwhile others, such as F1, F2, S, A and Q cannot. In Figure F.3surface curvature index (SCI) is shown for bituminous and granularbases versus H. In both cases SCI can discern between the variousesubgrade effective elastic moduli. The gradients for these func-tions of the bitumen base pavements correlate well with bitumen basepavements with three layers (SCI with r = 500 mm) (Molenaar and VanGurp, 1980). The gradients for the relationships of the granularbase pavements though, are shallow and reflect a greater sensitivityto changes in H .e

Flexible pavements in general were grouped together in Figure F.4 toshow that H correlates well with vertical subgrade strain (e: ).e vsThe various values of effective elastic moduli of the subgrade leadto different relationships as shown in Figure F.4. In Figure F.5the other distress determinant, horizontal asphalt tensile strain(e:HA) , at the bottom of the bituminous base, is shown versus He'Here again, there is a clear discernment between the elastic moduliof the subgrade. It is however not possible to develop the samerelationship between e:HA and He for the thin surfacings of granularbase pavements. One of the reasons for the latter situation seemsto be that the thickness, Poisson ratio and elastic modulus ratio ofthe thin surfacing, compared to that of the base and even subgrade,differ markedly from that of a bituminous base pavement. This is

0enZ0I-UW...lIJ..W0IJ..0

Wa..0...lCJ)

CJ)CD

-•...•.0to(\J10I

.;tI

0.;ten

-IJ..

a::0I-U

~ 0,5wa..<tJ:CJ)

0,2

0,10, I 0,2 0,5 t 2 5 10

EQUIVALENT LAYER THICKNESS (He) (m)

FIGURE F. IEQUIVALENT LAYER THICKNESS VERSUS SHAPE

FACTOR F!

100,I 0,2 0,5 I 2 5

EQUIVALENT LAYER THICKNESS (He)(m)

FIGURE F.2EQUIVALENT LAYER THICKNESS VERSUS SLOPE

OF DEFLECTION

EE10

1000I'f)

II•..--E::L

tjU')

IGRANULAR BASES---

"- ~ I- Es = 50 MPa-'" ""'lIl

~Es = 70 MPa

~ ~ lC""" ~

"' '" ~ Es = 150 MPa

~~

"'"~ ~~....•~

~,.~

\ ~

~

..\ ' ,

1\ ~\ \ ,\ ~ \

~,.\, 1\\

BITUMEN BASES~ \~.Es=50MPa "Es=70 MPa

"\~\Es= 150 MPa

\ ,\ .

100,3 I 2

EQUIVALENT LAYER THICKNESS (Hel (ml

FIGURE F.3Equivalent layer th ickness versussurface curvature index

z~ 500~(J)

I::i..

1000,3 I 2EQUIVALENT LAYER THICKNESS (HeJ (m)

FIGURE F.4VERTICAL SUBGRADE STRAIN VERSUSEQUIVALENT LAYER THICKNESS FOR

FLEXI BLE PAVEMENTS

.0111.•.......utotoI~Io'f~--

~ 100<tQ:I-(/lI::t Es = 50 MPo

Es = 70 M Po

Es =150 MPo

10O,~____ I 2

EQUIVALENT LAYER THICKNESS (HeHml

FIGURE F.5

EQUIVALENT LAYER THICKNESS VERSUSMAXIMUM ASPHALT STRAIN FORBITUMEN BASE PAVEMENTS

clear when one looks at the formula for the calculation of H • givene

Equivalent layer thickness (H ) can be used to indicate whether ae

pavement structure with cemented subbases or bases is in the flex-ible state, with the cemented layers in the cracked phase exhibitingequivalent granular behaviour according to the definition given byFreeme (1983). In Figure F.6, H for the pre-cracked life ofepavements with cemented subbases and bases is shown in terms ofstandard 80 kN axle repetitions (E80s) determined as prescribed byFreeme et al. (l982a). A distinction can be made based on thevariance of the elastic modulus of the subgrade. It can be seen,however, that an H value of at least 1,1 m is required for aesubgrade modulus of 70 MPa to have any significant pre-cracked lifeof cemented layers. This is rather high and reaffirms that themajor portion of the structural life of typical TRH4 (NITRR, 1985a)pavement structures with cemented layers is in the cracked phase or

flexible behaviour state.

