a procedure for quantification and optimization of stabilized subgrade pavement materials

A Procedure for Quantification and Optimization of Stabilized Subgrade Pavement Materials

Moustafa Ahmed Kamel(*) Asisstant Professor, Public Works Dept., Faculty of Engineering, Mansoura University, 35516 Mansoura, Egypt. E-mail: [email protected]

Mohamed El-Shabrawy Ali Professor, Former Dean of the Faculty of Engineering, Faculty of Engineering, Mansoura University, 35516 Mansoura, Egypt. E-mail: [email protected] Hamad M. El-Ajmi Trainer, Department of Civil Engineering, College of Technological Studies, Public Authority for Applied Education and Training. Kuwait E-mail: [email protected]

(*) Corresponding Author

Moustafa Ahmed Kamel et al. / (IJAEST) INTERNATIONAL JOURNAL OF ADVANCED ENGINEERING SCIENCES AND TECHNOLOGIES Vol No. 2, Issue No. 1, 025 - 035

ISSN: 2230-7818 @ 2011 http://www.ijaest.iserp.org. All rights Reserved. Page 25

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mailto:[email protected]



ABSTRACT

This paper presents a comparative laboratory study for optimization and quantification of the beneficial effects of stabilization of subgrade soils in flexible pavement systems. Two types of Kuwaiti soils; inorganic silt and clayey sand were selected. A total of six different groups of stabilizers were added to the two soils. They are, cement, lime, a mixture of cement and polystyrene fibers, a mixture of lime and polystyrene fibers, a mixture of lime and fly ash and finally a mixture of lime, cement and fly ash. Unconfined compressive strength tests were performed on all combinations of variable ratios of stabilizers to evaluate the unconfined compressive strength and the modulii of elasticity (E-values). It was found that the unconfined compressive strength increases with the increase of the stabilizer content. However, E-values increased till certain percentage of the stabilizer and then decreased. A procedure is outlined to quantify the beneficial effects of subgrade soils stabilization based on the extension of pavement service life or reduction in the pavement thickness. It was found that cement content of 7% by dry weight of the soil is the best stabilizing group and the mixture of 7% lime and 15% fly ash is the poorest group amongst the selected groups of stabilizers.

KEY WORDS

Subgrade – Stabilization – Traffic benefit ratio – Layer thickness reduction.

INTRODUCTION

The total pavement rutting as well as longitudinal and alligator fatigue cracking of hot mix asphalt (HMA) are affected by the quality of the foundations materials, (El-Badawy, 2008, El-Basyouny et. al., 2005). Desirable properties of the subgrade are: high compressive and shear strength, permanency of strength under all weather and loading conditions, ease and

permanency of compaction, ease of drainage and low susceptibility to volume changes and frost action. For this reason, soil stabilization processes are practiced in road construction to improve certain undesirable properties of soils, such as excessive swelling or shrinkage, high plasticity, difficulty in compaction etc. Although, good amount of research has been conducted on soil stabilization in the form of laboratory and field-tests or experience, but limited research has related the properties of such materials (e.g., shrinkage) to the pavement performance. In addition, The AASHTO Interim Mechanistic-Empirical Pavement Design Guide Manual of Practice (MEPDG) provides a methodology for the analysis and performance prediction of pavements incorporating stabilized layers, however, the characterization of such materials, the changes in their properties over time, and their distress models have not been adequately addressed in the MEPDG, (NCHRP 1-37A Report, 2004). Also, limited material properties have been considered; other properties may have significant influence on the long-term performance and need to be considered. Also, the beneficial effects of subgrade soil stabilization in pavement systems should be quantified either in terms of extension of service life of pavements or in terms of reduction in the thicknesses of pavement layers.

The present study is targeted to determine the optimum ratio of the different investigated stabilizing materials, which yields maximum benefits. Also, it aims to study the stress-strain characteristics of the studied Kuwaiti soils with different types of stabilizers. Quantification of the beneficial effects of subgrade soil stabilizations with different stabilizers as well as evaluation of the cost of a stabilized pavement are also highlighted.


