SUBGRADE CBR

th

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

DESIGN SUBGRADE CBR FOR FLEXIBLE PAVEMENTS: COMPARISON OF PREDICTIVE METHODS A. Nataatmadja, Roads R oads and Maritime Services, Ser vices, New South Wales, W ales, 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 during construction, provide good support for placement and compaction of pavement layers, limit pavement rebound deflections to acceptable limits, restrict the development of excessive permanent deformation (rutting) in the subgrade during the service life of the pavement and minimise effect of changes in moisture level. When the subgrade does not possess these attributes, corrective action in the form of a subgrade treatment is needed. The method of excavation and replacement is commonly adopted in situations where the subgrade soaked CBR is less than the assumed design soaked CBR. This paper discusses various methods used to obtain the design (effective) subgrade CBR for use in a mechanistic design procedure for flexible pavements. The results from the Odemark Transformation Method, both with and without a correction factor, are compared with the 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 the performance of a number of typical pavement structures.

INTRODUCTION In case of weak subgrade, it is common to use capping materials or working platforms of suitable quality such as select material, chemically modified soil, geogrid reinforced soil, etc. In this case, the effective or the composite strength of its subgrade and the capping material given would then be used for the design of flexible pavements. The RMS Austroads Guide Supplement to Pavement Technology Part 2 (RMS (RMS 2010) gives presumptive subgrade CBR values which may be used in pavement design for various working platforms (Table 1).

© ARRB Group Ltd and Authors 2012

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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 (Austroads 2012) 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 effective subgrade strength. For pavements with thin bituminous surfacing, Figure 8.4 of Austroads Guide Part 2 seems to suggest that it may be used to calculate the thicknesses of capping layers and other pavement layers above the original subgrade for a certain design ESA. For example, from Figure 1 it may be inferred that 110 mm of material with a CBR of 3% may be used as a capping layer on top of a natural subgrade with a CBR of 2% to produce a subgrade with an effective CBR of 3% for a 6 DESA of 10 (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 layer composition of a pavement with thin bituminous surfacing. It can be shown that for such a pavement, CIRCLY modelling (with maximum base modulus = 500 MPa) can produce similar layer thicknesses based on the limiting strain criterion of the natural subgrade. However, if the chart is used to obtain the capping layer thickness for subgrade improvement, the thickness so obtained may not be appropriate for other pavement configurations where pavement life may be controlled by a layer other than the natural subgrade. This paper examines the issue of selecting an effective material property, CBR or modulus value, for the combination of a capping layer and a semi-infinite subgrade. In this case, it is important to note that for a certain traffic loading it is possible to find one pavement configuration that will perform similarly on a homogeneous semi-infinite subgrade and a twolayer subgrade (capping plus homogeneous semi-infinite subgrade). However, the ‘equivalency’ of 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 are presented and their validity examined. The results from the calculations are compared with those obtained from multilayered elastic theory on the basis of equal surface deflection so that the effective subgrade CBR so obtained will be applicable to any flexible pavement types and not 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%

ODEMARK’S METHOD OF EQUIVALENT THICKNESS Odemark has developed an approximate method to calculate stresses and strains in multiplayer pavement systems by transforming this structure into an equivalent one-layer system with equivalent thicknesses of one elastic modulus. This concept is known as the Method of Equivalent Thickness (MET) or Odemark’s Method, which assumes that the stresses and strains below a layer depend only on the stiffness of that layer. If the thickness, modulus and Poisson’s 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, the stiffness of a layer is proportional to the following term (Ullidtz 1987): (1)

3

h E 2

1 " !

where h

=

thickness of the layer (m)

E

=

elastic modulus (MPa)

!

=

Poisson’s ratio.

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

3

3

h

h

E 1

= 2

1 " !

E 2

1

2 2

1 " !

