USE OF CAPILLARY ACTION TO CONTROL SOIL MOISTURE by MAHYAR HEIDAR BARGHI A thesis submitted to the University of Birmingham for the degree of DOCTOR OF PHILOSOPHY Department of Civil Engineering School of Engineering College of Engineering and Physical Sciences The University of Birmingham August 2018 University of Birmingham Research Archive e-theses repository This unpublished thesis/dissertation is copyright of the author and/or third parties.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 Heavy rainfall on sloping ground preceded by prolonged dry period can lead to increased risk of failure of slopes. This can lead to significant impact on infrastructure (both road and rail), which invariably comprises both embankments and cuttings. With global warming, there is an increase in risk of extreme weather and hence likelihood of failure incidents is higher. Capillarity is one of the major water movement mechanisms in soil and thus, there was the need to study the subject. A laboratory based investigation was conducted with the aim of raising water by capillary action and removal of water from the soil surface by the action of wind. The first series of experiments were conducted to investigate the capillary rise of water in soils and more importantly how to improve the height of capillary rise and the volume of water that could be drawn up using capillary action. It included column tests with the base of the soil columns in water and in soil with a range of moisture contents. Final series of tests were conducted to assess the feasibility of using a soil column to draw up water from a free water surface to a higher level where water was removed from the surface by the action of wind with a view to continuously remove water. This involved placing the top of the column in a wind tunnel while the column was stood in water. Overall this study shows that both capillarity and suction created by the wind has the potential to be developed for successful lifting of water. Such a system would not require much energy input, however, it may take longer to lift water at a lesser rate compared to conventional pumping systems. ii Dedication This work is dedicated to Mahsa, Moonia, Fariba and Kazem. iii Acknowledgements I will always feel indebted to both my supervisors Dr. Gurmel Ghataora and Dr. Michael Burrow. Their continuous support and enthusiasm during all stages of the project always drove me forward and made me feel passionate about the subject throughout my research. I would like to express my special thanks and appreciation to Dr Ghataora and Dr Burrow for the critical review of my thesis. I must acknowledge the support of laboratory technicians Mr. Sebastian Ballard, Mr. Luis Portela, Mr. Michael Vanderstam, Mr. James Guest, Mr. David Allsop, Mr. David Cope, Mr. Mark Carter and Mr. James Glover at the University of Birmingham. I would like to thank Emmanuel Hitimana, Nowsherwan Abbas and Mengqi Lyu, M.Sc. students at the Department of Civil Engineering, for their assistant during the laboratory work. Special thanks goes to Stefanie Gillmeier for kindly demonstrating the use of smoke generator in the laboratory. I would also like to acknowledge the support of my friends, colleagues and all the staff at the University of Birmingham. Finally, I most gratefully acknowledge my family, Kazem, Fariba, Mahsa and Moonia for their love, encouragement, patience and support in all of my endeavours in my life. iv Table of Contents 1 Introduction ..................................................................................................................... 1 1.1 Statement of the research problem ........................................................................... 1 1.2 Potential impacts of climate change on earth slopes ................................................ 2 1.3 Failure modes of slopes due to climate change ........................................................ 5 1.3.1 Shrink–swell ...................................................................................................... 5 1.3.2 Progressive failure ............................................................................................. 5 1.3.3 Pore water pressure equilibration (re-wetting) .................................................. 6 1.3.4 Surface creep ..................................................................................................... 6 1.4 Methods of slope drainage ....................................................................................... 7 1.5 Background Theory of the research ....................................................................... 12 1.6 Current commercialised capillary drainage technology ......................................... 14 1.7 The Aim and Objectives of the research ................................................................ 16 1.8 Scopes and limitations of the study ........................................................................ 16 2 Literature review ........................................................................................................... 17 2.1 Physical properties of soils ..................................................................................... 17 2.1.1 Soil type based on particle size ....................................................................... 17 2.1.1 Soil particle density ......................................................................................... 18 2.1.2 Soil bulk density .............................................................................................. 18 2.1.3 Soil porosity .................................................................................................... 19 2.1.4 Soil water content ............................................................................................ 20 2.2 Mechanisms of water movement in soils ............................................................... 21 2.2.1 Pressure potential ............................................................................................ 23 2.3 Development of surface tension at the gas-liquid interface ................................... 26 2.4 The importance of wetting on capillary rise ........................................................... 27 2.4.1 Pressure difference across an interface and contact angle .............................. 27 2.5 Capillarity ............................................................................................................... 31 2.5.1 Theoretical considerations of capillary rise .................................................... 31 2.5.2 Source of the energy for capillary rise ............................................................ 37 2.5.3 Concluding considerations on capillary rise ................................................... 40 2.5.4 Conceptual capillary finger model .................................................................. 42 2.5.5 Height of capillary rise in soils ....................................................................... 43 v 2.6 Summary of previous experimental studies related to the research ....................... 47 2.7 Evaporation and Evapotranspiration ...................................................................... 50 2.7.1 General ............................................................................................................ 50 2.7.2 Physical Conditions of Evaporation from Soils .............................................. 50 2.7.3 Evaporation processes ..................................................................................... 52 2.7.4 Stages of evaporation ...................................................................................... 52 2.7.5 Controlling parameters of evaporation from soil surfaces .............................. 54 2.7.5.1 Radiation ....................................................................................................... 54 2.7.5.2 Temperature .................................................................................................. 54 2.7.5.3 Wind .............................................................................................................. 55 2.7.5.4 Humidity ........................................................................................................ 55 2.7.5.5 Soil moisture content ..................................................................................... 56 2.7.5.6 Vegetation ..................................................................................................... 57 2.8 Effects of layering of soils on water movements in a soil profile with a water table……………………………………………………………………………………….. 58 2.8.1 Water movement in homogeneous soils .......................................................... 58 2.8.2 Water movements in layered soils .................................................................. 59 2.8.2.1 Downward water movement in layered soils ................................................ 60 2.8.2.2 Upward water movement in layered soils ..................................................... 61 3 Materials used and testing methodology ......................................................................