The recommended vertical subgrade strain (e ) criteria for diffe-vsrent road categories (Freeme et al., 1982a) were used to calculatethe standard 80 kN axle repetitions for all the flexible pavementstructures for their respective values of H. This relationshipebetween He and E80s is shown in Figure F.7 for all flexible pavementstructures. In this figure the fatigue life of bitumen basepavements was also calculated with respect to maximum asphalt strain(eRA) and correlated with the respective He value. The recommendedfatigue life criteria for thick bitumen base pavements were used inth 1 1 t· (Freeme et al., 1982a). The recommended shifte ca cu a J.onfactors shown in Table F.1 were applied to the calculated fatiguelives.

'0m~"'-CDoII')I

q-Io'f'

-Q'I

-Ul0CDIJJ

CJ)Z0!::~IJJCl.IJJ

105a::IJJ...JX«z..lie:0CD

0a::«0z«~CJ)

104~u«a::uIJJa::Cl.

Es50 MPo70 MPo

150 MPo'"

j

1030,20 1,0 5,0

EQUIVALENT LAYER THICKNESS (He) (m)

FIGURE F.GInitiation of cracking of cementedbases and su bbases in terms ofequivalent layer thickness

en0COW

107C/)z0I-

~WCl.W0::

W...JX«a0::« 106az«I-C/)

-toI

VIoV

--"""---------

I

- E I FORI I_ vs r- FLEXIBLE- PAVEMENTS

I I I

I I ITRH4 (NITRR 19850TRAFFIC CLASSES

I

t- E4 -

I- E3

-I- E2 ,.,. = 70 MPo"'s

-~EI

J -- EHA FOR~

BITUMENEO BASE

PAVEMENTS105

0,1 1,0

EQUIVALENT LAYER THICKNESS(He) (m)

FIGURE F.7Pavement life for maximumasphalt strain and verticalsubgrade strain criteria interms of equivalent layer thickness

The equivalent layer thickness (H ) concept proved to be a conceptethat more or less represents the structural capacity of flexiblepavements. Deflection basin parameters correlate well with a valuesuch as H in general, as calculated for flexible pavements. It isehowever only such deflection basin parameters, that normally usepoints of deflection near each other in the calculation procedure(e.g. scr, R, BCI, BDI and SD), that can discern the effect ofvariance in subgrade elastic moduli. Such relationships however donot have much value except as for an interim step towards establish-ing relationships between the distress determinants (£RA and £VS)and H .e

He correlates well with subgrade vertical strain (£VS) for flexiblepavement structures and discerns the effect of variance of subgradeelastic moduli. Granular bases on the other hand do not give anyclear relationships between maximum asphalt strain (£RA) and He asis the case with bitumen base pavements. The reason seems to be theratios of the thickness, elastic modulus and Poisson ratio of thesurfacing and the base as well as that of the subgrade, in thecalculation of· H , which leads to this marked difference betweenegranular and bitumen bases.

The value of H can be used in a mechanistic design or analysiseprocedure to establish the structural life of a flexible pavementwith regard to the distress determinants (£VS and £RA)' The pre-cracked life of a cemented base and subbase layer can be determined.It must be remembered though, that in order to use H in such a way,ethe effective elastic moduli of all the layers as well as thethicknesses have to be known. This restricts H to an interim valueein the determination of the distress determinants (£VS and £RA) inthe mechanistic analysis of a pavement.

REFERENCES

ABBOT, L M. (1977). Stresses and strains in layered systems, CHEV4.NITRR, Computer program guideline, P4. (CSIR, Pretoria)

ANANI, B A (1979).deflection basinsDepartment of CivilPark, Pennsylvania.

An evaluation of in situ elastic moduli from surfaceof multi-layer flexible pavements. Ph.D Thesis,Engineering, Pennsylvania State University, University

ANDERSON, D T. (1977). The design of asphalt concrete overlays forflexible highway pavements. Department of Civil Engineering, Universityof California, Berkeley.

ANDERSON, D T. (1984) A new approach to asphalt overlay design. Proc ..11TH ARRB Conf .., 12(3), pp. 55-66.

ASPHALT INSTITUTE, (1977). Asphalt overlays and pavement rehabilitation.MS-17 College Park, Maryland.

BASSON, J E B. (1985). The measurement of the deflection and curvature ofa road surface when loaded by a standard axle. NITRR Technical Note,TP/71/85 (CSIR, Pretoria).

