"THE NATURE AND ENGINEERING PROPERTIES OF SOME RED SOILS FROM NORTH-EAST BRAZIL" BY Siyanbola Samuel Malomo M.Sc. A Thesis submitted in fulfilment of the requirements of the degree of Doctor of Philosophy. Department of Civil Engineering, University of Leeds, July 1977. "To Jbidunni Akintokun" (i) SYNOPSIS Researcher* over the years have demonstrated the need for the determination of the nature and fundamental properties of soils as an approach to the understanding of engineering behaviour. This has teen shown to be particularly true in the case of tropical soils. This thesis approaches the analyses of engineering behaviour from a standpoint of the study of the intrinsic properties. The mineralogy, chemistry, structure and strength behaviour of three concretionary red soils from Paraiba State in North-East Brazil, have been determined. The mineralogy- of the red soils were determined using X-ray analysis, differential thermal analysis and thermogravlmetric techniques. The microstructure of the red soils has been examined with the optical and scanning electron microscopes. The strength behaviour of compacted specimens was examined in the oedometer, direct shear and triaxial machines. A phenomenon of breakdown of soil particles under stress is isolated. The influence of the phenomenon on the strength behaviour is demonstrated. The soil elements and properties responsible for the phenomenon are discussed. (ii) LIST OF SYMBOLS i shear stress max. shear stress ft normal stress (f effective normal stress major principal stress 6 1 minor principal stress U pore pressure Ua pore-air pressure pore-water pressure £ axial strain ji axial deformation n B Skempton's pore pressure parameters coefficient defining effective stress in partially saturated soils C cohesion C effective cohesion C u cohesion in the undrained test cohesion in the consolidated-undrained test C y residual cohesion ^ angle of friction effective angle of friction ^ angle of friction in the undrained test (S? angle of friction in the consolidated-undrained test Qj) residual angle of friction dry density specific gravity void ratio porosity moisture content degree of saturation liquid index liquid limit plasticity index plastic limit (iv) ACKNOWLEDGEMENT The author wishes to express his most sincere thanks to Hr. J.G. Cabrera, Dip.Eng., Dip.Dev., Admin., C.Eng., M.I.M.M. F.R.M.S., under whose supervision this work was carried out. He would also like to express his appreciation: To Professor A.M. Neville, M.C. T.D. D.Sc.(Eng.),, Ph.D., M.Sc., C.Eng., F.I.C.E., F.I.Struct.E., F.Am.Soc.C.E., M.Soc.C.E.(France) F.A.C.I. F.I.Arb, Head of the Department of Civil Engineering, for allowing the use of facilities in his Department. To Dr. I.J.Smalley, Ph.D., D.C.T., C.Eng,, who co-supervised the work. To Mr, ± ,F, Johnston of the Department of Earth Sciences who provided facilities for sectioning. To Dr, E.v7. Roberts of the Department of Ceramics for the loan of a microscope. To Mr. R. Duxbury who took the optical photographs. To The Department of Metallurgy forthe use of the Scanning Electron microscope. The research could not have been carried out without the visiting Assistant Professorship offered to the author by the Co-oraenacao da Postgraduacaa, Universidade Federal da Paraiba, Brazil, where most of the experimental work was done. For this, and for the hospitality extended during the author's stay in Brazil, the author would like to thank Professor Jose Luiz Almeida, Professor Jose Elias Borges, Professor Francisco Barbosa de Lucena and Sr. Ailton Alves Dinis. (v) And last by no means the least, the author would like to thank Professor M.O. Oyawoye of the University of Ibadan, Ibadan, Nigeria and Professor O.S. Adegoke of the University of „lfe, lie-'Ife, Nigeria, who helped in providing financial assistance for the work. All who have helped in the production of the thesis, I am most grateful. TABLE OF CONTENTS PAGE NO. CHAPTER 1 INTRODUCTION 1 CHAPTER 2 HISTORICAL BACKGROUND AND GENERAL REVIEW 4 OP LITERATURE. 2.1 Definition ^ 2.2 Nature of Red Soils 14 2.2.1 Colour and Chemistry 14 2.2.2 Structure 16 2.2.3 Mineralogy -jy 2.3 Engineering Properties -jg 2.3.1 Grain Size 18 2.3.2 Compaction Characteristics 19 2.3»3 Shear Strength 20 2.4 Genesis of Red Soils 22 2.4»1 Historical Background 22 2.4.2 Weathering of Minerals 26 2.4.3 Secondary Minerals Formed 28 2.4.4 Accumulation Theories 31 CHAPTER 3 PROBLEMS PECULIAR TO RED SOILS 35 3.1 Introduction 35 3*2 The Peculiar Problems 35 3«3 Causes of Mechanical Instability 37 3.4 Causes of Thermal Instability 39 3.4.1 Iron Oxides and Hydroxides 39 3.4.2 Alumina Oxides and Hydroxides 41 3.4.3 Silica Oxides and Hydrated Oxides 42 3.5 Effects of Mechanical Instability 43 3.5.1 Atterberg Limits 43 PAGE NO. 3®5.2 Particle Size Distribution 44 3.5.3 Compaction Characteristics 44 3.5.4 California Bearing Ratio 44 3.6 Effects of Thermal Instability 45 3.6.1 Atterberg Limits _ 45 306.2 Particle Size Distribution 47 3*6.3 Moisture-Density Characteristics 48 3.6.4 Strength 49 3.6.5 Swelling and YJater Absorption 50 Characteristics. 