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Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. GSP 300 PanAm Unsaturated Soils 2017 Plenary Papers Papers from Sessions of the Second Pan-American Conference on Unsaturated Soils Dallas, Texas November 12–15, 2017 Edited by Laureano R. Hoyos, Ph.D., P.E. John S. McCartney, Ph.D., P.E. Sandra L. Houston, Ph.D., D.GE William J. Likos, Ph.D. Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. GEOTECHNICAL SPECIAL PUBLICATION NO. 300 PANAM UNSATURATED SOILS 2017 PLENARY PAPERS SELECTED PAPERS FROM SESSIONS OF THE SECOND PAN-AMERICAN CONFERENCE ON UNSATURATED SOILS November 12–15, 2017 Dallas, Texas SPONSORED BY International Society of Soil Mechanics and Geotechnical Engineering The Geo-Institute of the American Society of Civil Engineers EDITED BY Laureano R. Hoyos, Ph.D., P.E. John S. McCartney, Ph.D., P.E. Sandra L. Houston, Ph.D., D.GE William J. Likos, Ph.D. Published by the American Society of Civil Engineers Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Published by American Society of Civil Engineers 1801 Alexander Bell Drive Reston, Virginia, 20191-4382 www.asce.org/publications | ascelibrary.org Any statements expressed in these materials are those of the individual authors and do not necessarily represent the views of ASCE, which takes no responsibility for any statement made herein. No reference made in this publication to any specific method, product, process, or service constitutes or implies an endorsement, recommendation, or warranty thereof by ASCE. The materials are for general information only and do not represent a standard of ASCE, nor are they intended as a reference in purchase specifications, contracts, regulations, statutes, or any other legal document. 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Errata: Errata, if any, can be found at https://doi.org/10.1061/9780784481677 Copyright © 2018 by the American Society of Civil Engineers. All Rights Reserved. ISBN 978-0-7844-8167-7 (PDF) Manufactured in the United States of America. PanAm Unsaturated Soils 2017 GSP 300 iii Preface Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. The Second Pan-American Conference on Unsaturated Soils (PanAm-UNSAT 2017) was held in Dallas, Texas, November 12-15, 2017, featuring the latest research advances and engineering‐practice innovations in the area of Unsaturated Geotechnics, with a focus on characterization, modeling, design, construction, field performance and sustainability. PanAm-UNSAT 2017 follows a now well-established series of regional and international conferences on Unsaturated Soils, bringing together researchers, practitioners, students and policy makers from around the world, particularly the Americas. The conference built upon the success of PanAm-UNSAT 2013 (First PanAmerican Conference on Unsaturated Soils, Cartagena, Colombia), as well as that of previous conferences on unsaturated soils hosted in the United States, including UNSAT 2006 (Fourth International Conference on Unsaturated Soils, Carefree, Arizona) and EXPANSIVE’92 (Seventh International Conference on Expansive Soils, Dallas, Texas, 1992). Proceedings of PanAm-UNSAT 2017 have been documented in four Geotechnical Special Publications (GSP) of ASCE including Volume 1: Plenary Session Papers; Volume 2: Fundamentals; Volume 3: Applications; and Volume 4: Swell-Shrink and Tropical Soils. Current Volume 1 (Plenary Session Papers) consists of three sections: Section I includes 4 papers documenting the invited Keynote Lectures delivered by Profs. Delwyn Fredlund, Ning Lu, Bernardo Caicedo and Tacio de Campos, respectively; and 2 more companion papers documenting the First Distinguished Pan American Lecture on Unsaturated Soils delivered by Prof. Sandra L. Houston. Section II includes 6 papers documenting the invited Fredlund Symposium Lectures delivered by distinguished scholars in honor to the decades-long contribution of Prof. Delwyn G. Fredlund to the discipline of Unsaturated Geotechnics. Section III includes 6 more papers documenting the invited State-of-the-Art and State-of-the-Practice Lectures