BASSON, J E B,deflectometer:deflections andNITRR Technical

WIJNBERBER, 0 J and SKULTETY, J. (1980). The multi depthA multistage sensor for the measurement of resilient

permanent deformation at various depths in road pavements.Note, TP/85/80. (CSIR, Pretoria).

BEDFORD, F Wand DIVIVEDI, T D. (1970). Vector calculus. McGraw-HillBook Company.

BERGER, L and GREENSTEIN, J. (1985). Use of pocket computers forrehabilitation or rural roads in Dominica. TRB, Transportation ResearchRecord 997, Washington, DC.

BROWN, S F. (1979). The characterization of cohesive soils for flexiblepavement design. Proc. 7th Euro. Conf. Soil Mech. and Fnd. Engrg., Vol. 2.pp. 15-22.

BURMISTER, D M. (1945). The theory of stresses and displacements inlayered soil systems. Journal of Applied Physics, Vol. 16.

BUSH, A J. (1980). Non-destructive testing for light aircraft pavements,Phase I, Evaluation of non-destructive testing devices. Final reportprepared for U.S., DOT, Federal Highway Administration.

CLEASSEN, A I M and DITMARSCH, R. (1977). Pavement evaluation andoverlay design, The SHELL Method. Proc. of the 4th Int. Conf.· on theStructural Design of Asphalt Pavements. Vol. I. Ann Arbor.

COETZEE, C H. (1982). CHEVRON program for calculating stresses, strainsand displacement in a layered pavement system having a maximum of fifteenlayers. NITRR Technical Note TC/27/82. (CSIR, Pretoria).COETZEE, CHand HORAK, E. (1981). "PaSSing van elastisiteitsmoduli vanplaveisellae met die CHEVRON program vir dubbelwiele en defleksie gemeet OR

die laagvlakke-CHEVMF Program-". NITRR, Technical Note Tc/44/81. (CSIR.Pretoria) .

COETZEE, N F and MONISMITH, C L. (1979. Analytical study of minimizationof reflection cracking in asphalt concrete overlays by use of arubber-asphalt interlayer. TRB, Transportation Research Record No. 700.

DE BEER, M. (19983). HVS site selection and material description atMalmesbury test sections - Report on Main Road 18. NITRR Technical NoteTP/50/83. (CSIR, Pretoria).

DE BEER, M. (1986). Die ontwikkeling van 'n DKP-klassifikasiesisteem virplaveiselstrukture met ligte gesementeerde lae. NITRR Technical NoteTP/53/86. (CSIR, Pretoria).

DEHLEN, G L. (1961). The use of Benkelman beam for the measurement ofdeflections and curvatures of a road surface between dual wheels. CSIRSpecial report R.2 NITRR, Rs/11/6l. (CSIR, Pretoria).

DEHLEN, G L (1962a. A simple instrument for measurin~ the curvatureincluded in a road surfacing by a wheel load. The Civil Engineer in SouthAfrica. Vol. 4, No.9.

DEHLEN, G L. (1962b). Flexure of road surfacings, its relation to fatiguecracking and factors determining its severity. HRB, Highway Research BoardBulletin No. 321.

DORMAN, G M and METCALF, C T. (1963). Design curves for flexiblepavements based on layered system theory. Highway Research Record No. 71,Washington, D.C.

EPPS, J A and HICKS, R G. (1982). Moderator's summary papers in SessionV, Rehabilitation of pavements. Proc. of the 5th Int. Conf. on theStructural Design of Asphalt Pavements. Vol. II.

FEDERAL AVIATION ADMINISTRATION (U.S.) (1979). Use of non-destructivetesting devices in the evaluation of airport pavements. Advisory CircularNo. 15015370-11. Washington, D.C.

FEDERAL HIGHWAY ADMINISTRATION (FHWA). U.S. DEPARTMENT OF TRANSPORTATION.(1984). Synthesis study of non-destructive testing devices for use inoverlay thickness design of flexible pavements. FWHA/R9-83/097.Washington, DC.

FORD, Jr. M C and BISSETT, J R. (1962). Flexible pavements performancestudies in Arkansas. Highway Research Board Bulletin 321.FREEME, C R. (1983).Rehabilitation of Roads.

Evaluation of Pavement Behaviour for MajorNITRR Technical Report RP/19/83 (CSIR, Pretoria).

