1607507773

PROCEEDINGS OF THE 15TH AFRICAN REGIONAL

CONFERENCE ON SOIL MECHANICS AND

GEOTECHNICAL ENGINEERING

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Proceedings of the 15th African

Regional Conference on Soil

Mechanics and Geotechnical

Engineering

Resource and Infrastructure Geotechnics in Africa:

Putting Theory into Practice

Edited by

Carlos Quadros

TCNICA-Engenheiros Consultores, Maputo, Mozambique

and

S.W. Jacobsz

Department of Civil Engineering, University of Pretoria, Pretoria, South Africa

Amsterdam Berlin Tokyo Washington, DC

2011 The authors and IOS Press.

All rights reserved. No part of this book may be reproduced, stored in a retrieval system,

or transmitted, in any form or by any means, without prior written permission from the publisher.

ISBN 978-1-60750-777-2 (print)

ISBN 978-1-60750-778-9 (online)

Publisher

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Preface

The Mozambican Geotechnical Society (SMG) organized with great pleasure the 15th

African Regional Conference on Soil Mechanics and Geotechnical Engineering in

Maputo. The valuable contribution of the South African Geotechnical Chapter particu-

larly in the review of the abstracts and papers is gratefully acknowledged.

The general theme of the conference was Resource and Infrastructure Geotechnics

in Africa: Putting Theory into Practice. More than half of the papers submitted by au-

thors are related to the construction of geotechnical works in Africa. Roads, airports,

bridges, dams, railways, among other significant works were the subject of these papers.

This signals a remarkable growth in the number of infrastructure projects that have

been carried out or are under construction in Africa.

The increasingly specialized nature of the construction works and some very diffi-

cult local conditions demand a deeper knowledge of soil mechanics and geotechnical

engineering and the involvement of large numbers of geotechnical engineers, as well as

specialists of related areas such as geology, rock mechanics, subsurface investigation

and field and laboratory testing. The drastic increase in the number of projects in the

mining industry will also create additional opportunities and challenges for geotechni-

cal engineers. The proper training of these individuals must be a priority in Africa. We

hope that this conference has made a significant contribution towards this goal.

The 94 papers submitted to this Conference are presented in 8 sections namely

Roads (17), Foundations (14), Lateral Support and Retaining Walls (11), Materials

Testing (16), Site Investigation (20), Environmental Engineering (5), Slopes (3), Dams

(2) and General (6). Three Keynote Lectures presented at the Conference on relevant

issues for the African continent are included in this volume.

The Editors wish to thank the authors for their valuable work in the preparation of

the papers and the members of the Organizing Committee and of the Scientific Com-

mittee for the assistance and engagement that made this publication possible.

The Editors

Proceedings of the 15th African Regional Conference on Soil Mechanics and Geotechnical EngineeringC. Quadros and S.W. Jacobsz (Eds.)IOS Press, 2011 2011 The authors and IOS Press. All rights reserved.

v

Conference Advisory Committee (CAC)

Samuel EJEZIE Vice-President of ISSMGE for Africa

Jean-Louis BRIAUD President of ISSMGE

Pedro Sco PINTO Immediate past President of ISSMGE

Neil TAYLOR Secretary General of ISSMGE

Mounir BOUASSIDA Immediate past Vice President of ISSMGE for Africa

Carlos QUADROS President of Mozambican Geotechnical Society (SMG)

Peter DAY Past Vice-President of ISSMGE for Africa

Etienne KANA Co-Chairman of 14th

ARC

Saturnino CHEMBEZE Secretary of Mozambican Geotechnical Society (SMG)

Conference Organizing Committee (COC)

Carlos QUADROS

Saturnino CHEMBEZE

Ivan MINDO

Adozinda MANHIQUE

Daniel TINGA

Elis JOS

Ernesto PALAVE

Fleyd CAMBALA

Sidney DE ABREU

Salomo JAMBE

Ilda SANTOS

Conference Scientific Committee (CSC)

Alan PARROCK

Ahmed ELSHARIEF

Carlos QUADROS

Deolinda NUNES

Eduard VORSTER

Esve JACOBSZ

Etiene KANA

Gavin WARDLE

Gerhard HEYMANN

Heather DAVIS

John MUKABI

John STIFF

Kamel ZAGHOUANI

Kolawole OSINUBI

M-Abdel BENLTAYEF

vii

Michelle THERON

Mounir BOUASSIDA

Nico VERMEULEN

Nicol CHANG

Peter DAY

Phil PAIGE-GREEN

Protus MURUNGA

Richard PUCHNER

Samuel AMPADU

Samuel EJEZIE

Trevor GREEN

List of Exhibitors

Organization/Company Country

ANE Mozambique

APAGEO France

ARA SUL Mozambique

CETA Mozambique

COBA Portugal

COLLINS Mozambique

CONTROLLAB France

DURA SOLETANCHE BACHY South Africa

FORDIA France

FRANKI AFRICA South Africa

GAST INTERNATIONAL South Africa

GEOCONTROLE Portugal

GEODRILL Mozambique

GEOMECHANICS South Africa

GIGSA South Africa

GUNDLE South Africa

HUESKER Germany

KAYTECH South Africa

LEM Mozambique

MACCAFERRI South Africa

MODENA Mozambique

MOTA- ENGIL Portugal

NAUE Germany

SEDIDRILL France

SOILLAB South Africa

STEFANUTTI STOCKS South Africa

TECNICA Mozambique

TEIXEIRA DUARTE Portugal

ZAGOPE Portugal

viii

Main Sponsors

ROAD FUND, Mozambique, www.fe.gov.mz

TCNICA-Engenheiros Consultores Ltd, Mozambique, www.tec.co.mz

CETA Construes e Servios S.A., Mozambique, www.ceta.co.mz

ROYAL EMBASSY OF DENMARK, Mozambique

TEIXEIRA DUARTE Engenharia e Construes, S.A., Portugal, www.teixeiraduarte.pt

FRANKI AFRICA, South Africa, www.esorfranki.co.za

Gold Sponsors

DURA SOLETANCHE BACHY, South Africa, www.durasb.co.za

SOARES DA COSTA, Mozambique, www.soaresdacosta.pt

MACCAFERRI Southern Africa, South Africa, www.maccaferri.co.za

Sponsors

GEOKON, USA, www.geokon.com

COBA Consultores de Engenharia e Ambiente, Portugal, www.coba.pt

ARQ Consulting Engineers, South Africa, www.arq.co.za

COLLINS Sistemas de guas Ltd, Mozambique, [email protected]

MODENA DESIGN Ltd, Mozambique, [email protected]

IT.COM Tecnologias de Informao e Comunicao, Mozambique, www.itcom.co.mz

HUESKER, Germany, www.huesker.com

SINAVIA Sinalizao e Pintura, Ltd, Mozambique, [email protected]

JONES & WAGENER Consulting Civil Engineers, South Africa, www.jaws.co.za

GUNDLE GeoSynthetics (Pty) Ltd, South Africa, [email protected]

ARA-SUL, Mozambique, [email protected]