delivered by distinguished researchers and experienced practitioners from the region. Each paper was subject to rigorous technical review and received a minimum of two positive peer reviews before final acceptance by the conference technical committee. © ASCE PanAm Unsaturated Soils 2017 GSP 300 Acknowledgments Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. The following individuals deserve special acknowledgment and recognition for their direct involvement and efforts in making this regional conference a success: PanAm-UNSAT 2017 Program Committee Conference Chair: Laureano R. Hoyos, Ph.D., P.E., University of Texas at Arlington Conference Co-Chair: John S. McCartney, Ph.D., P.E., M.ASCE, University of California, San Diego Technical Program Chair: Sandra L. Houston, Ph.D., D.GE, M.ASCE, Arizona State University Technical Program Co-Chair: William J. Likos, Ph.D., M.ASCE, University of Wisconsin, Madison Local Chair: Marcelo J. Sanchez, Ph.D., Aff.M.ASCE, Texas A&M University Local Co-Chair: Gerald A. Miller, Ph.D., P.E., M.ASCE, University of Oklahoma Logistics Coordinator: Majid Ghayoomi, Ph.D., A.M.ASCE, University of New Hampshire Sponsorships/Exhibits Chair & Liaison from the G-I Technical Coordination Council (TCC): Anand J. Puppala, Ph.D., P.E., D.GE, F.ASCE, University of Texas at Arlington The Geo-Institute (G-I) of the ASCE Brad Keelor, Director Helen Cook, Board and Meetings Specialist Lucy King, Senior Manager, Conferences Cristina Charron, Manager, Conferences Drew Caracciolo, Manager, Sponsorships and Exhibits Rachel Hobbs, Administrator, Conferences The conference Program Committee would also like to acknowledge the officers of the TC106 Committee on Unsaturated Soils (ISSMGE), and all members of the Technical Advisory and International Technical Committees, who provided guidance and support during the early planning phases of the conference. TC106 Committee on Unsaturated Soils (ISSMGE) David Toll, Chair, University of Durham, UK Bernardo Caicedo, Vice Chair, Universidad de Los Andes, Bogotá, Colombia Adrian Russell, Secretary, University of New South Wales, Australia Technical Advisory Committee Sai Vanapalli, University of Ottawa, Canada Greg Siemens, Royal Military College, Canada Kanthasamy (Muralee) Muraleetharan, University of Oklahoma, USA © ASCE iv PanAm Unsaturated Soils 2017 GSP 300 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Xiong Zhang, University of Cincinnati, USA Ning Lu, Colorado School of Mines, USA Claudia Zapata, Arizona State University, USA Jorge Zornberg, University of Texas at Austin, USA Jorge Abraham Diaz-Rodriguez, UNAM, Mexico Bernardo Caicedo, Universidad de Los Andes, Bogotá, Colombia Julio E. Colmenares, Universidad Nacional, Bogotá, Colombia Orencio Villar, University of São Paulo, São Carlos, Brazil Tacio de Campos, PUC-Rio, Brazil Fernando Marinho, University of São Paulo, Brazil Manoel Porfírio Cordão Neto, Universidade de Brasília, Brazil Diego Manzanal, University of Buenos Aires, Argentina Alejo Sfriso, University of Buenos Aires, Argentina International Technical Committee David Toll, University of Durham, UK Adrian Russell, University of New South Wales, Australia Eduardo Alonso, UPC, Barcelona, Spain Antonio Gens, UPC, Barcelona, Spain Lyesse Laloui, EFP Lausanne, Switzerland J. Carlos Santamarina, KAUST, Saudi Arabia Charles Ng, HKUST, Hong Kong PanAm-UNSAT 2017 Session Chairs The conference Program Committee would also like to acknowledge the conference Session Chairs, who guided authors and reviewers through the draft and final phases of paper submission and review. In most cases, these chairs also served as on-site moderators during the conference itself. 01/ Dynamic Behavior of Unsaturated Soils, part I Majid Ghayoomi, Ph.D., A.M.ASCE, University of New Hampshire 02/ Dynamic Behavior of Unsaturated Soils, part II Nadarajah Ravichandran, Ph.D., M.ASCE, Clemson University Laureano R. Hoyos, Ph.D., P.E., M.G-I, University of Texas at Arlington 03/ Expansive Soils and Volume Change, Part I Rifat Bulut, Ph.D., M.ASCE, Oklahoma State University 04/ Expansive Soils and Volume Change, Part II Jairo E. Yepes, Ph.D., Universidad Santo Tomás, Bogotá, Colombia Ujwalkumar D. Patil, Ph.D., P.E., M.ASCE, University of Guam Liangbo Hu, Ph.D., A.M.ASCE, University of Toledo © ASCE v PanAm Unsaturated Soils 2017 GSP 300 05/ Expansive Soils and Volume Change, Part III Iraj Noorany, Ph.D., P.E., G.E., F.ASCE, Noorany Geotechnical Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. 