FREEME, C R, MAREE, J Hand VILJOEN, A W. (1982a). Mechanistic design ofasphalt pavements and verification of designs using the Heavy VehicleSimulator. Proc. 5th Int. Conf. on the Structural Design of Asphaltpavements. Vol. 1, pp 156-173 (CSIR Reprint RR362).FREEME, C R, MAREE, J H and WALKER, R N. (1982b). User's experience withthe South African Heavy Vehicle Simulators. Proc. of Bearing Capacity of

Roads and Airfields. Vol. II. The Norwegian Institute of Technology,Norway.

FREEME, C R, MEYER, R G and SHACKEL, B. (1981). A method for the adeguacyof road pavement structures using a heavy vehicle simulator. Paperpresented at the Int. Road Federation World Meeting in Stockholm.

FREEME, C R. SERVAS, V P and WALKER, R N. (1986). Pavement behaviour asdetermined from Heavy Vehicle Simulator Testing. Paper prepared for the1986 Int. Conf. on Bearing Capacity of Roads and Airfields.

FRyBA, L. (1967). Vibration of solids and structures under moving loads.Research Institute of Transport, Prague. Noordhof InternationalPublishing, Groningen.

,GRANT, M C and CURTAYNE, P C. (1982).past experience of pavement behaviour.Structural Design of Asphalt Pavements.

Rehabilitation design incorporatingProc. of the 5th Int. Conf. on theVol. II. Delft.

GRANT, M C, MARAIS, C P and UYS, D G. (1979). An investigation of anasphalt overlay on a lightly trafficked road showing premature cracking.Proc. of the 3rd Conf. of Asphalt Pavements for Southern Africa. Vol. I.University of Natal, Durban.

GRANT, M C and WALKER, R N. (1972) The development of overlay designprocedures based on the application of elastic theory. Proc. 3rd Int.Conf. on the Structural Design of Asphalt Pavements. Vol. 1, pp 1155-1166.(CSIR Reprint RR145).

GREENSTEIN, J. (1982) . Pavement evaluation and upgrading of low-costroads. TRB, Transportation Research Record 875. Washington, D.C.

HETeNYI, M. (1971). Beams on elastic foundation. Theory withapplications in the fields of civil and mechanical engineering. Ann Arbor.The University of Michigan Press. Ninth edition.

HOFFMAN, M S and THOMPSON, M R. (1981). Mechanistic interpretation ofnon-destructive pavement testing deflections. Transportation EngineeringSeries No. 32. Illinois Co~operative Highway and Transportation ResearchProgram Series No. 190. University of Urbana-Champaign.

HOGG, AHA. (1944). Eguilibrium of a thin slab on an elastic foundationof infinite depth. Phil. Mag. Vol. 35 (234), pp 265-276.

HORAK, E. (1984). Deflection-based mechanistic overlay design for flexibleavements in South Africa: A literature surve. NITRR Technical Report

RP/7/84. CSIR, Pretoria)

HORAK, E. (1985). Curve fitting of deflection basin measurements. NITRRTechnical Note TP/82/85. (CSIR, Pretoria).

HORAK, E. (1986a)accelerated testing.

Analysis of deflection basins measured duringNITRR Technical Note TP/34/86. (CSIR, Pretoria).

HORAK, E. (1986b) Investigation of relationships between deflection basinparameters, distress determinants and overlay thickness for flexiblepavements. NITRR Technical Note TP/29/86. (CSIR, Pretoria).

HORAK, E (1986c). Effective elastic moduli determined from Road surfaceDeflectometer measurements. NITRR Technical Note TP/40/86. (CSIR,Pretoria) .HORAK, E and MAREE, J H. (1982. Behaviour of a slag base pavementstructure in Heavy Vehicle Simulator testing in the Transvaal.. NITRRTechnical Report. RP/5/82. (CSIR, Pretoria).

HORAK, E and OTTE, J R. (1985). Deflection basin data preparation forcurve fitting and parameter calculation. NITRR, Technical Note TP/96/85.(CSIR, Pretoria).

HOYINCK, W T, VAN DER BAN. R and GERRITSEN, W. (1982). Lacroix overlaydesign by three-layer analysis. Proc. 5th Int. Conf. on the StructuralDesign of Asphalt Pavements. Vol. I Delft.