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LITERATURE REVIEW

Soil stabilization is carried out by physically mixing additives with surface layers or borrow materials. Additives include natural soils, industrial by-products or waste materials, and cementitious and other chemicals which react with each other and/or the ground, (El-Ajmi, 2008). The choice of a method of ground improvement for a particular object will depend on many factors such as; type and degree of improvement required, type of soil, cost (the size of the project may be decisive) and availability of equipment and materials as well as the quality of work required, (Yamanouchi et al. 1988). The most common artificial additives are, in order of usage: Portland cement (and cement-fly-ash), lime (and lime-fly-ash) and bitumen and tar. The reason for their popularity is that they are applicable to considerable range of soil types, they are widely available, their costs are relatively low, and they are environmentally acceptable, (Hoshiya et al. 1984).

Generally, the benefits of pavements layers stabilization or reinforcement are applicable for situations where pavement life is governed by excessive pavement surface deformation due to the development of permanent strain in the unbound aggregate and subgrade layers (Perkins and Edens, 2002). Previous experimental work has demonstrated that values of benefits are strongly dependent on pavement design parameters such as thickness of the structural section and properties and type of the stabilizing material (Berg et al., 2000). Different terminologies are reported to quantify the benefits of stabilization of pavement layers. Haas et al, (1988), Webster, (1992), Thomas et al. (1998) and Perkins and Edens, (2003) quantified benefits of stabilization or reinforcement in terms of traffic benefit ratio (TBR). The TBR may be defined in different terms to represent the gained benefit in specified design element like service life and surface rutting of a stabilized pavement as compared to an equivalent unstabilized pavement. The base course reduction ratio (BCR) is another quantified benefit of geosynthetic reinforcement

of pavement layers which leads to reduction in base thickness for equivalent service life (Perkins and Eden's, 2002). These concepts could be adopted to be used as a quantification tool for stabilized pavements.

MATERIALS AND TESTING PROGRAM

Two types of soils were selected for this study and hereafter are called soil A and Soil B. These soils were collected respectively from El-Wafra area and Boubyan island in Kuwait. Routine tests were conducted on both soils in order to identify and classify the selected soils. Table 1 shows the physical properties of such soils as well as their classification as per the unified soil classification system (USCS). The selected soils were classified as clayey sand (SC) and inorganic silt of low plasticity (ML).

Table 1 Physical Properties and Classifications of the Investigated Soils

Property Soil A Soil B

Liquid Limit, (%) 45 37 Plastic Limit, (%) 36.2 34 Plasticity index, (%) 8.8 3 Optimum Moisture Content (OMC), %

7.6 15

Maximum Dry Density (MDD), (t/m3)

1.95 1.63

Classification as per USCS

SC ML

Typical Name Clayey Sand

Inorganic Silt

Four types of additives are considered. They are Portland cement, hydrated lime, polystyrene fibers and fly ash. Table 2 summarizes the different specified groups of stabilizers and admixtures with fixed and variable components used for stabilizing the two selected soils.



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Table 2 Different Considered Groups of Stabilizers and Admixtures

Percentage of the variable additive Soil

Typ

e

Additive

Gro

up

No.

11 9 7 5 4 Soil A Cement 1 11 9 7 5 4 Soil B 9 7 5 3 1.5 Soil A Lime 2 9 7 5 3 1.5 Soil B

----- 0.7 0.5 0.3 0.1 Soil A 5 % Cement + Polystyrene Fibers 3 ----- 0.7 0.5 0.3 0.1 Soil B 7 % Cement +Polystyrene Fibers ----- 0.7 0.5 0.3 0.1 Soil A 7 % Lime +Polystyrene Fibers 4 ----- 0.7 0.5 0.3 0.1 Soil B ----- 25 20 15 10 Soil A 7 % Lime +Fly ash 5 ----- 25 20 15 10 Soil B ----- ----- 3 2 1 Soil A 7 % Lime +15 % Fly ash + Cement 6 ----- ----- 3 2 1 Soil B

Standard proctor tests were conducted on the two types of soils mixed with the different additives as given in Table 2 to evaluate the maximum dry density (MDD) and optimum moisture contents (OMC) for each admixture. In addition, the unconfined compression tests were performed on the different soil mixtures. Samples were prepared at the OMC and MDD determined through Proctor tests, to study and evaluate the stress-strain behavior of the stabilized soils with different combinations of stabilizers. The modulii of elasticity (initial tangent values) which represent the slope of the straight part of the stress-strain curves were also determined. This parameter is later used in the pavement response model to analyze the induced strains.