3.7 Implications to Classification 5-I CHAPTER 4 COATING AND AGGREGATION OF SOIL PARTICLES , 53 4.1 General Background 53 4.2 Mechanism of Coating 54 4.2.1 Role of Iron Oxide 54 4.202 Possible Role of other Oxides and 59 Properties. 4«3 Concluding Remarks 60 CHAPTER I GEOLOGY AND SETTING 63 5.1 Location, Physiography and Drainage 63 5.2 Geology 65 5.5 Materials for the Study 69 5.3.1 Sape 69 5.3.2 Cuite and Nova Floresta 72 5.4 Sample Collection 76 5.4.1 Mineralogy and Chemical 76 Invest igations. 5.4.2 Compressibility and Shear Strength 78 CHAPTER I MINERALOGY AND CHEMISTRY 81 6.1 Methods 81 6.1.1 X-ray Diffraction 81 6.1.2 Thermal Analysis 91 PAGE NO. 6<> 1.3 An Appraisal of the Different 102. Methods. 6.2 Results and Observations 105 6.2.1 X-ray Analysis 105 6.2.2 Differential Thermal Analysis 113 6.2.3 Thermogravimetry and Derivative 118 The rmogravimet ry. 6.2.4 Chemical Composition 122 6.3 Discussion -J32 6.3.1 Form and Distribution 132 6.3.2 Formation of the Deposits 141 CHAPTER 7 STRENGTH BEHAVIOUR OF THE SOILS 146 7.1 Method of Testing N 7.1.1 Compressibility -jr.6 7.1.2 Direct Shear Strength 7.1.3 Triaxial Strength Tests 154 7o2 Results 7.2.1 Direct Shear 156 7.2.2 Triaxial Tests 163 7.2.3 Compressibility 184 7»3 Discussion 192 7.3.1 Direct Shear 192 7.3.2 Triaxial 200 7.3.3 Compressibility 203 CHAPTER 8 MICROSCOPIC INVESTIGATION OF STRUCTURE 210 8.1 Introduction 210 8.2 General Comparison of Cuite, Nova 211 Floresta and Sape Soils. 8.2.1 Optical Microscopy 212 8.2.2 Electron Microscopy 231 8.3 The Formation of Aggregation in Red Soils 231 PAGE NO. 8.4 The Need for the Investigation of 239 Microstructure in the Study of Red Soils. CHAPTER 9 THE RELATION BETY/EEN THE PROPERTIES INVESTIGATED 242 9®1 General 242 9o2 Relationship Between Mineralogy Structure 244 and Strength. 9<>2.1 Mineralogy and Engineering 245 Properties. 9.2.2 Structure and Engineering Properties 9 ).£ CHAPTER 10 CONCLUSION 249 CHAPTER 11 SUGGESTIONS FOR FURTHER RESEARCH || REFERENCES OCO APPENDIX A - 269 APPENDIX B 272 1 CHAPTER 1 INTRODUCTION Major construction (particularly dams, roads and airfields) in countries lying within the tropical regions of the world, necessitates the use of local materials. Many of these materials are suitable from an engineering point of view, some are not, but the onus of the different­ iation lies with the engineer who, by and large, has been instructed in the methods for materials found elsewhere (temperate regions) which might not be directly applicable to those of these areas0 The main problem wj.th regard to construction with tropically weathered soils is not in non—suitability but lack of adequate knowledge of behaviour under different conditions and at varying states. In the last few years a number of studies have been carried out covering problems, properties and behaviours encountered with the use of tropical soils. Most of this work largely dealt with characteristics observed during testing and evaluation of these materials, but few have actually gone 'beyond the bridge' to procure reasons for these character­ istics. Gidigasu (1970) mentioned that the behaviour of red soils cannot be adequately explained by consideration of physical properties alone, emphasis has to be placed on the intrinsic properties and physico-chemical factors that make for the genesis of the soils. He particularly states that classification of the soils would have to be based on these factors before any reasonable 'sorting' can be achieved. Lohnes and Demirel (1973) agreed with Gidigasu in the use of soil forming factors as a basis for correlation. 2 These factors have influence on the physico-chemical, chemical and mineralogical properties which, in turn, play a hand in the engineering behaviour and, it is felt that any study of the engineering characteristics must be linked with the mentioned properties for full under s t and ing. De Graft-Johnson and Bhatia (1970) called attention to the scarcity of information on the engineering characteristics of these soils, for if knowledge about them is to be advanced, information and behaviour of materials from various parts of the world has to be known for any meaningful correlations.