1 the Role of Enhanced Research in Geotechnical Engineering - PAPER (KEYNOTE LECTURE)

8/2/2019 1 the Role of Enhanced Research in Geotechnical Engineering - PAPER (KEYNOTE LECTURE)

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[JN Mukabi (Ph.D) KEYNOTE LECTURE] Page 1

The Role of Enhanced Research in Geotechnical Engineering for PragmaticInfrastructure Development within the Vision 2030.

John MUKABI11Kensestu Kaihatsu Consultants Ltd. [email protected]/[email protected]

Abstract: This paper summarizes some of the State of the Art technologies and advancesmade recently in the Eastern Africa region based on Research and Development (R&D),tailored particularly for developing countries.It introduces newly developed scientific and engineering theories, concepts, techniques,technologies as well as various analytical, design and construction methods.Practical examples of the prevalent engineering challenges and Geotechnologies that wouldprovide pragmatic solutions for sustainable infrastructure development are proposed.Further discussions are made on the most appropriate and suitable approach for the Engineerto practically adopt in order to realize the Kenya Vision 2030 Objectives by introducing someof the achievements made by post World War II Japan through examples of some megastructures designed and constructed on the basis of R&D Oriented Techniques.

1. INTRODUCTION

Infrastructure development is the heart and key to any visionary and pragmatic socio-economic growth of a country. The Kenya Vision 2030 aims at maintaining a sustainedeconomic growth of 10% p.a. over the next 25 years through the direction that the VisionStrategy be accompanied with realistic and concrete action plans upon expiry of the EconomicRecovery Strategy (ERS) in December 2007.The overarching component of the Vision is that Kenya transforms into a globally competitiveand prosperous nation with a high quality of life by 2030.

Nevertheless, the major question still remains; how can this vision actually be achieved inreality?In order for the Vision to be realized within the designated time-frame, it is imperative that thetargeted economic growth is achieved through rapid industrialization, enhanced agriculturalproduction and agro-industry development, booming tourism, advanced education (scienceand technology) among other factors. Such goals can only be achieved through rapidinfrastructure development based on innovative techniques, methods and technologies as aprimary driving factor.In this Paper, innovative methods that can realize the practical achievements of suchadvancement are also discussed in terms of cost-effectiveness, performance andenvironmental considerations. In order to achieve these fundamental goals, the paper alsoemphasizes the need to enhance capacity building programmes through the development ofstrong Young Engineers Programmes (YEPs) for public, private and academic institutionsthrough technology transfer, technical training and R&D activities.The versatility of advanced research based Consolidation and Shear Stress Ratio (CSSR)Functions in the prediction of ground, pavement and foundation behaviour is alsodemonstrated. It further proposes that the application of CSSR Functions in F.E analysis orother constructive models may reduce the complexity of the models and/or number ofparameters required in such modelling. Further demonstration on the application of CSSRFunctions in relation to the design of appropriate testing, experimental and research regimesthrough the conceptual correlation of loading rates, reconsolidation, aging, geomaterial

characteristics, ground structure and re-constitution in relation to multi-stage construction ofembankments and foundations, precise determination of bearing capacity factors numerical


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computerized modelling and prediction of ground and foundation behaviour, as well as theoverall enhancement of engineering parameters.The Paper also introduces and discusses some recently developed research orientedgeotechnical engineering solutions to problems related to tropical problematic soils andrecommends appropriate methods of design and construction that would ensure theapplication of such geomaterials. The ongoing research regarding this topic is also introduced.

The strength and deformation characteristics derived from the interaction of geogrids,geotextiles and tropical geomaterials are discussed from a scientific and engineeringperspective.Recently developed techniques and geotechnical and engineering concepts for groundimprovement, OPMC Stabilized retaining walls and enhancements of design, construction andmaintenance engineering aspects are also introduced.The paper demonstrates and concludes that for purposes of achieving the Kenya Vision 2030,sustainable development and maintenance, Research and Development (R&D) is absolutelynecessary.

2. INTRODUCING SOME EXAMPLES OF POST WORLD WAR II RAPID DEVELOPMENTS

Japan is usually cited as a typical example of one of the countries that has made the mostrapid technological and economic growth and development in the post World War II era. Thishas made Japanese technology become the focus and model for the Tigers and developingcountries.Sections 2.1 ~ 2.11 demonstrate some of the technological advances in civil engineering thatJapan has achieved based on enhanced Research and Development (R&D).All the examples cited were either fully or partly constructed by Kajima Corporation, while theAuthor of this Paper participated in the research and design studies of most of the projectsduring his graduate and post graduate studies.The harbour and railway structures were basically designed by Katahira and Engineers

International.

2.1 Highways and Bridges

Figs 2.1.1 ~ 2.1.4 show examples of the magnificent bridges that have already beenconstructed in Japan. The Akashi Kaikyo Bridge is the longest suspension bridge in the worldwith a centre span of 1991 metres (approximately 2km) and an overall length of 3,911 metres(approximately 4km).Initially, this bridge was designed to have a centre span of 2,000m (2km). However, duringconstruction, the great Kansai earthquake prevailed causing the bridge to experience a totalshift of 9metres. Nevertheless, the bridge stayed intact without experiencing or exhibiting anycritical technical problems.


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Fig 2.1.1 Overview of Kurishima Kaikyo Bridge stretching across Kirishima Straits. Total length 4.105km(4,105m) (Kajima Corporation)

Fig 2.1.2 Akashi Kaikyo Bridge,3-span 2-hinged truss Stiffened Suspension Bridgewith 6 Lanes. LongestSuspension Bridge in the worldwith centre Span of 1991m(Approx 2km) overall length of3,911m (approx 4km)

Fig 2.1.3 Akashi Kaikyo Bridge Anchorages, Structural Elements and Profile


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Fig 2.1.4 Akashi Kaikyo Bridge Cross section of strata, stiffening girder Techniques and constructionarea

2.2 Airports

Due to the lack of ample existing land space in Japan, most airports and other mega civilengineering structures have been constructed on reclaimed land. Figs 2.2.1 are some of suchexamples.

Fig 2.2.1 Tokyo International Airport (Haneda) and Kansai International Airport

Fig 2.2.2 New Tokyo Int. Airport (Narita) and Colombo Int. Airport, Sri Lanka on the right


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2.3 Dams

Figs 2.3.1 and 2.3.2 show rock-fill arch dams and gravity dams respectively.The rock-fill dam is simulated after Kajimas 3D-Dam-CAD Techniques which are applied inoptimizing the construction, quality and material control vis a vis cost reduction, while the480m height Miyagase dam was constructed by employing the RCD Method, also developed

by Kajima Corporation for the construction of large dams.

Fig 2.3.1 Dams thathave been appliedkajimas 3D-Dam-CAD Technique,ensuring HighQuality Structuresvis a vis, costreduction

Fig 2.3.2 GravityDam Miyagasedam constructedemploying the RCDMethod developedfor construction oflarge dams

2.4 Tunnels

As a mountainous country, tunnels are a common geotechnical engineering feature.Furthermore, Japan is one of the pioneer countries that developed under sea tunnels.

Fig 2.4.1 is a depiction of the Tokyo Wan Aqualine under sea tunnel along the Trans TokyoBay Highway which is a 15.1km route connecting Kawasaki and Kisarazu man made islands.The route traverses mainly for 4.4km above sea vide bridges, for 9.4km under sea via tunnelsand two man-made islands.


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Fig 2.4.1 TransTokyo Bay

Highway a15.1km routeconnectingKawasaki andKisarazu.

2.5 Buildings

Some of the mega building structures in Tokyo are shown inFigs 2.5.1.The 240m (80 stories) building is the headquarters of theNippon Telephone and Telegraphic DOCOMO in Yoyogi,while the JR Osaki train station on Tokyos Yamanote line hasa floor space of more than 80 acres (320,000m2) andaesthetically integrates business and amenity within limitedspace.

2.6 Railway Systems

After the end of the 2nd World War, Japan embarked on a technological mission anddeveloped the Shinkansen(bullet train), a supersonicspeed electric train just beforethe Tokyo Olympics in 1964.Along with this developmentbecame the necessity to

construct high-tech railwaylines and systems.

Currently, Japan has one ofthe most advanced railwaynetwork, underground(subway) and Mass Transit(MT) systems in the world.

Fig 2.6.1 Railway Systems


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Fi 2.8.1 Land Reclamation

2.7 Harbours

As an island country, Japan is whollysurrounded by sea. Ports and Harboursdevelopment is therefore a keyprerequisite.

An example is depicted in Fig 2.7.1

2.8 Land Reclamation

As stated earlier, Japan is not only asmall country (approximately half the sizeof Kenya), but it is also so mountainousso much so that less than 20% of its landarea is habitable. Furthermore it has a

population of more than 120million people.These are the reasons why Japan is considered as one of the countries with the highestpopulation density in the world.Consequently, the development of landreclamation technology became one ofthe primary components of realizingreasonable urban development.