UEM Universidade Eduardo Mondlane, Mozambique

ix

Contents

Preface v

The Editors

Committees and Exhibitors vii

Sponsors ix

Section 1. Keynote Lectures

The Advances in Everyday Geotechnics in Southern Africa over the Past

40 Years 3

Alan Parrock

Towards Developing Paving Materials Acceptance Specifications for Lateritic

and Saprolitic Soils 10

Mensa David Gidigasu

Use of Geosynthetics to Improve Seismic Performance of Earth Structures 40

Junichi Koseki

Section 2. Dams

Pathology of Foundation of Ghezala Dam, a Tunisian Case History 63

Mounir Bouassida, H. Karoui and Moncef Belaid

Injection of Contraction Joints at Pretarouca Dam 71

Antnio Costa Vilar and Duarte Cruz

Section 3. Environmental Engineering

The Challenge of Designing & Constructing Steep Landfill Capping Sealing

Systems Using Geogrid Veneer Reinforcement 77

Jrg Klompmaker and Burkard Lenze

Design of Soil Covers in Tropical Africa: A Perspective 83

Celestina Allotey and Nii Kwashie Allotey

Is There a Future for GCLs in Waste Barrier Systems? 89

Peter Legg and Molly McLennan

Design of Hazardous Waste Landfill Liners: Current Practice in South Africa 97

Riva Nortj, Danie Brink, Jonathan Shamrock, David Johns and

Jabulile Msiza

Geosynthetic Clay Liners: A Useful New Tool for Environmental Protection

in the Engineers Toolbox 104

Peter Davies

xi

Section 4. Foundations

Numerical Modeling of Skirted Foundation Subjected to Earthquake Loading 113

W.R. Azzam

Prediction of the Axial Capacity of Bored Piles Using Methods Based on CPT

and Static Analysis Approaches 119

Abdul Karim M. Zein and Samah B. Mohammad

Case History on the Design of Foundation for Oil Storage Tank on Coastal

Plain Sands 127

E.A.J. George, T.J. Atuboyedia and M. Oju

Moment-Induced Displacement of Offshore Foundation in the Niger Delta 133

S.U. Ejezie and S.B. Akpila

Lateral Response of Suction Caissons in Deep Water Floating Structures

off Niger Delta Coast 139

Samuel U. Ejezie and Baribeop Kabari

Foundation Design and Construction for an LPG Terminal in a Difficult Geology

and Constrained Waterfront in Coastal Lagos 145

Olaposi Fatokun and Gianguido Magnani

Variation of Hydrodynamic Forces and Moments on Offshore Piles in the Niger

Delta 152

S.B. Akpila and S.U. Ejezie

Contribution lAnalyse du Comportement des Pieux sous Chargement

Vertical Analyse dUne Base de Donnes Locale 158

Ali Bouafia and Abderrahmane Henniche

The Use of Micropiles as Settlement Reducing Elements 165

H.N. Chang and T.E.B. Vorster

Rigid Inclusions in Sand Formation Resting on Compressible Clay 175

Mounir Bouassida

Dynamically Loaded Foundations 183

Andr Archer

Construction of a Bridge over the Kwanza River at Cabala in Angola 190

Duarte Nobre, Francisco Caimoto and Baldomiro Xavier

Case Studies to Support Recent Advances in Geogrid Technology 196

Clifford D. Hall

Shaft Resistance of Model Pile in Wet Soil 202

Mohamed M. Shahin

Section 5. Lateral Support and Retaining Structures

The Effect of Anchor Post-Tensioning on the Behaviour of a Double Anchored

Diaphragm Wall Embedded in Clay 215

Amr Elhakim and Abdelwahab Tahsin

xii

Observed Axial Loads in Soil Nails 221

S.W. Jacobsz and T.S. Phalanndwa

Deformations of Soil Reinforced Walls in Relationship with Reinforcement

Used 228

Edoardo Zannoni, Marco Vicari and Moreno Scotto

Performance Comparison of Vertical-Horizontal with Conventional Reinforced

Soil Walls Using Numerical Modelling 237

Binod Shrestha, Hadi Khabbaz and Behzad Fatahi

The Behaviour Under Excavation of the Luandas Sandy Formation: Case

Studies 243

Duarte Nobre, Joo Pina and Baldomiro Xavier

Theoretical Evaluation of the Influence of Cohesion on Lateral Support Design 249