1

2

For the case of two materials with equal Poisson’s ratio, the following equation will hold: 3

h h

=

E 1

3

E 1 =

2

h 1

E

1

3

2

E 2

Therefore, for a system with two finite layers with equal Poisson’s ratio as shown below, layer 1 of modulus E 1 can be represented by an equivalent thickness (h e) of modulus E2:

E h

=

e

h

1

3 1

E 2

Note that the correction factor f of Odemark’s method is different from f = Ev / (1 + !v) used in the CIRCLY computer program. Researchers reported that the value of the correction factor ‘ f ’ depends on the layer thicknesses, 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 agreement between the two methods (Subagio et al. 2005).

APPLICATION OF ODEMARK’S METHOD If a finite subgrade layer of (h 1, E1) is placed on top of another finite subgrade layer of (h 2, E2) then an equivalent subgrade layer (h e, Ee) can be defined by means of the previously described principle of layer equivalency. (2)

For layer 1:

h

=

e

1

f ! h

E 3 1

1

E

e

For layer 2:

h

=

e

2

f ! h

E

2

3 2

E

e

Therefore,

h h

e

e

=

=

f ! h

E 3 1

f ! E

E

1

f ! h

3 2

e

1/ 3

"

e

+

E

!

(h E 1

E

1/ 3 1

+

2 e

h E 2

1/ 3

)

2

Thus,

E

e

& (h 1 E 1 1 / 3+ h 2 E 2 1 / 3) # f ' $ ! he $% !"

3

=

Note that in the above equation, E e and he are variables. If h e is taken as (h 1 + h2), then

E

e

& (h 1 E 1 1 / 3+ h 2 E 2 1 / 3) # f ' $ ! h + h 1 2 %$ "!

3

=

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


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E

=

e

& (n h E 1 / 3 # i i ! f ' $ 1 n $ ( ! h i $% 1 !"

3

(3)

This equation is known as the Japan Equation in the Austroads Guide Part 2 (Austroads 2012), where CBRi replaces Ei, with f =1 and " hi = 1 metre. The Japan Equation (Japan Road Association 1989) implicitly assumes the following condition: •

•

•

all layers are isotropic and have the same Poisson’s ratio both the original structure and the transformed structure have the same stress & strain distribution ( f = 1) the existence of a semi-infinite subgrade thickness is ignored. Figure 3 (a) and 3 (b) shows that only 1 metre upper layer depth is considered. In other words, the effect of applied stress is assumed to be negligible below this depth. This is an assumption that may be acceptable for 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 a design (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 original subgrade CBR of 2%, a 560 mm thick capping layer of CBR 4% would be needed to produce an effective CBR of 3%.

900 Capping CBR 4%

800

Capping CBR 5%

) m700 m (

Capping CBR 6%

g 600 n i p p 500 a C f o 400 s s e 300 n k c i h 200 T

Capping CBR 7% Capping CBR 8% Capping CBR 9% Capping CBR 10%

100 0 1

1.5

2

2.5

3

3.5

Original CBR (%)

