Evaluation and characteristics of embankment fill and sub

24th ARRB Conference – Building on 50 years of road and transport research, Melbourne, Australia 2010

© ARRB Group Ltd and Authors 2010 1

EVALUATION AND CHARACTERISTICS OF EMBANKMENT FILL AND SUB-GRADE MATERIALS

Mohd Hizam Harun, Public Works Department, Malaysia Fazleen Hanim Ahmad Kamar, Public Works Department, Malaysia

ABSTRACT

Excessive sub-grade deformation and settlement of embankment and back fill are major contributors to premature pavement failures and to surface irregularities in Malaysia. Current Public Works Department (JKR) specifications for earthworks are not optimised in terms of composition and strength of sub-grade materials. Currently, JKR uses traditional methods for determining soil moisture content and density, as well as soaked CBR testing which are time consuming and cumbersome. A simplified sub-grade material testing and analysis program is proposed to provide essential input for the development of JKR Pavement Design Manual. The extension of this program is to generate sufficient research data for the statistical analysis and the formulation of recommendation for inclusion in future revisions of JKR specifications. This paper focuses on reviewing and improving specifications for embankment fill and sub-grade materials and investigates different methods of testing and evaluation of the materials strength and density.

INTRODUCTION

Excessive sub-grade deformation and settlement of embankment and back fill form one of the major contributions to premature failures and to surface unevenness in Malaysia. This type of distress decreases safety and comfort of road users, and requires frequent resurfacing and other repairs.

Current Public Works Department of Malaysia (JKR) specifications for earthworks are not optimized in terms of composition and strength of sub-grade soils; also the damage that construction traffic causes through remolding of wet cohesive sub-grade soil is not adequately addressed when compared to current European standards and practices. Arahan Teknik (Jalan) 5/85 - a technical instruction produced by JKR, which has been used in Malaysia for the last twenty five years as guideline for structural design of flexible pavement, for instance, uses California Bearing Ratio (CBR) to solely characterize sub-grade materials.

Many pavement engineers, however, have come to the conclusion that CBR testing can lead to serious misjudgment of the strength of the sub-grade, sub-base and granular base for the following reasons:

Applied stress and strain are not representative of traffic loading.

The volume of sub-grade material evaluated is very small as the conduct CBR testing is time consuming, thus limiting the number of the test results that are available for quality acceptance.

Correlation between CBR values and mechanistic design parameters are weak, thus further decreasing the probability that granular or cohesive materials are precisely characterized when using CBR as sole basis for evaluating strength and stiffness.

Most European countries have twenty or more years ago discontinued using CBR. The new AASHTO 2002 Pavement Design Guide recommends using elastic stiffness values obtained through resilient modulus or falling weight deflectometer testing.



OBJECTIVES

The objectives of this study were;

1. To investigate different methods of testing and evaluation of embankment fill and sub-grade strength and density.

2. To evaluate test results from three on-going road construction project sites and determine tentative embankment fill and sub-grade input parameters for the new JKR pavement design manual.

METHODOLOGY

Field and Laboratory Tests

The following field and laboratory tests complying to established methods for evaluation and characterization of sub-grade soil were considered:

1. Determination of soil moisture content through Oven-Drying (AASHTO T 265 and ASTM D 2216) and Calcium Carbide Gas Pressure or Speedy Moisture Method (AASHTO T 217 and ASTM D 4994).

2. Determination of soil in-place density through Sand Cone Method (AASHTO T 191 and ASTM D 1556) and through drive or cutting cylinders (ASTM D 2937).

3. Modulus measurement using a hand-held falling weight deflectometer (HH-FWD). As a control, a DYNATEST or similar standard FWD was used, with operations adjusted to direct measurement of sub-grade soil.

4. In-situ CBR value measurement using Clegg Impact Hammer, Dynamic Cone Penetrometer (DCP) and JKR Probe.

Notes on JKR Probe:

Light dynamic cone penetrometer is widely used in Malaysia as a tool for preliminary site investigation works. In 1972, JKR introduced a light dynamic cone penetrometer, known as JKR probe, based on the principles outlined by Hvorslev (1949) for driving rods as sounding. The geometry of the JKR Probe is derived from the recommended method for static and dynamic penetrometer tests by the European Group Sub-Committee (1968).