Jacobus Breyl, Gavin Wardle and Peter Day

Internally Instrumented Soil Nail Pull Out Tests 255

Jacobus Breyl and Gavin Wardle

Reinforced Soil Retaining Wall Systems Reach New Heights in the Middle East 262

Peter G. Wills and Chaido Doulala-Rigby

Deep Excavations in Luanda City Centre 269

Alexandre Pinto and Xavier Pita

Geotechnical Innovation in Shaft Sinking in the Zambian Copper Belt 275

G.C. Howell

The Use of Reinforced Soil to Construct Steep Sided Slopes in Order to Create

a Safer Highway Ruhengeri to Gisenyi Road, Rwanda 284

Peter Assinder, Heribert Schippers and Giuseppe Ballestra

Section 6. Materials Testing

Characterization of Shear Strength of Abandoned Dumpsite Soils, Orita-Aperin,

Nigeria 293

Kolawole Juwonlo Osinubi and Afeez Adefemi Bello

The Use of the Crumb Test as a Preliminary Indicator of Dispersive Soils 299

Amrita Maharaj

Some Engineering Properties of Fine and Coarse Grained Soil Before and

After Dynamic Compaction 307

Brian Harrison and Eben Blom

Using Electro-Osmosis Technique in the Improvement of a Ugandan Clay Soil 313

Denis Kalumba, Brenda Umutoni, Robinah Kulabako and

Stephanie Glendinning

Derived Empirical Relations and Models of Vital Geotechnical Engineering

Parameters Based on Geophysical and Mechanical Methods of Testing 320

John Mukabi

xiii

Quantitative Analysis to Verify the Theory of Soil Particle Agglomeration and

Its Influence on Strength and Deformation Resistance of Geomaterials 330

Sirmoi Wekesa, John Mukabi, Vincent Sidai, Sylvester Kotheki,

Joram Okado, Julius Ogallo, George Amoyo and Leonard Ngigi

Characterizing Bulk Modulus of Fine-Grained Subgrade Soils Under Large

Capacity Construction Equipment 337

Joseph Anochie-Boateng

Aspects Gologiques et Gotechniques Associs au Projet et la Construction

dun Tronon de lAutoroute de Dakar (Sngal) 343

Rui Freitas, Virglio Rebelo, Lus Ferreira and Andr Cabral

Characterization of Granular and Bitumen Stabilised Materials Using Triaxial

Testing 349

Kim Jenkins and William Mulusa

The Effect of Iron Oxide on the Strength of Soil/Concrete Interface 355

F. Okonta and A. Derrick

Moisture Retention Characteristics of Some Mine Tailings 360

S.K.Y. Gawu and J. Yendaw

Prediction of Over-Consolidated-Ratio for African Soil 366

Diganta Sarma and Moumy Dsarma

The Strength of Compacted Sand in a Modified Shear Box Apparatus 376

F. Okonta and D. Schreiner

Experimental Study on Use of Mechanically Stabilized Residual Soils for

Pavement Layers in Magoe, Mozambique 382

Raphael Ndimbo

Effects of Compaction on Engineering Properties of Residual Soils of Tete

Mozambique 389

Carlos Quadros and Raphael Ndimbo

Selection of Pavement Foundation Geomaterials for the Construction of a New

Runway 396

Joseph Anochie-Boateng

Suggested Improvements in Site Investigation and Numerical Characterization

Procedures for House Foundation Design 403

John Terry Pidgeon and Rachael Govender

Section 7. Roads

Improvement of Unbound Aggregates in Khartoum State 415

O.G. Omer, A.M. Elsharief and A.M. Mohamed

Applying the Dynamic Cone Penetrometer (DCP) Design Method to Low

Volume Roads 422

Philip Paige-Green

xiv

The Use of a Sedimentological Technique for Assessing the Engineering

Performance of Sands in Roads 431

Philip Paige-Green and Michael Pinard

Characterization of Pozzolanic Geomaterial for the Construction of Pavement

Structures of Songwe Airport in Tanzania 439

Paul Omindo, John Mukabi, Prosper Tesha, Vincent Sidai,

Sylvester Kotheki and Leonard Ngigi

Correlation Between the Dynamic Cone Penetration Index and the Falling

Weight Deflectometer-Determined Subgrade Resilient Modulus 446

Samuel I.K. Ampadu and Emmanuel Klu Okang

Fundamental Theory of the ReCap Technique and Its Application in the

Construction of Pavement Structures Within Problematic Soils 453

John N. Mukabi, Bernard Njoroge, Tilahun Zelalem, Samuel Kogi,

Maurice Ndeda and David Kamau

Utilisation des Btons Compacts au Rouleau (BCR) 460

I.K. Cisse and A. Sall

Pavement Rehabilitation Options for Developing Countries with Marginal

Road-Building Materials 468

Khaimane M.D. de Deus and Wynand Jvd Steyn

Applications of Participatory Road Maintenance Using Do-nou Technology

in Kenya 476

Makoto Kimura and Yoshinori Fukubayashi

Modlisation Numrique du Renforcement des Chausses non Revtues par

Gogrille 482

Mohamed Saddek Remadna, Sadok Benmebarek and Lamine Belounar

Reducing the Cost of Road Construction Through Targeted Geotechnical and

Geophysical Investigations A Case Study of Road Section Re-Design in the

Hwereso Valley of Ghana 489

C.F.A. Akayuli, S.O. Nyako and J.A. Yendaw

Appropriate Engineering Solutions for Rural Roads in Mozambique 495

Luis Fernandes and Irene Simoes

Preliminary Studies on the Utilization of Sand Treated with Emulsion 501

Luis Fernandes, Irene Simoes and Hilrio Tayob

Geosynthetics in Road Pavement Reinforcement Applications 507

Garth James

Treatment and Stabilization of the National Road E.N. 379-1 Hillsides,

Between Outo and Portinho da Arrbida 518

Jorge Dinis, Joo Pina and Baldomiro Xavier

Contraintes Gotechniques Associes la Construction de la Deuxime Piste

de lArodrome dOran en Algrie 524

Vicente Rodrigues, Mrio Roldo and Antnio Silva

xv

Effect of Geosynthetic on the Performance of Road Embankment on Algeria

Sabkha Soils 532

Sadok Benmebarek, Naima Benmebarek and Lamine Belounar

Section 8. Site Characterisation

Geotechnical Characteristics of the Portuguese Triassic Mudstones 541

Mrio Quinta-Ferreira

Hydraulic Conductivity of Compacted Foundry Sand Treated with Bagasse Ash 545

Kolawole Osinubi and George Moses

Subsurface Conditions in Central Khartoum 551

Eisa A. Mohamed and Ahmed M. Elsharief

An Alternative to the Re-Drive for Determining Rod Friction Exerted in DPSH

Testing 559

Charles MacRobert, Denis Kalumba and Patrick Beales

Empirical Equivalence Between SPT and DPSH Penetration Resistance

Values 565

Charles MacRobert, Denis Kalumba and Patrick Beales

The Dynamic Probe Super Heavy Penetrometer and its Correlation with

the Standard Penetration Test 571

Brian Harrison and Tony ABear

The Potential of Using Artificial Neural Networks for Prediction of Blue Nile

Soil Profile in Khartoum State 580

H. Elarabi and M. Mohamed

Using a Modified Plate Load Test to Eliminate the Effect of Bedding Errors 587

Hennie Barnard and Gerhard Heymann

Geotechnical Characterization and Design Considerations in the Moatize

Coalfields, Mozambique 593

Gary N. Davis, T.E.B. Vorster and Clia Braga

Estimating the Heave of Clays 599

A.D.W. Sparks

Instrumentation and Monitoring During Construction of the Ingula Power

Caverns 605

G.J. Keyter, M. Kellaway and D. Taylor

Piezocone Investigation of Paleo River Channels at Changane River,

Mozambique, for a Railway Embankment 611

H.A.C. Meintjes and G.A. Jones

Site Selection of the Mathemele Landfill 620

Carlos Quadros and Ivan Mindo

Hazard Assessment on Shallow Dolomite 626

Tony ABear and Lindi Richer

xvi

Correlations of DCPT and SPT for Analysis and Design of Foundations 632

Dalmas L. Nyaoro and Mwajuma Ibrahim

The Effective Porosity Paradigm and the Implications on Empirical

Permeability Estimations 638

Matthys A. Dippenaar and J. Louis van Rooy

Numerical Modelling of Wave Propagation in Ground Using Non-Reflecting

Boundaries 644

S.J. Mbawala, G. Heymann, C.P. Roth and P.S. Heyns

Geotechnical Characteristics of the Red Sands of Chibuto, Mozambique 653

H.A.C. Meintjes and G.A. Jones

Simple Expansion Model Applied to Soils from Three Sites 663

A. Dereck W. Sparks

Correlation Studies Between SPT and Pressuremeter Tests 669

Emmanuel Kenmogne and Jean Remy Martin

Section 9. Slopes

The Value of Slope Failure Back-Analysis in Open-Pit Slope Design: A Case

History from the South African Coalfields 679

Mmathapelo Selomane and Louis van Rooy

General Slope Stability Using Interslice Forces and Flow Nets but Avoiding ru

Factors 685

A.D.W. Sparks

Pit Slope Design Near Tete, Mozambique, Without the Benefit of Previous

Slope Performance Experience 691

Phil Clark

Section 10. General

quations et Exemple de Calcul Hydrique dans les Sols Non Saturs 701

Abdeldjalil Zadjaoui

Processus de la consolidation des sols peu cohrents saturs 709

Mohamed Salou Diane and Salou Diane

The African Regional Conferences as an Indicator of Research Trends

in South Africa 719

Philip Paige-Green

Geotechnical Investigations: Over-Regulated or Under-Investigated? 726

Tony ABear and Louis van Rooy

Challenges to Geotechnical Engineering Practice in the Urbanization of the City

of Accra, Ghana 730

J.K. Oddei

xvii

Soil Improvement Through the Utilization of Agricultural Residues from

Nigeria 736

N.L. Obasi and E.B. Ojiogu

Subject Index 743

Author Index 747

xviii

Section 1

Keynote Lectures

THE ADVANCES IN EVERYDAY

GEOTECHNICS IN SOUTHERN AFRICA OVER

THE PAST 40 YEARS

Alan PARROCK

Managing Director/geotechnical principal of ARQ Consulting Engineers (Pty) Ltd

Abstract. In this paper, the author looks back at the developments in everyday

investigations, testing and analysis that have taken place in geotechnical

engineering during his 40 year career in the industry to date. Demonstrating how

the use of public information freely available on the internet can allow

geotechnical practitioners to reduce early project risk, the author goes on to discuss

and explore modern equipment and techniques that allow important information to

be more-readily and less-intrusively recovered and processed; providing

substantially better strength information and predictions of behaviour under load.

The use of the computer to reduce human error and involvement in testing is

discussed, alongside the obvious benefits now routinely possible through broader

and more sophisticated and representative analysis techniques. Looking forward

on the basis of past and recent technological progress, the author attempts to

explore and predict the developments in geotechnical engineering that we might be

likely to see over the coming 4 decades.

Keywords. Past, present future, satellite imagery, hyperstectral, fibre optics.

Introduction

This paper initially examines the early years in the authors geotechnical career and

how the mode of operation changed from those basic computer starts to what is now

the norm. It ends by attempting to make a prediction of what the next 40 years has in

store for the geotechnical practitioner.

1. The Early Years

The four decades prior to 2011 comprised the 70s, 80s, 90s and the post millennium

2000s.

1.1. The 70s

During the 1970s the computer was a monster tucked away in a locked air conditioned

room, computer input was via punched cards, programming via FORTRAN and

certainly in the early years of that decade, not many people utilised an electronic

calculator. The authors first purchase of a calculator was in 1973 and, as it cost four

Proceedings of the 15th African Regional Conference on Soil Mechanics and Geotechnical EngineeringC. Quadros and S.W. Jacobsz (Eds.)IOS Press, 2011 2011 The authors and IOS Press. All rights reserved.doi:10.3233/978-1-60750-778-9-3

3

times his monthly salary, he was forced to share it with his brother. They alternated on

six month cycles. The authors first exposure to some form of desktop computer was

when he was employed in the Natal Roads Department and the Materials department

owned a Wang. Wikipedia indicates that this was likely to be the LOCI-2 introduced

in 1965. It was the first desktop calculator capable of computing logarithms which

apparently was quite an achievement as it did not use integrated circuits but was

equipped with 1275 discrete transistors.

Wang Laboratories (WL) was founded in 1951, peaked in 1981 with annual

revenues of $3billion and employed 33 000 people at the time. WL filed for

bankruptcy in 1992.

The Wang in the Materials department was used to write a program to calculate

gradings, Atterberg limits and the A type classifications (A1 to A7).

In the absence of what are now readily-available geological maps, not much data

could be gleaned in the pre-investigation phase other than that known to locals and

available at small-scale in geological literature. The industry thus developed a means

to address this and many soil survey firms were active in establishing the geology of

routes traversed by roads. Roads were enjoying their heyday at that time [1].

It is of interest to note that the first Bidim geosynthetic was imported from France

to RSA in 1971. Local manufacture of the product started in 1978 and during the 70s

some 1-2 million m2

were used in civil engineering projects. [2].

The norm for a geotechnical foundation investigation comprised backactor-

excavated test pits for shallow deposits while deeper profiles were characterised via

core drilling supplemented with Standard Penetration Testing (SPT) and possibly vane

shear testing [3]. Undisturbed samples were retrieved from the core via U4 or Shelby

tubes.

Triaxial testing of undisturbed samples was conducted via hand or machine

controlled rates of deformation, which were measured by dial gauges read and recorded

manually.

Analysis of results and calculations were performed using a slide rule in

conjunction with trigonometric tables. The time thus taken, for example, to perform a

single circle slope stability evaluation was usually about an hour when the somewhat

inaccurate Fellenius solution method of slices was used.

This error was reduced when the formulations of Bishop [4] were incorporated, but

additional time was required to generate an answer as a process of successive

approximation was necessary to obtain a solution to an equation in which the required

variable F appeared on both sides of the equation.

The first Brink book was published in 1979 and the wealth of information held

privately was made available to a much wider audience via reports on case studies.

Although the proceedings of the 5th

Regional Conference for Africa (ARC) held in

Luanda in 1971 and the 6th

in Durban in 1975 occupy the authors bookshelf, he did not

attend them as he was no doubt much too young and inexperienced to know about

those illustrious authors and occasions. The 7th

ARC took place in Ghana in 1979 but

South Africans were not permitted to attend. [5] Davis [5] also details that the 1st

ARC

was held in Pretoria in 1955, the 2nd

in Loureno Marques, Mozambique (sounds

familiar) in 1959, the 3rd

in the then-named Salisbury of Southern Rhodesia, and the 4th

in Cape Town in 1967. It certainly is good to have it back here in 2011 after an

absence of 52 years.

A. Parrock / The Advances in Everyday Geotechnics in Southern Africa over the Past 40 Years4

1.2. The 80s

Much progress had taken place on the computer front especially during the last few

years of the 1980s. Word processing, which had started out with WordStar, had

progressed to WordPerfect. The spreadsheet of choice was Lotus 123. Certainly, the

technical computer programs were still dominated by those based on the programming

language FORTRAN and it was only in the later stages of the 80s that the platforms

that these ran on became PCs as opposed to the mainframe VAXs and PRIMES which

appeared to rule the roost technically.

Local geological maps were more readily available with the Geological Map of

Johannesburg at a scale of 1:5 000 being prepared by JH de Beer in 1985. In addition,

detailed data for the area was available from records held by the Johannesburg Data

Bank.

Volume 2 of Brink was published in 1981, Volume 3 in 1983 and the final Volume

4 in 1985.