Fig 2.8.1 is a basic example of one ofsuch technologies.

2.9 Amenity Facilities

Figs 2.9.1 and 2.9.2 are examples ofsome of the amenity facilities thathave been developed on the basis ofJapanese technology.

2.10 Example of Modern UrbanDevelopment IncorporatingFuturistic Components

Minato Mirai 21 (MM21), firstconceived as an Idea almost 3

decades ago, was Yokohama's vision of the future. It was practically realized in 1997 once,only dockyards, the city is turning this harbour front area into a world class business /recreation complex with one of the most advanced information infrastructure. The main crown

Fig 2.7 Ports and Harbors Development


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is the Landmark Tower - at 296m, the tallest building in East Asia. It was meant to be higher,but flight restrictions at the Haneda airport prevented it. It boasts the latest in computerizedanti-earthquake and anti-motion equipment and the fastest elevator in the world ascending ata speed of 45km/hr (12.5m/s).

Intended to be a cultural cosmopolitan and information city of the 21st Century with superior

environment, the Intelligent City is a manifestation of the success of Public and Private Sectorjoint partnership.

Figs 2.10.1 ~ 2.10.9 depictvarious aspects andcomponents of the MinatoMirai 21 in Yokohama City,Japan.

Some of the major conceptsfor the Nairobi metropolitan

Development for Vision2030 can be modelled onthe MM21 Yokohama City.

Fig 2.10.1 Partial Scenery of the sea front of MM21

Fig 2.10.2 Mode of Realizing a visionary Urban Development Fig 2.10.3 Land Use Map of Minato Mirai (MM21)Fig 2.10.4 Satellite Image of Minato Mirai (MM21)

Fig 2.10.5 A General View of Minato Mirai 21 (MM21)

Fig 2.10.7 Various Perspectives of the MM21Fig 2.10.6 Various Perspectives of the MM21


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Fig 2.10.9 Demonstration Test of ITV in MM21

2.11 Examples of Mega Floating Structures

With a large sea area, Japanesemarine and geotechnicalengineering technology has alsobeen strongly geared towards thedevelopment of mega floatingstructures.

Figs 2.11.1~2.11.9 give examplesof such floating structures. Fig2.11.2 depicts the maincomponents within a megafloating system.

Fig 2.10.8 MM21 Intelligent Transport System

Fig 2.11.1 General View of Very Large Floating Structure

Fig 2.10.7 MM21 Intelligent Transport System


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Fig 2.11 5 Floating Pier at Ujina, Japan

Fig 2.11.2 Components of a Mega-Float System Fig 2.11.3 Examples of Mega-Float Structures

Fig 2.11.4 Examples of Mega-Float Structures

Fig 2.11.6 Proposed Floating Runway at TokyoInternational Airport (Haneda)


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Fig 2.11.8 Osaka Focus A by Japanese Society of Steel Construction Fig 2.11.7 Marine Uranus by Nishimimatsu Corporation


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3. EXAMPLES OF INNOVATIVE TECHNIQUES FOR ADVANCED GEOTECHNICALINVESTIGATIONFor the successful design and construction of any civil engineering structure, comprehensivegeotechnical engineering investigations are a definite prerequisite. On the other hand, due tolack of sufficient funds, human resources and technical capacity, the Engineer in developing

countries, particularly in Africa, is faced with situations whereby they have to either adopt theexisting sub-standard and/or outdated techniques or innovate methods that optimize the useof the available equipment, human resources and technical capacity.This section presents examples of some of the recently developed innovative geotechnicalengineering testing and analytical techniques that form a concrete basis in realizing the designand construction of sound civil engineering structures.

3.1 Example of Innovative In-situ Testing Method

Fig 3.1 Mode of Achieving Objectives

Objectives of StudyNecessity for Innovative Modification

Fig 3.2 Load, Speed and Pavement StructureEffects on Deflection Measurements

Fig 3.3 Innovative NDT Method Theoretical Considerations


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Fig 3.4 Innovative NDT Method TheoreticalConsiderations Resilient Deviation Fig 3.5 Need for Innovation

3.2 Example of Innovative In-situ Analytical Techniques

Fig 3.3 Major Objective

Fig. 3.5 Effects of Pre-loading and Load Intensity on Deflection Fig. 3.6 Correlation of Pr-loading and Deflection Basin Concept


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Fig. 3.7 Theory of Damped Oscilatory Motion Impacted by Layer Stifness

Fig. 3.8 Influence of Confining Stress on DeflectionMeasurement

Fig 3.9 Influence of Confining Stress on Deflection Basin Characteristics Fig 3.10 Influence of seasonal Changes on Deflection Measurement

Fig. 3.11 Significance of Temparature Effects on the Elastic Modulus of AsphaltConcrete

3.3 Innovative Methods of Analyzing Environmental FactorsEnvironmental factors are known to highly affect the concepts of design, actual constructionand ultimate performance of highway pavement structures. In this study, some comprehensivemethods that may be effective for evaluating the impact of these factors are proposed. A newconcept of evaluating the deterioration of the structural thickness as a result of infiltration of

underlying material to the upper layers is also introduced. Application of these concepts and


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methods show that the impact of environmental factors over a given period of time can bemore detrimental than commonly considered in most cases

The main objective of undertaking this research therefore was to develop new quantitativeanalytical concepts and methods of effectively evaluating the impact of environmental factorssuch as geology, topography and climate (seasonal changes) on the performance of highwaypavement structures.

The major environmental factors considered which highly depend on topographic,geographical, geological, climatic and other changes are depicted in Figure 3.12 and 3.13.

3.3.1 Evaluation of The Effects of Moisture~Suction VariationThe effect of moisture changes on the current strength, durability and bearing capacity of thepavement and roadbed materials is evaluated on the basis of three concepts predominantlyrelated to saturation levels, swelling and variation in the design moisture content.

The detrimental effects of moisture~suction variation on strength and deformationresistance are depicted in Figs. 3.14.

(1) Effect of Saturation Level

Fig 3.12 Effect of Dynamic Loading on StrengthCharacteristics of Tropical Soils

9.10362.09.1max

max

PI

E

E

imc

vmcmc

0

200

400

600

800

1000

1200

1400

1600

1800

2000

0 0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7 3 3.3 3.6 3.9 4.2

Axial Strain e a (%)

AxialStress,

UCS(kN/m2)

Dynamic (Mc=10.2%)

Static (Mc = 12.1%)Dynamic (Mc=12.1%)

Proposed by Mukabi et al. (2001c) for

Tropical Soils with a PI


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Figure 19 Effect of Saturation Level

1

10

100

1000

1 10 100 1000

Unsoaked CBR(CBRus)

Soaked

CBR(CBRs)

Sr = 0.90.8

0.7

0.4

0.6

0.5

0.3

0.2Sr = 0.1

S = Soaked,

US = Unsoaked,

Sr = Degree of Saturation

CBRS = e500(0.9-Sr) x CBRUS(0.1+Sr)

1

10

100

1000

1 10 100 1000

Unsoaked CBR(CBRus)

Soa

ked

CBR(CBRs)

Sr = 0.90.8

0.7

0.4

0.6

0.5

0.3

0.2Sr = 0.1

S = Soaked,

US = Unsoaked,

Sr = Degree of Saturation

CBRS = e500(0.9-Sr) x CBRUS(0.1+Sr)Figure 3.14 Impact of Moisture ~ Suc

(2) Effect of Swelling

Figure 3.16 and 3.17 show thecompound effects of compaction,surcharge pressure and monotonicloading-unloading-reloading cycles onexpansive soils. The swell related

equations derived from the generalizedequation proposed by Mukabi et al.(1999c and 2003d) are also presented.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 10 20 30 40 50 60 70 80 90

Soaking Time, t (hours)

Swellas,(%)

Stat ic 2.90 SP 97%Compact ion Static 7.30 SP 96%CompactionDynamic 2.90 SP 108%compaction Dynamic 7.30 SP 108%compaction

ReloadingLoading Unloading

Start of Reloading PointStart of UnloadingPoint

Start of UnloadingPoint



Start of ReloadingPoint



F

SP

iSRfS

S H

aa

a max

Fig 3.16 Swell vs. Soaking Time Characteristics

Fig. 3.15 Effect of Saturation Level


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Figure 3.17 Swell vs. Surcharge Pressure

Characteristics

(3) Effect of Variation in DesignMoisture Content

The selection of an appropriate design

moisture content and density condition iscritical to the design analysis. Themoisture content at which subgradestrength should be assessed is thatwhich can be expected to be exceededonly rarely. Pronounced exceedance ofthis factor is known to have adverseeffects on the pavement structure.Fig. 3.18 shows the coupled effects ofseasonal changes and plasticity index onthe design moisture content, while Fig.

3.19 introduces equations that can be applied in correcting for seasonal effects forreconstruction and overlay design.