Unlike the DCP which has 60º and 20 mm diameter cone, the probe consists of a cased harden steel pointer of 25 mm diameter and 60º cone. The pointer is screwed onto the lower end of the rod. The rod is of 12 mm diameter.

In contrast to the DCP which has 8 kg hammer with a free fall height of 575 mm, JKR Probe is driven with a hammer of 5 kg in weight, falling through a fixed height of 280 mm.

The limitation of the JKR Probe is that it has a limited driving energy because the hammer is light and the fall is small. It is unable to penetrate through hard layers and problem may arise when softer layers underlie these hard layers. It is also unable to penetrate deeply into medium strength material and gravelly ground. When probing at great depths in the soft soils, a further problem is that the wall of the probe hole may collapse and the side friction on the rod is measured together with the resistance, thus giving results, which may be misleading. It is not suitable to be used in stony grounds as the pointer and rod would be damaged.



Scope of Works For this study, the scope of works encompassed the following items;

1. Selection of three on-going different road projects.

2. Designation of six lots of testing area, each lot representing about 3000 to 5000 m2 of sub-grade for each site (18 lots).

3. Within each lot, the following tests were carried out;

Soil moisture content test using Oven-Drying and Speedy Moisture Methods.

Soil in-place density test using Sand Cone and Core Cutter Methods.

Modulus measurement using hand-held and standard falling weight deflectometer (FWD).

In-situ CBR value measurement using the Clegg Impact Hammer, DCP and JKR Probe.

Soaked CBR and soil classification test (laboratory).

Sampling of Soil for Laboratory Testing

Six numbers of bulk samples of about fifty kilograms of sub-grade materials were collected at each site for laboratory testing. The bulk samples that were collected were carefully sealed and covered to avoid losses in moisture content. Each lot of sample was labeled and transported to laboratory for testing.

Analysis of Test Results (Field and Laboratory)

All test results were analyzed according to the present standards and guidelines. Suitable correlation between the different test methods would then be made for each test parameter.

1. Field Density (Sand Cone and Core Cutter Methods).

2. Moisture Content (Oven-Drying and Speedy Moisture Methods).

3. Modulus (hand-held and standard FWD).

4. In-situ CBR (Clegg Impact Hammer, DCP and JKR Probe).

Photo 1: Test site. Photo 2: Carrying out various tests at the test site.



CURRENT PRACTICE

Typical Engineering Parameters Used for Characterization and Quality Control of Sub-Grade and Embankment Fill

Generally, the following properties are specified and controlled during construction to ensure adequate sub-grade support:

1. Soil composition.

2. Soil classification.

3. Density (and moisture content).

4. Laboratory soaked CBR.

5. Elastic stiffness (determined using static plate load testing or FWD).

Current JKR Practice on Characterization and Quality Control of Sub-Grade and Embankment Fill

Standard Specification for Road Works of JKR (JKR/SPJ/1988) defines sub-grade as that part of the embankment or existing ground in cutting which is immediately below the sub-base or lower sub-base of the road pavements and shoulders. It specifies that materials for embankment fill or for the top 300 mm of sub-grade shall be of suitable materials. For the sub-grade, the material shall have a minimum designed CBR value of 5% when compacted to 95% of the maximum dry density in the BS 1377 Compaction Test (4.5 kg rammer method) under 4 days soaked condition. Suitable materials shall mean those materials other than unsuitable materials defined below:

i. Running silt, peat, logs, stumps, perishable or toxic material, slurry or mud; or

ii. Any material;

a. consisting of highly organic clay and silt;

b. which is clay having a liquid limit exceeding 80% and /or a plasticity index exceeding 55%;

c. which is susceptible to spontaneous combustion;

d. which a loss of weight greater than 2.5% on ignition;

e. containing large amounts of roots, grass and other vegetable matter.

Generally, soils and aggregates should only require visual examination by an experienced earthwork inspector to determine whether it is suitable or unsuitable material for use in embankment, fill and backfill construction. However, in some cases determination of Atterberg limits, swelling/shrinkage characteristics, organic content, plasticity index and gradation are carried out.

