THE EFFECT OF TROPICAL WEATHERING ON THE STRENGTH

AND ANISOTROPY INDEX OF WEATHERED SHALE

OLUMORIN MICHAEL MAIYE

A project report submitted in partial fulfilment of the

requirements for the award of the degree of

Master of Engineering (Civil-Geotechnics)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

JANUARY 2014

iii

To my sweet heart wife Adeola and my children Ayomide and Adebola

iv

ACKNOWLEDGEMENT

First and foremost, I express my utmost gratitude to God Almighty who has

been with me always in terms of protection and provision of knowledge to complete

this research successfully. May all glory and honour be returned unto God.

My appreciation is extended to my supervisor Associate Professor Dr. Edy

Tonnizam Bin Mohamad for his encouragement, valuable input and suggestions

towards the successful completion of my research and the program. His contribution

of wealth of knowledge has greatly assisted me a lot and will continue to be useful in

my lecturing work and professional practice. I would also like to express my profound

gratitude to my lecturers Dr. Rini Asnida, Professor Dr. Aminaton Marto, Madam

Fauziah Kasim, Engr. Dr. Mua’zu Mohammed, Assoc. Prof. Ir. Dr. Ramli Nazir,

Assoc. Prof. Mohd For Mohd, Assoc. Prof. Ir. Dr. Azman Kasim, Assoc. Prof. Dr.

Nazir Ali and others in the Faculty of Civil Engineering, Universiti Teknologi

Malaysia for their useful knowledge impacted in me during the course of study.

Similarly, I appreciate other laboratory Technicians for their assistance during all the

laboratory tests and the Universiti Teknologi Malaysia for given me the opportunity to

study in this great institution. My unreserved gratitude goes to the management of

Kaduna Polytechnic for approving my sponsorship to study Master of Civil

Engineering program in Malaysia.

I would also like to thank my colleague Engr. (Dr.) Oyeleke Raifu Brown who

has encouraged me in the pursuance of this program in Malaysia and for his

unquantifiable input in the academic program for me to excel. I am also grateful to

Engr. (Dr.) Sulaimon Shodiya, Engr. Gambo Yunsa Haruna, my course mate Elfira

Warni, my friends in Malaysia and other well-wishers for their prayers,

encouragements and support.

Finally, I would like to appreciate my lovely wife Adeola Olumorin for her

fervent prayers, immense support and care at home and even while away. I also

express my gratitude to my children Deborah Ayomide Olumorin and Precious

Adebola Olumorin for their understanding while in thousands Kilometres apart and

their prayers for me to excel and come back home safely.

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ABSTRACT

Sedimentary rocks to be specific shale as it is the rock being studied can be

adversely affected by weathering action; hence the alteration of its engineering

properties is incontestable. The manipulation of the engineering properties of shale

becomes more significant as it possesses fine lamination structures which tend to split

unevenly, parallel to the weakness plane. It becomes so severe when the rock material

is subjected to structural loads, slope cut and higher weathering process in tropical

region. This study focus on the effect of weathering on the strength, and anisotropy

index Ia(50) of shale of fresh to highly weathered (grades I–IV) shale collected at

Nusajaya,west of Johor Baharu, Malaysia. A total of 96 samples representing various

weathering grades were collected from the field and tested using 24 samples for each

different weathering grade at varying moisture by immersing them in water at different

duration of time ranging from 15, 30 and 60 minutes. Point load tests for the

determination of the strength index Is(50) of the rock were measured at 0o and 90

o

orientations. For weathered shale (grade I to IV), the mean initial moisture content

ranges from 0.12% to 10.69 respectively, while the initial mean strength index has

maximum of 7.78 MPa and 0.4 MPa respectively. The results revealed that there is a

significant relationship among weathering grades, moisture absorption, strength and

anisotropy index of shale. The moisture absorption is dependent on the amount of clay

minerals present in the rock material which indirectly affects the strength. In addition,

the result shows a unique pattern on the range of anisotropy index for various

weathering grades. In conclusion,this study also indicates that shale with higher

moisture content and increase in weathering grade exhibits wider range of anisotropy

index with lower strength values.

vi

ABSTRAK

Batuan sedimen terutamanya jenis syal berupaya terjejas kualitinya dengan

tindakan cuaca dan luluhawa. Justeru itu perubahan sifat kejuruteraan baginya adalah

sangat penting untuk diramalkan. Sifat kejuruteraan batu syal adalah unik kerana ia

mempunyai struktur laminasi halus yang cenderung kepada pecahan tak sekata, selari

dengan satah kelemahan. Ia menjadi lebih teruk apabila bahan batuan ini tertakluk

kepada beban struktur, potongan cerun dan proses luluhawa yang tinggi di rantau

tropika. Fokus kajian tentang kesan luluhawa kepada kekuatan dan indeks anisotropi Ia