Dmc = -0.0093PI2 + 1.1745PI + 3.2

Dmc = -0.0063PI2 + 0.9384PI + 5.4

10

15

20

25

30

35

40

45

0 10 20 30 40 50 60 70 80

DesignMoistureContent(Dmc)

Plasticity Index(PI)

Wet Season Dry Season Poly. (Wet Season) Poly. (Dry Season)

Wet Season

Dry Season

Average of 10 dataPoints

94.0013.0

1

PIPIfdPIfD PImc

a

Figure 3.18 Influences of Seasonal Changes and Plasticity on DMC

PIeAPIPB

pd

Correcting for Seasonal Effects forReconstruction Design

03.0,10

mm

dmc

Bmm

wmc

BA

DeAD

02.0,12

PP

wBP

Pd

BA

PIeAPI

dmc

Bmmc DeAD

m

Correcting for Seasonal effects forOverlay Design

sfEP

Df tSdfxxR

T

TI 1

fIdmc

mBm

wmc eDeAD

1

fI

wBP

Pd ePIeAPI

1

Figure 3.19 Influences of Seasonal Changes and Plasticity on DMC

(4) Seasonal and Soaking Condition Effects on Bearing Capacity


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Figure 3.20 Seasonal and Soaking Effects

CBRus = 1.8CBRs + 3.7

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Soaked CBR

UnsoakedCBR

WetS ea s on D ry S ea so n Linear (Ser ies2) L inear (WetSeason)

(Linear Regression)

1:1 (Line of Ideal Relation)

CBRus = 1.8CBRs + 3.7

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70 80 90 100

Soaked CBR

UnsoakedCBR

WetS e as o n D ry S ea s on L in ea r ( Se ri e s2 ) L in ea r ( We tS ea s on )

(Linear Regression)

1:1 (Line of Ideal Relation)

The combined effects of seasonal changes and soaking conditions on the bearing capacityof some subgrade materials is depicted in Figure 3.20, while the equation that can beapplied to correct for this effect is also presented in the same figure.

3.3.2 Intrusion of Native subgrade Material into

Upper Layers of Pavement StructureVarious research undertaken by Mukabi (2001)and Mukabi et al. (2003) indicate that Intrusion ofnative subgrade material into the overlyinglayers of the pavement usually results in theultimate degradation of the layers. Depending onthe nature of the subgrade, topography ofenvironment and seasonal changes, intrusion ofnative subgrade material into overlying layers ofthe pavement structure, as depicted in Figure3.21, can be rampant and extremely detrimental.

0

20

40

60

80

100

120

140

160

180

0 10 20 30 40 50 60

Plasticity Index, PI (%)

SoakedCBR

'1:1 '2:1 '3:1 '4:1 '5:1 '1:0

Optimum Batching Ratio

Reduction in CBR Practically Linear

Rate of Reduction and Reduction Characteristics Dependent on Batching

Ratio and Quality of Bearing Material

Lower Bound Limits are Distinctly Dependent on Ba tching

Ratio

CBR Reduction ~ PI Threshold @PI =40%

Relation with Structural

Thickness

Tendency to Residural (Threshold) Value

Fig. 3.21 Intrusion of Subgrade Material Fig. 3.22 Impact of Inferior Material Intrusion

The consequences of such a physical action are the deterioration of bearing capacity,

cohesion intercept (c) and internal friction () as well as mechanical stability.Some of the results of the quantitative analysis of this factor are presented in Fig.3.22 and

further discussed for expansive soils in Mukabi and Gono (2007f, This Conference) andMukabi et al. (2003c).

In this series of experimental testing, materials with varying qualities and properties wereinfiltrated into high quality crushed aggregate base course material mechanically stabilized at

varying ratios (0~40mm:0~5mm aggregate).Fig.3.22 clearly indicates that: 1) inferior material intrusion into the upper layers drastically

reduces the bearing strength. 2) The magnitude and rate of reduction in bearing capacity is adirect function of the quality of material and batching ratio. 3) The threshold of the CBRreduction is at approximately PI=35%. 4) The effect of subgrade material intrusion ceasesafter the PI reaches the threshold value.

The results indicate therefore, that it is absolutely imperative to take this fact intoconsideration during the structural design and analysis of a pavement.

3.3.3 Evaluation of Variation in Quality of Pavement Layer MaterialsThe quantitative assessment of deficiency in the physical properties of pavement materialswith time through the intrusion of fines to upper pavement layers is undertaken by employing

the following equation:


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USmmS CBRPIBACBR (3.1)

where, CBRs = soaked CBR, CBRus = unsoaked CBR, Am and Bm are material relatedconstants which were generally determined as 0.97 and 0.027 respectively for materialstested in this study. This equation enables the evaluation of the effect of increased FinesContents (FC) and PI on the bearing capacity.

3.3.4 Deterioration of Pavement Structural ThicknessExamples of the quantitative changes in pavement structural thickness, which is defined asthe effective thickness that acts structurally are discussed extensively in Mukabi (2002a). Thedeterioration of pavement structural thickness occurs mainly due to cyclic action of increasedaxle loading, water infiltration and intrusion of subgrade fines to upper layers as brieflyintroduced in the preceding sections. The Intensity Factor I f, proposed by Mukabi et al.(2002a) is expressed as follows :

sdff

EP

D

f txSxR

T

TI 1

(3.2)

where, TD = design thickness, TEP = measured thickness of the existing pavement, Rf

= roughness factor expressed as

25.0

2

it

i

RR

RRf given, Rf = roughness factor Ri =

initial roughness value, Rt= terminal roughness value, Sdf = rate of surface distressdepreciation factor, ts = time lapsed since the previous study or survey was undertaken .

3.4 Innovative Material Characterization Techniques

Prompted by the lack of suitable subbase material due to weathering and high plasticity inmost areas of the Addis Ababa ~ Goha Tsion Trunk Road in Ethiopia, innovative tests tocharacterize various physical and chemical properties of the available materials were carriedout. Analyses of the test results were done in respect to the intrinsic plasticity characteristics ofthe geomaterials under the influence of chemical and physical changes on the one hand, andthe effect of the resulting variation and magnitude of the consistency limit values on thebearing capacity of the geomaterial, on the other.

Influence of clay content - The relationship between clay content and plasticitycharacteristics is mostly dependent on the geological origin and mineralogy of a geomaterial.Typical results of the soils tested from the Project area exhibited a Liquidity Limit (LL) ofapprox. 50% (47~52) for various conditions. Plotting the results from the tests conducted in

this study in Fig.3.23 indicated that the level of enhanced clay activity was only 6.4%. Thisimplied that the clay content activity influencing the variation of plasticity characteristics wasvery low, hence low potential to swell (ref. to Fig.3.24). Furthermore, due to the low claycontent of the Project material tested, it was considered that the main cause for the initial highplasticity index is the low degree of leaching and laterization due to the low amounts ofmineral coatings by sesquioxides which act to suppress the activity of the clay minerals. Sincethis effect is probably mainly due to the titration of clay particles from the overburden materialand weathering, the subsequent geological effect in the post inter-particle state was toincrease the sesquioxide influence.


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Fig.3.23 Typical Colloidal Activity Fig. 3.24 Typical Swell Potentional

Due to the foregoing discussion therefore, it was considered that the clay content and activityeffect on the variation of the plasticity characteristics and in particular the plasticity index of theProject geomaterials designated for use as subbase materials was quite negligible.

Influence of nature of soil material -The contribution of the nature of soil materials to theplasticity characteristics highly depends on the shape and structure of the soil minerals inrelation to the surface area in contact. In other words, the soil particle orientation and micro-aggregate cluster formation become increasingly important in consideration of the magnitudeof consistency limits. The global effect is considered to be related to the ultimate magnitude ofthe surface of activity of clay minerals in reference to the interaction of sesquioxides.Interpretation of this influence would therefore be related to the genesis, degree of weatheringand clay mineralogy. The results from the study showed that:

Contribution of the chemical composition of the colloid -The practical significance of the liquid

and plastic limits lies in their ability to reflect on the types and amounts of clay minerals

present in the fine fraction (Skempton, 1953). For natural soils, the plasticity index has been

found to increase in proportion to the amount of clay size particles present whereby the

relationship is practically linear and passing through the origin as shown in Fig.3.25. As can be

noted from the same figure, very different relationships between the plasticity index and the

percent clay-fraction size are obtained for three clay minerals namely kaolinite, illite and

montmorilonite for some temperate-zone clay soils. Wu (1966) suggested that the slope of thelines indicate the relative magnitudes of the surface forces which are representative of the

colloidal activity. The active clay characterized by large colloidal activity exhibit plastic

i) Virtually negligible variation existed between the plasticity parameters of oven dried and air dried

samples. This implied that the clay mineral surfaces do not orient in full contact position as this shouldhave enhanced the degree of saturation and intrinsic localized suction stresses analogous tosurcharge stresses whereby the plasticity index of the oven dried sample should have been muchlesser than the air dried sample.

ii) The addition of sodium chloride did not seem to have considerable impact in the plasticity behaviour ofthe clay minerals tested in this study. This may imply that due to the nature and the structure of theclay minerals, the osmotic suction stress levels were not affected to such an appreciable extent.

iii) Although addition of hydrated lime caused reduction in the plasticity limits and index to a level belowthe lower threshold of PI=16, the effect of drying, water, and temperature in relation to the chemicalreaction prompted by addition of CaCo was not apparent. This implied that the nature of the clayminerals was appreciably stable hence drastic variation in the plasticity characteristics was notexpected.