For top 300 mm of sub-grade, comprehensive testing are required for each 1,500 m3 of material to be placed. The tests include:

i. Atterberg limits and plasticity index.

ii. Gradation analysis.

iii. Compaction test.

iv. Soaked CBR test.



However, these test methods do not yield results in a short period of time and because only a small number of tests are carried out within a lot, acceptance is rarely based on a meaningful statistical analysis.

The substantial delay associated with getting the test results would affect the overall work progress and in some cases the test results were subjected to manipulation to ensure compliance with the specification criteria.

Table 1: Methods of determining sub-grade properties (JKR).

Item Type of Test Laboratory/Field Control Parameter 1 Soil Composition Laboratory Suitable/Unsuitable Material 2 Liquid Limit Laboratory Suitable/Unsuitable Material 3 Plastic Limit Laboratory Suitable/Unsuitable Material 4 CBR (Soaked) Laboratory Strength 5 Density Field Compaction 6 Moisture Content Laboratory Compaction

Current International Practice (Europe, USA, Australia)

Most countries use at least two (2) different test methods for specification and quality control of embankment fill and sub-grade soils:

1. Dry density expressed as a percentage of a reference density (which requires determination of moisture content), and

2. Elastic stiffness or some indication of strength (such as CBR).

In addition, the suitability of sub-grade soil of embankment fill is expressed in terms of gradation and other compositional parameters, and included in the material specifications. All European countries use dry density expressed as relative compaction (or relative density in the case of granular cohesionless soil) as an important acceptance criteria and quality control parameter. To determine dry density, the moisture content of the sampled soil must be determined. For characterization of elastic stiffness, either a stiffness modulus derived from static plate load testing (for example in Germany, Austria, Switzerland) or a dynamic modulus derived from FWD testing is used. In some European countries, continuous methods of checking compaction (vibratory proof rolling) are used as an additional construction control measure. In Germany, specifications have been issued for this type of continuous and real time compaction control. When properly calibrated, this method provides instant information about the degree of compaction. For final acceptance, additional tests such as density and modulus are carried out. However, a diligent use of continuous compaction control based on measuring acceleration of the roller frame greatly reduces incidents of not meeting compaction criteria after compaction has been completed. In the USA, density and CBR are key parameters for control of sub-grade properties. In the new AASHTO 2002 mechanical-empirical pavement design methodology, CBR has been replaced by resilient modulus testing. Based on NCHRP 1-37, a hierarchical level of design inputs is recommended. Level 1 is for primary highways that are of strategic importance to the economy. For Level 1 pavement design, the use of the best available technology (direct dynamic testing) is recommended for the determination of input parameter. In contrast, a Level 3 approach will rely upon engineering judgment, such as correlation models or simple empirical relationships to arrive at the design input parameters. In general, the following methods of characterizing sub-grade soil for input into the AASHTO 2002 pavement design method can be considered;

1. Laboratory repeated load (resilient modulus) test.



2. Analysis of FWD data.

3. Correlation of design input parameter (elastic modulus) with physical properties of sub-grade material (composition, density, etc)

Sub-Grade Physical Properties Sub-grade materials are typically characterized by their resistance to deformation under load (stiffness) and their bearing capacity (strength). In general, the more resistant to deformation a sub-grade is, the more loads it can support before reaching a critical deformation value. Although there are other factors involved when evaluating sub-grade materials, stiffness is the most common characterization. There are two basic sub-grade stiffness/strength characterizations commonly used:

California Bearing Ratio (CBR). A simple test that compares the bearing capacity of a material with that of a well-graded crushed stone (thus, a high quality crushed stone material should have a CBR of 100%). CBR is basically a measure of strength. It is primarily intended for, but not limited to, evaluating the strength of cohesive materials having maximum particle sizes less than 0.75 inches (AASHTO, 2000). It was developed by the California Division of Highways around 1930 and was subsequently adopted by numerous state, countries, U.S federal agencies and internationally. Most agency and commercial geotechnical laboratories in the world are equipped to perform CBR tests.