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


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ODEMARK’S METHOD VERSUS ELASTIC ANALYSIS From the above, it is clear that a multilayered elastic half-space analysis which considers anisotropic soils layers (such as CIRCLY) will produce capping thicknesses (and effective CBRs) that are different from those obtained from the use of the Japan Equation. Note that the sublayering technique used to simulate the nonlinear modulus variation (Austroads 2012) will also affect the results. El-Badawy and Kamel (2011) carried out an extensive study to quantify the influence of layer thickness, depth, and modular ratios on the correction factor f of the Odemark’s transformation method. A two-layer isotropic system with the first layer thickness (h 1) values of 50, 150, 250 and 375 mm were used in the analysis. A total of 5 different modular ratios of E 1/E2 = 3.33, 16.67, 33.33, 50.00, and 66.67 for each thickness were analysed. A Poisson’s ratio of 0.35 was assumed in all computations. Figure 5 shows the applied load and the properties of the two layer system used in their analysis. A linear elastic analysis was performed on the two-layer isotropic subgrade using the KE NPAVE software to calculate the vertical and radial stresses at different depths measured from the surface of the upper layer under the centerline of the load. Then Odemark’s method was used to 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 the correction factor f on the computed stresses of the transformed system using Odemark’s method was studied. Comparing Odemark’s method without using a correction factor ( f = 1) to KENPAVE solution yielded different stress values at the points of interest. A correction factor f was then introduced into the equation to calculate the corrected equivalent depth. First, a unique f value was applied to all points of interest for each modular ratio. The results showed good agreement only for the vertical stresses calculated at the interface between the two layers when using f of 0.8 to 0.9. However, at any depth other than the interface between the two layers the results showed a significant difference between the two solutions (Figure 6). This means that the correction factor f is 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 ELASTIC ANALYSIS Considering the highly variable nature of the correction factor f , the authors of the present study did not attempt to find the exact value or correct variation of f . Rather, the objective of this study was focussed on finding a typical f value that can be used to correct Odemark’s method for the purpose of finding the thickness of capping layer required to convert a subgrade with low CBR values 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 were chosen. While research overseas and in Australia has shown that non-stress dependent relationships 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 instead of 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 the same magnitude of surface deflection (i.e. method of equivalent deflection) under a circular loading representing a dual wheel assembly with 550 kPa tyre pressure (lower than the actual tyre pressure acting on the pavement surface), at point A (centre of the load) as shown below in Figure 7. The method of equivalent surface deflection is based on the premise that if a correct thickness of a capping layer of a certain CBR value is used over a subgrade with a certain CBR value, the two 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 to be influenced by the choice of pavement type (and the corresponding fatigue equations) and hence, 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 CHEVRON and the Japan Equation, which suggests that the latter requires greater capping thickness over a subgrade of various CBR values to produce an effective design CBR of 3%. It is seen that for a subgrade of CBR 2%, CHEVRON suggests that a 280 mm capping layer with CBR 4% can be used to reach an effective CBR of 3%. It is interesting to note that Equation 3 indicates that the equivalent CBR of a multilayered subgrade would be less than what is predicted from the Japan Equation if f < 1 and thus the correct capping thicknesses should be greater than those suggested by the formula. The calculated capping thickness values vary with the case studied (Table 2); however, in all values but one, it was found that the capping thicknesses from CHEVRON linear elastic and isotropic analyses are less than those obtained from the Japan Equation. While the Japan Equation seems to produce adequate capping thicknesses if the soil layers are assumed to be linear elastic and isotropic, such assumptions are not in accordance with current method for pavement design (Austroads 2010, 2012).

Figure 8: Comparison capping thicknesses – Japan Equation vs. CHEVRON for an effective 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 capping layer and subgrade soil were considered cross-anisotropic with E V/EH = 2. The Poisson’s ratio was assumed 0.45 for both the capping and subgrade layers. Sublayering of the capping was done according to Austroads (2012). Similar to the previous case, the load chosen for this study was a half-axle configuration with 550 kPa tyre pressure. CIRCLY analyses were carried out to find the thickness of capping layer that 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 equivalent deflection) 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 a capping 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 Odemark’s 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 capping thickness values could be minimised (Table 3). In contrast with the results of Subagyo et al. (2005) the f values obtained from the present study is variable, which support the results of El-Badawy and Kamel (2011). When the ratios between effective CBR over original subgrade CBR are plotted against the f values, it becomes clear that f varies with the ratio between effective CBR to the original, semi-infinite, subgrade CBR (Figure 10). Therefore, the following equation can be used to find the correction factor f :

f

=

1.5251 (0.5251'

& CBR Effective # $ ! CBR Original ! %$ "

(4)

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


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Table 3: Calculation of coefficient f by minimising sum of differences

CBR eff. (%)

3

4

4

5

5

6

6

7

CBR of capping layer (%)

CBR original (%)

Method

2

CIRCLY

765

615

535

490

455

430

ODEMARK

793

640

546

482

435

399

Differences

-28

-25

-11

8

20

31

CIRCLY

980

875

800

ODEMARK

965

871

798

Differences

15

4

2

2

3

3

4

4

5

5

5

6

7

8

9

10

Capping thickness (mm)

