University of Tennessee, Knoxville TRACE: Tennessee Research and Creative Exchange Doctoral Dissertations Graduate School 5-2019 EVALUATION OF TIME RATE OF CONSOLIDATION AND UNDRAINED SHEAR STRENGTH OF HYDRAULICALLY PLACED FINE COAL REFUSE Cyrus Jedari Sefidgari University of Tennessee, [email protected] Follow this and additional works at: https://trace.tennessee.edu/utk_graddiss Recommended Citation Jedari Sefidgari, Cyrus, "EVALUATION OF TIME RATE OF CONSOLIDATION AND UNDRAINED SHEAR STRENGTH OF HYDRAULICALLY PLACED FINE COAL REFUSE. " PhD diss., University of Tennessee, 2019. https://trace.tennessee.edu/utk_graddiss/5408 This Dissertation is brought to you for free and open access by the Graduate School at TRACE: Tennessee Research and Creative Exchange. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of TRACE: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. To the Graduate Council: I am submitting herewith a dissertation written by Cyrus Jedari Sefidgari entitled "EVALUATION OF TIME RATE OF CONSOLIDATION AND UNDRAINED SHEAR STRENGTH OF HYDRAULICALLY PLACED FINE COAL REFUSE." I have examined the final electronic copy of this dissertation for form and content and recommend that it be accepted in partial fulfillment of the equirr ements for the degree of Doctor of Philosophy, with a major in Civil Engineering. Angelica M. Palomino, Eric C. Drumm, Major Professor We have read this dissertation and recommend its acceptance: Khalid A. Alshibli, John S. Schwartz Accepted for the Council: Dixie L. Thompson Vice Provost and Dean of the Graduate School (Original signatures are on file with official studentecor r ds.) EVALUATION OF TIME RATE OF CONSOLIDATION AND UNDRAINED SHEAR STRENGTH OF HYDRAULICALLY PLACED FINE COAL REFUSE A Dissertation Presented for the Doctor of Philosophy Degree The University of Tennessee, Knoxville Cyrus Jedari Sefidgari May 2019 Copyright © 2019 by Cyrus Jedari Sefidgari All rights reserved. ii DEDICATION I dedicate my work to my beloved wife Mina for her endless love and support. iii ACKNOWLEDGEMENTS I would like to express my gratitude to my advisors Dr. Angel Palomino and Dr. Eric Drumm for providing me with the opportunity to work in this project. It could not be accomplished without their kind supports. Also, I am thankful for Dr. Khalid Alshibli and Dr. John Schwartz for serving on my committee and for their valuable guidance throughout the study. I would like to gratefully acknowledge financial support for this project received from the Office of Surface Mining and Reclamation Enforcement (OSMRE) of US Department of Interior. I would also like to acknowledge the assistance of Howard Cyr, Daniel Boles, Dr. John Dunlap, Nancy Roberts and Andy Baker, for their support in performance of experiments. Also, I would like to thank Ryan Livesey, Kendra Jackson, Rebekah Kish, James Throckmorton and Laura Ferrer to help on laboratory experiments. Finally, I would like to express my deepest gratitude to my parents and my family. I would like to thank my wife Mina Irani and her parents for their love and support through path of self-discovery and my friends for staying in touch despite the distance. iv ABSTRACT Fine coal refuse (FCR) refers to the fines generated during the processing of raw coal. FCR is usually mixed with flocculant and water and hydraulically placed behind impoundments. It is generally assumed that the FCR in these impoundments will consolidate over time due to the overburden weight of the materials above, losing some of the fluid-like properties that it possessed when initially placed. However, some in situ observations have shown that there exists under-consolidated material within slurry impoundments even after many decades of deposition. These under-consolidated materials can be prone to destabilization and flow, which can result in fatalities and environmental disasters. The purpose of this study is to investigate the consolidation behavior and effect of flocculant on the material properties and flowability of the FCR. Traditional consolidation tests were conducted on in situ FCR samples obtained from a range of depths behind an impoundment. The consolidation response of the in situ samples was compared with companion samples of fresh liquid slurry pre-consolidated to stresses corresponding to the depths of the recovered in situ samples. A finite difference model used to calculate time rate of consolidation of the FCR using variable coefficient of consolidation which was obtained by consolidating FCR slurry under different pressures. The results were compared to traditional Terzaghi method with constant coefficient of consolidation. Laboratory vane shear tests were conducted to study the influence of flocculant on undrained shear strength of the FCR and modified flow table tests performed on consolidated FCR slurry samples prepared with different background fluids. The results suggest that the variable coefficient of consolidation method may best predict the time rate of consolidation for the FCR slurry compared to traditional methods which use the in situ coefficient of consolidation. Although the particle size analysis revealed that the effect of flocculant degrades over the time, vane shear results suggest that the flocculant increases the undrained shear strength and can improve the FCR resistance to flow at early stages of consolidation. The results of this study give a better understanding of the consolidation behavior and undrained shear resistance of the hydraulically placed FCR behind impoundments. v TABLE OF CONTENTS 1 CHAPTER I INTRODUCTION .......................................................................................................... 1 PROBLEM STATEMENT ............................................................................................................... 2 OBJECTIVES ................................................................................................................................ 4 RESEARCH QUESTIONS .............................................................................................................. 4 ORGANIZATION .......................................................................................................................... 5 REFERENCES ............................................................................................................................... 6 2 CHAPTER II LITERATURE REVIEW ............................................................................................. 7 2.1. PHYSICAL CHARACTERIZATION AND INDEX PROPERTIES OF FCR ........................................ 9 RHEOLOGICAL BEHAVIOR OF FCR ........................................................................................ 15 CHARACTERISTICS OF IN-PLACE REFUSE .............................................................................. 19 MECHANICAL PROPERTIES OF FCR ....................................................................................... 21 EFFECTS OF FLOCCULANTS AND DISPERSANTS ON SOIL STRUCTURE AND ASSOCIATED MATERIAL RESPONSE ........................................................................................................................... 23 ACCELERATION OF CONSOLIDATION USING WICK DRAINS ................................................. 25 SITE INFORMATION .................................................................................................................. 25 REFERENCES ............................................................................................................................. 27 3 CHAPTER III IN SITU CHARACTERISTICS OF FINE COAL REFUSE .................................... 31 ABSTRACT ................................................................................................................................. 32 INTRODUCTION ......................................................................................................................... 32 EXPERIMENTAL METHODS ...................................................................................................... 34 RESULTS AND DISCUSSION ....................................................................................................... 35 CONCLUSIONS ........................................................................................................................... 43 REFERENCES ............................................................................................................................. 44 4 CHAPTER IV RHEOLOGY AND THE PARTICLE AND FLOC SIZE DISTRIBUTION OF FCR 45 ABSTRACT ................................................................................................................................. 46 INTRODUCTION ......................................................................................................................... 46 EXPERIMENTAL METHODS ...................................................................................................... 50 4.3.1 MATERIALS .......................................................................................................................... 50 4.3.2 METHODS ............................................................................................................................. 51 RESULTS .................................................................................................................................... 56 4.4.1 HYDROMETER ANALYSIS ...................................................................................................