HUSIAN, S and GEORGE, K P. (1985). In situ pavement moduli from Dynaflectdeflection. Paper prepared for presentation at the Transportation ResearchBoard Meeting, Washington D.C.

HVEEM, F N. (1955). Pavement deflection and fatigue failures. HighwayResearch Board Bulletin 114.

IRWIN, L H.University.

JORDAAN. G J.design methods ..

(1986). The classification of pavement rehabilitationNITRR Technical Note, TC/12/86. (CSIR, Pretoria).

JORDAAN, G J and SERVAS, V P. (1983).for flexible pavements in pavementreport, RC/7/83. (CSIR, Pretoria).

Su~~ested condition classificationrehabilitation design. Technical

KENNEDY, C K and LISTER, N W. (1978). Deflection and pavementperformance: The experimental evidence. TRRL Laboratory Report No. 833.Great Britain.

KILARESKI, W P and ANANI, B A. (1982). Evaluation of in situ moduli andpavement life from deflection basins. Proc. 5th Int. Conf. on theStructural Design of Asphalt Pavements. Vol. 1.

KLEYN, E G, FREEME, C Rand TERBLANCHE, L J. (1985). The impact of theHeavy Vehicle Simulator testing in the Transvaal. Annual TransportationConvention. Session-:- ~Transport Infrastructure: Accelerated testing ofpavements. Pretoria.

KLEYN, E G and VAN HEERDEN, M J J. (1984). Swaarvoertuigspektrumsimulasiemet behulp van enkelvoudige verkeerstellings. Paper presented at theAnnual Transportation Conference, Pretoria.

KLEYN, E G, VAN HEERDEN, M J J and ROSSOUW, A J. (1982). An investigationto determine the structural capacity and rehabilitation. Utilization ofroad pavement using the Pavement Dynamic Cone Penetrometer .. Proc. BearingCapacity of Roads and Airfields. Vol. II. The Norwegian Institute ofTechnology, Trondheim, Norway.

KOOLE. R C. (1979). Overlay design based on Falling Weight Def1ectometermeasurements. TRB. Transportation Research Record No. 700. WashingtonD.C.KUNG. K Y. (1967). A new method in correlation study of pavementdeflection and cracking .. Proc. of the 2nd Int. Conf. on the StructuralDesign of Asphalt Pavements. Ann Arbor.

LISTER, N E and KENNEDY, C K. (1977). A system for the prediction ofoavement life and design of pavement strengthening .. Proc. of the 4th Int.Conf. on the Structural Design of Asphalt Pavements. Vol. 1 Ann Arbor.

MARCHIONNA, A, CESARINI, M FORNACI, M G and MALGARINI. M. 1985) .Pavement elastic characteristics measured by means of tests conducted withthe FWD. (Method for flexible and semi-rigid pavements considered asnon-linear multi-layer structures). Paper prepared for TRB meeting,Washington D.C.

MAREE, J H. (1978) Ontwerpparameters vir klips1ag in plaveise1s. M.Sc.(Eng.) Thesis (in Afrikaans). University of Pretoria, October 1972.

MAREE, H J and FREEME, C R. (1981a). The mechanistic design method usedto evaluate the pavement structures in the Catalogue of the Draft TRH4,1981. NITRR. Technical Report RP/2/81. (CSIR. Pretoria).

MAREE. J H. FREEME, C R, VAN ZYL. N J Wand SAVAGE, P F. (1982). Thepermanent deformation of pavements with untreated crushed stone bases asmeasured in Heavy Vehicle Simulator tests. Proc. 22nd ARRB Conf. 2(2), pp16-28 (CSIR Reprint RR355).

MAREE. J H. VAN ZYL, N J Wand FREEME, C R. (l981b). The effective moduliand the stress-dependence of pavement materials as measured in some HeavyVehicle Simulator tests. Paper prepared for TRB meeting, Washington, D,C.Also as NITRR Technical Report RP/7/81. (CSIR. Pretoria).

MOLENAAR. A A A. (1983). Structural performance and design of flexibleroad constructions and asphalt concrete overlays. Thesis for the Doctor inTechnical Science. Technische Hogenschoo1. Delft, The Netherlands.

MOLENAAR. A A A. (1984). Structural performance of flexible pavements.Proc. 11th AARB Conf. 12(3), pp 48-54.

