SUBGRADE CBR

7/22/2019 SUBGRADE CBR

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ARRB Conference Shaping the future: Linking policy, research and outcomes, Perth, Australia 2012

ARRB Group Ltd and Authors 2012 1

DESIGN SUBGRADE CBR FOR FLEXIBLEPAVEMENTS: COMPARISON OF PREDICTIVEMETHODS

A. Nataatmadja, Roads and Maritime Services, New South Wales,Australia

S.Y. Tao, Roads and Maritime Services, New South Wales,Australia

K. Chim, Roads and Maritime Services, New South Wales, Australia

ABSTRACT

Subgrade performance is a function of a soil's strength and its behaviour under traffic loading.

The subgrade should be sufficiently stable to prevent excessive rutting and shoving duringconstruction, provide good support for placement and compaction of pavement layers, limitpavement rebound deflections to acceptable limits, restrict the development of excessivepermanent deformation (rutting) in the subgrade during the service life of the pavement andminimise effect of changes in moisture level.

When the subgrade does not possess these attributes, corrective action in the form of asubgrade treatment is needed. The method of excavation and replacement is commonlyadopted in situations where the subgrade soaked CBR is less than the assumed design soakedCBR. This paper discusses various methods used to obtain the design (effective) subgradeCBR for use in a mechanistic design procedure for flexible pavements. The results from theOdemark Transformation Method, both with and without a correction factor, are compared withthe results from multi-layered elastic analyses for both isotropic and anisotropic conditions. A

new method for calculating the effective subgrade CBR is proposed and validated based on theperformance of a number of typical pavement structures.

INTRODUCTION

In case of weak subgrade, it is common to use capping materials or working platforms ofsuitable quality such as select material, chemically modified soil, geogrid reinforced soil, etc. Inthis case, the effective or the composite strength of its subgrade and the capping material givenwould then be used for the design of flexible pavements.

The RMS Austroads Guide Supplement to Pavement Technology Part 2(RMS 2010) gives

presumptive subgrade CBR values which may be used in pavement design for various workingplatforms (Table 1).


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Table 1: Presumptive effective subgrade CBR for various working platforms

Source: RMS (2010).

On the other hand, the 2010 version of Austroads Guide to Pavement Technology Part 2

(Austroads 2010) specified that (in Section 3.14.1):

The above clause is no longer mentioned in the current Austroads Guide Part 2(Austroads2012) since it is generally accepted in practice that the thickness and strength of working

platform or capping layer should be taken into account to achieve the nominated effectivesubgrade strength.

For pavements with thin bituminous surfacing, Figure 8.4 of Austroads Guide Part 2seems tosuggest that it may be used to calculate the thicknesses of capping layers and other pavementlayers above the original subgrade for a certain design ESA. For example, from Figure 1 it maybe inferred that 110 mm of material with a CBR of 3% may be used as a capping layer on top ofa natural subgrade with a CBR of 2% to produce a subgrade with an effective CBR of 3% for aDESA of 10

6(Figure 2). This is certainly not in agreement with RMS Supplement as shown in

Table 1.

The chart shown as Figure 1 has been empirically developed to determine the layercomposition of a pavement with thin bituminous surfacing. It can be shown that for such apavement, CIRCLY modelling (with maximum base modulus = 500 MPa) can produce similarlayer thicknesses based on the limiting strain criterion of the natural subgrade. However, if thechart is used to obtain the capping layer thickness for subgrade improvement, the thickness soobtained may not be appropriate for other pavement configurations where pavement life may becontrolled by a layer other than the natural subgrade.

This paper examines the issue of selecting an effective material property, CBR or modulusvalue, for the combination of a capping layer and a semi-infinite subgrade. In this case, it isimportant to note that for a certain traffic loading it is possible to find one pavementconfiguration that will perform similarly on a homogeneous semi-infinite subgrade and a two-layer subgrade (capping plus homogeneous semi-infinite subgrade). However, the equivalencyof both subgrade types may not hold for other pavement configurations or traffic loadings.


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In the subsequent sections of this paper, empirical methods for finding the effective CBR arepresented and their validity examined. The results from the calculations are compared withthose obtained from multilayered elastic theory on the basis of equal surface deflection so thatthe effective subgrade CBR so obtained will be applicable to any flexible pavement types andnot affected by the choice of pavement materials and their fatigue characteristics.

Source: Austroads (2012).

