Physical Modelling of Vibro Stone Column Using Recycled Aggregates

PHYSICAL MODELLING OF VIBRO STONE COLUMN USING RECYCLED AGGREGATES by ROXANA AMINI A thesis submitted to the University of Birmingham for the degree of DOCTOR OF PHILOSOPHY School of Civil Engineering College of Engineering and Physical Sciences University of Birmingham January 2015 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties. The intellectual property rights of the author or third parties in respect of this work are as defined by The Copyright Designs and Patents Act 1988 or as modified by any successor legislation. Any use made of information contained in this thesis/dissertation must be in accordance with that legislation and must be properly acknowledged. Further distribution or reproduction in any format is prohibited without the permission of the copyright holder. Abstract Vibro-stone column (VSC) is one of the most commonly used ground improvement techniques worldwide. It provides a column-soil composite to reinforce soft ground; increasing the bearing capacity and improving the settlement characteristics. The performance of the VSC depends on the quality of aggregates used and the interaction with the surrounding soil. The overall mechanism is understood. However, the impact of installation methods used and the choice of aggregates to form the columns are still unknown which can result in short and long-term failures of the columns. This is further hampered by the use of aggregate index tests that do not represent the actual environment of the installation process. As opposed to previous research where only sand, gravel and primary aggregates were used in the unit cell modelling of the VSCs, in this research a selection of primary (granite) and three recycled aggregates (crushed concrete and brick, incinerator bottom ash aggregate types 1 and 2) which are commonly used in the practice of VSCs were compared in the actual context of the installation and loading of a single stone column in soft clay. The aggregate index tests recommended by the standards were performed on all of the primary (PA) and the recycled aggregates (RA). The results showed that in most of the index tests, the RAs performed poorly compared to the granite and based on these criteria they could not be used for the construction of VSCs. However, in this research the aggregates were modelled in two sets of the large and the small unit cell tests (LUC and SUC) which were designed for the study of the behaviour of a single column in the short-term in which the dry top feed method of installation ii was used on the actual PA and the RAs, despite their unacceptable aggregate index tests results. In both of the unit cell tests, the RAs behaved comparable to the PA in terms of the load carrying capacity and showed that the aggregate index tests results alone should not be considered for the selection of the materials for the use in the context of the VSC. The particle size distribution (PSD) and well-graded or uniformly graded range of the aggregates were found to be one of the most important factors affecting the column density and formation and ultimately its load carrying capacity. In the LUC tests it was concluded that the existence of the VSC increased the load carrying capacity of the host ground by approximately 60% regardless of the type of the aggregates used. Despite the unacceptable results in the index tests, the RAs performed satisfactorily in the unit cell tests and improved the load carrying capacity of the ground by up to 190% and also, due to their well-graded PSD and the level of packing achieved in the column outperformed the PA in the stress-strain comparison under similar installation and loading conditions. The condition of the aggregates (wet/dry) was an important factor in terms of the performance.The columns of wet aggregates performed between 10 to 15% poorer in the LUC compared to the columns of the dry aggregates under the loading, especially when the wet recycled material was loaded. In the SUC, three series of tests were performed to understand: 1) the effect of installation versus the loading on the crushing of both the PA and the RAs, 2) the effect of the time (energy) of compacting of each layer of the PA during installation on the load carrying capacity and 3) the effect of contamination of the PA with fine material on the load-settlement behaviour of the VSC. iii In the first series of the SUC tests the RAs were crushed up to 5% more than the PA during the installation. The level of crushing of the RAs was up to 2% during the loading and the crushing of the PA was minimal during both the installation and loading stages. It was concluded that the installation forces can cause more change in the PSD of the materials whereas, during the loading the nature of the RAs can hold the particles together and prevent any further crushing. In the second series of the small unit cell tests it was observed that 50% reduction in the duration (energy) of installation resulted in 10% reduction in the density of the column and ultimately 40% reduction in the load carrying capacity of the composite (column of the PA and the soft clay); whereas an increase of three times in the time of vibrations increased the bearing capacity by almost 35%. The time of installation per layer of aggregates should be sufficient enough for the column formation (proper diameter and length should be achieved) to carry the loads and over-treatment should be avoided due to ground heave and a less cost-effective project. In the third series of the SUC tests the addition of fines to the column of granite reduced the bearing capacity by approximately 40% when 10 and 20% fines were added compared to the column which was free from fines. During the storage, transportation and the installation process fines might be introduced to the column material that can affect the performance of the VSCs in the short-term. iv Dedication For my dearest parents Azita and Bahram And my beloved brother Khashayar v Acknowledgements First of all I would like to thank my supervisor Professor Ian Jefferson for his unconditional help, patience and support throughout my entire studies at University of Birmingham. Professor Jefferson always had faith in me and believed that I could do this research and kept encouraging me even at times I never believed in myself. I cannot fully express my thanks and gratitude to my wonderful family for giving me this opportunity to study these many years; my father who not only helped me all the way as a most knowledgeable and experienced Civil engineer but also always valued my happiness and studies above everything else in his life. My mother who was always so patient and understanding; it would not have been possible without her motivation and encouraging words. I am truly grateful to my talented brother who helped with technical drawings and also made difficult times easier through laughter and friendship. I could not have done this without any of you. I am very grateful for all the support from school of civil engineering, academics and staff and specially my co-supervisor Dr. Gurmel Ghataora who helped me enormously in laboratory modelling; I cannot thank him enough. I would specially like to thank all the technicians at civil engineering laboratories, Mr. Michael Vanderstam, Mr. James Guest, Mr. Mark Carter, Mr. David Coop, Mr. Bruce Reed and specially Mr. Sebastian Ballard whose help was priceless. I am so thankful for Mr. Ballard’s attitude who transformed my visions to reality. I would also like to express my sincere thanks to all my friends in F55 office, especially Mehran, Sahand, Tom, Jabbar and Aria who were always helping and encouraging vi friends. I would like to specially thank Mr. Matthew Bailey for his help in my laboratory tests and Mr. Charles Marshall for his advice on my writing. vii Abbreviations AA Alternative aggregate ACV Aggregate crushing value AIV Aggregate impact value CC/CB Crushed concrete and crushed brick GWL Ground water level IBAA Incinerator bottom ash aggregate LA Los Angeles LUC Large unit cell PA Primary aggregate PSD Particle size distribution RA Recycled aggregate SA Secondary aggregate SUC Small unit cell TFV Ten percent fines value VSC Vibro stone column viii Table of Contents 1. INTRODUCTION ................................................................................................................. 1 1.1 Background ................................................................................................................... 2 1.2 The use of alternative aggregates .................................................................................. 4 1.3 Research aim ................................................................................................................. 4 1.4 Research objectives ....................................................................................................... 5 1.5 Thesis outline ................................................................................................................ 8 1.6 Summary ..................................................................................................................... 12 2. LITERATURE REVIEW ON PEROFRMANCE OF VIBRO STONE COLUMN ........... 14 2.1 Ground improvement and vibro techniques ................................................................ 15 2.1.1 Introduction to ground improvement ......................................................................... 15 2.1.2 Vibro stone column ...................................................................................................

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