For the unconfined compressive strength (UCS) tests, cylindrical specimens of 71.5 mm diameter and 145 mm length were prepared according to ASTM D2850. The water corresponding to the optimum moisture content (OMC) was added and mixed thoroughly. Care was taken during the compaction procedure to ensure that the samples are uniform throughout their height, with little or no variation in density. The dry densities of the samples were checked and were within the range of ± 3% of the maximum dry density obtained through Proctor tests. All samples mixed with cement were cured

for 7 days in a humid environment by placing the samples below water level in a closed partially filled water tank. The samples mixed with lime were cured for 48 hours in 50° C temperature. It is worth mentioning that, the specimens prepared for group No.6 were only cured for 48 hours at 50°C temperatures for 7 days in a humid chamber.

Optimization of The Stabilizer Content

The results of the unconfined compression tests were plotted in the form of stress-strain curves for both soils investigated with different percentages of stabilizers as well as the virgin soils. A total of 52 plots were made for all the test specimens under different conditions. These curves were used to determine the unconfined compressive strength (failure stress) and also the modulii of elasticity of the investigated mixtures. It should be noted that the modulus of elasticity is usually calculated from the straight portion of the stress-strain curve. For most cases, however, the stress-strain curve of the mixture was not straight for an appreciable distance but rather was curved. Thus, the modulus of elasticity was calculated corresponding to the initial tangent of the stress-strain curve. Figure 1 depicts an example for the typical stress-strain relationship for Soil B stabilized with 1.5% lime.



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Figure 1 Stress-Strain Relationship for Boubyan Soil (Soil B) with 1.5% Lime

There are many factors affecting the selection of a stabilizer such as, the type of soil to be stabilized, the purpose for which the stabilized layer will be used, the type of soil improvement desired, the required strength and durability of the stabilized layer and the cost and environmental conditions. For the optimization of the stabilizer content, the variation of unconfined strength values (qu) and E-values of subgrade soil with different specified groups of stabilizers were studied. The stabilizer content that provides higher values of both (qu and E-Value) was considered for further investigations.

Table 3 summarizes the different groups of stabilizers, the optimum percentage of each variable component of the stabilizer and the unconfined compression strength values and E-values corresponding to the optimum contents. It should be noted that in most cases, the chosen optimum content does not give the highest value of both unconfined compressive strength and E-values at the same time. Therefore, the optimum content corresponding to higher E-value was chosen and the corresponding unconfined compressive strength is reported in Table 3.

Table 3 Optimization of the Stabilizer Content for

Different Groups of Stabilizers

E-V

alue

(M

Pa)

q u (k

N/m

2 )

Opt

imum

(%

)

Soil

Typ

e

Components

Gro

up N

o.

8.33 2577 7 A Cement 1

6.25 3750 9 B 1.57 1253 7 A

Lime 2 1.09 3400 7 B

2.07 1700 0.1 A 5 % Cement + Polystyrene Fibers 3

0.86 1364 0.1 B 7 % Cement + Polystyrene Fibers

1.83 1900 0.5 A 7 % Lime + Polystyrene Fibers 4

0.92 2933 0.4 B 2.33 880 15 A 7 % Lime + Fly

ash 5 1.54 2064 15 l B 1.78 897 3 A 7 % Lime + 15 %

Fly ash + Cement 6 0.72 1151 1 B

DESIGN STRATEGIES WITH STABILIZED SUBGRADE

There are two models given in literature for quantifying the benefits of stabilization. These are Traffic Benefit Ratio (TBR) and Base Course Reduction (BCR). Both of these models are used in this research study.

