Durham E-Theses The response of coarse and ne coal-mine discards under controlled load triaxial testing Kennedy, George W. How to cite: Kennedy, George W. (1977) The response of coarse and ne coal-mine discards under controlled load triaxial testing, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/8986/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk 2 THE RESPONSE OF COARSE AND FINE COAL-MINE DISCARDS UNDER CONTROLLED LOAD THIAXIAL TESTING by George' W. Kennedy being a Thesis submitted for the Degree of Master of Science in the University of Durham. September 1977 The copyright of this thesis rests with the author. No quotation from it should be published without '::J his prior written consent and information derived ^ "" from it should be acknowledged. (i:): ABSTRACT The aim of the project was to investigate the behaviour of coar.se and fine colliery discards with respect to liquefaction potential, using controlled load triaxial testing. It was hoped to relate the behaviour in these tests to measured material properties such as strength, shape,.chemistry and mineralogy. The investigation of coarse discards contrasted the behaviour of a weak,- seatearth-rich discard from Gedling Colliery with that of a strong shale-rich discard from Abernant Colliery. The former showed some liquefaction potential at low confining pressures, while the latter showed no liquefaction potential. A seatearth and a shale from County Durham were used to demonstrate any possible links between these basic materials and the 'behaviours observed. However, both showed responses similar to the Gedling discard. Investigation of material properties indicated that the strength of material, its stability in water and its facility for pore pressure equalisation were the most important factors influencing response during controlled load testing. The strength and stability of the material are probably related to its organic carbon content. The Aberrant discard had a high strength and stability in water and showed'good potential for equalisation of pore pressures during testing, in contrast to the other three materials. Tests on mixtures of Abernant discard and the Durham seatearth showed a transition between the behaviours of the end materials for a mixture containing between 20 and 25 per cent seatearth. Tests on .fine discard from Peckfield Colliery showed significant differences in behaviour between samples from the lagoon and those fabricated in the laboratory. The former showed strong dilatant behaviour, v.uile the latter showed some potential for liquefaction. This is probably due to differences in soil structure (organisation of particles). Tests on fine discard from Abernant showed a hxgh potential for liquefaction. The most significant difference, possibly affecting liquefaction potential, between this discard and that from Peckfield was the uniformity of grading, the Abernant discard being considerably more uniform. The results for the Abernant fine discard showed no correlation with those for the coarse discard from the same colliery. Uii) ACKN0WIJi3)GEMEMTS I would like to express my gratitude to the following people for their help during this investigation': Dr. Roy Taylo1" as my supervisor for his help and advice throughout the project. Giles Morrell for his useful discussions as a result of his associated work, and his contribution in the development of the revised method on the small controlled load rig. Laurie Gunson for his work nn the Abernant fine discard. Eon Hardy for mineralogical and chemical analyses. Bernard McEleavey, Phillip Xay and Alan Swann for their friendly assistance in the laboratory and workshop. The National Coal Board who provided the necessary financial support via a. current research contract under Dr. Taylor's supervision. Mr. A.E. Taylor (Chief Civil Engineer) and Mr. A.H. Bacon (Senior Civil Engineer, Soil Mechanics) are particularly thanked for their help and Support. The opinions expressed in this thesis are those of the writer and not necessarily those of the Board. Finally I would like to thank