The use of the pressuremeter as an investigation tool was introduced to South

Africans in 1980 by Professor CP Wroth of Cambridge University [5] and locally

Michael Pavlakis was a proponent of its use. It was used by the author during 1982 as

part of the investigation for a 26m deep basement for the planned SA Transport

Services Computer Centre located in the Ventersdorp lava of the Johannesburg graben.

Probabilistic analysis methods were first mooted in RSA by Milton Harr in 1980

and this was followed in 1982 by Dimitri Grivas who expanded on Harrs initial

approaches. The attributes of the beta distribution and the point-estimate method were

certainly employed by the author in many applications, especially as the computer was

becoming more useable for everyday analyses.

The development in the 80s was frenetic and this was reflected in the number of

courses, symposia and conferences which were organized: grouting; ground anchors,

slope stability and piling to name a few. The problem materials, collapsible and

dispersive soils, soft and heaving clays and dolomites and their residuum were also

very well covered. On the investigation front, other than the Pressuremeter, the Dutch

probe and the later derivative, the Piezocone, were enjoying much success especially

when used as an investigation tool for the soft alluvial deposits of the Kwa-Zulu Natal

coastline. Essentially the same techniques employed in the 70s were used in the 80s for

shallow and deeper drilling projects.

The now ubiquitous 1:250 000 geological maps issued by the Council for

GeoScience were also making their appearance. Initially confined to the more

populated areas, the series was later expanded to include all of RSA. It was

supplemented on a regional basis by 1:50 000 scale versions for the Pretoria region.

The 8th

ARC took place in Salisbury in 1983 and the 9th

in Lagos Nigeria in 1987

(again South Africans were not permitted to attend).

1.3. The 90s

The Lateral Support Code, although dated 1989, was released in 1990 and offered

many opportunities to those involved in this exciting field.

The XT computers of the late 80s were replaced by the 286s and 386s and most

engineers had one on their desks. The DOS operating system gave way to Windows

and Quattro Pro was the spreadsheet of choice at the beginning of the decade later to be

replaced by Excel. On the word processing front, WordPerfect was superseded by

A. Parrock / The Advances in Everyday Geotechnics in Southern Africa over the Past 40 Years 5

Word, AutoCad was the draughting package used by most and programming was a

mixture of C, Pascal and other languages. Finite element analyses, almost exclusively

the domain of larger organisations, universities and research establishments, were now

being used more and more as the PC become more powerful. Certainly the authors

first stab at a geotechnical FE package came about in 1994 running SOILSTRUCT on a

286. This used the non-linear hyperbolic Duncan Chang [6] and Duncan et al [7]

formulations as the basis for the code which was written in FORTRAN.

The Prokon geotechnical computer programs were released in 1994 running under

the DOS operating system. These packages were a joint venture between ARQ and

Prokon and all incorporated probabilistic modules which were initially written in the

late 80s and early 90s in FORTRAN. The programs operated under DOS and it was

not unusual during the simulation routines which often comprised 10 000 iterations,

that the computer would be busy for 5-10 minutes.

The electronic aspects of geotechnical engineering certainly came of age in the

90s. The first e-mail was installed at ARQ in 1996 and in 1998 the Geotechnical

Division of SAICE established their web site.

Reports with many pages in colour became the norm, although drawings were

almost exclusively issued in black and white. The issue of reports to Clients was

however usually only done in hard copy paper format.

The use of Bidim geosynthetic had increased to 5million m2

per year. Recycled

two litre cool drink bottles were initially used in the manufacture of this product

starting at a rate of 10% and reaching 100% in 1995. The first high strength

geosynthetics were imported from overseas sources circa 1995 which was

supplemented later by local manufacture

The 10th

ARC took place in Lesotho in 1991 and as political change was about to

happen, South Africans were permitted to attend. The 11th

ARC was held in Egypt in

1995.

The highlight of the 90s, certainly from a personal knowledge point of view, was

attending the International Conference on Soil Mechanics and Foundation Engineering

hosted in Hamburg Germany in 1997. At that conference it was decided that the

Foundation part of the title would be replaced and that the organisation would in

future be known as the International Society for Soil Mechanics and Geotechnical

Engineering or ISSMGE. Here the most significant part of the proceedings which

impacted the author was the work which had been conducted by Oshima and Tokada

[8] on dynamic/ram compaction and that by Mark Randolph on the beauty of using

piled rafts to equalise settlements under large structures.

This occasion was complemented two years later when attending the 12th

African

Regional Conference held in 1999 in Durban. The information provided at the mini

symposium on the Sunday preceding the conference by Chris Clayton on the SPT has

been used on numerous occasions in the intervening 12 years.

2. The New Millenium

The start of 2000 was meant to be the time when the Y2K pandemonium reigned. Of

course, it was only a perceived threat dreamed up by the computer guys to increase

revenue. The effect on the geotechnical fraternity was minimal.

Perhaps the defining moment in 2003 for the author was the 2nd

Jennings lecture

delivered by Harry Poulos entitled Foundation design: the research practice gap in


which this eminent pragmatist demonstrated that much common sense is necessary in

interpreting high level (theoretical) analysis. This was aptly illustrated when in 2003

the ARQ foundation design for a 20 storey building in Luanda, comprising a piled raft

solution, was challenged by an international expert (IE) as to the settlement predictions

made. ARQ predicted the central raft would settle between 11 and 20mm while the IE

was of the opinion that the value would be some 175mm. Serious political fallout

followed this assertion and thousands of additional hours and R1m extra was spent in

ensuring a deflection of this magnitude could be accommodated by the building. The

deflection of the building was monitored and needless to say when, at the end of

construction, deflection was only 12mm, the IE was nowhere to be seen.

The 14th

ARC held in December 2003 was attended in beautiful Marrakech,

Morocco. Many delegates had a nightmare trip to get there [9] as most either had first

to fly to Paris or jet in from Dubai. The author had a most memorable return trip 1st

class on Air France due to a mix up in booking. The six course meal (with a different

wine for each course) was something to behold and when he awoke (somewhat

groggily) the next morning, the plane was directly over an airstrip which he had built in

1978/79 in the central Caprivi of Namibia. The memories flooded back and who says

it is not fun being a geotechnical engineer?

In 2005 a personal highlight was being asked to be the Godfather to the Young

Geotechnical Engineers Conference held at the Swadini Spa. Much useful information

was gained from the many and divergent papers presented and it was a delight when a

Black man and a young lady were adjudged to have the best technical paper and the

best presentation respectively. The prize for this was a trip to attend an international

conference in Tokyo and for the recipients this was one of the highlights of their lives.

The Commemorative Journal of the SAICE Geotechnical Division was published

and much of the data contained in this presentation comes from that publication. the

author gives eternal thanks, to his friend and colleague, Heather Davis.

Computers became faster (they never get cheaper), colour reports and drawings

were the order of the day, although most reports and plans are exchanged electronically

in .pdf format. The cost of finite element (FE) software for the modeling of complex

geotechnical solutions enabled most geo-practitioners to at least own a 2-d version.

Google became part of our lives. It was established in 1998, and its initial public

offering followed in 2004. The companys stated mission from the outset was to

organize the worlds information and make it universally accessible and useful.

Google Earth is used on every ARQ geotechnical report for the location of the project.

The 3d viewing facility enables geological formations to be spotted with ease by the

trained eye and the Street View facility provides the ultimate in gaining information at

the desk top study stage. This latter facility has been used extensively to provide input

to the designers of fibre-optic cable routes in establishing quantities of hard and soft

material.

On the investigation front, continuous surface wave (CSW) testing is now the

norm for most projects where knowledge of the stiffness of material at depth is

required. Recent advances in interpreting the data have eliminated the hard layer

overlying a soft one conundrum.


3. Summary

Thus whereas the practice of test-pitting, core-drilling and seismic testing have

essentially remained constant over the past 40 years, other field investigation

techniques including piezocone, pressuremeter, CSW, resistivity, gravity and the like

have seen the light of day and are now considered the norm.

However, with the advent of fast computers, analysis techniques have progressed

in leaps and bounds.

4. The Next 40 Years

The past has been easy to document, but what about the future?

No doubt, computing power will increase exponentially as it always has. This will

enable finite element and/or finite difference models to be constructed, probably in

three dimensions, and analyses to be performed in static and dynamic modes and the

outputs represented either deterministically or as single-valued solutions.

Alternatively, it may well be more common to have the answers registered in a

probabilistic sense where the solution will be depicted in a band of values with variable

probabilities assigned.

Remote sensing will in all likelihood become the order of the day. It is not

difficult to imagine electronically flying to your site of choice, requesting

information such as elevation, slope-angles, rainfall, geology at surface and depth,

geothermal attributes (conductivity) and any other available attributes which have been

put together in a public domain data base populated from information gathered during

numerous satellite passes over the site.

Already change in groundwater depth is determined by mapping, on successive

satellite passes, the change in surface elevation [10]. It is not difficult to comprehend

why. A change in, say, 10m depth of water table induces an effective stress change of

some 100kPa. 100kPa acting over a soil profile with an E-value of, say, 50MPa would

induce a surface deflection change of some 20mm. This is well within the accuracy of

satellite predictions at present.