MOLENAAR, A A A and KOOLE, R C. (1982). Moderator's report. Papers insession III. Pavement evaluation. Proc. of the 5th Int. Conf. on theStructural Design of Asphalt Pavements. Vol. II Delft.

MOLENAAAR, A A A and VAN GURP. CAP M. (1980). Optimization of thethickness design of asphalt concrete. 10th ARRB Conf. 10(2) pp 31-44.

MONISMITH, C L (1966) Design considerations for asphalt pavements tominimize fatigue distress under repeated leading. Berkeley, University ofCalifornia.

MONISMITH, C L. (1977). Pavement evaluation and overlay design: Summaryof methods. Transport Research Record No. 700, Transport Research Board.Washington, D.C.

MONISMITH,mixtures.

C L and DEACON, J A. (1969) Fatigue of asphaltTransportation Engineering Journal of the ASCE, May 1969.

MONISMITH, C L. and MARKEVICH, N (1983). Progress report on structuralpavement evaluation and overlay design for low volume roads. Dept. ofCivil Engineering, University of California, Berkeley.

MONISMITH, C L and McLEAN, D B. (1982). Structural desi~n considerations.Symposium on the technolo~y of thick asphalt construction. Proc. of theAssociation of Asphalt Technologists.

MONISMITH, C L, SECOR, K E and BLACKMER, E W.behaviour in repeated flexure. Proc. of theTechnologists. Vol. 30. Minneapolis.

(1961). Asphaltic mixAssociation of Asphalt

MOORE, W M HANSON, D I and HALL, J W. (1978).non-destructive structural evaluation of pavements.Research Circular No. 189.

An introduction toTRB, Transportation

NATIONAL INSTITUTE FOR TRANSPORT AND ROAD RESEARCH. (1971). Bituminoussurface treatments for newly constructed rural roads. TRH3. (CSIR,Pretoria) .

NATIONAL INSTITUTE FOR TRANSPORT AND ROAD RESEARCH. (1978). Selection anddesign of hot-mix asphalt surfacings for highways. TRH8. (CSIR,Pretoria) .

NATIONAL INSTITUTE FOR TRANSPORT AND ROAD RESEARCH. (1983). Structuraldesign of pavement rehabilitation. Draft TRH12. (CSIR, Pretoria).

NATIONAL INSTITUTE FOR TRANSPORT AND ROAD RESEARCH.design of inter-urban and rural road pavements. TRH4

(198Sa). Structural(CSIR, Pretoria).

NATIONAL INSTITUTE FOR TRANSPORT AND ROAD RESEARCH. (198Sb. Standards forroad construction materials. TRH14 (CSIR, Pretoria).

NIE, N H, HULL, C H, JENKINS, J G, STEINBRANNER, K AND BRENT, D H.SPSS Statical package for the social sciences. SecondMcGraw-Hill Publishing Company.

(UPS).Edition.

ODEMARK, N. (1949.) Investigations as to the elastic properties of soilsand design of pavements according to the theory of elasticity. StatensVaeginstitut, Stockholm, Sweden.

OPPERMAN, R A. (1984). Die swaarvoertui~naboorsertoetse (SVN-toetse) opPad 30, naby Hornsnek. NITRR Technical Report, RP/3/84 (CSIR, Pretoria).

OPPERMAN, R A, HORAK, E and VILJOEN, A W. (1983) . The Heavy VehicleSimulator (HVS) tests on freeway N3/1 between Paradise Valley andFarnningham interchange. NITRR Technical Report, RP/7/83 (CSIR, Pretoria).

PATTERSON, W D O. (1985). Prediction of road deterioration andmaintenance effects: Theory and guantification. The highway design andmaintenance standards study. Draft Vol. III. Transportation Department.The World Bank, Washington, D.C.

PATTERSON. W D 0 and VAN VUUREN. D J (1974). Diagnosis of working strainsin a pavement using deflection profiles. ARRB Proc •• Vol. 7. Part 6.

PERMANENT INTERNATIONAL ASSOCIATION OF ROAD CONGRESSES. (1983). Technicalconunittee report on flexible roads. XVII World Road Congress. Sydney.Australia.

PRONK. A C and BUITER. R. (1982). Aspects of the interpretation andevaluation of Falling Weight Deflectometer (FWD) measurements. Proc. ofthe 5th Int. Conf. on the Structural Design of Asphalt Pavements. Vol. 1Delft.