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properties over a wide water content range. This is generally considered to be the result of the

strong interaction between the surface forces and water molecules.

The results from this investigation showed that although the material exhibited plasticity

indices greater than 15 (the Specified value), the subsequent variation in plasticity

notwithstanding varying conditions was fairly low. This may be attributed to the presence of

mica in the silt fraction of the soil as suggested by Ruddock (1967).This substantiates the fact that the geomaterial along the Project Road was mainly

influenced by Kaolinite clay fractions and as a consequence, its plasticity characteristics arehardly influenced by the local history of large seasonal movements.

Influence of exchangeable cations According to Houghs (1957) proposal, Sodium

(Na), Potassium (K), Calcium (Ca), Hydrogen (H) and Magnesium (Mg) ions in the

montmorillonite mineral exhibit the highest values to Atterberg limits, while those of the

Kaolinite mineral exhibit the lowest values. For all minerals, however, the sodium ion is the

most exchangeable. In this investigation, sodium chloride (NaCl) and hydrated lime in the form

of CaCo3 were adopted as catalistic agents to study to presence and effect of exchangeable

ions. The addition of these agents had little influence on the variation of the plasticity values ofthis material. It was therefore considered that the available exchangeable ions were quite

limited and were virtually in an inert state.

0

20

40

60

80

100

0 20 40 60 80 100

PLASTISITYINDEX-%

- 2m CLAY CONTENT - %

PLASTICITY CHARACTERISTICS OF LATERITE SOILS

London Clay

lllite

Horton Clay

Kaolinite

Co Montmorillonite

Data from this study

Data from

Fig.3.25 Clay Content and Plasticity Index Fig.3.26 Impacts of Environmental Factors

Following this study therefore, it was concluded that the materials could be adopted for subbase purposes despite their relatively high PI values. Analysis of their vital engineeringproperties such as strength, bearing capacity and deformation resistance determined from

both laboratory tests and field trial sections indicated high values well beyond the specifiedones.

3.5 Innovative Method for Back-Analysis of distressed Pavement StructureThe Constitutive model on cyclicplasticity for geomaterials based onnon-linear kinematic hardening theoryproposed by Yashima et al. (1994) isadopted in attempting to back analyzethe deformation history of the

pavement structure. This model waschosen because of its incorporationof the non-linear kinematics

Fig.3.27 Results From Back Analysis

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 0 0 0 0 0

Defelctionrd

(x10-2mm)

Deflection Basin, DB (m)

Lower PavementLayers

Upper

Distressed

Virgin

a Constitutive Model for Lower Pavement Layers

a Constitutive Model for Upper Pavement Layers

a Estimation of Consolidation and Shear Stress History

0121

****

1 Dijijijijy Rxxf

''/'exp1 '0

*'dZZZZ

Tij

ZO

ij

NCoc

o

NC

o

NCNC

ooc

CSRAKK

qKq

..

.max

max

NC

C

NC

f

OC

C

NCOC

O

NC

O

NC

OOC

fp

PP

CSRAKK

Kq

'

''

'

.


22/55


0121

****

1 Dijijijijy Rxxf

(3.3)

vpijvpijij dxdeABdx *1*1* (3.4)

21vpijvpijvp deded (3.5)

0')1(

'1

*~21

****1

mamnMijxijijxijg (3.6)

01~ ' )1('**0 mamnmb Mf (3.7)

''*~ mcmnM (3.8)

hardening rule. When incorporated into an overstress type of model, it is found to be effectivein expressing the changes in retardation in the strain rate direction upon a correspondingchange in the direction of the stress. Furthermore this model is found to reproduce to anappreciable extent, the plastic damage during cyclic or repeated loading. By taking intoaccount the effects of sub grade layer material into the sub base, the constitutive model forclay is adopted in simulating the composite yield characteristics of these layers, while the

distress behaviour of the upper pavement consisting of the unbound crushed aggregate basecourse and the asphalt concrete, are analyzed by modifying the theories in the constitutivemodel for soft rock. A representation of the results of this concept is given in Fig.3.27.

3.5.1 Constitutive model applied for lower pavement layersThe viscoplastic model for over consolidated clay extended to a cyclic model by Oka (1988) isapplied. The static yield functions that account for changes in the stress ratio are given asfollows:

where, 1DR = parameter defining the elastic

region and*

ijx =the kinematics hardening tensor.By introducing the non linearity of the kinematics hardening, *

ijx can be written as

In which*

1A and

*

1B are the material constants

and *ij

de is the increment of the viscoplastic

deviatoric strain. The second invariant of the increment of the plastic deviatoric strain isderived as:

For the first yield function, the plastic potential is assumed to be:

where, ')1(ma = material parameter and

*~M is the stress ratio when the layersare under maximum compression condition: Considering the over consolidated boundarysurface between the NC and OC zones to be expressed as:

In the NC Zone 0bf , *~M is kept constant i.e., *

~M = *

~mM

region, it is defined as: 0bf ,*~M is defined as:whereas in the OC

where, the current stress ratio 2

1***

ijij and''

mbmc exp(

**

0 / mM )

3.5.2 Estimation of Consolidation and Shear Stress PathsThe input parameters for the constitutive model introduced in the preceding section werederived from the following theories and concepts. As the repeated loading progresses, thecumulative effects are back analyzed by applying the concepts of consolidation and shearstress ratio functions under normally consolidated (NC) conditions introduced by Mukabi andTatsuoka (1996) and Mukabi (2001d). In so doing, the initial stresses are computed from theexperimental results of full scale trial sections (Mukabi, 2002; Gono et al., 2003, this

conference) .The cumulative stresses are then derived by considering the average loadingrate and cumulative repeated loading over a given period of time. Once the maximum deviatorand mean effective stresses are determined, the stress ratio functions, defined from the


23/55


BA CSR (3.9)

SRSRSR /' (3.10)

CSRK CSRI

I

.

max

(3.11)

NCoc

o

NC

o

NCNC

ooc

CSRAKK

qKq

..

. maxmax

(3.12)

NC

C

NC

f

OC

C

NCOC

O

NC

O

NC

OOC

fp

PP

CSRAKK

Kq

'

''

'

.

''/'exp1 '

0

*'dZZZZ

Tij

ZO

ij (3.15)

01~ ''

*21

****

1

b

bMxxg

mb

m

nijijijij

following expressions proposed by Mukabi and Tatsuoka (1999b) and Mukabi (2001d) areapplied.

Where, A and B are material properties, and the consolidation

function CSR , which is independent of the effects of loading rate, isstress ratio

derived from the relationmax

1

~ qCSR , whereby ' = function of normalized angle of internal

friction expressed as IQ

A /' (A: An isotropic I: Isotropic) and maxq = maximum deviator

stress. ' can be determined from the quasi-empirical equation (Mukabi, 2001d) expressed in

general form as:

Where, ASR and BSR are stress ratio constants and 'pqSR is

the invariant stress ratio variable.The antistrophic stress path is derived from the isotropic one by introducing a modifier

proposed by Mukabi and Tatsuoka (1999b) expressed as:

where, max = (q/p) at qmax, KI=1 and CSR= consolidations

stress ratio. The modifier is applied in the relation pq .

On the other hand, the invariant stresses and angle of internal friction under overconsolidated (OC) condition were derived from the flowing correlations proposed by Mukabi(2001d).

where, OCOxK'

sin fOCRKOC

Ox

and f

OC

OxK 'sin1 .

The corresponding mean effective stress, OCfp' and angle of

internal friction OCf'

are given by:

(3.13)

and ,

NC

fNCOC

O

NC

O

NC

OOC

fCSRAKK

K '1

'

.

(3.14)

3.5.3 Constitutive Model Applied for Upper Pavement LayersAdachi and Oka (1992) proposed that the stress history tensor is a function of the effective

stress history with respect of the strain measure. This history tensor, *'Oij is given by

where, dz= Zdede ijij ,21 = strain measure, T=materialparameter which controls the strain-hardening and

strain-softening phenomena and de ij is the increment of deviator strain tensor.