Figure 1: Austroads chart for designing thin bituminous pavement

Figure 2: Thickness of capping layer inferred from Fig. 8.4 of Austroads (2012) for an

effective CBR of 3%

ODEMARKS METHOD OF EQUIVALENT THICKNESS

Odemark has developed an approximate method to calculate stresses and strains in multiplayerpavement systems by transforming this structure into an equivalent one-layer system withequivalent thicknesses of one elastic modulus. This concept is known as the Method ofEquivalent Thickness (MET) or Odemarks Method, which assumes that the stresses andstrains below a layer depend only on the stiffness of that layer. If the thickness, modulus and

Poissons ratio of a layer is changed, but the stiffness remains unchanged, the stresses and


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strains below the layer should also remain (relatively) unchanged. According to Odemark, thestiffness of a layer is proportional to the following term (Ullidtz 1987):

2

3

1 !"

Eh

(1)

where

h = thickness of the layer (m)

E = elastic modulus (MPa)

! = Poissons ratio.

For the two layers of different materials shown below, it can be stated that both are of equivalentstiffness if

2

1

1

3

1

1 !"

Eh=

2

2

2

3

2

1 !"

Eh

For the case of two materials with equal Poissons ratio, the following equation will hold:

3

2

1

1

3

2

1

3

1

2 E

E

hE

Eh

h ==

Therefore, for a system with two finite layers with equal Poissons ratio as shown below, layer 1of modulus E1can be represented by an equivalent thickness (he) of modulus E2:

3

2

1

1 E

E

hhe

=

Note that the correction factor f of Odemarks method is different from f= Ev/ (1 + !v) used inthe CIRCLY computer program.

Researchers reported that the value of the correction factor f depends on the layerthicknesses, modular ratios, and the number of layers in the pavement structure. However, it


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was mentioned that the use of f values of 0.8 to 0.9 leads to a reasonably good agreementbetween the two methods (Subagio et al. 2005).

APPLICATION OF ODEMARKS METHOD

If a finite subgrade layer of (h1, E1) is placed on top of another finite subgrade layer of (h2, E2)then an equivalent subgrade layer (h

e, E

e) can be defined by means of the previously described

principle of layer equivalency.

(2)

For layer 1:

3 1

11

e

e E

Ehfh !=

For layer 2:

3 2

22

e

e E

Ehfh !=

Therefore,

)(3/1

22

3/1

11

3/1

3 2

23

1

1

EhEhEfh

E

Ehf

E

Ehfh

ee

ee

e

+!!=

!+!=

"

Thus,

!!"

#

$$%

& +'=

e

E

h

EhEhf

e

)( 3/1

22

3/1

11

3

Note that in the above equation, Eeand he are variables. If heis taken as (h1+ h2), then

!!"

#

$$%

&

+

+

'=21

3/1

22

3/1

11 )(

3

hh

EhEhf

eE

and if there are i layers to be combined, the following equation can be used to find Ee:


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!!!

"

#

$$$

%

&

'(

(

=

i

n

ii

n

E

h

Ehf

e

1

3/1

1

3

(3)

This equation is known as the Japan Equation in the Austroads Guide Part 2(Austroads 2012),

where CBRireplaces Ei, with f=1 and "hi= 1 metre. The Japan Equation (Japan RoadAssociation 1989) implicitly assumes the following condition:

all layers are isotropic and have the same Poissons ratio

both the original structure and the transformed structure have the same stress & straindistribution (f = 1)

the existence of a semi-infinite subgrade thickness is ignored. Figure 3 (a) and 3 (b) showsthat only 1 metre upper layer depth is considered. In other words, the effect of applied stressis assumed to be negligible below this depth. This is an assumption that may be acceptablefor designing concrete pavements but is erroneous in the case of flexible pavements.

Figure 3: Application of subgrade equivalency based on the Japan Equation

Figure 4 shows the required capping thickness according to the Japan Equation to achieve adesign (effective) CBR of 3% for a semi-infinite subgrade CBR of 1% to 3.5%. The capping

materials in this figure can have a CBR between 4% and 10%. It is seen that for an originalsubgrade CBR of 2%, a 560 mm thick capping layer of CBR 4% would be needed to produce aneffective CBR of 3%.