Resilient Modulus. A test used to estimate elastic modulus (a material’s stress-strain

relationship). The resilient modulus test applies a repeated axial cyclic stress of fixed magnitude, load duration and cyclic duration to a cylindrical test specimen. While the specimen is subjected to this dynamic cyclic stress, it is also subjected to a static confining stress provided by a triaxial pressure chamber. It is essentially a cyclic version of a triaxial compression test; the cyclic load application is thought to more accurately simulate actual traffic loading. Resilient modulus is basically a measure of stiffness.

Development of Test Methods and Devices for Characterization of Sub-Grade

Many methods have been developed to enable the precise evaluation of sub-grade properties at high precision and quality. The advancement of science and technologies has also contributed to the invention of new devices. Table 2 presents the properties used to characterize sub-grade in different countries/region whilst Table 3 shows methods and devices used to evaluate the respective sub-grade properties.



Table 2: Methods of determining sub-grade properties in various countries.

Countries Methods

Malaysia 1. Soaked CBR 2. Density 3. Moisture Content 4. Soil Composition

Europe 1. Elastic Stiffness 2. Density 3. Moisture Content 4. Soil Composition

Australia 1. Soaked CBR 2. Density 3. Moisture Content 4. Soil Composition

USA (New AASHTO 2002) 1. Elastic Stiffness 2. Density 3. Moisture Content 4. Soil Composition

Table 3: Methods of evaluating sub-grade properties.

Soil Density Moisture Content Stiffness & Strength Measurements

1. Sand Cone 1. Oven Drying 1. Standard FWD 2. Radiometric 3. Water Balloon

2. Calcium Carbide Gas Pressure (Speedy Moisture Tester)

2. Hand‐held FWD 3. Dynamic Cone Penetrometer

4. Core Cutter 3. Radiometric 4. JKR Probe 4. Microwave 5. Plate Bearing 6. Humbolt Geogauge 7. Soil Stiffness Gauge

Factors that Determine Effectiveness of Sub-Grade Characterization and Quality Control

There are several factors that determine the usefulness of a test procedure for providing data for design, specifications and quality control of road pavements. The method and type of test used to determine the sub-grade properties depend on the following criteria;

1. Ease of testing;

Time required to carry out the test and to get the required test results.

Complexity of equipment and the test method used.

Manpower required to operate the test equipment.

2. Reliability and consistency of test results;

Limitation/restriction of test method in relation to type of sub-grade material and stiffness.

Ability to generate within a reasonable period of time a sufficiently large number of random test results for statistical analysis (which should form the basis for acceptance or rejection of materials).

Susceptibility of test procedure to manipulation of test results.



3. Reproducibility of test results.

4. Cost of test equipment.

Many traditionally used test methods, including soil density and moisture content, and especially soaked CBR, are time consuming and cumbersome. Also, because of the many manual measurement and recording steps, they are susceptible to manipulation of the test results. A summary of the advantages and limitations of the various tests for sub-grade characterization are given in Table 4.

Table 4: Limitation and advantages of each test method/equipment.

Test Parameter

Test Device

Cos

t of

Eq

uip

men

t (

RM

)

Tim

e to

Com

ple

te T

est

(Hou

r)

Eas

e of

T

esti

ng

Man

pow

er

Rel

iab

ilit

y

Res

tric

tion

Mai

nte

nan

ce

Field Density Test Sand Cone 3,000-5,000 1 M 2 M M M

Core Cutter 1,000 1 E 2 M M H

Radiometric 30,000-50,000 Immediate E 2 M M H

Water Balloon 1,000 1 M 2 L L M

Nuclear Gauge 50,000-70,000 Immediate E 1 H H H

Moisture Content Oven Dry 5,000-10,000 2 E 1 G G M

Speedy Moisture 3,000 Immediate E 1 M M L

Radiometric 30,000-50,000 Immediate E 2 M M H

Microwave 1,000-2,000 2 E 1 M M M

Modulus/Stiffness/CBR FWD 500,000 Immediate E 3 H H H

HH-FWD 70,000-100,000 Immediate E 2 H H L

DCP 2,000-3,000 1 E 3 H H L

Clegg Impact 12,000-15,000 Immediate E 1 M M L

JKR Probe 2,000-3,000 1 E 3 M M L

Plate Bearing 15,000-20,000 Immediate E 2 M M L

Stiffness Gauge 20,000-50,000 Immediate E 2 M M L

H‐High, M‐Moderate, L‐Low, G‐Good, Q‐Quick, S‐Slow, E‐Easy

RESULTS AND DISCUSSIONS

General

Field and laboratory tests were carried out at three (3) selected sites. The tests comprised of field density, moisture content, modulus and CBR. Bulk samplings were also carried out for laboratory test purposes such as sieve analysis, Atterberg limit and soaked CBR.