The plastic potential is assumed to be:

(3.16)


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01~

'

'**

0

b

bMf

mb

mnmb

The OC boundary is given as :

(3.17)

The OC region is therefore defined as:

b

bM

mb

mn '

'*~

(3.18)

4. APPLICATION OF CONSOLIDATION AND SHEAR STRESS RATIO CONCEPTSLaboratory tests are primarily carried out for purposes of obtaining engineering parameterswhich can be directly applied to conditions in the field. Such an exercise would not onlyprovide parameters for design and construction quality control but also an insight into thefundamental processes which affect the field behaviour. In developing countries, bothaffordability and accessibility to high quality testing equipment are major curtailing factors torealizing this aim. This situation therefore necessitates the development of empirical methodsthat can aid in providing estimated parameters that are reasonable enough for the design andmodelling of foundations bearing civil engineering structures. In this paper, unique methodsderived as Consolidation and Shear Stress Ratio (CSSR) Functions that were recentlydeveloped, providing solutions on how to circumvent these problems, are presented.

4.1 Brief background of developing CSSR ConceptsLaboratory tests can for example, be employed to investigate how strength and stiffnessdevelop during large strain consolidation and how this behaviour is dependent on variousfactors such as loading rate and direction, principal stress rotation in relation to location withinthe foundation etc. However, the precision of adopting these results involves an analytical

approach that would be appropriate in simulating as accurately as possible, the actual fieldconditions. Furthermore, precise determination of such parameters for natural clays usuallyrequires high quality sampling and testing techniques for a reliable laboratory investigation.This translates to high costs and long time durations for performing the tests. The method thatis described in this paper is based on that proposed by Mukabi and Tatsuoka (1999b) whichmodified some aspects of the Critical State Soil Mechanics (CSSM) theories. This wasprompted by their (Mukabi and Tatsuoka 1992) investigation into the effects of consolidationstress ratio and strain rate on the peak stress ratio of clay which concluded that the shear

stress ratio (q/p)max, increases as the consolidation stress ratio''acK decreases based on

high-precision automated CD/CU triaxial compression and extension tests performed on high-quality undisturbed samples of various natural soft to very stiff clays, related to prediction of

ground displacement in actual construction projects. For control purposes, commerciallyproduced Kaolin which contains appreciable quantities of mica and quartz was also used.Their study also confirmed that the shearing stress ratio at failure Kf is a function of the initialconsolidation stress ratio and that it decreased proportionally with decreasing K c parameters.Furthermore, having characterized the effects of loading rate into a generalized state, amethod of unifying the behaviour of anisotropically consolidated clay into a coherent form was

considered. A -function which relates the determined from various tests performed by

applying different CSRs was defined as =/ qm. This relationship was found to be virtuallyconstant and related closely to a reference line considered to be analogous to a modified CSL

(i.e., constant when Kc = 1). In order to compute , a relation between the invariant stress

ratio (SR) and the angle of internal friction was derived from linear regressional analysis ofexperimental data on various clays. Based on the foregoing fundamental theories, versatilefunctions and parameters related to the concepts of loading rate, SHANSEP consolidation,


25/55


ageing and reconstitution that can be applied effectively during multi-stage construction ofgeostructures such as deep excavations, tunnels, embankments and foundations, precisedetermination of bearing capacity factors, numerical modelling and prediction of ground andfoundation behaviour, as well as the overall enhancement of engineering parameters.

4.2 Derivation of Application Functions

The derivation of the CSSR application functions are presented in Mukabi (2007c).

4.3 Application of CSSR Functions in simulating Field Conditions

4.3.1 Functions and parameters based on SHANSEP consolidationAs was discussed by Mukabi and Tatsuoka (1999a and 1999b) and Mukabi (2001d), theintact specimen exhibits much more superior engineering properties in comparison to thespecimens reconsolidated applying the SHANSEP method. It was also derived that the higher

the stress level of the consolidation stress ratio c=(qc/pc), the more the structure is destroyedthrough remoulding. This implies that specimens reconsolidated by applying the SHANSEPmethod can not be representative or correctly simulate the in-situ conditions. Consequently,

correction factors have to be applied on the parameters determined adopting such a method .Based on the concepts of consolidation and shear stress ratio functions, the following

correlations for qmax, pf and f were derived for these purposes.

NCS

OCS

NCS

NCSc

OCScNCS

NCSOCS

CSRAK

qKq

max

max

0

max0

max

'

(4.1)

NCSc

OCSc

NCS

NCSc

OCScNCS

NCSf

NCS

OCSf

P

p

CSRAK

pKp

'

'

'

''

0

0

(4.2)

NCS

NCSc

OCScNCS

NCSf

NCS

OCSf

CSRAK

K

'0

0 ''

where, subscript f denotes failure, superscript OCS and NCS denote Over Consolidated andNormally Consolidated under the SHANSEP method.

4.3.2 Functions and parameters related to the concept of ageing

Ageing is considered to constitute mainly of two components; namely secondary

consolidation associated with creep 0' tae and thixotropy defined as a gain in strength at

constant water content. Creep is basically caused by a continuing re-arrangement of the soilparticles after the overburden pressure is fully supported by the soil skeleton, whereby theexcess pore pressure has dissipated. Kuhn and Mitchell (1993) proposed that creepdeformation is due to sliding between particles and that although the sliding is thought to occurat solid contacts, it is visco-frictional in nature and the sliding velocity at each contact dependson the ratio of tangential to normal components of contact force. Whether the creep strains intriaxial tests accelerate or not depends principally on the magnitude of the deviator stresscompared to the strength or compressibility of the sample. Mitchell (1976) proposed the

following general creep equation:

(4.3)


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mrRa ttAe

dt

d/

ae (4.4)

tlAe nR

aa

a

aee

(4.5) 0/ttlC na ae (4.6)

STCn

STC

fcaSTC

STCLTCf

CSRAtttK

K

'/1/

'

00

0

e

(4.9)

where R=qt/qf delineates the deviator stress level, tr is a reference

time and A and a are solid constant parameters. When m=1 thestrain rate continues to decrease with time, while the strain rate accelerates towards failure

when m


27/55


1/

feRR

eRcf

Rc

ReI

pqCSRAK

ff

(4.12)

Fig.4.3-Effect of OCR and LTC on elastic strain

e BASRan 1max (4.13)

e

e BA

RSRa

ASRa

nSR

1

where superscripts I and R denote intact and

reconstituted respectively and Rc=(q/p)fR,

c=(q/p)c, and KR

cf = (r/a)R

ec.

4.4 Application of Consolidation and ShearStress Ratio (CSSR) Functions in Estimatingand/or Predicting Consolidation StressHistoryDiscussions from the preceding sections of thispaper as well as Fig.4.1~4.3 clearly demonstratethe importance of predicting and/or retracing(back-analyzing) the consolidation and shearstress path and history of ground foundation orgeostructure subjected to loading or otherwise to

beconstruc

ted.For deep braced excavations in soft ground forexample, the movement of the soil surrounding anexcavation must be taken into account with dueconsideration of the its interaction with the retainingsystem or structure. The application of CSSRconcepts in undertaking such estimation or in F.Eanalysis and other constitutive models is one of themethods that can be effective and appreciably precise.Due to the underestimation of the elastic modulus

mainly due

to sample disturbance for example, most predictionoverestimates the lateral movement. Since CSSRconcepts can be applied in simulating the actualground and field conditions to an appreciable levelof accuracy, this problem can be circumvented.In Kenya, Ethiopia and Southern Sudan, theconcepts have been successfully applied in thedesign and construction of various geostructuresIncluding deep braced excavations, padfoundations, embankments, slope stability and

pavement structures. Various practical examples of such application have also been given in

other publications by Mukabi et al. in this Conference.A discussion regarding the back analysis of distressed pavement deformation history hasbeen made by Mukabi et al. (2007h).

4.5 Application of CSSR Functions during Multi-stage Construction4.5.1 Functions and parameters related to the concept of loading rateDue to the importance of incorporating the analysis of the effects of loading on foundationsand embankments of clayey geomaterials during modelling and design, Mukabi and Tatsuoka

(1999b) developed a relation between the stress ratio at failure max (q/pm) and axial strain

rate (ea) expressed in a generalized state as:

where constants AI and B were determined as AA =

0.037, BA = 0.858 and AI=0.043, B

I=0.76(Superscripts denote; A: Anistopic; I: Isotropic; SR: Strain Rate). Based on

Fig.4.1-Stress paths during loading and unloading

Fig.4.2-Emax OCR relations(D70-3)


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RSRASR

max

1

max

(4.15)

(%)

max

50

Aij

a

ij

ELS

ij

aij

ELSa

e

ee

(4.16)

xE

EELS

max

50 , (4.17)

comprehensive analysis of various clays subjected to different axial strain rates and alsoapplying Equation 35, the following co-relations were derived:-

(4.14)

and

where SR is a strain rate function and superscripts ASRand RSR denote Applied Strain Rate and Reference

Strain Rate respectively.