(50) batuan segar kepada luluhawa tinggi (gred I-IV) syal diperolehi dari Nusajaya,

Johor Bahru, Malaysia. Sebanyak 96 sampel yang mewakili pelbagai gred luluhawa

dikumpulkan dari kawasan dan diuji menggunakan 24 sampel bagi setiap gred

luluhawa pada kelembapan yang berbeza-beza dengan merendamkannya ke dalam air

pada tempoh masa 15, 30 dan 60 minit. Ujian beban titik bagi penentuan indeks

kekuatan batu Is (50) telah diukur pada orientasi 0 o dan 90

o. Hasil kajian mendapati

syal terluluhawa (gred I hingga IV), mempunyai kelembapan min awal antara 0.12%

kepada 10.69%, manakala indeks kekuatan min awal adalah 7.78 MPa dan 0.4 MPa

masing-masing. Keputusan kajian menunjukkan terdapat hubungan di antara luluhawa

gred, penyerapan kelembapan, kekuatan dan indeks anisotropi syal. Penyerapan

kelembapan adalah bergantung kepada jumlah mineral tanah liat di dalam bahan

batuan yang secara tidak langsung memberi kesan kepada kekuatan. Di samping itu,

keputusan menunjukkan corak unik pada julat indeks anisotropi bagi pelbagai gred

luluhawa. Kesimpulannya, syal dengan kandungan lembapan yang lebih tinggi dan

peningkatan dalam gred luluhawa menghasilkan indeks anisotropi yang berjulat besar

dengan nilai indeks kekuatan yang lebih rendah.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xii

LIST OF SYMBOLS AND ABBREVIATIONS xiv

LIST OF APPENDICES xvi

1 INTRODUCTION 1

1.1 Background of the Problem 1

1.2 Problem Statement 2

1.3 Aim and Objectives 3

1.4 Scope of the Study 3

1.5 Significance of the Study 4

2 LITRATURE REVIEW 5

2.1 Introduction 5

2.2 Weathering of Rocks 5

2.2.1 Engineering Classification of Weathering 7

2.3 Effect of Weathering on Rock Strength 12

viii

2.3.1 Moisture Content Effect 13

2.3.2 Physical Weathering Effect 13

2.3.3 Chemical Weathering Effect 14

2.4 Sedimentary Rocks 15

2.4.1 Sedimentary Structure 16

2.4.2 Sedimentary Texture 17

2.4.2.1 Clastic Sedimentary Rock 18

2.4.2.2 Shale 18

2.5 Mineralogy of Shale 21

2.6 Engineering Properties of Rocks 21

2.7 Point Load Strength Index 22

2.8 Anisotropy Strength of Sedimentary Rock 25

2.8.1 Reduction in Strength from Anisotropy 28

2.8.2 Reduction in Strength from Weathering and

Alteration 30

2.9 Anisotropy Index 31

2.10 Mode of Failure for Point Load 32

3 METHODOLOGY 35

3.1 Introduction 35

3.2 Fieldwork 37

3.2.1 Determination of Weathering Grade 37

3.3 Laboratory Works 40

3.3.1 Samples Preparation 40

3.3.2 Determination of Moisture Contents 41

3.3.3 Point Load Index, Is(50) 44

3.3.4 Anisotropy Index, Ia(50) 49

4 LABORATORY RESULTS AND DISCUSSIONS 51

4.1 Introduction 51

4.2 Variation in the Absorption of Moisture Content

with Time 51

4.3 Effects of Weathering Grades on Absorption of

ix

Moisture Content 53

4.4 Effect of Moisture Content on the Strength Index, Is(50) 54

4.5 Effect of Weathering on Anisotropy Index, Ia(50) 62

4.6 Standard Deviation 68

5 SUMMARY, CONCLUSIONS AND

RECOMMENDATIONS 70

5.1 Summary 70

5.2 Conclusions 70

5.3 Recommendations

71

REFERENCES 72

APPENDICES A-H 74-82

x

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Classification for Rock Material 8

