Assessment and stabilization of micaceous soils By Jiahe Zhang BSc (Hons) Thesis submitted in fulfillment of the requirements for the degree of Doctor of Philosophy The University of Adelaide Faculty of Engineering, Computer and Mathematical Sciences School of Civil, Environmental and Mining Engineering Copyright © May 2019 Summary Mica is a mineral widely distributed around the world. This mineral generally occurs in igneous, sedimentary and certain metamorphic rocks and, if breaks down from the parent rocks, shows a unique platy structure and high elasticity. These features may affect performance of soils adversely which mica lies in, causing instability concerns to construction work or infrastructure systems involving the micaceous soils. One of the solutions is to assess the adversities arising from occurrence of mica and, using chemical and mechanical techniques, to stabilize the micaceous soils. The research presented in this thesis was conducted to develop the solution and to provide suitable guidance to implement it. The research was divided into three important aspects: i) assessing the effect of mica content on the mechanical properties of clays, ii) stabilizing the micaceous soils mechanically or chemically with jute fiber, lime, granulated blast furnace slag (GBFS), and slag-lime, and iii) formulating the stabilization outcomes using the surface response methodology and optimizing the stabilization. Different contents of mica were added to the soils to form the micaceous soils for testing. The experimental program consisted of consistency limits, standard Proctor compaction, unconfined compression (UC), direct shear and scanning electron microscopy tests. The test results suggested that the liquid and plastic limits exhibited a linearly increasing trend with an increase in the mica content. The rate of increase in the plastic limit, however, was observed to be greater than that of the liquid limit, thereby leading to a gradual transition towards a non- plastic behavior. The spongy nature and high-water demand of the mica minerals led to higher optimum water contents and lower maximum dry unit weights with an increase in the mica content. Under low confinement conditions, the strength properties were adversely affected by mica. However, the closer packing of the clay and mica components in the matrix under high confinement conditions offsets the adverse effects of mica by inducing the frictional resistance at the shearing interface. A series of soil stabilization attempts were made to reinforce the micaceous soils. The combined capacity of mechanical stabilizer, jute fiber and different cementitious binders such as lime, GBFS and slag-lime, were examined towards ameliorating the inferior properties of micaceous clays. The test results indicated that the inclusion of fiber consistently improved the I ductility and toughness of the composite, and the addition of cementitious binders into soil- fiber composite further improved the connection interface, and thus led to the improvements in the composites’ strength, stiffness and toughness. Moreover, a non-linear, multivariable regression model was developed to quantify the peak UC strength as a function of the fiber content, slag content and the curing time, and the predictive capacity of the proposed models was examined and further validated by statistical techniques. A sensitivity analysis was also carried out to assess the relative impacts of the independent regression variables on the UC strength. The proposed regression model contained a limited number of fitting parameters, all of which can be calibrated by a standard experimental effort, as well as simple explicit calculations, and hence implemented for preliminary design assessments and predictive purposes. Response surface methodology (RSM) was employed to design the experiments, to evaluate the results and finally to optimize the binders’ content. The results showed that slag exhibited a noticeable synergistic effect and greatly contributed to the stabilization of micaceous soils with the presence of fiber or polyacrylamide. The RSM-based optimization was able to determine the additives dosage in terms of targeted UC strength values, and based on the developed models, to identify the most efficient dosage of improving micaceous soils for backfilling or other construction works. This research has delivered important outcomes for publications. The publications are listed below: J-H Zhang, A Soltani, A Deng and M Jaksa, 2019. Mechanical performance of jute fiber- reinforced micaceous clay composites treated with ground-granulated blast-furnace slag. Materials. DOI: 10.3390/ma12040576 J-H Zhang, A Soltani, A Deng and M Jaksa, 2019. Mechanical behavior of micaceous clays. J Rock Mech Geotech Eng. DOI: 10.1016/j.jrmge.2019.04.001 J-H Zhang, A Deng and M Jaksa, 2019. Mechanical behaviour of micaceous soils stabilized by lime, slag-lime with fibers. Written in manuscript style for submission in one month J-H Zhang, A Deng and M Jaksa, 2019. Optimization of slag and fiber/polymeric agent to reinforce micaceous soils using response surface methodology. Written in manuscript style for submission in one month II Keywords: Geotechnical engineering; micaceous clays; strength and testing of materials; scanning electron microscopy; multivariable regression; jute fibers; ground- granulated blast-furnace slag; polyacrylamide; polypropylene fibers; central composite design; response surface methodology III Statement of Originality I certify that this work contains no material which has been accepted for the award of any other degree or diploma in my name, in any university or other tertiary institution and, to the best of my knowledge and belief, contains no material previously published or written by another person, except where due reference has been made in the text. In addition, I certify that no part of this work will, in the future, be used in a submission in my name, for any other degree or diploma in any university or other tertiary institution without the prior approval of the University of Adelaide and where applicable, any partner institution responsible for the joint– award of this degree. I acknowledge that copyright of published works contained within this thesis resides with the copyright holder(s) of those works. I also give permission for the digital version of my thesis to be made available on the web, via the University’s digital research repository, the Library Search and also through web search engines, unless permission has been granted by the University to restrict access for a period of time. I acknowledge the support I have received for my research through the provision of an Australian Government Research Training Program Scholarship. Jiahe Zhang BSc (Hons) Signature: __ __ Date: _______________02/05/2019 IV Acknowledgements This Ph.D. research began in October 2015 and has been carried out on a full-time basis ever since. I would like to express my sincere gratitude to my supervisor, Dr. An Deng and Prof. Mark Jaksa, of the School of Civil, Environmental and Mining Engineering, for the patience, motivation, and continuous support throughout this Ph.D. study. Their guidance and encouragement have been of great value to me, and I could not have imagined Besides my supervisors, I would like to thank my fellow Dr. Amin Soltani, not only for his invaluable contribution to this research, but also the encouragement, and kind support in life throughout the period of my candidature. I am thankful to the School of Civil, Environmental and Mining Engineering, particularly the laboratory staff, Mr. Gary Bowman, Mr. Dale Hodson and Mr. Simon Golding, for their kind assistance with the experimental work. Last but not the least, I would like to thank my family, especially my mother, for supporting me spiritually throughout this Ph.D. study, and the sacrifice she made throughout my life. She is the most important person in my world and I dedicate this thesis to her. V Table of Contents Summary .................................................................................................................................... I Statement of Originality ........................................................................................................... IV Acknowledgements ................................................................................................................... V Chapter 1: Thesis Overview....................................................................................................... 1 1.1. Problem Statement .............................................................................................................. 1 1.2. Research Gaps ..................................................................................................................... 2 1.3. Research Objectives and Thesis Layout ............................................................................. 3 1.4. Concluding Remarks ........................................................................................................... 4 References .................................................................................................................................. 8 Chapter 2: Mechanical Behavior of Micaceous Clays ............................................................... 9 Abstract ...................................................................................................................................... 9 Abbreviations ..........................................................................................................................