0

100

200

300

400

500

600

700

800

900

1 1.5 2 2.5 3 3.5

Original CBR (%)

ThicknessofCapping(mm)

Capping CBR 4%

Capping CBR 5%

Capping CBR 6%

Capping CBR 7%

Capping CBR 8%

Capping CBR 9%

Capping CBR 10%

Figure 4: Thickness of capping layer from the Japan Equation (effective CBR = 3%)


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ODEMARKS METHOD VERSUS ELASTIC ANALYSIS

From the above, it is clear that a multilayered elastic half-space analysis which considersanisotropic soils layers (such as CIRCLY) will produce capping thicknesses (and effectiveCBRs) that are different from those obtained from the use of the Japan Equation. Note that thesublayering technique used to simulate the nonlinear modulus variation (Austroads 2012) willalso affect the results.

El-Badawy and Kamel (2011) carried out an extensive study to quantify the influence of layerthickness, depth, and modular ratios on the correction factor fof the Odemarks transformationmethod. A two-layer isotropic system with the first layer thickness (h1) values of 50, 150, 250and 375 mm were used in the analysis. A total of 5 different modular ratios of E1/E2= 3.33,16.67, 33.33, 50.00, and 66.67 for each thickness were analysed. A Poissons ratio of 0.35 wasassumed in all computations. Figure 5 shows the applied load and the properties of the twolayer system used in their analysis.

A linear elastic analysis was performed on the two-layer isotropic subgrade using the KENPAVEsoftware to calculate the vertical and radial stresses at different depths measured from thesurface of the upper layer under the centerline of the load. Then Odemarks method was usedto convert the two-layer problem into one layer with equivalent thicknesses and one modulus. A

comparison between stresses calculated from both systems was made. The influence of thecorrection factor f on the computed stresses of the transformed system using Odemarksmethod was studied.

Comparing Odemarks method without using a correction factor (f= 1) to KENPAVE solutionyielded different stress values at the points of interest. A correction factor fwas then introducedinto the equation to calculate the corrected equivalent depth. First, a unique f value was appliedto all points of interest for each modular ratio. The results showed good agreement only for thevertical stresses calculated at the interface between the two layers when using fof 0.8 to 0.9.However, at any depth other than the interface between the two layers the results showed asignificant difference between the two solutions (Figure 6). This means that the correction factorfis also dependent on the depth.

Source: El-Badawy and Kamel (2011).

Figure 5: Two-layer model used by El-Badawy and Kamel


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Figure 6: Variation of correction factor (f) with depth (after El-Badawy and Kamel 2011).

FURTHER COMPARISON WITH ISOTROPIC ELASTICANALYSIS

Considering the highly variable nature of the correction factor f, the authors of the present studydid not attempt to find the exact value or correct variation of f. Rather, the objective of this studywas focussed on finding a typical f value that can be used to correct Odemarks method for thepurpose of finding the thickness of capping layer required to convert a subgrade with low CBRvalues to reach an equivalent half-space CBR of 3% based on surface deflection calculation.For the purpose of this study, a subgrade with original (semi-infinite) CBR values of 1, 1.5, 2

and 2.5 percent and a capping layer with CBR values of 4, 5, 6, 7, 8, 9 and 10 percent werechosen. While research overseas and in Australia has shown that non-stress dependentrelationships between CBR and resilient modulus have some limitations (Austroads 2009), in

this paper it is assumed that E (in MPa) = 10 #CBR for subgrade soils.

To simplify the analysis, a 5-layer linear elastic computer program CHEVRON was used insteadof CIRCLY since both programs can produce similar results for isotropic conditions. Firstly,CHEVRON analyses were carried out to find the thickness of capping layer that will produce thesame magnitude of surface deflection (i.e. method of equivalent deflection) under a circularloading representing a dual wheel assembly with 550 kPa tyre pressure (lower than the actualtyre pressure acting on the pavement surface), at point A (centre of the load) as shown below inFigure 7.

The method of equivalent surface deflection is based on the premise that if a correct thicknessof a capping layer of a certain CBR value is used over a subgrade with a certain CBR value, thetwo layer system can represent a semi-infinite subgrade with a single design (effective) CBR(Reddy et al. 2001). By using this method, the capping thickness so calculated is not going tobe influenced by the choice of pavement type (and the corresponding fatigue equations) andhence, can be used for designing flexible pavement of any configurations.


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Figure 7: Subgrade model used in the present study (isotropic case)

Figure 8 shows comparison between the capping thickness requirements based on CHEVRONand the Japan Equation, which suggests that the latter requires greater capping thickness overa subgrade of various CBR values to produce an effective design CBR of 3%. It is seen that fora subgrade of CBR 2%, CHEVRON suggests that a 280 mm capping layer with CBR 4% can beused to reach an effective CBR of 3%.