4.5.2 Application of the Elastic Limit StrainAs can be derived from the preceding discussions, the determination of the linear elasticrange of geomaterials defined as the region of the initial yield surface within which thebehaviour of the geomaterial is virtually linear elastic and recoverable, is of paramountimportance for various reasons. Consequently, based on long-term research undertakensince 1991, Mukabi (1995) proposed the following equation expressing the Elastic Limit Strainfor estimating the linear elastic range.

Where ESL

is a function of the level of max)( ae and A is a

constant depending on the physical properties of thegeomaterial.

For most clays is defined as,Based on empirical relations for most clayey geomaterials, A =603 and = 462 are good estimates as constants where the curve

is considered to be positive in all quadrants.The theory of the Elastic Limit Strain has since been

applied in the control of loading imposition duringstaging construction and excavation particularly whendealing with soft and problematic soils in the easternAfrica region.Figs. 4.4-4.6 are a demonstration of how this theorycan be applied in combination with the CSSR concepton stress path, in monitoring the behaviour ofgeostructures in the field under various loading andunloading conditions.

Fig.4.4 Stress states for DC1 specimens

Fig.4.5-Effect of pressure level on elastic limit strain Fig.4.6-Effect of pressure level on elasticlimit strain (DC1-4)


29/55


Table 5.1 Summary of results calculated using proposed equations

5. NECESSITY TO RECONSIDER SOME ASPECTS OF CRITICAL STATE SOILMECHANICSThe existing theories that define lateral pressures, under the framework of classical soilmechanics assume that failure for normally consolidated clayey geomaterials occurs at theCritical State Line (CSL) irrespective of drain condition, loading rate and stress path traversed

towards the CSL.On the other hand Critical State Soil Mechanics has been developed on the basis of Rendulicsgeneralized principle of effective stress which states that for a soil in an initial state of stressand stress history there exists a unique relationship between voids ratio (e) and effectivestress for changes in stress, (a,' or p'). Most of the existing theories for deformation andstrength characteristics of clays therefore assume this principle. Within this context, it ispresumed that for a given normally consolidated clay, failure occurs at a unique line called theCritical State Line (CSL) defined by q=Mp', without allowing the stress paths to locate above it

at all stages irrespective of drain conditions,strain rate and stress path traversed towardsthe CSL. Most finite element basedanalytical tools and simulation of such casesas multi-stage embankment design andconstruction widely employ Critical Statemodels. While studying the influence ofinitial shear on undrained behaviour ofnormally consolidated kaolin, Ampadu (1988)concluded that the existing theory of CriticalState Soil Mechanics alone cannotadequately explain the differences inbehaviour between isotropically and

anisotropically consolidated samples of thekaolin tested. It has also been reported by various researchers that the shapes andmagnitudes of yield envelopes are influenced mainly by the composition, anisotropy andstress history of the clay features which have been inadequately modelled on the basis of theCritical State Soil Mechanics theory. Rigorous examination however, of the behaviour of claythat has been subjected through various stress ratios other than isotropic during consolidationand the corresponding relations is yet a subject to be exhausted.

As can be seen from Fig.5.1, Mukabi and Tatsuoka (199b) proposed some modification ofcertain aspects of the existing theory of Critical State Soil Mechanics.

Reference of the details on the background can be made from subsection 6.5.1 of this report.The relationship of the function ( ) and , a function of the normalized angle of internal

friction ( ) in reference to that of developed from Fig. 6.87(a), is represented by a

linear equation in the

Figure 5.1 Proposed Modification of The CSSM Theory

Fig. 5.2(a) Effect of CSR on Angle of Internal friction Fig. 5.2 (b) Effect of CSR on Angle of Internal friction


30/55


form , where and mean value in this case)

are constants. In normalizing, the was determined for the two

respective strain rates from the linear regression of the NC line of the semi-log plot ofshown in Fig. 5.2. The linear relation in Fig. 6.87(b) is virtually similar and shows no

dependency on the various strain rates . This suggests that this

equation uniquely relates and and may be applied in developing further mathematicalrelations that may aid in redefining the basic parameters related to the without particular

reference to strain rates effects.


31/55


Fig. 5.3 Effects of CSR on kfunction

Fig. 5.4(a) CSR factor

Fig. 5.4(b) a measured a calculated relations

Fig. 5.5 (qmax) measured vs. (qmax) calculated

Fig. 5.6 (qmax) measured vs. (qmax) calculated


32/55


Fig.5.7 Comparison of Critical State Lines based oncalculated values compared to measured values


33/55


6. NECESSITY TO RECONSIDER SOME ASPECTS OF CONVENTIONAL DESIGNPRINCIPLESThe importance of applying advanced and appropriate analytical design techniques can beobserved from Fig.6.1. Based on comprehensive research undertaken under JICA funding, itwas found that the equation proposed by the Asphalt Institute tends to over-estimate the

structural capacity of the existing pavement structure as a result of the lack of consideringvarious factors related to environmental and structural depreciation with time, as inputparameters in the equation. Based on elastic moduli results from advanced testing of variousgeomaterials and by applying environmental and structural depreciation components asintegral in-put parameters that would characterize the elastic behaviour of the respectivegeomaterial, Mukabi (2000) proposed the modified equation expressed in Equation 6.1.

OVERLAY DESIGNS (Discrepancy of AAI Equation)

Convetional Approach Recently Developed Approach

MrCBR

= 10.3 CBR d (MPa)

t'AC AC t2

AC

t'BC BC

t2BC

t'SB SB t2

SB

Note

AC = Asphalt Concrete t'AC = t2

AC

BC = Base Course t'BC < t2

BC

SB = Subbase t'SB < t2

SB

(proposed by the Asphalt Institute)

MrCBR

nMrCBR

nMrMr

A

CBRMrCor

Mr

ll

38.0

ln5.97

RECONSTRUCTION DESIGNS (Anomaly in Appling E 50 Equation)

ConventionalApproach Recently Developed Approach with example

Where,

and

t3AC t4

AC

: Reference strength i denotes trialsectionNo. and

jdenotes layerNo.Applyingequation (2.1) t4BC

t3BC

t3SB t4SB

t3AC = t

4AC

t3BC > t4

BC

t3SB > t

4SB

(conventional)

5050 a

CE e )/(13920782.0

max cmkgfxexmEuq

sc

SC

dg

ija

78.0)1(89.142.0

uSC

dgqa

2)1(/3.3;85.0)( cmkgfqqqm R

q

RuSCu

Figure 6.1 Proposed Method of Estimating Resilient Modulus

775.0623.00012.0102263 CBRCBRCBRcorr MrMrxMrxM (6.1)

where,CBR

Mr = 10.3xCBR proposed by the Asphalt Institute for the Full-Depth overlay design method.

Results from Case Study Analysis undertaken for road projects designed by applying theproposed method indicate that substantial cost savings can be realized relative to the designlife of the road pavement structure.

7. MUKABIS THEORY OF LATERAL EARTH PRESSURESBased on the foregoing concepts, Mukabi (2008d) modified the lateral earth pressureequations as subsequently defined.

Active Pressure for smooth surfacesFor cases assuming no friction is exhibited between the soil and the retaining structure,

(7.1)

where,

(7.2)

and,


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(7.3)

Passive Pressure for smooth surfacesThe expressions for passive pressure assuming a retaining structure with a smooth surface.

(7.4)

where,

(7.5)

Active Thrust for frictional surfacesIn cases where friction between the soil and retaining structure is considered, the followingequations may be applied.

(7.6)

where,

(7.7)

Passive thrust for frictional surfacesThe passive thrust is computed as follows under the framework of the modified theory.

(7.8)

where,

(7.9)

8. SOME RECENTLY DEVELOPED RESEARCH AND DEVELOMENT (R&D)TECHNOLOGIES FOR ENHANCING GEOMATERIAL PROPERTIES8.1 Problematic Soils

8.1.1 Rerap Methods


35/55


PdPdPP

bP

DN

CBRCCBRBAt

/log

loglog2

(8.4)

5.0//1 edCBRSP eS a (8.3)

cneee MLLVCBee eA

a(8.5)

Fig. 8.2 Quality Control normograph

Determination of appropriate counter-measures1) Replacement Method - Tables 2 and 3 aswell as Figs. 8.1 and 8.2 show the design and QC criteria developed on the basis of researchand adopted for the construction of the Addis Ababa ~ Goha Tsion Trunk Road Project. Indetermining the necessary thickness tCL to replace the expansive soil, the following equationsproposed in this study were adopted.

SPbpPCL xStTt The total pavement thickness TP is expressed as:

vfbPP txRtT

And the coefficient of subgrade structural performance SSP is computed from:

On the other hand, the basic pavement thickness tPb from Eq.

(3.10) is computed from the following equation.

