FRAMEWORK FOR ESTIMATION OF THE LATERAL EARTH PRESSURE ON RETAINING STRUCTURES WITH EXPANSIVE AND NON-EXPANSIVE SOILS AS BACKFILL MATERIAL CONSIDERING THE INFLUENCE OF ENVIRONMENTAL FACTORS by Jiaying Guo Thesis submitted to the Faculty of Graduate and Postdoctoral Studies in partial fulfillment of the requirements for the degree of Master of Applied Science in Civil Engineering Department of Civil Engineering Faculty of Engineering, University of Ottawa Ottawa, Ontario, Canada © Jiaying Guo, Ottawa, Canada, 2016 DEDICATION I dedicate this thesis to my beloved parents ii ACKNOWLEDGEMENT The completion of this thesis could not have been possible without the help of Prof. Sai K. Vanapalli, my beloved supervisor. His expertise, patience, consistent guidance and unconditional supports have helped me bring this thesis into reality. I would like to thank my colleagues at the University of Ottawa: Zhong Han, Hongyu Tu, Shunchao Qi, Yunlong Liu, Ping Li, Penghai Yin, and Junping Ren. These graduate students are extremely hardworking individuals and passionate with their research in the area of unsaturated soils. It has been a great pleasure jointly working with this talented group of students. I have immensely benefited from their friendship, encouragement and continuous support. I would also like to take this opportunity to thank my parents. Without their support, encouragement and understanding, it would not have been possible for me to achieve my goals of higher education. iii ABSTRACT Lateral earth pressures (LEP) that arise due to backfill on retaining structures are typically determined by extending the principles of saturated soil mechanics. However, there is evidence in the literature to highlight the LEP on retaining structures due to the influence of soil backfill in saturated and unsaturated conditions are significantly different. Some studies are reported in the literature to interpret the variation of LEP on the retaining structures assuming that the variation of matric suction in unsaturated backfill material is hydrostatic (i.e. matric suction is assumed to decrease linearly from the surface to a value of zero at the ground water table). Such an assumption however is not reliable when the backfill behind the retaining wall is an expansive soil, which is extremely sensitive to the changes in variation of water content values. Significant volume changes occur in expansive soils due to the influence of environmental factors such as the infiltration and evaporation. In addition to the volume changes, the swelling pressure of the expansive soils also varies with changes in water content and can significantly influence the LEPs behind the retaining wall. In this thesis, a framework for estimating the LEPs of unsaturated soils is proposed considering the variation of matric suction with respect to various water flow rates (i.e. infiltration and evaporation). The proposed approach is extended for expansive and non-expansive soils in this thesis taking into account of the influence of both the cracks iv and the lateral swelling pressure with changes in water content. A program code LEENES (Lateral pressure estimation on retaining walls taking account of Environmental factors for Expansive and Non-Expansive Soils) in MATLAB is written to predict the LEP. The program LEENES is valuable tool for geotechnical engineers to estimate the LEPs on retaining structures for various scenarios that are conventionally encountered in geotechnical engineering practice. The studies presented in this thesis are of interest to the practitioners who routinely design retaining walls with both expansive and non-expansive soils as backfill material. v CONTENTS .............................................................................................................................. 1 INTRODUCTION.....................................................................................................................1 1.1 Statement of the problem...........................................................................................1 1.2 Objectives................................................................................................................... 5 1.3 Novelty of the research..............................................................................................7 1.4 Thesis layout...............................................................................................................9 ............................................................................................................................ 11 LITERATURE REVIEW....................................................................................................... 11 2.1 Introduction.............................................................................................................. 11 General.............................................................................................................. 13 Classification.................................................................................................... 14 Mineralogy........................................................................................................19 Swelling Mechanics......................................................................................... 23 2.2 Steady-state water flow............................................................................................25 2.3 Swelling pressure..................................................................................................... 28 Laboratory tests................................................................................................ 29 Semi-empirical and empirical equations........................................................ 30 Relationship between the lateral and vertical swelling pressures.................32 2.4 Fissures and cracks in unsaturated expansive soils...............................................37 vi The formation and propagation of fissures and cracks..................................37 The effect of fissures and cracks.....................................................................38 Determination of fissures and cracks..............................................................38 2.5 Stress state variables for unsaturated soils.............................................................42 2.6 Soil-water characteristic curve................................................................................43 Laboratory tests................................................................................................ 46 Mathematical models for the SWCC..............................................................51 2.6.3 Shear strength of unsaturated soils..................................................................55 2.6.4 Tensile strength of unsaturated soils...............................................................59 2.7 Retaining walls.........................................................................................................61 2.7.1 Categories of retaining walls and their failure modes...................................62 2.7.2 Backfill material............................................................................................... 66 2.7.3 Lateral earth pressure.......................................................................................67 2.8 Summary...................................................................................................................75 ............................................................................................................................ 76 PREDICTION OF THE DEPTH OF CRACKS AND LATERAL SWELLING PRESSURE..............................................................................................................................76 3.1 Introduction.............................................................................................................. 76 3.2 Background...............................................................................................................77 3.3 Prediction of the depth of cracks............................................................................ 79 3.4 Prediction of the lateral swelling pressure............................................................. 81 Determination of the elastic modulus of unsaturated expansive soil...........81 vii Proposed method for the relationship between the vertical and lateral swelling pressure.............................................................................................................83 3.5 Example problem..................................................................................................... 87 3.6 Summary...................................................................................................................92 ............................................................................................................................ 94 PROPOSED APPROACH FOR PREDICTING LATERAL EARTH PRESSURE......... 94 4.1 Introduction.............................................................................................................. 94 4.2 Background...............................................................................................................95 4.3 Lateral earth pressure...............................................................................................97 Earth pressure during drying process..............................................................97 Earth pressure during wetting process..........................................................101