Permeability of the worlds surface to depths of 100m has also recently become the

norm [11]. Imagine the benefit to groundwater studies.

Hyperspectral imagery [12] obtained from an airborne platform enables spectral

signatures of various minerals e.g. quartz and kaolinite, plant types and salts, to be

mapped over vast areas. These, in turn, can be interpreted to yield probable

performance in terms of suitablity for road aggregates, expansivity and salt damage

potential, to mention but a few.

The performance of structures will be monitored, especially during extreme events,

via fibre-optic cables installed within structural elements embedded in the earth.

Compressive and tensile forces in foundation elements would be able to be monitored

under, say, earthquakes or tsunamis. The propensity for movement of high rock slopes

in open pit mines or railway/road cuttings would be monitored remotely and if a danger

to personnel or the public was imminent, this could be communicated to them via

variable message signs or SMSs on cell phones.

Top-of the-range construction machinery will become larger and more powerful

although, as has been demonstrated in the airline industry, the majority of the work will

in all likelihood be done by a much more modest machine. It is, however, not difficult


to imagine that auger machinery of the future may well be able to install piles in excess

of 3m diameter to depths which may be as deep as 100m. Geothermal drill holes to

some 100m depth will be done with specialised multi-casing percussion rigs such that

pollution of the substrata does not result.

Intelligent geosynthetics will be the order of the day. They will be able to sense

pollutants and, via either chemical injection or electrical change, alter the pollutants to

render non-toxic end products.

The day-to-day investigations may well be accomplished in a non- destructive

manner. Prior planning based on Google Street View images will enable estimates to

be made of depth to hard material by examining the plant types present and knowing

root penetration potential. Waves will be injected into the ground and response

measured. Here one or more of the following: CSW, infra-red, ground penetrating

radar, resistivity, magnetics and the like, will probably form the core of what will be

done. However one asks, will the backactor be made superfluous ? Probably not.

5. Conclusion

This note has attempted to span some 80 years, the past 40 and those that lie ahead.

Future predictions are notoriously arbitrary and it may well be that the predictions

made by the author could be way off and a technology that does not even exist at

present, could become the norm. Watch this space.

References

[1] Taute A 2011. Personal communication. Speech delivered at the offices of Vela VKE during the going-

away ceremony for a retiring staff member.

[2] James G. 2011. Personal communication. Telephone conversation with the marketing director of a

large geosynthetics company .

[3] Blight, GE. 1970. In situ strength of rolled and hydraulic fill. ASCE Journal of Soil Mechanics and

Foundations Division. May. pp. 881-899.

[4] Bishop AW. 1955. The use of the slip circle in the stability analysis of earth slopes. Geotechnique No 4

pp 128-152.

Bishop AW. 1955. The use of the slip circle in the stability analysis of earth slopes. Geotechnique No 5

pp 7-17. Bjerrum L. 1963. Discussion, Proceedings of the European Conference on Soil Mechanics and

Foundation Engineering, Wiesbaden. Volume 3.

[5] Davis, H. 2006. Concise history of the geotechnical division of the South African Institution of Civil

Engineering. pp xi-xxix. Extract from the Commemorative Journal of the Geotechnical Division of the

South African Institution of Civil Engineering.

[6] Duncan, JM and Chang, C-Y. 1970. Nonlinear analysis of stress and strain in soils. Journal of the Soil

Mechanics and Foundation Division of the ASCE. Volume 96 Number SM5 September pp 1629-1653.

[7] Duncan, JM, Byrne, P, Wong, KS and Mabry, P. 1980. Strength, stress-strain, and bulk modulus

parameters for finite element analyses of stresses and movements in soil masses. Report No

UCB/GT/80-01 of the Charles E. Via, Jr. Department of Civil Engineering, Virginia Polythechnic

Institute and State University. 70 pp plus Appendix detailing FORTRAN computer printout listing.

[8] Oshima, A and Takada, N. 1997. Relation between compacted area and ram momentum by heavy

tamping. Proceedings of the 14th International Conference on Soil Mechanics and Foundation

Engineering, Hamburg 6-12 September Volume 3. pp. 1641 - 1644.

[9] Vermeulen N 2003. Personal communication during an airport meeting to the 14th

ARC in Morocco.

[10] Young, Susan. 2011. Monitoring groundwater aquifers in agricultural regions. www.stanford.eu

[11] Balma, Chris. 2011. Global map of surface permeability. [email protected]

[12] Fortescue, Alex. 2011. Hyperspectral imagery solutions. Position IT March 2011 pp. 54-58.


Towards Developing Paving Materials

Acceptance Specifications for Lateritic and

Saprolitic Soils

Mensa David Gidigasu1

Comptran Engineering and Planning Associates, Accra, Ghana,

Formerly: Director, Building and Road Research Institute (BRRI/CSIR)

Kumasi-Ghana

Abstract. The principle of ideal grading, low plasticity and higher compactive

effort producing higher density and higher bearing strength of the compacted

material for satisfactory pavement performance has characterized pavement

materials acceptance specification requirements and practices related to the

temperate zone countries. Investigations of cases of premature distress and

deteriorations of pavements in some tropical environments have revealed that in

addition to selecting well-graded gravels and aggregates to produce high

compaction densities and bearing strengths for design, serious attention should

also be given to the influence of the nature, geo-chemical, chemical and

mineralogical compositions of the materials, testing and geomechanical rating

procedures, construction techniques, as well as pavement maintenance history and

environmental conditions. For tropically weathered materials formed in diverse

climatic and drainage conditions, there is the need for materials oriented approach

that integrates relevant aspects of such fields as engineering geology,

geomorphology, geochemistry, petrography, pedology, climatology, rock and soil

mechanics, innovative roadway design and construction methods as well as cost-

effective roadway management and maintenance strategies, etc. A key component

of this approach would be the construction and instrumentation of road test

sections in relevant climatic, geologic, soils and drainage conditions for long-term

serviceability and structural integrity assessment and evaluation. The objective of

this lecture is to highlight the key factors, characteristics and parameters useful for

developing materials oriented paving materials acceptance specifications for

lateritic and saprolitic soils.

Keywords. Geomechanical rating, pedology, acceptance specification, lateritic

soils, saprolitic soils.

1. Introduction

Highway geomechanical engineering and roadway construction in the tropics are very

important as many countries are expanding their road networks to improve

communication and infrastructural developments. As part of this development, roads

are built to a wide range of standards from simple earth roads to provide rural access to

all-weather gravel roads and to paved roads usually with bituminous surfacings which

are designed to carry heavier traffic.

1

Corresponding Author.

Proceedings of the 15th African Regional Conference on Soil Mechanics and Geotechnical EngineeringC. Quadros and S.W. Jacobsz (Eds.)

IOS Press, 2011 2011 The authors and IOS Press. All rights reserved.

doi:10.3233/978-1-60750-778-9-10

10

The design standards of the roadways need to be appropriate to the type of road

that is being built so that total transportation costs can be minimized. One way of

helping to achieve this is to ensure that best use is made of the locally occurring

materials and aggregates that are available. The development of specifications for

temperate zone paving materials has been the results of tedious and long-term

laboratory and field studies. The process has been a combination of theoretical and

practical definition of optimum grading characteristics of materials that would yield the

highest compaction density (e.g. Fuller and Thompson, 1907; Zemour and Durrier,

1966) and the relation between the fines, gravel contents and plasticity and the desired

grading curves (e.g. Dunn, 1966). The strength and breakage behaviour of aggregates

during construction and under traffic loads have also been extensively studied both in

the laboratory and during pavement construction and in-service (e.g. Shelburne, 1939,

1941; Shergold, 1948; Shergold and Hosking, 1963; Melville, 1948; Dunn 1966; Day,

1962; Farrah and Thenoz, 1960). The effects of geological, petrographical, physical,

chemical and mineralogical factors on the laboratory and field test data for paving

gravels and aggregates have also received serious studies (e.g. Hartley, 1974; Lee and

Kennedy, 1975; Reed, 1967; Scott, 1955; Wylde, 1975, 1976). The results of these and

other investigations have resulted in the formulation of useful specifications for paving

gravels and aggregate materials in different temperate zone countries (e.g. Zemour and

Durrier, 1966).

The development of paving materials specifications for tropical materials has not

resulted from systematic European and North American methodologies of long-term

laboratory and field construction and in-service performance studies. In fact, the

temperate zone paving materials specifications have in some cases been transferred to

tropical environments without local assessment for application in varied tropical and

sub-tropical climate conditions. The use of non-traditional tropical lateritic and

saprolitic materials in pavement construction has posed many problems. Some light

has been thrown on the difficulties involved in utilizing other equally abundant and

unpredictable tropical and residual materials. For example, collapsing residual and

transported materials constitute problem paving materials in different parts of the

tropics (e.g. Knight and Delhen, 1963). Similarly, the salt bearing soils are problem

road materials in the Mediterranean areas and extensive studies on these materials have

resulted in developing some useful guidelines relating to their utilization (e.g. Fookes

and French, 1977). Failure resulting from the use of natural aggregates containing

soluble salts has also been reported by Blight (1976). Pavement performance on

expansive soils has also been a source of concern in many parts of the tropics. For

example, cases of heave of pavements on these soils have been extensively reported

(e.g. Williams, 1965). As regards lateritic and saprolitic paving materials a lot of

published information is available scattered in various sources.

