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
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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 90o
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.
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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.
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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
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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
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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
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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
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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
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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
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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
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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 e D
- 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
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
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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
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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
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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
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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.
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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.
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