Strategy-1

If the designer decides to extend the service

life of the pavement, the TBR value can be obtained using Equation 1. This equation correlates the number of traffic loads necessary to produce the allowable rut depth in the pavement with the vertical compressive strain on the top of the subgrade. Since the number of traffic load repetitions will be inversely related to the strain level, Equation 1 provides a direct definition of TBR based on rutting criteria.

B

UV

SV

U

S

N

NTBR

(1)



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where:

N is the number of traffic passes required to produce an allowable rut depth in the pavement. εv is the vertical compressive strain at the top of subgrade that can be obtained through any multi layer elastic software. The symbols S and U denote stabilized and unstabilized pavement sections. B is a constant equal to 4.477 as per Asphalt Institute Model. Strategy-2

If the designer decides to keep the same service life for the stabilized and unstabilized sections, the total thicknesses of the pavement system rested on stabilized subgrade can be reduced. The layer thickness reduction (LTR) can be calculated with the help of Equation 2.

U

SU

T

TTLTR

100 (2)

where:

TU and TS are the layer (HMA or base or sub base) thicknesses of unstabilized and stabilized pavements, respectively.

It should be noted that the value of LTR is 100% or 1.0 for a given value of TBR as the thickness is same in both stabilized and unstabilized sections. On the other hand, the value of TBR is 1.0 for a given value of LTR as the strain level (vertical compression) is assumed to be constant for the stabilized and unstabilized sections.

DESIGN OPTIONS

For the investigated subgrade soils taken

from Kuwait and the 6 types of stabilizers, six different design alternatives were studied for each subgrade soil in a flexible pavement system. These are as follows:

1. Stabilization of subgrade soil with 7% cement

(for soil A) and/or (9% cement for soil B) by dry weight of the soil mass.

2. Stabilization of subgrade soil with 7% lime by dry weight of the soil mass (for both soils)

3. Stabilization of subgrade soil with (5% cement + 0.1% polystyrene fibers) for soil A and/or (7% cement + 0.1 polystyrene fibers) for soil B by dry weight of the soil mass, (for both soils).

4. Stabilization of subgrade soil with (7% lime + 0.1% polystyrene fibers) by dry weight of the soil mass, (for both soils).

5. Stabilization of subgrade soil with (7% lime + 15 % fly ash) by dry weight of the soil mass, (for both soils).

6. Stabilization of subgrade soil with (7% lime + 15 % fly ash + 3 % cement) by dry weight of the soil mass for soil A and/or (7% lime + 15 % fly ash + 1 % cement) by dry weight of the soil mass for soil B.

These alternatives were evaluated and a complete comparative study is carried out to select the optimum alternative for the investigated stabilizers. Selection of the Optimum Stabilized Section

The optimum section for stabilized pavements was selected on the basis of the following criteria:

a. The most beneficial section with subgrade

stabilization i.e., the section that has the highest values of TBR or LTR.

b. The most economical section based on the economic evaluation of construction costs by any recognized method of analysis.

c. The most beneficial section in field in terms of savings of natural resources like aggregates.

The priority of all design options should be

achieved for each case and then the optimum designed section is the one having the highest priority. It should be noted that there may be many other factors that may govern the choice such as, two stage construction or one stage construction. But the most important issue must be the availability of natural resources which in turn supports the alternative that leads to



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considerable contribution in saving of these resources regardless of the cost. For complete clarification of the adopted procedure, one example is worked out here by adopting the different design alternatives for stabilization of subgrade soil A. WORKED EXAMPLE

A typical section for flexible pavements in El-Wafra area (soil A) in Kuwait adopted by the Ministry of Public Works in Kuwait is shown in Figure 2.

The KENPAVE multilayer elastic analysis software was used for the stress-strain analysis of the section. Loading conditions were assumed as a single axle load with 40 KN wheel load and contact radius of 15 cm. The material properties of different pavement layers were assumed as shown in Table 4.

Table 4 Material Properties for the Worked

Example

Layer E-value (MPa) Poisson's

Ratio (μ) Unstabilized Stabilized

SUBGRADE (SOIL A) 0.8 As per

Table 2 0.35

Base Course 6.5 ----- 0.35 Bituminous

Concrete 26 ----- 0.35

In this study, only rutting was considered.