Mrs.Audrey Taylor for typing this thesis. (iv) LIST OF CONTENTS Page CHAPTER ONE INTRODUCTION 1 1.1 Aims of Project 1 1.2 The Concept of Liquefaction and Flow Slides 2 I.J Flowslides in Colliery Waste 2 1.4 Review of some recent work 5- 1./|.1. Critical voids ratio, E and F lines and flow structures 5 1.4-2. Liquefaction and Associated Results 8 1.4.3- Sample Preparation anJ the Effects of Soil Structure 9 1.5 Colliery Waste Disposal 12 1.6 Revised methods of Waste Disposal 14 1.6.1. Spoil Heaps 15 1.6.2. Lagoons % 16 CHAPTER TWO MATERIALS INVESTIGATED 20 2.1 Geographical Locations 20 2.2 General Description of Sites 20 2.2.1. Gedling 20 2.2.2'. Abernant 21 2.2.3- Peckfield 22 2.3 Description of Materials 23 2.3.1. Gedling 23 2.3.2. Abernant 23 2.3-3* Durham Seatearth 24 2.3.4. Durham Shale 24 2.3.5. Peckfield Slurry 24 (v) 2.2-6. Abernant Fine Discard. 25 2.4 Mineralogy and Chemistry 25 2.4-1. Methods of Analysis 25 2.4-2. Chemical apportionments in colliery wastes 26 2.4«3- Discussion of Results 27 CHAPTER THREE APPARATUS USED 55 3.1. Introduction 55 3-2. The large Controlled Load Rig 55 3.2.1. The Cell 55 3-2.2. The Loading Beam 56 3-3 The Small Controlled Load Rig 57 3.3.1. The Cell 57 3.3.2. The Loading System 58 3-4 The Bishop Self Compensating Pressure Control System 58 3.5 Volume Change Apparatus 59 3.6 Instrumentation 60 3.6.1. The U.V. Recorder 60 3.6.2. Amplification 61 3-6.3« Power Supply 62 3.6.4. large Rig Load Cell , 62 . 3-6.5- Small Rig Load Cell 63 3-6.6. Pressure Transducers 63 3.6.7. 'The Strain Transducer 6/1 3.7 The Controlled Strain Rig 66 (vi) CHAPTER FOUR EXPERIMENTAL METHOD 7-3 if. 1 Boils Classification Tests 73 4.1.2. Slaking Test 73 4.1.3- Aggregate Impact Test 7'4 4.1.4- Organic Carbon Determination 74 4.2 The Large Controlled Load Rig Method 75 4-2.1. Samp1e Pr eparat ion 7 5 4.2.2. Mounting of Sample 7.7 4-2.3- Saturation 79 4.2.4. The B-Test 7-9 4.2.5- Instrument Preparation $0 4-2.6. Consolidation 81 4.2.7. Testing 82 4-3 Controlled-strain Tests 83 4.4 The Small Controlled Load Rig Method 83 4.4-1- Sample Preparation 8.4 4-4.1.1- In Situ Samples 8'4 4-4-1-2. Made up Dense Samples 8-5 4-4-1-3- Made up Loose Samples 8 5 4-4-2. Mounting .the Sample 8;6 4-4-3. Saturation 88 4.4.4. Consolidation 88 4- 4-5- Testing . 8-9 CHAPTER FIVE CALCULATION OF RESULTS 9.0 5.1 Presentation of Controlled Load Test Results 90 5.1.1. Failure Envelopes -90 5- 1-2. Stress Paths 9;.1 5.2 Calculation of Results 9''+ (vii) 5-3 Rubber Membrane Correction 95 5.4 Coefficient of Consolidation 9^ CHAPTER SIX RESULTS FOR COARSE DISCARDS 97 CHAPTER SEVEN RESULTS FOR FINE DISCARDS 118 CHAPTER EIGHT DISCUSSION FOR COARSE DISCARDS 131 8.1 General 131 8.2 Controlled Strain Test Results 13.1 8.2.1. Gedling 132 8.2.2. Abernant -133 8.3 Gedling Controlled Load Tests 134 8.3.L Consolidation 134 8.3.2. Behaviour During Testing 135 0.3.3- Stress Paths and Stress-Strain Curves 13& 8.3'4» Possible Implications of a Partial Liquefaction 138 8.4 Abernant Controlled Load Tests 1.41 8.4.1. Consolidation 1.4;i 8.4.2. Behaviour During Tests 141 8.4.3. Stress Paths and Stress-Strain Curves 1if2 8.5 Pore Pressure versus Strain Plots 14 4 8.6 The Durham Seatearth and Shale Investigation 145 8.7 The Durham Shale 145 8.8. The Durham Seatearth 147 8.9 The Seatearth/Abernant Mixtures 14:8 8.10 Discussion of differences in material properties influencing the behaviour in the controlled load tests 151 8.10.1. Shape 151 (viii) 8.10.2. Grading 152 8.10.3. Strength 153 8.10. if. The Effects of Water 156 8.10.5. Pore Pressure Dissipation 15? 8.10.6. Chemistry and Mineralogy 158 8.11 Conclusions 15§ CHAPTER NINE DISCUSSION OF FINE DISCARDS 161 9.1 General 161 9.2 Peckfield Slurry 162 9.2.1. The Made-up Samples 163 9*2.2. The In Situ Samples 164 9.2.3. Reasons for the Differences 166. 9.2.4. Conclusions 16? 9-3 Abernant Fine Discard 167 9.3.1.. Behaviour During the Tests 167 9-3-2. Stress Paths and Stress-strain Curves 16$ 9.3.3. The E Line 170 9-3-4- Effects of Liquefaction 172 9-3-5- Conclusions 173 9.4 Factors affecting Behaviour 173 9.^.1.