2.2 Weathering profile classification of rock mass 9

2.3 Weathering classification used to describe the

rock mass/material 11

2.4 Engineering behavior from weathering grade 11

2.5 Sediments and Clastic Sedimentary Rocks 19

2.6 Characteristic of shale 20

2.7 Classification based on point load strength index 25

2.8 Summary of test results on uniaxial compressive

strength and Young’s Modulus 27

2.9 Classification of Anisotropy 29

2.10 Isa(50) axial load Strength 33

2.11 Anisotropy classification according to anisotropy

index 34

3.1a Physical Characteristics of Shale for the Study

(Grade I) 38

3.1b Physical Characteristics of Shale for the Study

(Grade II) 39

3.1c Physical Characteristics of Shale for the Study

(Grade III) 39

3.1d Physical Characteristics of Shale for the Study

(Grade IV) 40

4.1 Mean Values of Moisture Content and Time of

Immersion for Shale Grades 52

4.2 Summary of Moisture Content at Various

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Soaking Period 55

4.3 Summary of Result for Point Load Test of Weathered

Shale at Various Moisture Contents 56

4.4 Percentage Reduction in Initial Strength Index of

Weathering Grades 61

4.5 Summary of results for Anisotropy Index and

Moisture Content 62

4.6 Summary of Results for Point Load Test of

Weathered Shale 63

4.7 Mean values of Anisotropy Index of Weathered

Shale 67

4.8 Standard Deviation for Moisture Content and

Strength Index 68

4.9 Standard Deviation for Moisture Content and

Anisotropy Index 68

xii

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Inclined bedding plane on folded strata 17

2.2 Images for estimating shape 17

2.3 Specimens shape requirement for the irregular lump test 23

2.4 Anisotropy behaviour of uniaxial compressive

strength at different Orientations of lamination planes 27

2.5 Compressive strength anisotropy in bedding and foliated rocks 29

2.6 Correlation between weathering grade I-IV and

point-load strength values Is50 30

2.7 Typical modes of failure for valid and invalid tests 34

3.1 Research Methodology Flowchart 36

3.2 Site location of shale samples in Nusajaya, Johor Bahru 37

3.3 Some rock expose where the samples were collected 38

3.4 Irregular Shale Lumps of grade III and IV 41

3.5 An Oven capable of maintaining a temperature at105oC 42

3.6 Samples kept cooling in Desiccator for 30 minutes 43

3.7 Samples covered with plastic after removing from

desiccator and before weighing as W3 44

3.8 Point Load Apparatus 45

3.9 Grade I core sample under point load, perpendicular

to lamination 46

xiii

3.10 Grade IV (irregular lump) under point load at,

perpendicular to lamination 47

4.1 Variation of Moisture Absorption with Time for

each Weathering Grade 52

4.2 The pattern of water absorption with different

stage of weathering 53

4.3 Decrement of strength index, Is(50) due to moisture

content increase for Grade I 57

4.4 Reduction in Strength Index due to Moisture

Content increase for Grade II 58

4.5 Trend of strength index reduction due to Moisture

Content increase for grade III 59

4.6 Strength index reduction with increment in

moisture content 59

4.7 Trend on the decrement of strength index, Is(50)

with the increment of moisture content for

weathered shale 60

4.8 Increment of anisotropy index due to the increase

in moisture content of shale 64

4.9 Relationship of anisotropy index due to the increase

in moisture content of shale 65

4.10 Increment in anisotropy index as moisture

content increases 66

4.11 Pattern of increment of anisotropy index due to

weathering increase 67

xiv

LIST OF SYMBOLS AND ABBREVIATIONS

A - The Minimum Cross-Sectional Area

β - The Orientation Angles to the Direction of Loading

CO2 - Carbon Dioxide

cm - Centimeter

D - Depth

2

eD - The Distance between the Loading Points

F - A Size Correction Factor

Ia(50), AI - Anisotropy Index

Is(50), Is - Strength Index

Is(50)┴ - Perpendicular Point Load

Is(50)// - Parallel Point Load

ISRM - International Society for Rock Mechanics

Iσc - Uniaxial Compression Strength Index

Iσc(90) - Uniaxial Compression Strength at 90° from Axial.

Iσc(30) - Minimum Uniaxial Compression Strength at 30o

kN - Kilo Newton

kN/m3 - Kilo Newton per Cubic Meter

L - Length, mm

M/C - Moisture Content

Min - Minutes

mm - Millimeter

MN - Mega Newton

MN/m2 - Mega Newton per Square Meter

Mpa - Mega Pascal

OMC - Original Moisture Content

P - Point Applied Load on Sample

UCS, σc - Uniaxial Compressive Strength

xv

W - Width

W1 - Upper Width, mm

W2 - Lower Width, mm

WG - Weathering Grade

W (%) - Moisture Content

π - Pi = 3.142

°C - Degree Celsius

% - Percent

xvi

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Moisture Content of Shale Grade I 75

B Moisture Content of Shale Grade II 76

C Moisture Content of Shale Grade III 77

D Moisture Content of Shale Grade IV 78

E Point Load Test and Anisotropy Index of Shale Grade I 79

F Point Load Test and Anisotropy Index of Shale Grade II 80

G Point Load Test and Anisotropy Index of Shale Grade III 81

H Point Load Test and Anisotropy Index of Shale Grade IV 82

1

CHAPTER 1

INTRODUCTION

1.1 Background of the Study

Weathering can be described as process involving mineral alteration on the rock

structure caused by exposure of the rock to the denudation agents such as water, wind and

organic fluids in order to be more stable material in natural environment. Water is a

triggering factor which plays a major role in both physical and chemical weathering of

rocks especially in tropical climate. This leads to significant changes in most of the

engineering properties of rocks, particularly in slope, foundation and excavation works.