Attempts have been made to summarize relevant information relating to

developments in road way construction practices using some of these problem

materials in the tropics (e.g. ISSMFE, 1982-1985). It has been shown (e.g. Little, 1969;

Lohnes et al., 1971, 1976; Gidigasu, 1974, 1976; Brand and Philipson, 1985; ISSMFE

1982, 1985, 1988) that lateritic and saprolitic materials constitute a chain of materials

ranging from decomposing rocks to lateritic (pedogenic) rocks. These materials differ

from one another in many respects; compositional (physically, chemically, structurally

and mineralogically) and useful methods of testing and evaluating each group or grade

of these materials for construction have been shown to be different in many respects

(e.g. Gidigasu, 1976).

M.D. Gidigasu / Towards Developing Paving Materials Acceptance Specications 11

The purpose of this lecture generally stems from the recognition that a need exists

to build knowledge of problem and unstable tropically weathered and residual soils

relative to highway geomechanical practice in the tropics. The lecture attempts to

highlight elements of good (acceptable) and poor (unacceptable) aggregates, gravels

and soil specification practices It is hoped that this and other contributions will

engender a renewed appreciation of the importance of soil science (pedology), geology

and mineralogy to understanding the engineering behaviour of major soils, tropical and

non-tropical (Clemente, 1981).

2. PROBLEMS OF DEVELOPING SPECIFICATIONS FOR TROPICAL

PAVING GRAVELS AND AGGREGATES

Generally, many local gravels abound in the tropics. The characteristics of some

lateritic gravels and stones are discussed elsewhere (e.g. Hammond, 1970).. The degree

of desiccation, clay mineralogy and the cementing effects of salts (Al2O

3 or Fe

2O

3)

have significant influence on the grading, Atterberg limits and strength of some

lateritised soils (Lohnes et al., 1971, 1976). For detailed discussion on this subject one

could refer to other sources (e.g. De Graft-Johnson, Bhatia and Hammond, 1972; De

Graft-Johnson, Bhatia and Gidigasu, 1969; Gidigasu, 1976; Millard, 1962; Nanda and

Krishnamachari, 1952; Philip, 1952). Careful choice of pretesting preparation of

samples and testing procedures are required to obtain reproducible results.. Most of the

standard aggregate tests are applicable to most tropical decomposing rocks, soft

aggregates, lateritic gravels, and crushed lateritic stones (e.g. De Graft-Johnson et al.,

1972; Gidigasu, 1976). There are, however, cases where these tests are unable to

provide good prediction of their behaviour in pavements. Sometimes, climatic

conditions and rapid rate of chemical weathering of pavements negate the usefulness of

these tests. Consequently, attempts have been made to evolve new and non-traditional

test procedures which are more predictive of their in-service behaviour. For example,

the so-called modified aggregate impact test, ten percent fines test, drying and wetting

test, acidity soundness tests have been found very useful (e.g. Tubey and Beaven, 1966;

De Graft-Johnson et al., 1972; Hosking and Tubey, 1969; Netterberg, 1971).

The most significant contribution to the study of doubtful tropical and sub-tropical

aggregates have been made in Australia by Wylde (1975, 1976), and in South Africa by

Weinert (1961, 1964, 1965, 1968, 1980; Weinert and Clauss, 1962, 1967). Other areas

of significant contributions have been shrinkage, specific surface tests (e.g. Roper,

1950), Methylene absorption test (e.g. Davidson, 1972). Washington degradation test

(e.g. Davidson, 1972) and secondary mineralogical studies (e.g. Weinert, 1964, 1980;

Scott, 1955) as well as petrographical and mineralogical tests (e.g. Wylde, 1976).

Typical results of factors affecting the compaction results are also reported elsewhere

(e.g. Gidigasu, 1976; De Graft-Johnson et al., 1972). The genetic variability and

influence of compositional factors have also been shown to influence correlations

between properties for some soil deposits and no correlations for similar deposits (e.g.

Gidigasu and Bhatia, 1971). Climatic conditions of the formation of the soils have also

been found to influence correlations between index and significant highway

geotechnical properties (e.g. Gidigasu and Mate-Korley, 1984). Consequently, it is

appropriate to emphasize the need to introduce climatic indicators in evaluating paving

materials in the tropics.

M.D. Gidigasu / Towards Developing Paving Materials Acceptance Specications12

2.1. Importance and Limitations of Ideal Grading Specifications for Paving

Aggregates and Gravels

Grain size distribution is a key property of aggregates. It affects the stability and

durability of bituminous concrete, as well as the stability and drainage of pavement

layers. Aggregates may be dense, well-graded, uniform, open, gap or skip graded. The

densest aggregate gradation provides the greatest durability by minimizing air voids,

but sufficient room will not be available for traffic compaction, and the asphalt cement

may flow to accumulate at the surface of the mix, a phenomenon known as bleeding.

Of the many methods of expressing size distribution, the most important one relates to

Equation 1 where d represents the sieve size in question, P is the percent finer than the

sieve, D is the maximum size of the aggregate, and n is a coefficient which adjust the

curve in a finer or coarser position:

n

D

d

100P

=

Equation 1

Studies by Fuller and Thompson (1907) have indicated that a maximum density

may be achieved for an aggregate when n = 0.5. The Fullers Curve is only an

approximation of maximum density, since actual gradation required for maximum

density depends partly on the nature of the materials. However, it is a remarkably

useful point of reference for designing aggregate blends for maximum density. Control

of gradation to yield the type of base sought, whether it be densely graded for

maximum stability or open graded for maximum drainage is of particular importance.

Relating to this control is the hardness of the aggregate, since soft or weak aggregates

may undergo degradation, a process whereby fines are generated by aggregate

breakdown during placement and use. The aggregate property most important to base is

gradation, including per cent fines or binder.

Theoretically, for a maximum stability, a base course aggregate should have

sufficient fines to just fill the voids among aggregate particles, with the entire gradation

representing a very dense mixture resembling that of Fullers maximum density curve.

The extent to which fines may increase or reduce stability are discussed elsewhere

(Yoder and Woods, 1946; Dunn, 1966). The fines content of base-course aggregate

may be considerably influenced by changes in aggregate gradation caused by physical

and chemical action during storage, transportation, construction, and in service (Wylde,

1976). Most paving material specifications are based on the Fuller gradation curve. A

critical evaluation of the formula in a more generalized form in relation to the

performance of gravel in roads in some tropical environments (Fossberg, 1963)

revealed that usually where n is less than 0.25 the fines content is excessive and the

gravel often lacks stability, particularly in the wet weather conditions. Where n is

greater than 0.5, the gravel tends to be stony and porous and usually requires additional

soil binder for satisfactory behaviour, particularly in dry weather conditions.

Apparently, the desired grading envelope for a particular climatic condition has to be

determined in the light of local experience and local pavement performance records.

Adequate cohesion of pavement materials is achieved by also specifying the plasticity

index, a parameter which is roughly proportional to the amount of fines in the materia l.


3. ELEMENTS OF STANDARD SPECIFICATION REQUIREMENT FOR SUB-

BASE AND BASE MATERIALS

3.1. The Implications of Ideal Grading Requirements

The most stable soils and aggregates in the pavement structure are those possessing

high degree of mechanical interlock together with good cohesion. Good interlocking is

obtained when the larger particles are angular with rough surfaces and cohesion is

dependent on the fines and clay size content. To achieve maximum stability of road

pavements attempts have been made to select materials that satisfy these requirements.

The grading limits adopted by some Highway Authorities in Standard specifications in

Europe and North America for paving aggregates and gravels approximate the Fuller

and Thompson (1907) formula (i.e. ASTM, 1964; AASHO, 1966). Similar grading

specifications have been proposed by the British Road Research Laboratory (1952) on

the basis of theoretical considerations and the Fuller-Thompson curves (Fig. 1).

Fig. 1 Ideal grading envelope for selection of paving material

The combinations of the ASTM, AASHO and British Standard specifications are

used in many temperate as well as tropical countries for selecting pavement

construction materials. It is usual to limit the maximum size in order that the material

can be laid by machine and, for the top layers, to give a smooth finish suitable for

traffic or for sealing. It is also usual to require that the particles be approximately

cubical for good packing. Elongated or round particles are not easy to compact into a

dense mass and long, thin particles may fracture during placing and compaction

altering the grading, usually detrimentally. Fines content is rather easier to control;

with the much fine material, interlock between the larger particles is prevented and

shear strength much reduced; with too little fine material, the material will be harsh to

work, difficult to compact (and the resulting loss of density will reduce strength)

permeable to moisture and likely to have a coarse open surface. The risk of segregation

during construction is also much increased. The most relevant property of the fines is

essentially that they should not be susceptible to the action of water, that is, they should

not swell or shrink to excess with change in water content. The limitation of this

susceptibility are usually by means of a restriction on the nature of the clay content of

the fines, the presence of highly plastic fines being undesirable. It is common, therefore,

to place restrictions on the Atterberg limits of the fines (the material smaller than

0.425mm).