It is interesting to note that Equation 3 indicates that the equivalent CBR of a multilayeredsubgrade would be less than what is predicted from the Japan Equation if f< 1 and thus thecorrect capping thicknesses should be greater than those suggested by the formula. Thecalculated capping thickness values vary with the case studied (Table 2); however, in all valuesbut one, it was found that the capping thicknesses from CHEVRON linear elastic and isotropicanalyses are less than those obtained from the Japan Equation. While the Japan Equationseems to produce adequate capping thicknesses if the soil layers are assumed to be linearelastic and isotropic, such assumptions are not in accordance with current method for pavementdesign (Austroads 2010, 2012).

Figure 8: Comparison capping thicknesses Japan Equation vs. CHEVRON for aneffective CBR of 3%

Table 2: Capping thickness ratios - Japan Equation vs. CHEVRON

Subgrade

CBR (%)Capping CBR (%) 4 5 6 7 8 9 10

1.0 Japan/CHEVRON 0.9805 1.2952 1.4125 1.4578 1.4783 1.4819 1.4845

1.5 Japan/CHEVRON 1.4769 1.7533 1.8115 1.8084 1.7846 1.7569 1.7251

2.0 Japan/CHEVRON 2.0036 2.1094 2.0311 1.9510 1.8779 1.8049 1.7436

2.5 Japan/CHEVRON 2.3654 2.1140 1.8878 1.7191 1.5904 1.5128 1.4267


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COMPARISON WITH ANINSOTROPIC ELASTIC ANALYSIS

In accordance with the current Austroads mechanistic pavement design procedure both cappinglayer and subgrade soil were considered cross-anisotropic with EV/EH= 2. The Poissons ratiowas assumed 0.45 for both the capping and subgrade layers. Sublayering of the capping wasdone according to Austroads (2012).

Similar to the previous case, the load chosen for this study was a half-axle configuration with550 kPa tyre pressure. CIRCLY analyses were carried out to find the thickness of capping layerthat can convert a subgrade with lower CBR values to an equivalent half-space CBR of 3, 4, 5,6 and 7 percent for the same magnitude of surface deflection (i.e. method of equivalentdeflection) under a dual wheel assembly, at point A (centre of the wheel) as shown in Figure 9.For the purpose of this study, a semi-infinite subgrade CBR of 2, 3, 4 and 5 percent and acapping layer with CBR values of 5, 6, 7, 8, 9 and 10 percent were chosen.

Figure 9: Subgrade model used in the present study (anisotropic case)

Furthermore, to match the calculated capping thicknesses from CIRCLY runs with those from

Odemarks method (Equation 3 with "hi = 1 metre), a trial and error process was done by

inputting f values such that the sum of differences between two corresponding cappingthickness values could be minimised (Table 3).

In contrast with the results of Subagyo et al. (2005) the f values obtained from the present studyis variable, which support the results of El-Badawy and Kamel (2011). When the ratios betweeneffective CBR over original subgrade CBR are plotted against the fvalues, it becomes clear thatfvaries with the ratio between effective CBR to the original, semi-infinite, subgrade CBR (Figure10). Therefore, the following equation can be used to find the correction factor f:

!!"

#

$$%

&'(=

Original

Effective

CBR

CBRf 5251.05251.1

(4)

Figures 11 and 12 show the variation of capping thickness with the original subgrade CBR toachieve an effective CBR of 3% and 5%, respectively (for this study the maximum capping layerthickness was 1000 mm). The existence of double curvature relationships is evident in bothcharts, which is similar to that of the previous CHEVRON isotropic analysis (Figure 8).


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Table 3: Calculation of coefficient fby minimising sum of differences

CBR eff.

(%)

CBRoriginal

(%)

Method

CBR of capping layer (%) CBReffective

CBRoriginal

fSum

ofdiff.

5 6 7 8 9 10

Capping thickness (mm)

3 2 CIRCLY 765 615 535 490 455 430

ODEMARK 793 640 546 482 435 399 1.5 0.71

Differences -28 -25 -11 8 20 31 -5

4 2 CIRCLY 980 875 800

ODEMARK 965 871 798 2 0.52

Differences 15 4 2 21

4 3 CIRCLY 680 545 480 435 400

ODEMARK 714 569 480 420 376 1.33 0.8

Differences -34 -24 0 15 24 -19

5 3 CIRCLY 980 835 745

ODEMARK 972 850 761 1.67 0.64

Differences 8 -15 -16 -23

5 4 CIRCLY 640 515 445 405

ODEMARK 669 528 442 384 1.25 0.85

Differences -29 -13 3 21 -18

6 4 CIRCLY 905 765

ODEMARK 893 776 1.5 0.72

Differences 12 -11 16 5 CIRCLY 960 615 490 425

ODEMARK 918 642 503 419 1.2 0.88

Differences 42 -27 -13 6 8

7 5 CIRCLY 845

ODEMARK 848 1.75 0.77

Differences -3 -3


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Figure 10: Variation of coefficient f with CBREff/CBROriginal(one point was ignored as it was from one pavement configuration only)