Vasarhelyi et al., (2006) reported that weathering in rock structure would affect the

engineering properties of rock, such as porosity, degree of saturation, and strength. All

rock engineering activities are conducted either on the surface of the Earth or within a

relatively shallow depth beneath it. This thin mantle of the top crust is the zone where the

processes of weathering, erosion, transportation and deposition are active (Price, 1995).

It is worth noting that the response of a rock mass to weathering is directly related

to its internal surface area and average pore size (Bell, 2007). He further stressed that

coarse-grained rocks generally weathered more rapidly than fine-grained ones. Also the

amount of water that a rock contains influences mechanical breakdown and this action

adversely affect the strength of rocks. Furthermore, the degree of interlocking between

component minerals is also particularly important textural factor, since the more strongly a

rock is bonded together, the greater is the resistance to weathering. The closeness of

interlocking of grains governs the porosity of the rock. This, in turn, determines the

amount of water it can hold, and this signifies that, the more porous the rock, the more it is

2

susceptible to chemical attack.

The degree of weathering varies from region to region as a result of changes in

climatic conditions. In tropical region, high temperature is usually being experienced and

in dry air, rocks decay very slowly but the presence of moisture hastens the rate of decay.

Shale is one of the fine-grained sedimentary rocks that has fissility structures or fine

lamination that are built parallel to the weakness plane. These cause shale rocks to be

easily broken into flakes and tend to split unevenly under applied loads or influence of

weathering agents, especially water (Abhijit, 2010). There is no doubt that it is critically

important to understand the effect and influence of extent of weathering on the

engineering properties of rock material, particularly on the strength and anisotropy index.

Shale is universally recognized as an anisotropic rock. Palmstrom (1995) defined

anisotropy in rock material is mainly caused by schistosity, foliation or bedding and the

different in properties is determined by the arrangement and amount of flaky and

elongated mineral.

The strength and anisotropy behaviour of rock is considered to be a major

importance in a number of key geotechnical structures, for example, the design of tunnels,

dams, underground space and the stability of rock slopes. Consideration must be made to

take into account the effect of water such as groundwater table or rainfall on the

geotechnical structure especially in terms of strength and anisotropy index of the rock

material. Strength and strength anisotropy index of weathered shale influence by water are

the main parameters studied in this research. It is critical to understand the correlation and

influence of moisture content to the engineering properties of rock especially in term of

strength index and strength anisotropy index.

1.2 Problem Statement

In rock engineering project, the effect of weathering is an important issue and

therefore requires special attention in dealing with slope stability safety and underground

3

openings. It has been discovered that, most of the present studies focused on the influence

of water to the strength of sandstone (Vasarhelyi et al., 2006; Edy Tonnizam et. al., 2008;

Kwasniewski et. al., 2009) and metamorphic rock (Saroglou et al., 2004; Eduardo et al.,

2006). (Sarout et al., 2006; Sung et al., 2002) studied the anisotropy index of Shale but no

reference can be made for the study in influence of various water content to the strength

anisotropic index of weathered shale. Meanwhile, Ajalloeian et. al., (2000) study on

strength anisotropies in mud rock whereas he was focused on correlation between strength

index and anisotropies of siltstone and siltshale but not correlated with influence of water.

For these reasons, experimental programs are proposed with the primary objectives of

investigating the effect of moisture content to the strength index and the effect of

weathering to the anisotropy index under various moisture contents.

1.3 Aim and Objectives

The aim of this research is to investigate the effect of weathering to the strength

and anisotropy index of rock material. In this study, two objectives have been identified.

i. To investigate the effect of moisture contents to the strength index of shale.

ii. To study the effect of weathering stages on the anisotropy index of shale.

1.4 Scope of the Study

In order to achieve the goal of this project, the scope of this work need to be

specified. The scopes of this research include the analyses of the effect of tropical

weathering to the strength index on shale materials using the point load test in the

laboratory and changes to anisotropy index, then finally develop a guideline on the

strength and anisotropy index of shale under different degree of weathering.

4

1.5 Significance of the Study

Most weathered rocks strength has been altered because of weakness plane or

lamination formation when compared with the parental rock strength. For this reason, the

behavior of laminated rock such as shale as it is the focus on this study requires strength

and anisotropy index determination. The results obtained will be established as guideline

for design in geotechnical structures such as tunnels, slope stability of rock as well as

underground space work.

72

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