Fig. 2 General properties of mechanically stable gradings (from Ingles and Metcalf, 1972)

These limits must be treated with caution because as Morgan, (1972) noted, the

test is carried out on only the fine portion of the material which is often less than 20 per

cent of the mass and of which the plastic fines (clay) content might be one-quarter, or 5

to 10 per cent of the total. Morgan showed that the compressive strength of a crushed

rock was insensitive to plasticity, however, the CBR tended to decrease as plasticity

index increased for samples at optimum moisture content and laboratory maximum

density. But if a material with a high plasticity index is kept dry it has a high crushing

strength and it is possible to use such materials in well-drained and dry environments.

4. REVIEW OF STANDARD PAVING MATERIALS ACCEPTANCE

SPECIFICATION REQUIREMENTS

4.1. General

Wooltorton (1954, 1968) who has been associated with paving materials specification

development, pavement design, and construction quality control in many climatic areas

of the world including the United States, United Kingdom, Africa, Asia and Australia

has emphasized that the definition of plasticity index (or potential swell) should in

theory be modified to suit specific climatic and drainage conditions. Wooltorton

explained that the upper and lower moisture content limits within which potential swell

would take place should be the maximum and minimum moisture contents likely to be

found under a given climatic and drainage condition.

4.2. Plasticity and Shrinkage Properties Requirements

In a theoretical explanation of existing specifications, Wooltorton (1954) suggested that

for no overall swelling of a coarse granular system, the product of the plasticity index

and the fines content should not be greater than the volume of voids between granular

aggregates to accommodate swelling. On this basis, he established the following

relationship:

d

ap

V

100

X.I

p Equation 2


Where: X=percentage of fines in 100gm total mix;, Ip=plasticity index %; Va=% of

entrapped air between fines and coarse material (air voids); d=apparent dry density of

compacted mixture (gm/cc); (X).Ip=binder plasticity index product. For example,

one state in Australia specifies the maximum value of the binder plasticity product of

200 for base course materials and 360 for sub-base course materials (Frost, 1967). A

similar approach was reported in the determination of maximum permissible value of

liquid limits. The most important assumption above is that of the definition of plasticity

index (or potential swell) and Wooltorton suggested that this should, in theory, be

modified to suit local conditions. For example, the upper and lower moisture content

limits within which the potential swell may take place would be the maximum and

minimum moisture contents characteristic of given materials, as well as climatic,

physical and drainage conditions. This means that considering the four significant

moisture content phases in soil-air-water system of the liquid limit (WL, plastic limit

(Wp), field moisture equivalent (FME), and shrinkage limit (W

s), the plasticity index Ip

(or potential swell) may be defined as (WL W

p) or (FME W

s) depending upon the

site conditions. For example, in a temperate zone condition with no appreciable

cementation and with possibility of frost action, the maximum moisture content would

be the liquid limit and the minimum moisture content, the plastic limit which gives the

well-known definition for plasticity index as liquid limit minus plastic limit. Frost

(1967) emphasized that there are many natural soils which would appear to be

troublesome on the normal basis for determining the Ip , (W

L W

p) but which in fact

make excellent road sub-bases. For example, he noted that the desiccated soils of

Burma have a Ip of 48 on the basis of (W

L W

p) but only 10 on the basis of (FME -

Ws) in which case the latter value of Ip more closely represented the true plasticity

index.

The importance of soil fines in evaluating the strength and durability properties of

pavement construction materials are also illustrated by the inter-relationships between

the maximum dry density and optimum moisture content, triaxial shear strength and the

California Bearing Ratio on the one hand, and the fines content and plasticity index on

the other (Figs. 3/4).

Fig. 3a Effect of fines on Compaction

(from Yoder and Witczak, 1975)

Fig. 3b Effect of fine content on triaxial strength of a gravel

(maximum aggregate size is 25mm) (from Yoder and Witczak,

1975)


Fig. 4 Effect on soaked CBR of the plasticity of the 20% passing No. 36 sieve contained in crushed

basalt aggregate compacted at modified AASHO, OMC (from Dunn, 1966)

It is noted that the higher the fines content the lower the strength and bearing

properties. Similarly, the plasticity index significantly influences the bearing strength

of compacted soil mass, apparently, here lies the need to control the fines content and

their plasticity index in paving materials acceptance specifications. The product of the

fines content and the plasticity index has also been known to affect the compaction

density, strength and the compressibility ratio (Fig. 5). Field experimental evidence of

the influence of fines on the suitability of aggregate bases has also been investigated

and is illustrated in Fig. 6.

Fig. 5 (a) Effect of fines on density achieved during compaction

on test track, relative to standard MDD obtained by vibration.

(b) Relationship between compressibility ratio and product of %

minus No. 40 U.S.sieve and PI illustrating that fines tend to

reduce air voids (from Dunn, 1966)

Fig. 6 Experimental evidence of the

influence of fines on the suitability of

aggregates for base (from Dunn, 1966)


Consequently, most current paving materials specifications in different countries

have stated maximum limits for the fines content (Passing No. 200 sieve size), the

liquid limit and the plasticity index (Table 1).

Table 1. Typical Temperate zone acceptance specifications for surfacing, base and sub-base course gravels

(from Zeymour and Durrier, 1966)

Country Properties of materials for different layers

U.S.A. United Kingdom Germany

Sufacing:

Plasticity of fraction passing BS sieve No.

36

4

grade courses at optimum moisture content or local insitu equilibrium moisture content

of the project sites has been suggested as alternative solution (e.g. Gidigasu, 1980).

Indeed, most of the temperate zone material specifications have not been modified

in relation to specific local pavement performance data and experiences. Because there

is limited knowledge of geotechnical characteristics of many unusual tropical materials

and their performance in pavements for most tropical environments, some tropical

paving materials specifications tend to reflect those of temperate zone countries with

which local engineers are familiar. However, because differences in soil genesis, nature

of the materials, climate and drainage conditions produce different lateritic materials

and pavement construction and quality control difficulties, specifications have to be

tailored for specific materials occurring in specific environments to meet local road

construction challenges. There is a real need to develop materials oriented paving

materials acceptance specifications requirements, and roadway construction methods

which take cognizance of the unique genetic and geotechnical characteristics of the

material (i.e. gravels and aggregates) and the construction equipment available for

specific climatic and drainage conditions

5. ELEMENTS OF SPECIFICATION REQUIREMENTS FOR NON-

STANDARD AGGREGATES

Materials that do not accord with one or more of the temperate zone requirements for a

first-class base material are non-standard (Wylde, 1979). Temperate zone current

standard requirements were developed by an ad-hoc process of excluding materials to

which have been attributed some inadequacy in performance in the pavement or some

difficulty during construction. Thus, a standard material is one which has

conservative properties of the major performance (or, rather classification) parameters.

It will be tolerant of construction mishandling and environmental conditions, and

probably, will perform well in most instances. It is also contended that almost any

earthen material can be used for pavement construction, provided the appropriate

design, construction and maintenance procedures are applied and the resulting

performance assessed with proper regard for overall economy.

5.1. Durability and Strength Specifications for Concretionary Lateritic Aggregates and

Gravels

A critical parameter for evaluating laterite gravels for road construction is the durability

of the coarse particles (Bhatia and Hammond, 1970). Other significant properties of the

coarse particles are the chemical composition, specific gravity, and water absorption

(Ackroyd 1967; USAID/BRRI, 1971; De Graft-Johnson et al., 1972). Concretionary

lateritic boulders may be used in pavement construction as long as they are sufficiently

durable. For example, the use of lateritic rock pieces as road base is shown in Fig. 7.

Studies have also shown (Bhatia and Hammond, 1970) that in addition to the aggregate

tests, the pH and heat treatment tests could be used for assessing probable performance

of lateritic rock aggregates and pisoliths in road pavements. Experience in the use of

concretionary lateritic gravels for pavement construction has also shown (Ackroyd,

1985, 1967) however, that the durability is very variable.


Fig. 7 The use of lateritic crushed stones for road base construction (from Persons, 1970)

For example, some of the materials do breakdown during field compaction

(Arulanandan, 1969) rapidly losing strength on wetting and most of such aggregates are

unacceptable as base material. Attempts have been made to define durability criteria for

selecting lateritic gravel sizes for pavement construction. Criteria based upon modified

Aggregate Impact value was also suggested for selecting lateritic gravels for pavement

construction (De Graft-Johnson et al., 1972) (Table 2). Millard (1962) and Ackroyd

(1967) have reported that the durability of lateritic concretions and their probable

performances in pavements depends on the content of sesquioxides, especially, on the

iron oxide content (Table 3). Clearly, the rating system that is based upon the durability

and weathering characteristics are useful for distinguishing good, critical and poor

concretionary aggregates for pavement construction

Table 2. Recommended criteria for rating West African lateritic rock aggregates and pisoliths for pavement

construction (from De-Graft Johnson et al., 1972)

Specific

gravity

Water absorption after

24 hours soaking (%)

Aggregate Impact

Value (%)

Los Angeles

abrasion value (%)

Rating based on

probable in-service

performance

>2.85

construction. On the basis of studies on over 800 lateritic soils in Nigeria, upper linear

shrinkage limits of 6% and 7% were suggested respectively for accepting sand-clays

and gravel-sand-clays for base courses. For the sub-base course material the respective

values are 12% and 13% for sand-clays and gravel-sand-clays.