Laboratory Test

Based on the soil classification analysis, it was found that generally the sub-grade materials for all three sites were considered as suitable material. However the soaked CBR values range from 3% to 15% for Site 1, 2% to 7% for Site 2, and 2% to 10% for Site 3.



Field Density

The field dry density as measured by Sand Cone method was found to be ranging between 1.500 Mg/m3 – 2.014 Mg/m3 with an average value of 1.938, 1.828 and 1.807 Mg/m3 for Site 1, Site 2 and Site 3 respectively. Correspondingly, the field density measured using Core Cutter method resulted in values that range from 1.521 Mg/m3 – 1.940 Mg/m3 with an average of 1.862, 1.800 and 1.656 Mg/m3 for Site 1, Site 2 and Site 3 respectively. Values from the Sand Cone method and the Core Cutter method correlate quite well, especially for Site 1 and Site 2 where a correlation coefficient, r2 of 0.79 and 0.84 were obtained. Figure 1 shows the correlation between Sand Replacement and Core Cutter methods. A summary of the correlation equations and r2 values are shown in Table 5.

Moisture Content

The moisture content as measured by Speedy Moisture Tester was found to be ranging between 10.4%-24.4% and the corrected speedy moisture content range from 11.6% - 32.3%. The Oven Dry method yields results which range from 9.2% - 24.2%. The results of Speedy Moisture method and Oven Dry method are as shown in Figure 2. The correlation equations and r2 were established for each site and are shown in Table 6.

Except for Site 2, the correlation coefficient between the moisture content as determined by the Oven Dry method to that as determined by the Speedy Moisture method are more than 0.8. Another important point to note is that the Speedy Moisture method always over estimated the moisture content by between 2% - 38% when compared with the Oven Dry method.

Site Equation r2

Site 1 y = 0.6695x + 0.5648 0.79

Site 2 y = 1.2586x - 0.5004 0.84

Site 3 y = 0.4276x + 0.8839 0.54

Combined y = 0.6756x + 0.5181 0.58

Site Equation r2

Site 1 y = 0.5332x + 3.2312 0.82

Site 2 y = 0.6238x + 4.7556 0.63

Site 3 y = 0.8864x – 1.8296 0.89

Combined y = 0.806x + 0.2303 0.85

Figure 1: Plot of Sand Cone and Core Cutter methods for Site 1, Site 2 and Site 3.

Table 5: Summary of equation and r2 value

(dry density).

Figure 2: Plot of Speedy Moisture and Oven Dry methods for Site 1, Site 2 and Site 3.

Table 6: Summary of equation and r2 value (moisture content).



Modulus

The modulus values measured using the standard FWD range from 95 MPa – 1284 MPa. Correspondingly, the modulus measured using by hand-held FWD range from 54 MPa – 370 MPa. The results show that the hand-held FWD tends to be lower than the standard FWD values by 5% to 88%. The correlation between the hand-held FWD and the standard FWD modulus are plotted in Figure 3 and the corresponding correlation coefficients are shown in Table 7.

0

50

100

150

200

250

300

350

400

0 200 400 600 800 1000 1200 1400

E‐Modulus (MPa) ‐HHFWD

E‐Modulus (MPa) ‐ FWD

FWD vs HHFWD Site 1, 2 and 3

The correlation of modulus obtained by the hand-held FWD when compared to the standard FWD is fairly good, therefore one may be used to substitute the other.

California Bearing Ratio (CBR)

The CBR values measured using the DCP range from 16% - 82%. Correspondingly, the CBR values measured using the Clegg Impact Hammer range from 10% - 133.6%. A summary of CBR test results are plotted and tabulated in Figure 4 and Table 8 respectively.