Figure 11: Capping thicknesses Proposed chart to obtain an effective CBR of 3%

Figure 12: Capping thicknesses Proposed chart to obtain an effective CBR of 5%


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In contrast with the previously described methods, it has been found that for a subgrade of CBR2%, it is not practical to place a capping layer with a CBR of 4% in order to obtain an effectiveCBR of 3% (the required capping layer thickness would have to be much greater than 1000mm). Instead, a 750 mm capping layer with CBR 5% would be needed. It is also interesting tonote that a typical RMS subgrade treatment is to place a 900 mm material with soaked CBR 8%on top of the subgrade which would, according to these two charts, produce an effectivesubgrade soaked CBR of 3% if the original subgrade soaked CBR is about 1.5% or an effectivesoaked CBR of 5% if the original subgrade soaked CBR is about 3%.

VALIDATION OF THE PROPOSED METHOD

As previously explained, Equation 4 was derived through the calculation of the surfacedeflection of the capping layer so that the resulting thickness should be applicable to any type ofpavements. In spite of that, the process of pavement design involves certain assumptions aboutthe material properties e.g. non-linearity, anisotropy, and fatigue characteristics. Therefore, it isimportant to validate the formula via mechanistic design of a number of flexible pavement types,which include granular, full depth asphalt and deep strength asphalt pavements (Table 4).

Table 4 shows that in all cases, pavements containing the calculated capping thicknesses

produced pavement lives comparable to those obtained from CIRCLY analyses with ahomogenous semi-infinite subgrade. It is interesting to note that for all pavement types, failuresoccurred in a layer other than subgrade.

The results also show that for deep strength asphalt pavement, in order to produce an equalcumulative damage factor (CDF), the LMC thickness may need to be increased by 2.5 mmwhen a capping layer is used. This additional thickness, which is related to the fatiguecharacteristics of LMC, may be considered insignificant since in practice, tolerances of10-20 mm may be applied.

CONCLUSIONS

It has been demonstrated that the effects of combining layers of different soils may alter notonly the stress and strain distributions within the individual layers but also the surface deflection.Odemarks method simplifies the effect of layering to produce an equation to predict thecombined modulus but does not produce an accurate representation of stress and straindistribution within multilayered pavement foundation. Correction factors have been proposed toimprove the accuracy of Odemarks method for a combined modulus, but their accuracy may bequestionable.

This paper presented the results of a preliminary investigation on the effect of layering and non-linearity on the combined modulus of a multilayered subgrade. The study was limited to a two-layer subgrade, being a capping layer with a maximum thickness of one metre, on top of asemi-infinite subgrade. Limited CBR combinations were analysed using the CIRCLY computerprogram with Austroads sublayering and anisotropy assumptions, which produced an equation

that can be used to find the appropriate correction factor for use with the Odemarks method.Subsequently, charts that can be used to obtain the capping layer thickness on top of asubgrade were proposed to obtain an effective subgrade CBR for pavement design purposes.Since the charts have been developed independent from pavement configurations, they can beused for any type of flexible pavement.

The results of this study indicate that the use of the Odemarks method without a correctionfactor (i.e. the Japan Equation) will underestimate the capping thickness requirement ifanisotropy and nonlinearity are considered. The validation process employed in the presentstudy demonstrates the accuracy of the proposed correction factor and the resulting charts.Further studies will be conducted to more comprehensively analyse the application of themethod for a wider range of CBR values, number of layers and layer thicknesses.