CIRCLY

680

545

480

435

400

ODEMARK

714

569

480

420

376

Differences

-34

-24

0

15

24

CIRCLY

980

835

745

ODEMARK

972

850

761

Differences

8

-15

-16

CIRCLY

640

515

445

405

ODEMARK

669

528

442

384

Differences

-29

-13

3

21

CIRCLY

905

765

ODEMARK

893

776

Differences

12

-11

CIRCLY

960

615

490

425

ODEMARK

918

642

503

419

Differences

42

-27

-13

6

CIRCLY

845

ODEMARK

848

Differences

-3


CBR effective CBR original

f

1.5

0.71

Sum of diff.

-5

2

0.52 21

1.33

0.8 -19

1.67

0.64 -23

1.25

0.85 -18

1.5

0.72 1

1.2

0.88 8

1.75

0.77 -3

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Figure 10: Variation of coefficient f with CBR Eff/ CBR Original (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 CBR 2%, it is not practical to place a capping layer with a CBR of 4% in order to obtain an effective CBR of 3% (the required capping layer thickness would have to be much greater than 1000 mm). Instead, a 750 mm capping layer with CBR 5% would be needed. It is also interesting to note 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 effective subgrade soaked CBR of 3% if the original subgrade soaked CBR is about 1.5% or an effective soaked 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 surface deflection of the capping layer so that the resulting thickness should be applicable to any type of pavements. In spite of that, the process of pavement design involves certain assumptions about the material properties e.g. non-linearity, anisotropy, and fatigue characteristics. Therefore, it is important 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 a homogenous semi-infinite subgrade. It is interesting to note that for all pavement types, failures occurred in a layer other than subgrade. The results also show that for deep strength asphalt pavement, in order to produce an equal cumulative damage factor (CDF), the LMC thickness may need to be increased by 2.5 mm when a capping layer is used. This additional thickness, which is related to the fatigue characteristics of LMC, may be considered insignificant since in practice, tolerances of 10-20 mm may be applied.

CONCLUSIONS It has been demonstrated that the effects of combining layers of different soils may alter not only the stress and strain distributions within the individual layers but also the surface deflection. Odemark’s method simplifies the effect of layering to produce an equation to predict the combined modulus but does not produce an accurate representation of stress and strain distribution within multilayered pavement foundation. Correction factors have been proposed to improve the accuracy of Odemark’s method for a combined modulus, but their accuracy may be questionable. This paper presented the results of a preliminary investigation on the effect of layering and nonlinearity on the combined modulus of a multilayered subgrade. The study was limited to a twolayer subgrade, being a capping layer with a maximum thickness of one metre, on top of a semi-infinite subgrade. Limited CBR combinations were analysed using the CIRCLY computer program with Austroads’ sublayering and anisotropy assumptions, which produced an equation that can be used to find the appropriate correction factor for use with the Odemark’s method. Subsequently, charts that can be used to obtain the capping layer thickness on top of a subgrade were proposed to obtain an effective subgrade CBR for pavement design purposes. Since the charts have been developed independent from pavement configurations, they can be used for any type of flexible pavement. The results of this study indicate that the use of the Odemark’s method without a correction factor (i.e. the Japan Equation) will underestimate the capping thickness requirement if anisotropy and nonlinearity are considered. The validation process employed in the present study demonstrates the accuracy of the proposed correction factor and the resulting charts. Further studies will be conducted to more comprehensively analyse the application of the method for a wider range of CBR values, number of layers and layer thicknesses.