RHOLF. J G and ROGNESS, R O. (1985). Multivariate analysis of pavementDynaflect deflection data. Paper prepared for the Transportation ResearchBoard Meeting. Washington. D.C.

ROBINSON. B. (1984). SPSS subprogram Non-linear regression. VogelbackComputer Centre. Illinois.

RUST. F C. (1984). Load-associated crack movements in road pavements.Paper presented at the Annual Transportation Conference. Pretoria.

RUST. F C. (1985). Sununary of crack movement measurement results on theMR27- Stellenbosch to Somerset West. NITRR Technical Note TP/149/85.(CSIR. Pretoria).

RUST. F C. (1986). Crack movement measurements on the N4/3. NITRR TechnicalNote. TP/86/86. (CSIR. Pretoria).

SHACKEL. B. (1980). The Heavy Vehicle Simulator system in South Africa.NITRR Technical Report RP/3/80. (CSIR. Pretoria).

SHELL INT. PETROLEUM CO. ((1978). Shell pavement design manual: Asphaltpavements and overlays.

SLAVIK. M M and BOSMAN. J.traffic observations.. PaperConference. Pretoria.

1984. Estimation of pavement loads frompresented at the Annual Transportation

SNAITH. M S. McMULLEN. D. FREER-HEWISH. R J and SHEIN. A. (1980).Flexible pavement analysis. Final Report. Dept. of Transportation andEnvironmental Planning. University of Birmingham.

STUBSTAD. R N and CONNER. B. (1983). Use of the Falling WeightDeflectometer to predict damage potential on Alaskan Highways during springthaw. TRB. Transportation Research Record 930.

STUBSTAD. R N and HARRIS. T B. (1984) . Personal conununication.DynatestConsulting, Ojia. California.

SWIFT. G. (1972). A graphical technique for determining the elasticmoduli of a two-layered structure for measured surface deflections.Research Report No. 136-3. Texas Transportation Institute.

SZENDREI. M E. (1974). Evaluation of Benkelman beam field data suppliedin the form of a deflection distance chart. NITRR Technical Note TI/8/74.(CSIR. Pretoria).

SZENDREI, M E. (1975). Benk 5 - An improved version of Benk 1. NITRRTechnical Note TI/4/75 (CSIR, Pretoria).

SZENDREI, M E. (1975b). A computer program to evaluate road deflectionsat various depths. NITRR Technical Note TI/5/75 ..(CSIR, Pretoria).

TAM, W S. (1985).Report No. WST/1.Nottingham.

Report on design of overlays for bituminous pavements.Department of Civil Engineering, University of

TAUTE, A, McCULLOUGH, B G and HUDSON, W R. (1981). Improvements to thematerials characterization and fatigue life prediction methods of the Texasrigid pavement overlay design procedure. Research report 249-1-(University of Texas at Austin.) Centre for Transportation Research,Bureau of Engineering Research, Austin.

THOMPSON, M R. (1982). Concepts for developing a non-destructive basedasphalt concrete overlay thickness desi~n procedure. Illinois Dept. ofTransportation Bureau of Materials and Physical Research. FHWA/IL/UI-194.

THOMPSON, M R and ELLIOTT, R P. (1986) .design of conventional flexible pavements.Record No. 1043.

ILLI-PAVE-Based algorithms forTRB, Transportation Research

THOMPSON,NDT-basedthickness.

M R and HOFFMAN, MS. (1983) . Conceptsdesign procedure for determining asphalt

TRB, Transportation Research Record No. 930.

of developing anconcrete overlay

TREYBIG, H J, McCULLOUGH, B F, FINN, F N, McCOMB, R and HUDSON, W R.(1978). Design of asphalt concrete overlay thickness .. Proc. of the 4thInt. Conf. on the Structural Design of Asphalt Pavements. Vol. 1., AnnArbor.

ULLIDTZ, P (1982). Management system for pavement maintenancerehabilitation based on analytic methods of pavement evaluation.Transportation Research Record 930.

andTRB,

ULLIDTZ, P and PEATTIE, KR. (1980). Pavement analysis by programmablecalculators. Transportation Engineering Journal of the American Societyof Civil Engineers. Vol. 106, No. TES.