For all types of lateritic gravels for use for unstabilized base-course, maximum

linear shrinkage of 5% is not to be exceeded for Nigerian environment. Nigerian

Ministry of Transport specified maximum linear shrinkage of 4 to 5% as corresponding

to the maximum liquid limit of 25% and plasticity index of 9%. The Zambian Public

Works Department also specified a maximum linear shrinkage of 3.3% for lateritic

gravels for road-base construction (Newill, 1961).OReilly and Millard (1969) and

Dreyfus (1962) have recommended linear shrinkage limits together with the liquid limit

and plasticity index, etc. for selecting materials for specific climatic conditions

(Table 4).

Table 4. Rating of potential laterite base materials performance under bituminous surfacing (See Dreyfus,

1952)

Field Performance Rating

Soil Properties

Excellent Average Poor

Linear Shrinkage (%) 0-4 4-6 above 6

Plasticity Index (%) 0-6 6-8 above 12

Liquid Limit (%) 14-21 22-30 above 30

Swell in CBR mould after saturation (%) 0-0.2 0.3-0.4 above 0.4

Optimum Moisture Content (%) - 8-10 -

5.3. Plasticity Modulus as a Specification Requirement Factor

An indication of the importance of plasticity modulus as a factor influencing the

stability of aggregates was given by Dunn (1966) (see Fig. 6). The plasticity modulus

has been variously defined as the product of fines (i.e. passing 0.425mm, 0.075mm

sieve sizes, etc.) and such plasticity parameters as the liquid limit, plastic limit,

*Federal Ministry of Works, Nigeria (See Teme et al., 1987)

(PI)x(%passing

0.075mm)

350 (Min) 350-400 500 (Max) 100-300(for Gravel base)

400-500 ( sandy clay base)

Plasticity Index (PI) 10 or15 (Max) 12(Max) - 20 (Max) 25(Sub-base)

(LL)x (% passing

0.075mm)

600 (Max) 900 (Max) 1250 (Max) 125-375 (for Gravel base) -

500-625 ( sandy clay base)

Liquid Limit (LL) 35 or 45 (Max) 40 (Max) - 25 (Max) 45(Sub-base)

Design CBR 80 or 100 (Min) 60 or 70 (Min) 50 (Min) 80 (Min) 30 (Sub-base)

Criteria

(Heavy Traffic) (Meduim Traffic) (Low Traffic)

Current FMW*

specifications

Class I Class II Class III

plasticity index, as well as linear shrinkage and optimum moisture content. This

parameter has been used for materials selection and in acceptance specifications (e.g.

Townsend et al., 1982; Cocks and Hamory, 1988; Bhatia and Yeboa, 1970;

USAID/BRRI, 1971; De Graft-Johnson et al., 1972). Typical specifications involving

the use of plasticity modulus are summarized in Table 5

Table 5. Recommended Criteria for selection of base course materials (from Townsend et al., 1982)

Road Classification


6. SOME PROBLEMS OF TESTING AND RATING OF TROPICAL PAVING

AGGREGATES AND SOILS

6.1. General

The contributions by Hamrol (1961), Duncan (1970), Clauss (1963) and Weinert

(1968) to the subject of evaluating weathering rocks and residual soils for engineering

purposes have emphasized the need to undertake detailed studies aimed at identifying

significant parameters for evaluating and rating various grades of tropically weathered

soils for engineering purposes. For example, the so-called saturation moisture content

(Duncan, 1969) and secondary mineral content (Scott, 1955) criteria are key parameters

for rating and predicting the engineering behaviour of decomposed rocks and tropically

weathered soils in the roadway.

As regards the fine-grained soils, the difficulties associated with obtaining

consistent particle size and Atterberg limit test results appear to be the main problem.

For example, the effect of pretest drying, type of dispersing agent and time of stirring

on the laboratory determined compositional and index properties for hydrated and

volcanic ash soils has been widely discussed (Townsend et al., 1971; Terzaghi, 1958).

It has been found that most tropical soils are amenable to satisfactory cement, lime

and chemical stabilization and considerable strength gains have been recorded for

typical tropical soils (e.g. Ingles and Metcalf, 1972). However, there are limited studies

related to the effect of pretest preparations and testing procedures on the strength gains

or strength losses for these soils. For example, significant effect of lapse of time

between mixing and compaction on the strength loss was reported for some West

African lateritic gravels (Gidigasu and Amankwa, 1975). This would suggest that if

cement and lime stabilization of lateritic soils for road construction is to prove useful

then intensive studies would be required to establish their usefulness and limitations.

There is the real need to evaluate fully the laboratory and field engineering behaviour

of cement and lime stabilized lateritic soils both in the laboratory and in the field.

6.2. Problems of Laboratory and Field Compaction and Quality Control Testing

Review of pavement engineering practice in some 30 tropical countries (Tanner, 1963)

revealed that pavement design based upon the CBR method has been established as

most applicable to tropical soils and climatic environments. For example, information

available indicate that provided realistic testing conditions are selected, the CBR

procedure provides a reasonable basis for estimating pavement thickness. However, to

ensure long-term pavement stability, the moisture content of the sub-grade should

preferably represent the stable moisture condition likely to prevail during the design

life of the pavement. Consequently, it is necessary, to define this equilibrium

moisture condition for most project sites at which to determine the strength of the sub-

grade in the laboratory as well as during field quality control testing. In some tropical

climates the equilibrium sub-grade moisture content under sealed pavements is noted to

rarely exceed the plastic limit of the soil and also the standard Proctor compaction

optimum moisture content may reasonably represent the equilibrium sub-grade

moisture content (e.g. OReilly and Baker, 1963). However, in some climates high sub-

grade moisture contents frequently approaching full saturation do occur. For such

conditions, we need the long-term mean insitu moisture content on which laboratory


and field compaction and strength control tests would be carried out to ensure long-

term stability of the pavement structure.

6.3. Insitu Moisture Content Vrs. Optimum Moisture Content

The relation between the insitu moisture content and the Modified AASHO compaction

optimum moisture content is illustrated for a group of lateritic gravels from the moist

sub-humid zone in Ghana (Fig. 8).

Fig. 8 Relation between the INSITU and Modified

ASSHO Compaction Optimum Moisture Contents

(from Ghana Highway Authority, 1970)

It is noted that for the given lateritic gravels (from the moist sub-humid zone), it would

be unrealistic to adopt the Modified AASHO compaction optimum moisture content-

related placement moisture content. This is because soils with insitu moisture contents

wet of optimum moisture contents would tend to absorb more water to attain the

equilibrium moisture content; this could lead to reduced strength of the pavement

structure. Similarly, soils with natural moisture contents generally wet of optimum

moisture content of an adopted compactive energy would present construction problem

(Gidigasu, 1980a). For example, in the dry sub-humid climatic zone, the insitu

moisture content of the gravels is lower than the optimum; in such a case, the strength

and stability of the pavement is not likely to undergo significant deterioration since

there would not be any additional water absorption to cause strength loss.

6.4. Effect of Compaction Moisture Content on Stability of Lateritic Gravels

The danger of specifying the optimum moisture content for pavement placement has

been noted for humid environments (e.g. Gidigasu, 1980). This is because the CBR at

the optimum moisture content may sometimes be as low as 30% of the peak values

obtainable at moisture content dry of optimum. Typical inter-relationships between the

moulding dry density and moisture content on the one hand and stability or bearing

strength (CBR) for a lateritic gravel on the other have been found by Hammond (1970).

It has been observed that at low moisture content, an increase in density improves the

stability of the soil; however, at moisture contents of say 10% and above the stability

Fig. 9 The relation between the optimum moisture

content and the moisture content corresponding to

maximum CBR value (from Gidigasu, 1980)


increases with density only up to a certain point and then further increases in density

produces a decrease in stability. Indeed, at moisture content of about 16% or higher, the

stability decreased with any density above 1752kg/m3

(110 lb/ft3

) (Gidigasu, 1991).

The relation between the optimum moisture content and moisture contents

corresponding to the maximum CBR for some fine-grained soils is given in Fig. 9. It is

noted that the moisture content at which the highest CBR is obtained is dry of the

optimum moisture content. The adverse effects of moulding moisture contents on the

stability of compacted micaceous sandy loamy soils have also been noted elsewhere

(e.g. Gidigasu and Mate-Korley, 1980). For example, it was noted that, for samples

compacted at optimum moisture content and at moisture contents dry of optimum the

stability is quite high. However, the same soil compacted at moisture content wet of

optimum gives very low stability. This phenomenon has been attributed to the over

compac

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