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Table 4: Results of validation process Pavement type

DESA

Effective subgrade CBR (%)

Input vertical modulus (MPa)

Pavement

Layers (critical Thicknesses layer is (mm) underlined) 350 Base 270 5 150 SMZ 300 50 Subgrade Semi-infinite Granular 1.43E+07 350 Base 270 150 SMZ 300 5** 90 Capping 834 30 Subgrade Semi-infinite 1700 Wearing AC 40 4000 AC14 50 4000 AC20 260 3 150 SMZ 300 50 UZF 300 30 Subgrade Semi-infinite 1700 Wearing AC 40 4000 AC14 50 4000 AC20 260 3** 150 SMZ 300 50 UZF 300 50 Capping 743 20 Subgrade Semi-infinite Full depth 1.52E+08 1700 Wearing AC 40 asphalt 4000 AC14 50 4000 AC20 260 3** 150 SMZ 300 50 UZF 300 70 Capping 512 20 Subgrade Semi-infinite 1700 Wearing AC 40 4000 AC14 50 4000 AC20 260 3** 15 SMZ 300 50 UZF 300 100 Capping 374 20 Subgrade Semi-infinite 1000 Wearing AC 40 2500 AC14 50 2700 AC20 85 3 10000 LMC 195 150 SMZ 300 50 UZF 300 30 Subgrade Semi-infinite 1000 Wearing AC 40 2500 AC14 50 2700 AC20 85 10000 LMC 197.5 Deep 3** strength 3.65E+07 150 SMZ 300 asphalt 50 UZF 300 50 Capping 743 20 Subgrade Semi-infinite 1000 Wearing AC 40 2500 AC14 50 2700 AC20 85 10000 LMC 197.5 3** 150 SMZ 300 50 UZF 300 70 Capping 512 20 Subgrade Semi-infinite ** With capping layer thicknesses from Equations 3 and 4 to improve the original subgrade CBR.


Cumulative Damage Factor (CDF)

9.08 E-01

9.57E-01

9.48E-01

9.72E-01

9.68E-01

9.70E-01

7.86E-01

7.9E-01

7.9E-01

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REFERENCES Austroads (2009), Review of Relationship to Predict Subgrade Modulus from CBR (California Bearing 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 the Odemark Transformation Method , International Journal of Advanced Engineering Sciences and Technologies, 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 Flexible Pavements, 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 Pavement Structural Analysis Using Method of Equivalent Thickness, Case Study: Jakarta-Cikampek Toll Road , 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 necessarily of 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, MEng AIT , PhD Monash, GradCert (Env) Melb., MIEAust

Dr. Nataatmadja is the Supervising Pavement Engineer (Design & Analysis) of Roads Traffic Authority-New South Wales in Parramatta. His previous position was Se nior Lecturer in Geotechnical and Pavement Engineering at QUT, Brisbane. He has published numerous papers in geotechnical engineering and pavement technology. With a research interest in the areas of material science, geotechnical and pavement engineering, Andreas has been working in the broad area of civil engineering for more than 30 years in industrial, consulting, research and 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 Materials Technology, Environmental Assessment, Geotechnical Science, Pavement Design and Analysis, and Bridge Technology areas of the RMS. She recently completed th e Pavement Technology 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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Mr. Kevin Chim , BE (Civil) Sydney

Kevin Chim joined the RMS in 2006 on the Graduate Recruitment and Development (GRAD) Program. He has worked in Ballina Road Services, Sydney Asset Management, Sydney Project Services, Hunter Project Management Service, as well as Road Design areas of the RMS. He is currently a Pavement Engineer of the Design & Analysis Unit in RMS Pavement Structures Section, and also involved in pavement material assessments (for Sydney region), section's quality system, pavement design reviews, and pavement investigations. Copyright Licence Agreement The Author allows ARRB Group Ltd to publish the work/s submitted for the 25th ARRB Conference, granting ARRB the non-exclusive right to: • publish the work in printed format • publish the work in electronic format • publish the work online. The Author retains the right to use their work, illustrations (line art, photographs, figures, plates) and research data in their own future works The Author warrants that they are entitled to deal with the Intellectual Property Rights in the works submitted, including clearing all third party intellectual property rights and obtaining formal permission from their respective institutions or employers before submission, where necessary.


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SUBGRADE CBR

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