Where the roughness factor 25.02 itif RRRR : R i isthe initial roughness factor and Rt is the terminal

roughness factor, tV is the positive value of the

specified tolerance for pavement thickness, AP=219, BP=211, CP=58 and DP=120. Theparameter ae is defined as:

where Ae=0.23, Be=0.54, Ce=0.08 are constants and

Ve=Annual Average Evapotranspiration in m/year (ref. to

Mukabi et al. (2003c), LL=liquid Limit in percentage and

Mcn=Natural Moisture Content of the subgrade material expressed in percentage form. All

thickness are calculated in mm. Continuous assessment and evaluation of the performance of

the sections already constructed by adopting this criteria indicates that the method has so far

been quite successful.

Table 8.1 - Determining Required Capping Layer Thickness (cm)

Notes Where the results are on the Boundary Limit or

within its vicinity, the Criteria of Clay Activity(Ac) expressed as Ac = 3.6R

-2.35(R=LL/PI) may

be adopted or otherwise as directed by theConsultant. For example, should the PI > 45

Fig.8.1 - BRI Vs. Voids Ratio

Voids ratio e reduces as BatchingRatio Index tends to an Optimum

Value. This increase shearModulus i.e.,

Gmax=m(a).m.(Am-e)2/(1+e.(0)

m

(8.1)

(8.2)


36/55


CodingOption

Plasticity andSwell

Condition

RequiredThickness for

DifferentSubgrade Bearing

Capacity

Plasticity

Index

Swell(%

)

Sm

CBR=1

CBR=2

CBR=3

CBR=4

410 40 0 0 60 30B 35


37/55


susceptible to moisture~suction variations, a fact that has also been discussed in Section 4 aswell as the preceding sections of this section. The ongoing research or this subject intends todevelop a technique of controlling the moisture content of a subgrade of an expansive natureby systematically and technically imbedding sand columns in predetermined areas or zones.Figures 8.5 ~ 8.6 present part of the preliminary results that have been obtained in the initialstages of testing. Although definite conclusions can not be derived from these results yet, the

trends exhibited from these graphs are distinctly clear. In other words, imbedment of sandinterface layers seams to be effective in reducing swell and increasing the bearing capacitynotwithstanding the magnitude of the surcharge pressure.

8.1.3 Suction Stress MethodResearch for purposes of developing this method isstill in the initial stages. The basic idea is to developa technique of constructing a subsurface drainagelayer underlain by a layer compacted to a higherdegree in order to induce high but varying suctionstresses. The layer is intended to facilitate in

directing any excess moisture away from thepavement structure. Reference can be made toMukabi (2004a). Fig.8.7 and 8.8 are arepresentation of how this technique was used byincorporating a suction stress column in the designof an OPMC Stabilized retaining wall andmaintenance along the Addis Ababa ~ DebreMarkos International Trunk Road, the all important

northern corridor that connects Sudan and Eritrea.

Fig.8.7 - Use of a Suction Column for OPMC Stabilized Retaining Wall.

Fig.8.6 Soaking period for CBR


38/55


tABC=15cm

tAf=12.5cm

tBf=20cmNatural Gravel BouldersFilter Course

Crushed Aggregate

Filter Course 0~40 only

Crushed Aggregate Base

Course M.S @ 3:20.5 : 0~40

Asphalt Concrete

Constructed to Specifications

Carriageway

Shoulder

Stepped & Compacted to higher degree

to achieve high suction stresses

Subgrade

10cm 25cm 75cm

tAS=7.5cm

Crushed Aggregate Base

Course M.S @ 3:20.5 : 0~40

tAf

=7.5cm

tAf2=7.5cm

Fig.8.8 Suction-stress method

8.2 Development and Application of Optimum Batching Ratio Method (OBRM) andOptimum Mechanical and Chemical Stabilization (OPMC) Techniques8.2.1 Basis for Development of OBRM and OPMC TechniquesThe necessity to develop the Optimum Batching Ratio Method (OBRM) Optimum Mechanicaland Chemical Stabilization (OPMC) prevailed due to the prevalence of the 1997~1998 El-Ninofloods coupled with the lack of suitable road construction materials along the B3 Malindi-Garissa Trunk Road. Details can be referenced from Mukabi et al (2003d) and Mukabi et al(1997).

1. Upon undertaking Case Study Analysis and analytical review of the post-El-Ninohydrological conditions, it was realized that additional hydraulic structures such asbridges and major culverts of appreciable dimensions would be necessary. These

structures would necessitate additional funding totalling to almost 30-40% of the totalProject cost. However, the economic and financial analysis revealed that investment ofsuch magnitude would not be cost beneficial. Consequently, a cost reduction plan wasembarked upon.

2. In order to reduce the costs, a plan to design and construct bridge approach abutmentsout of high reinforced soil embankments and reciprocal protection works, was proposed.Nevertheless, due to the non-availability of suitable geomaterials within the project areathe preliminary design revealed the cost of reinforcement and protection material wouldbe quite high due to the additional strength and stability required.

Fig. 8.9 Mode of Characterizing Particle Motion


39/55


Important factor

Objective of study

Develop a method of determiningoptimum Mixing ratios for geomaterials

with different grading characteristics inorder to achieve;

Better Compaction characteristics

Greater resistance to wear

Enhanced resilience properties

(c)

(e)

(d)

(f) (h) (g)

(a) (b)

Fig. 8.10 Theoretical and Engineering basis presented at the 14t

IRF World Road Congress,Paris 2001

Fig. 8.11 Mechanical Stabilization Effects


40/55


Fig. 8.12 Graphical Representation of Proposed BatchingRatio Method

Fig. 8.13 Proposed Optimum Batching RatioMethod

Fig. 8.14 Effect of OPMC on Strength andDeformation Resistance

Fig. 8.15 OPMC Stabilization Technique Fig. 8.16 OPMC Stabilization Technique


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8.2.2 Application of OBRM and OPMC Techniques in Reducing Cost and EnvironmentalImpact of Rural Road Construction include:Some of the aspects that were consideredApplication Of A New Mechanical Stabilization And Other Techniques In Reducing The CostAnd Impact Of Rural Road ConstructionThe major objectives of undertaking this Study included:

- Reduced volume of materials used by 40%- Sustained dust reduction- Cost-effective- Environmental friendly- Less disturbance of land for borrow pits- Reduced amounts of disposable soil during construction-

Enhancement of engineering properties of geomaterials- Reduced risk of collapse of civil engineering structures.- Enhancement of disaster avoidance and management

The Study undertook comprehensive appraisals and environmental assessments that wouldlead to sustainable development with minimal negative environmental impacts.A summary of the approach, considerations and contribution of OBRM and OPMC from ageotechnical engineering perspective are summarized in Figs. 8.20 to 8.28.

Fig. 8.18 OPMC Stabilization Technique

Fig. 8.20 Example of Negative Impacts of Rural Road Transport Infrastructure

on Ecology and Wildlife in Eastern Africa

Fig. 8.19 Quality Control Normogra h


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Fig. 8.21 Transport sector in industrialization and economic activities

Fig. 8.22 Road system effects on individualanimals and the wildlife population

Fig. 8.23 (a) Example of positive impacts ofrural road transport infrastructure on socio-economic development in Eastern Africa

Fig. 8.23 (b) Example of positive impacts ofrural road transport infrastructure on socio-economic development in E. Africa

Fig. 8.23 (c) Improved Livestock Health andMarkets


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Fig. 8.24 Importance of enhanced Research anddevelopment

Fig. 8.25 Application of SA&SEA using Technology andTechniques for Environment Impact

Fig. 8.26 OPMC: Drastic Reduction of Volume of Materials


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8.3 Strength and Deformation Characteristics of

OPMC Stabilized Geomaterials and GeogridsInteractionThe fundamental concept of incorporating geogridsfor purposes of stabilizing and/or reinforcing soils isillustrated in Figs. 8.29 to 8.30.

Fig. 8.27 some vital aspects of OPMC

Fig. 8.29 (c) Fundamental Concept of incorporatingGeo rids

Fig. 8.29(a) Fundamental Concept ofincorporating Geogrids

Fig. 8.29 (b) Fundamental Concept ofincor oratin Geo rids

Fig. 8.28 Construction Planning based on

Comprehensive Research and Technology


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Fig. 8.30 Effect of Interlocking and Grid AperturesFig. 8.32 Drawing to illustrate inclusion of Tensar Geogrid.

Geogrid was placed at 1/3 the height of the sample as shown

Fig. 8.32 shows a schematic drawing illustrating the placement of the geogrids, while Figs.8.33 and 8.34 depict the post-failure states of the specimens with OPMC and geogridcompared to OMC alone for varying geomaterials and positioning of the geogrids.The fact that the geogrids contribute largely to the tensile stresses and tensile strainresistance while OPMC contributes immensely to compressive stresses and compressivestrain resistance can be clearly derived from these figures.

Fig. 8.34 (a) and Fig. 8.34(b) Comparison of Geogrid and OPMC effects for varyingGeomaterials and Modes of Stabilization and/or Reinforcement


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Some of the typical results determined from this study are presented in Figs. 8.35 to 8.40.The fact that both OPMC Stabilization Technique and the application of geogrids greatlyenhances the performance of geomaterials by increasing their strength, bearing capacity and

deformation resistance can be clearly seen from these figures as well as Figs. 10.1~10.3under section 10.