The economic analysis was done based on the schedule of ratings (SOR) collected from the Ministry of Public Works in Kuwait. Two design

strategies were tried to give the designer more flexibility in the design process. The following steps summarize the procedure for optimization of the stabilized subgrade pavement section. Step 1: Use strategy -1 (Extension in service life)

The vertical compressive strain at the top of

subgrade soil for all alternatives of stabilization of subgrade soil was determined using KENPAVE. The unstabilized section was also analyzed and the critical strain values were determined. The TBR values were calculated for all the six groups of stabilizers using equation 1. Table 5 shows all the alternatives and their corresponding TBR values. It should be reported that, a TBR value of 3.31 indicates that the pavement life will increase by 3.31 times with stabilization of subgrade, which reflects the benefits of stabilization in terms of increase in the service life. The maximum TBR is achieved for group -1 alternative.

Step 2: Use strategy -2 (Same service life and reduction in thickness)

Keeping the same service life of stabilized

section as for unstabilized section is the second design strategy. This will lead to a reduction in thickness of the base course layer. The stabilized and unstabilized sections were analyzed for various thicknesses of base course for the same asphalt thickness and same properties of the unstabilized subgrade soil. Figure 3 shows the plots relating the base thickness to (εv) for different cases of stabilizers as well as the unstabilized section. This figure can be considered as a design chart to find out the corresponding base thickness. For design of stabilized sections, the vertical compressive strain at the top of subgrade for unstabilized section (εv-U), which is equal to 529.3 microns will be considered as a key value. By keeping the same value for stabilized sections also, different design alternatives may be evaluated and analyzed separately.

HMA LAYER

(Base Course)

Subgrade (Soil A)

15 c

m

15 c

m

Figure 2 Typical Cross-Section Used in El-Wafra Area in Kuwait



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0

100

200

300

400

500

600

700

800

900

0 5 10 15 20 25 30

Base Thickness (cm)

Ve

rtic

al C

om

pre

ss

siv

e S

tra

in

(m

icro

str

ain

)

Unstabilized

Group-1

Group-2

Group-3

Group-4

Group-5

Group-6

8

Table 5 TBR Values for soil a Based on Rutting Failure Indicator

Alternatives

Critical strains (micro strains)

for Rutting

(εv-

U)

TB

R

1- Stabilization of subgrade with 7% cement 405

529.

3

3.31

2. Stabilization of subgrade with 7% lime 436 2.38

3. Stabilization of subgrade with 5% cement and 0.1% polystyrene fibers

442 2.24

4. Stabilization of subgrade with 7% lime and 0.1% polystyrene fibers

462 1.84

5. Stabilization of subgrade with 7% lime and 15% fly ash

472 1.67

6. Stabilization of subgrade with 7% lime, 15% fly ash and 3 % cement

463 1.82

For example, consider the case of group-5 when subgrade is stabilized with 7% lime and 15% fly ash and intention is to reduce the thickness of the base layer. For a vertical compressive strain level of 529.3 microns, the required base thickness will be almost 11 cm. This means that the stabilized section can perform with lesser thickness to have the same service life as the unstabilized section.

Figure 3 Variation of vertical compressive strains with base thickness for different design

alternatives.

The corresponding LTR may be calculated using Equation 2 as 26.7 percent. This means stabilizing the subgrade with 7% of lime + 15% fly ash (group-5) can save 26.7 % of the thickness required in base for the same service life of the pavement. The corresponding TBR will be equal to 1.0. Table 6 shows all the possible cases with quantified benefits of stabilization of soil A expressed in LTR based upon rutting criteria.

Table 6 LTR values for Different Cases for

Strategy-2 for soil A and the Corresponding TBR Values

Alte

rnat

ive

No.

LT

R (%

)

TB

R (%

)

Remarks

1 67.0 2.29 The required base thickness will be zero as per Figure 3, base layer may be avoided (*).