Correlation Between Various Test Parameters The correlation between the various tests parameters as carried out at three selected sites are as follows;

Site Equation r2

Site 1 y = 0.2383x + 44.368 0.69

Site 2 y = 0.2595x + 47.116 0.68

Site 3 y = 0.5541x + 16.973 0.69

Combined y = 0.2279x + 63.368 0.65

Site Equation r2

Site 1 y = -0.0465x + 43.121 0.045

Site 2 y = 0.2873x + 48.07 0.031

Site 3 y = 0.8084x + 9.9277 0.951

Combined y = -0.0192x + 41.619 0.001

Table 8: Summary of equation and r2 value (CBR)

Figure 3: Plot of standard FWD and hand-held FWD for Site 1, Site 2 and Site 3.

Table 7: Summary of equation and r2 value (modulus).

Figure 4: Plot of Clegg Impact Hammer and DCP for Site 1, Site 2 and Site 3.



Correlation between Modulus (Hand-held FWD) and CBR (Clegg Impact Hammer)

Correlation between DCP and JKR Probe

Correlation between Bulk Density and Modulus (FWD)

Site Equation r2

Site 1 y = -0.013x + 93.602 0.002

Site 2 y = -0.0135x + 33.893 0.004

Site 3 y = 0.0328x + 23.834 0.048

Combined y = -0.1073x + 58.771 0.040

Site Equation r2

Site 1 y = 0.0837x + 14.205 0.384

Site 2 y = 0.998x + 7.9747 0.602

Site 3 y = 0.3719x + 10.866 0.303

Combined y = 0.0221x + 23.891 0.009

Site Equation r2

Site 1 y = -363.84x + 1015 0.219

Site 2 y = 151.09x – 229.76 0.156

Site 3 y = 6.4234x + 45.75 0.005

Combined y = -55.479x + 245.02 0.092

Figure 5: Plot of hand-held FWD and Clegg Impact Hammer for Site 1, Site 2 and Site 3.

Table 9: Summary of equation and r2 value.


Figure 6: Plot of JKR Probe and DCP for Site 1, Site 2 and Site 3.


Figure 11: Plot of Bulk Density and Modulus (FWD) for Site 1, Site 2 and Site 3.



Correlation between Bulk Density and Modulus (Hand-held FWD)

Correlation between Bulk Density and CBR (DCP)

CONCLUSIONS

Based on the study and analysis carried out, the following concluding remarks may be made;

It was observed that soil classification (AASHTO Classification) for Site 1, Site 2 and Site 3 are consistence (silt clay materials – A-7-5 or A-7-6), except for CH4800 and CH5320 at Site 1 that consisted of silty or clayey gravel and sand (A-2-7).

The results of Sand Cone and Core Cutter methods are found to correlate quite well, with two sites achieving r2 values around 0.8. However, the Core Cutter method generally provides more consistent density values with mean standard deviation ranging from 0.09 to 0.11 for all three sites.

While the measurement of moisture content by both Speedy Moisture and Oven Dry methods correlate quite well (r2 = 0.85), the Oven Dry method tends to provide more consistent results. The Speedy Moisture method always over-estimates the moisture content when compared with the Oven Dry method.

Although some technical/procedural errors were detected during testing such as testing on different day at different moisture condition and at different applied load pulse, the modulus

Site Equation r2

Site 1 y = -363.84x + 618.84 0.219

Site 2 y = 289.18x – 459.5 0.133

Site 3 y = 42.844x + 9.9514 0.024

Combined y = 152.56x – 186.42 0.016

Site Equation r2

Site 1 y = 27.611x – 20.96 0.291

Site 2 y = 116.51x – 189.55 0.187

Site 3 y = 5.8013x + 38.892 0.026

Combined y = 7.6626x + 24.398 0.005


Figure 12: Plot of Bulk Density and Modulus (HH-FWD) for Site 1, Site 2 and Site 3.

Table 17: Summary of equation and r2 value

Figure 13: Plot of Bulk Density and CBR (DCP) for Site 1, Site 2 and Site 3.



values as obtained by both the standard FWD and the hand-held FWD correlate quite well with r2 values for all three sites greater than 0.6.