Fig. 8.35 Effects of Various Geosynthetic Locations and OPMC Stabilization on Axial Stress

Fig. 8.36 Effects of Various Geosynthetic Locations and OPMC Stabilization on Emax


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9. APPLICATION OF SOME NEWLY PROPOSED QUALITY CONTROL METHODSMeasured and field data collection would certainly serve no purpose if appreciable accuracy andconfidence levels are not achieved. Accurate and precise definition of the boundary limits ofspecification control can prove to be costly if they are not properly considered or tailored for a specific

project.

The basic principles of some of the main quality control methods developed by Mukabi (2001a) andMukabi et al. (2003) previously on other projects modified to suit the design and constructionspecification requirements for various Projects are introduced by Mukabi (2005a). Research on variousother QC methodologies is still on-going.

10 ANALYSES AND PREDICTION OF STRUCTURAL CAPACITY OF PAVEMENTSTRUCTUREThe basic objectives of undertaking this Study were to develop formulae that would enable theprediction of structural capacity of any pavement structure notwithstanding type and

configuration at any particular time mainly for maintenance purposes (also refer to section 11in this paper).

Fig. 8.37 Effects of Various Geosynthetic Locations and OPMC Stabilization on Elastic Limit Strain

Fig. 8.38 Effects of Various Geosynthetic Locations and OPMC Stabilization on Angle of InternalResistance

Fig. 8.39 Effects of Various Geosynthetic Locations and OPMC Stabilization on Ea(ELS)


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15.1log teSCtSC Nxff (10.2)

It is imperative, when undertaking the evaluation of the structural capacity of flexible-pavementstructures, to consider factors such as subgrade characteristics, pavement layer strength andconditions, load and traffic parameters, environmental conditions

1) Initial Structural CapacitySome of the major factors that affect the status or condition of a pavement structure include the

Relative Damaging Effect (RDeff.) introduced by Mukabi (2002c), which is related to the ESAL, variationin quality of materials prompted by environmental factors, deterioration in pavement layer thicknessthrough loss of aggregates and infiltration of inferior lower quality materials into the upper layers of thepavement structure.

As proposed by Mukabi (2002c), the concept of remaining life can be transposed or defined in terms ofthe existing structural capacity by application of the following equation.

WhereRe

SCf represents the existing structural capacity,

RLf = Remaining Life Factor,Re

SCf = Structural

Capacity Factor of a newly constructed or reconstructed pavement structure in which caseRe

SCf =1

and .effRD = 0.298 is the damaging factor while rf = defines contribution of a multitude of factors

affecting the magnitude of the damaging effect.

2) Deterioration in Structural Capacity with TimeSome of the major factors that contribute to the deficiency of the structural capacity and serviceabilitylevel with time of an existing pavement structure were mentioned in the preceding sections. Thisdeterioration with time is known to grossly affect the performance of a highway pavement structure.

The deterioration with time of the structural capacity factort

SCf after Nt = 2.2 year can be defined by

Equation 44 below proposed by Mukabi (2002c).

Given that Nt > 2.2 years and applying the above equations,the deterioration with time, of the structural capacity of a road

in Ethiopia with varying AC thicknesses, was computed.

Further basic formulae developed and adopted are presented below, while Figs. 10.1~10.3depict some of the results derived through the adoption of theses formulae.

11. PROPOSED METHODOF DETEMINING PERIOD

AND LEVEL OFMAINTENANCEEffective maintenance is aprerequisite in realizing anefficient road network in anycountry. In order to achieve aneffective road maintenancesystem, it is imperative that theanomaly between the actualneeds and available resourcesfor road maintenance is resolvedand subsequent implementation

of appropriate measuresundertaken accordingly. For

rfeffSCRL

e

SC xRDfff .Re (10.1)

Fig.11.1 Approach To Realize An Effective Road Maintenance System


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vmsecidfc tePPtfR a ,,,,, (11.1)

oijyi

oc

f

oc

f

oc

fdhfqpf e ,,',,',',' (11.2)

purposes of achieving this, it is imperative that plausible road maintenance sceneries are constructedobjected towards assessing the existence and magnitude of the need gap in order to draw upproposals that are both comprehensive and pragmatic in nature to integrate the relevant roadmaintenance components. This is demonstrated in Figure 11.1.

The following facts can be derivedfrom Fig.11.2.

1. Traffic loading conditionsand environmental factorsreciprocally influence eachother with time.

2. As the pavement structuredeteriorates due to loading,the impact ofenvironmental factors

becomes greater3. Road surface type hasdirect influence on both thestructural capacity andserviceability level of aroad.

11.1 Choice of Effective Methodof Analysis(1) Theories And/Or

ConceptsConsidered

The choice of an effective analytical method depends predominantly on the choice of the backboneengineering theories, principles and concepts and the extent to which they translate to pragmaticapplication. For these purposes, the theories and concepts applied are based on fundamentaltheories, principles and concepts introduced by Mukabi (2002c).

The generalized equation of the existing road conditions can be expressed as a function of loadingconditions, pavement type (structurally), pavement layer quality, structural thickness as well as intrinsicmaterial properties depicted in Equation 11.1.

Where,

cR = road condition, df = dynamic load factor, it =

response mode factor of layer of the pavement structure, cP = pavement configuration, eP = pavement

layer quality, et = structural thickness,v

msa = parameter delineating moisture suction variation

On the other hand, the extent of distress of deformation can be derived based on the theoriesintroduced in the preceding sections applied for carrying out back analysis of the deformation history ofa distressed pavement structure. In a generalized state, this can be expressed as shown in Equation45.

where,

dhe = parameter delineating deformation

history ' = consolidation stress ratio, ' = modifier between Isotropic and Anisotropic stress paths,oc

f

oc

f qp ,' = invariant stress under over consolidation conditions,,

f = Angle of Internal Friction within the

failure zone

Fig.11.2 Major Factors Influencing Road Conditions and their Reciprocal Interaction


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Details of the mathematical computation of these parameters are presented by Mukabi (2007e).

(2) Proposed Method of Determining Appropriate Maintenance ScheduleThe proposed approach of evaluating the structural capacity of a pavement structure under section 10has been applied as an effective method of determining the maintenance works and the respectivelevels of maintenance required.

The three serviceability and structural capacity characteristic curves depicted in Fig.11.3, which provedto be quite precise, were applied in determining the appropriate maintenance schedule and level for aroad in Ethiopia. Application of this method realized appreciable maintenance cost savings on longterm basis.Mukabi (2005) presents more details on this subject matter.

Fig. 11.3 Depiction of Determining Period and Level of Maintenance

12. PROPOSED MODE OF EMHANCING RESEARCH AND DEVELOMENT (R&D)

Fig. below is a depiction of the importance of upholding a three-tier system in developingpragmatic maintenance policies and effective management techniques, standards and designengineering of road infrastructure assets for ensuring appropriate and sustainabledevelopment. The practical maintenance techniques are presented in section 3 of this paper.


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MaintenancePolicy

Application ofAppropriateTechnology

Contractual &Implementation

Policy

Private

Sector AcademicInstitution

GovernmentInstitutions

Achievement of apragmatic and Advanced

Road SectorImplementation Policy

MaintenancePolicy

Application ofAppropriateTechnology

Contractual &Implementation

Policy

Private

Sector AcademicInstitution



Achievement of apragmatic and Advanced

Road SectorImplementation Policy

Fig. 12.1 Essence of the Three-tier System in Achieving Appropriate Maintenance PolicyMaking

Examples of Capacity Building Programs developed within this Region (Particularly Ethiopia)

Young Engineers Programmes for Public, Private and Academic Institutions

Technology Transfer for Engineers

Direct technology Transfer During Construction

Sponsored Programmes for Overseas Studies

Technical Training Programmes for Technicians

Direct technology Transfer During Construction

Sponsored Programmes for Overseas Studies

Expansion of Capacity Building Institutes

13. ONGOING RESEARCH

Currently the ongoing research is mostly related to the following topics.Other Topics in Relation to the New Technologies Incorporating Tensar and OPMC

- Research Related to Black Cotton or Expansive Soil

- Research Related to Intrusion of Underlying Material

- Research Related To Temperature in Seasonal Cycle Effects on The Bearing Capacity and

Resilient Properties

- Research Related to NDT/DT Testing for Evaluation of the Existing Condition of a Flexible

Pavement Structure

- Proposed Research Related to Consolidation and Shear Stress Functions for Foundation

Design and Construction

- Proposed Research to Relate Road Surface Distress Condition and Deformation and Failure


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CONCLUSIONSComprehensive testing and analytical methods were employed in this Study in order to realizethe most Value Engineering base

Documents

1 the Role of Enhanced Research in Geotechnical Engineering - PAPER (KEYNOTE LECTURE)