2 67.0 1.55 The required base thickness will be 2 cm as per Figure 3 (*).

3 67.0 1.29 The required base thickness will be 3cm as per Figure 3(*).

4 60.0 1.0 The required base thickness will be 6 cm as per Figure 3(*).

5 26.6 1.0 The required base thickness will be 11cm as per Figure 3.

6 46.7 1.0 The required base thickness will be 8 cm as per Figure 3(*).

(*) a minimum value of 10 cm is suggested here for base course in stabilized sections hence, the thickness of the HMA layer could be also reduced.

Step 3: The economical evaluation

The construction costs were estimated for all

sections presented above to determine the optimally designed section. It should be reported that the maintenance costs are not included in the economic evaluation. The cost is worked out for 1 Kilometer section of 7.0 m wide road. The Schedule of Rates (SOR) for Ministry of Public Works, Kuwait was followed to carry out the economic analysis.



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Step 4: Selection of the optimum designed section

The priority of all designed sections must be

calculated based on the above-mentioned bases. The details of this optimization are as follows:

(a) Optimization of pavement sections designed as per strategy-1

Table 7 shows summary of resulted benefits

and increase in the cost of pavement due to stabilization under strategy-1. The savings in natural resources are not included here as thickness of each layer was constant. The designer

may assign different weightage to the TBR and extra cost to be incurred on stabilizers to arrive at the final priority for these cases. The minimum value of TBR is achieved in group 5 and this is taken as the datum to assign weights to the TBR in other cases as shown in Table 6. Similarly, the maximum cost of construction would be 41600 K. D. with group-6. If it is given the weightage of 1.0, the cost of construction with group-1 will have 1.09, weightage as the lower cost should be given higher priority. The total weight is considered to assign the final priority to all the cases reported in Table 6.

Table 7 Optimization of the Stabilized Sections with Strategy-1

G

roup

I. STABILIZATION BENEFIT II. ECONOMIC EVALUATION Total

Weight III. FIN

AL PRIORITY TBR Priority Weight Cost

(K. D.) Priority Weight

1 3.31 1 1.982 28184 1 1.476 3.458 1 2 2.38 2 1.425 33280 3 1.25 2.675 3 3 2.24 3 1.341 30760 2 1.352 2.693 2 4 1.84 4 1.101 33784 4 1.231 2.332 4 5 1.67 6 1 37063 5 1.122 2.122 5 6 1.82 5 1.09 41600 6 1 2.09 6

(b) Optimization of pavement sections designed

as per strategy-1 Table 8 shows priority of all sections

analyzed under strategy-2 based on different criteria. The priority of stabilization benefit may be based upon LTR and TBR both, but the final priority should include the saving in aggregate quantity also. Base materials are more expensive

and scarce in Kuwait. Therefore, more priority should be given to those sections, which show more saving in base thickness.

As it may be seen, the priority of a case changes with the basis of comparison of different values of LTR, TBR, cost of construction and saving in natural resources as shown in Table 8.



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Table 8 Weighted Priority of Stabilized Sections with Strategy-2

G

roup

No.

LTR TBR Cost Saving in Natural

Resources

Tot

al W

eigh

t

Fina

l Pri

ority

Val

ue

Wei

ght

Val

ue

Wei

ght

Val

ue

(K. D

.)

Wei

ght

Val

ue

m3 / K

m

Wei

ght

1 67.0 2.52 2.29 2.29 21184 1.732 700 2.5 9.042 1 2 67.0 2.52 1.55 1.55 26280 1.396 700 2.5 7.966 2 3 67.0 2.52 1.29 1.29 23760 1.545 700 2.5 7.855 3 4 60.0 2.26 1.0 1.0 27484 1.335 630 2.25 6.845 4 5 26.6 1.0 1.0 1.0 34263 1.071 280 1.0 4.071 6 6 46.7 1.76 1.0 1.0 36700 1.0 490 1.75 5.51 5

SUMMARY AND CONCULSIONS

In the present study, subgrade soil stabilization benefits in flexible pavements construction were evaluated in terms of their strength parameters; unconfined compressive strength and E-values. Two types of soils; [clayey sand, inorganic silt] were procured from Kuwait.