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Table 4: Results of validation process

Pavementtype

DESA EffectivesubgradeCBR (%)

Input verticalmodulus

(MPa)

Pavement CumulativeDamage Factor

(CDF)Layers (criticallayer is

underlined)

Thicknesses(mm)

Granular 1.43E+07

5

350

150

50

Base

SMZ

Subgrade

270

300

Semi-infinite

9.08 E-01

5**

350

150

90

30

Base

SMZ

Capping

Subgrade

270

300

834

Semi-infinite

9.57E-01

Full depthasphalt

1.52E+08

3

1700

4000

4000

150

50

30

Wearing AC

AC14

AC20

SMZ

UZF

Subgrade

40

50

260

300

300

Semi-infinite

9.48E-01

3**

1700

4000

4000

150

50

50

20

Wearing AC

AC14

AC20

SMZ

UZF

Capping

Subgrade

40

50

260

300

300

743

Semi-infinite

9.72E-01

3**

1700

4000

4000

150

50

70

20

Wearing AC

AC14

AC20

SMZ

UZF

Capping

Subgrade

40

50

260

300

300

512

Semi-infinite

9.68E-01

3**

1700

4000

4000

15

50100

20

Wearing AC

AC14

AC20

SMZ

UZFCapping

Subgrade

40

50

260

300

300374

Semi-infinite

9.70E-01

Deepstrengthasphalt

3.65E+07

3

1000

2500

2700

10000

150

50

30

Wearing AC

AC14

AC20

LMC

SMZ

UZF

Subgrade

40

50

85

195

300

300

Semi-infinite

7.86E-01

3**

1000

2500

2700

10000

150

50

50

20

Wearing AC

AC14

AC20

LMC

SMZ

UZF

Capping

Subgrade

40

50

85

197.5

300

300

743

Semi-infinite

7.9E-01

3**

1000

2500

2700

10000

150

50

70

20

Wearing AC

AC14

AC20

LMC

SMZ

UZF

Capping

Subgrade

40

50

85

197.5

300

300

512

Semi-infinite

7.9E-01

** With capping layer thicknesses from Equations 3 and 4 to improve the original subgrade CBR.


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REFERENCES

Austroads (2009), Review of Relationship to Predict Subgrade Modulus from CBR (CaliforniaBearing Ratio), Sydney, Australia.

Austroads (2010), Guide to Pavement Technology Part 2: Pavement Structural Design, Sydney,Australia.

Austroads (2012), Guide to Pavement Technology Part 2: Pavement Structural Design, Sydney,Australia.

El-Badawy, M. and Kamel, M.A. (2011),Assessment of Improvement of the Accuracy of theOdemark Transformation Method, International Journal of Advanced Engineering Sciences andTechnologies, 5 (2), pp.105-110.

Japan Road Association (1989), Manual for Asphalt Pavement, Japan Road Association,Tokyo.

Reddy, M.A., Reddy, K.S. and Pandey, B.B. (2001), Design CBR of Subgrade for FlexiblePavements, IRC Highway Research Bulletin, 64, pp. 61-69.

RMS (2010),Austroads Guide Supplement to Pavement Technology Part 2, Sydney, Australia.

Subagio, B., Cahyanto, H., Rahman A. and Mardiyah, S. (2005), Multi-layer PavementStructural Analysis Using Method of Equivalent Thickness, Case Study: Jakarta-Cikampek TollRoad, Journal of the Eastern Asia Society for Transportation Studies, Vol. 6, pp. 55-65.

Ullidtz, P. (1987), Pavement Analysis, Development in Civil Engineering, Vol.19, Elsevier,Amsterdam, the Netherlands.

ACKNOWLEDGEMENTS

The comments and views expressed in the paper are those of the authors and not necessarilyof the Roads and Maritime Services of NSW. The authors thank Messrs. D. Hazell and P.Tamsett for reviewing the manuscript.

AUTHOR BIOGRAPHIES

Andreas Nataatmadja, BE (Hons) Petra, MEngAIT, PhD Monash, GradCert (Env) Melb.,MIEAust

Dr. Nataatmadja is the Supervising Pavement Engineer (Design & Analysis) of Roads TrafficAuthority-New South Wales in Parramatta. His previous position was Senior Lecturer in

Geotechnical and Pavement Engineering at QUT, Brisbane. He has published numerouspapers in geotechnical engineering and pavement technology. With a research interest in theareas of material science, geotechnical and pavement engineering, Andreas has been workingin the broad area of civil engineering for more than 30 years in industrial, consulting, researchand teaching environments.

Ms. Su Yin Tao, BSc (App. Chem) UTS, Dip.Sci.Prac UTS, GradCert (Pavement Tech.) CPEE

Su Yin Tao joined the RMS in 2006 on the Graduate Program. She has worked in MaterialsTechnology, Environmental Assessment, Geotechnical Science, Pavement Design and

Analysis, and Bridge Technology areas of the RMS. She recently completed the PavementTechnology Graduate Certificate with CPEE and currently works at RMS in the Design and

Analysis Unit, focusing on pavement wear and design review.


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