For the measurement of the in-situ CBR values, poor correlation is observed between the Clegg Impact Hammer and DCP methods (r2 < 0.1). The DCP method however provides more consistent results with mean standard deviation of between 8 and 21.

The results of DCP and JKR Probe correlate fairly well with r2 value of 0.6 for one site. However, the correlation for the other two sites is weak with r2 values between 0.3 and 0.4.

There is no correlation between modulus obtained using FWD and CBR obtained using Clegg Impact Hammer.

There is no correlation between bulk density and modulus obtained using FWD.

There is no correlation between bulk density and CBR obtained using DCP.

RECOMMENDATIONS

Based on the findings from this study, the following recommendations should be considered;

The Speedy Moisture Tester, Clegg Impact Hammer and hand-held FWD are potential methods to determine the moisture content, in-situ CBR and stiffness of the embankment fill or sub-grade respectively quite accurately and speedily. However, a further study involving more samples and detailed statistical analysis should be carried out if a good correlation with standard test methods is to be established.

Since Poisson’s ratio is an important input parameter in mechanistic analysis, laboratory testing to establish the value for local material should be carried out.

Pending further detailed study, the following input parameters for embankment fill and sub-grade materials could be used;

Soaked CBR : 3.5% - 8.0% (mean 5.0%) Stiffness : 60 MPa - 190 MPa (mean 110 MPa) Irrespective of the method used to measure mechanistic embankment fill and sub-grade

parameters, minimum strength requirements are now defined based on bearing capacity needed during construction (SETRA/LCPC: “French Design Manual for Pavement Structures”, 1997) and on modulus values and modulus ratios for structural design and long-term performance of pavements. In many European countries, dynamic sub-grade modulus values of at least 100 MPa are now specified for the top three classes of roads. For silty sand and sandy sand (which represent about half of all naturally occurring sub-grade soils), this modulus would approximately correspond to minimum CBR values of 10% - 12%. Sub-grade materials of lower stiffness and strength must either be replaced with a capping layer of granular material, or adequately stabilized to increase stiffness and decrease moisture sensitivity.

REFERENCES

1. American AASHTO (2002). Standard Specifications for Transportation Materials and

Method of Sampling and Testing, (22nd Edition). Washington D.C., USA.

2. Guidelines for Inspection and Testing of Road Works. Public Works Department of Malaysia, JKR 20407-0001-90. Kuala Lumpur, Malaysia.

3. Standard Specification for Road Works (1988). Public Works Department of Malaysia,

JKR/SPJ/1988. Kuala Lumpur, Malaysia.



4. Manual on Pavement Design. Public Works Department of Malaysia, Arahan Teknik (Jalan) 5/85. Kuala Lumpur, Malaysia.

5. Annual Book of ASTM Standards (1997). American Society for Testing and Materials (ASTM). Section 4: Construction, Volume 04.04. Philadelphia, USA.

6. Annual Book of ASTM Standards (1993). American Society for Testing and Materials (ASTM). Section 4: Road and Paving Materials, Paving Management Technologies, Volume 04.03. Philadelphia, USA.

AUTHOR BIOGRAPHIES MOHD HIZAM HARUN is currently with the Road Facilities Maintenance Branch, Public Works Department (PWD), Malaysia. He has been with the PWD for 25 years. He graduated from University of Leeds, United Kingdom in 1984 and has Masters Degree in Highway Engineering from University of Birmingham, United Kingdom. His past designations include as a pavement research engineer at the Public Works Institute (IKRAM), and as a resident engineer in the KLIA project whereby his main responsibility then was to implement quality assurance programme on the field production of polymer modified binders and asphalt for the runways and taxiways. FAZLEEN HANIM AHMAD KAMAR is currently with the Road Facilities Maintenance Branch, Public Works Department (PWD), Malaysia. She graduated in University Putra Malaysia, Selangor in 2003 in Civil Engineering and has Master Science in Construction Management from University of Technology Malaysia, Johor. She has experience in road maintenance and responsible for developing, implementing and monitoring road maintenance program for Federal Roads in Malaysia.

Documents

Evaluation and characteristics of embankment fill and sub