Six different groups of stabilizers were used to stabilize the selected subgrade soils. The results of the laboratory investigations have been used to adopt an approach to quantify the beneficial effect of different stabilizers. The important findings of this research are summarized below:

i) The type of soil is a significant factor which

may affect the optimum ratio of stabilizer to be added.

ii) Based on the investigated materials with the determined optimum amount of stabilizers, the service life of the simulated pavement section was increased by 67% to 231%.

iii) On the other hand, if it is deiced to keep the same service life of a flexible pavement system, the designed thicknesses of all layers could be reduced by a considerable ratio depending upon the stabilizer type and amount.

iv) The suggested mechanistic design approach provides different alternatives to the designer to quantify the subgrade stabilization benefits

in terms of traffic benefit ratio (TBR) or layer thickness reduction (LTR). The proposed procedure includes the cost effective analysis as an integral part of the design of stabilized-pavements. Not only, the reduction of the construction costs is expected but also has a good economical and environmental contribution in terms of saving of natural resources.

REFERENCES

ASTM D 2850, Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils, American Society for Testing and Materials, West Conshohocken, Pennsylvania, USA, 2003.

Berg, R. R., Christopher, B. R. and Perkins, S. W., Geosynthetic Reinforcement of The Aggregate Base Course of Flexible Pavement Structures”, GMA White Paper II, Geosynthetic Materials Association, Roseville, MN,130, 2000.

El-Ajmi, H. M., A Comparative Study of Different Methods of soil stabilization for Highway Purposes: Case Study in Kuwiti soil, MSC Thesis, Faculty of Engineering, Mansoura Univesity, Mansoura, Egypt, 2008.

El-Badawy, S., Recommended Changes to Designs not Meeting HMA Fatigue Cracking and Rutting Criteria, 6th International Conference, Sharm Elsheikh, Egypt 21-23 March, 2008.



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El-Basyouny M., Witczak, M. W., and El-Badawy, S., Verification of the Calibrated Permanent Deformation Models for the 2002 Design Guide, Journal of the Association of Asphalt Paving Technologists, Vol 74, 2005, pp. 601-652.

NCHRP 1-37A Final Report, Guide for Mechanistic-Empirical Design of New and Rehabilitated Pavement Structures, Transportation research Board, National Research Council, Washington, DC., 2004.

Haas R., Jamie Walls and Carroll, R. G., Geogrid Reinforcement of Granular Bases in Flexible Pavements, TRB (1188), Washington, DC., USA, 1988, pp.19-27.

Hoshiya, M., and Mandal, J. N., Metallic Powder in Reinforced Earth, (1984) J. of Geotech. Eng., ASCE, 110(10), 1984, pp.1507-1511.

Perkins, S. W. and Edens, M. Q., Finite Element and Distress Models for Geosynthetic-Reinforced Pavements, International Journal of Pavement Engineering (IJPE), Vol. 3 (4), 2002, pp. 239 – 250.

Perkins, S. W. and Edens, M. Q., A Design Model for Geosynthetic-Reinforced Pavements”, International Journal of Pavement Engineering (IJPE), 4 (1), 2003, pp. 37– 50.

Thomas C. Kinney, Jeannette Abbott and John Schuler, Benefits of Using Geogrids for Reinforcement with Regard to Rutting, TRR (1611), Washington, D.C., USA, 1992, pp. 86-96.

Webster, S. L., Geogrid Reinforced Base Courses for Flexible Pavements for Light Aircraft: Test Section Construction, Behavior under Traffic, Laboratory Tests and Design Criteria, Technical Report GL-93-6, ASAE Waterways Experiment Station, Vicksburg, Mississippi, USA, 1992, pp. 886.

Yamanouchi, T., Miura, N., and Ochai, H., Theory and Practice of Earth Reinforcement, Proc. Int. Geotech. Symp. Theory and Practice of Earth Reinforcement, Fukuoka Kyushu, Japan, 1988.



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a procedure for quantification and optimization of stabilized subgrade pavement materials

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