ULLIDTZ, P and PEATTIE, K R. (1982). Programmable calculators in theassessment of overlays and maintenance strategies. Proc. of the 5th Int.Conf. on the Structural Design of Asphalt Pavements. Vol. I., Delft.

UNIVERSITY OF CALIFORNIA. (1972). ELSYMS. Unpublished report, Berkeley,California.

UNIVERSITY OF DUNDEE, DEPARTMENT OF CIVIL ENGINEERING. (1980). Pavementevaluation based on surface deflection. Dundee.

VAN DE LOO, P J. (1976). A practical approach to the prediction ofrutting in asphalt pavements - the Shell method. Transportation ResearchBoard, Washington, D.C.

VAN ZYL. N J Wand FREEME. C R. (1984). Determination of relative damagedone to roads by heavy vehicles. Paper presented at the AnnualTransportation Conference. Pretoria.

VAN ZYL. N J Wand TRIEBEL, R. (1984). Drie-maandeliksevorderingsverslag vir die tydperk Mei tot Julie 1982. NITRR Technical NoteTP!82!82. (CSIR, Pretoria).

VASWANI. N K. (1971). Method for separately evaluating structuralperformance of subgrades and overlaying flexible pavements. HRB, HighwayResearch Record No. 362.

VERSTRAETEN. J, VEVERKA. V and FRANCKEN, L. (1982). Rational andpractical designs of asphalt pavements to avoid cracking and rutting.Proc. of the 5th Int. Conf. on the Structural Design of Asphalt Pavements.Delft. Holland.

VEVERKA. V. (1979). Evaluation of rut depth in flexible pavements. LaTechnique Routiere. Vol. 24. No.3.

VILJOEN, A Wand MEADOWS, K. (1981). The creep test - A mix design toolto tank asphalt mixes in terms of their resistance to permanent deformationunder heavy traffic. NITRR. Technical Note TP!36!81. Pretoria).

VISSER, A T, MAREE, J H and MARAIS, G P. (1983). Implications of lightbituminous surface treatments on gravel roads. NITRR RR 350. Reprintedfrom Transportation Research Record No. 898, TRB, Washington. D.C.

WALKER, R N, PATERSON, W D O. FREEME, C R and MARAIS, C P. (1977). TheSouth African mechanistic design procedure. Proc. 4th Int. Conf. on theStructural Design of Asphalt Pavements. Vol. 2, pp 363-415.

WANG, M C, LARSON, T D, BHAHANDAS, A C and CUMBERLEDGE, G.road rater deflections in pavement evaluation. TRB.Research Record 666.

(1978). Use ofTransportation

WHITCOMB, W G (1982). Surface deflections and pavement evaluation -Equipment and analysis techniques. Transportation Engineering Report 82-4.Dept. of Civil Engineering. Oregon State University, Cornwallis, Oregon.

WISEMAN, G, UZAN, J, HOFFMAN, M S, ISHAI. I and LIVNEH, M. (1977). Simpleelastic models for pavement evaluation. Proc. of the 4th Int. Conf. on theStructural Design of Asphalt Pavements. Ann Arbor, Vol. 2.

YODER, E J and WITCZAK. M W. (1975). Principles of pavement design.Second Edition. John Willey and Sons. Inc.

Parameter Formula

I. Maximum deflection 80.

2. Radius of curvature Rr2 r = 127 mm= i

280 ( 80/8 r - \)

3. Spreadability S ::[( 80+81+82+ 83)/5] 100 . 81""83 spaced,

80 305mm

4. Area A = 6[1+ 2 (SI/80) +2(82/801"83/80]

5. Shape factors F = (80- 82) I 81 ; F2 = ( 8, -83) 182

6. Sur face curvature index SCI = 8o'-:8r , r = 305 or 500 mm

7. Base curvature index BCI = 8610 -8915

8. Base damage index BDI = 8305 -8610

9. Deflection ratio Or = 8r/80 , where 8r ~ 80/2

10. Bending index BI = 80/a , where a = deflection basin length

II. Slope of deflection SO = tan-1 (80-8r)/r ; where r = 610 mm

12. Tangent slope ST = (8 -8d/r . where r = distance too , inflection poi nt

13. Radius of influence RI = R'/80 ) where R I is the distance from80 to whe re basin is tangentto hori zontal.

Deflected /shape ofroad surface

a or R'Deflection basin length

P~Point of inflection

Positivecurvature