06/ Pore Fluid Retention Behavior, Part I William J. Likos, Ph.D., M.ASCE, University of Wisconsin, Madison Idil Deniz Akin, Ph.D., A.M.ASCE, Washington State University 07/ Pore Fluid Retention Behavior, Part II Corrie Walton-Macaulay, Ph.D., P.E., M.ASCE, Bucknell University 08/ Hydraulic Behavior, Part I Leonardo D. Rivera, METER Group 09/ Hydraulic Behavior, Part II Leonardo D. Rivera, METER Group 10/ Shear Strength Behavior Ali Khosravi, Ph.D., Aff.M.ASCE, Sharif University of Technology 11/ Innovations in Testing, Part I Morteza Khorshidi, Ph.D., Aff.M.ASCE, Geosyntec Consultants Xin Kang, Ph.D., ACI, ASTM, A.M.ASCE, Hunan University 12/ Innovations in Testing, Part II Morteza Khorshidi, Ph.D., Aff.M.ASCE, Geosyntec Consultants Xin Kang, Ph.D., ACI, ASTM, A.M.ASCE, Hunan University 13/ Innovations in Testing, Part III Morteza Khorshidi, Ph.D., Aff.M.ASCE, Geosyntec Consultants Xin Kang, Ph.D., ACI, ASTM, A.M.ASCE, Hunan University 14/ Field Applications of Unsaturated Soils Gerald A. Miller, Ph.D., P.E., M.ASCE, University of Oklahoma 15/ Stability of Unsaturated Slopes, Part I Navid H. Jafari, Ph.D., A.M.ASCE, Louisiana State University 16/ Stability of Unsaturated Slopes, Part II Soonkie Nam, Ph.D., EIT, A.M.ASCE, Georgia Southern University 17/ Numerical Modeling: Flow and Deformation, Part I Zhen Liu, Ph.D., P.E., M.ASCE, Michigan Technological University © ASCE vi PanAm Unsaturated Soils 2017 GSP 300 vii 18/ Numerical Modeling: Flow and Deformation, Part II Xiaoyu Song, Ph.D., A.M.ASCE, University of Florida Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. 19/ Numerical Modeling: Coupled Processes Giuseppe Buscarnera, Ph.D., Aff.M.ASCE, Northwestern University 20/ Foundations on Expansive Soils Xiong Zhang, Ph.D., P.E. A.M.ASCE, Missouri University of Science and Technology 21/ Expansive Soils: Mitigation Bhaskar C.S. Chittoori, Ph.D., P.E., M.ASCE, Boise State University 22/ Expansive Soils: Modeling Xinbao Yu, Ph.D., P.E., M.ASCE, University of Texas-Arlington 23/ Pipeline and Transportation Structures in Unsaturated Soils Claudia E. Zapata, Ph.D., A.M.ASCE, Arizona State University Mohammad Sadik Khan, Ph.D., P.E., M.ASCE, Jackson State University 24/ Modeling of Cracked Soils and Effects of Cracking Marcelo J. Sanchez, Ph.D., Aff.M.ASCE, Texas A&M University 25/ Constitutive Modeling: Micro to Macro Kalehiwot N. Manahiloh, Ph.D., P.E., M.ASCE, University of Delaware 26/ Climate Effects and Permafrost Farshid Vahedifard, Ph.D., P.E., M.ASCE, Mississippi State University 27/ Energy Geotechnics, Bio-Geo, and Sustainability John S. McCartney, Ph.D., P.E., M.ASCE, University of California, San Diego PanAm-UNSAT 2017 Draft Paper Reviewers Finally, the Program Committee would also like to acknowledge those who contributed to the conference by serving as the primary reviewers of draft papers. Their efforts in providing careful, thorough reviews of each submission form the backbone of quality assurance, providing organizers the confidence that conference content would represent the best of current thinking in the field, and allowing these Proceedings to be published as a multi-volume Geotechnical Special Publication (GSP). Murad Abu Farsakh Raju Acharya Marshall Addison © ASCE Asif Ahmed Beena Ajmera Amir Akbari Garakani Idil Akin Miguel Alfaro Saumya Amarasiri PanAm Unsaturated Soils 2017 GSP 300 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Omar Amer Ron Andrus Mohamed Arab Andrew Assadollahi Guillermo Avila Kleio Avrithi Muwafaq Awad Ramdane Bahar Aritra Banerjee Tugce Baser Munwar Basha Bate Bate Melissa Beauregard Craig Benson Riad Beshoy Tejovikash Bheemasetti Katia Bicalho Mahnoosh Biglari Hemanta Bista Amin Borghei Tommy Bounds Rifat Bulut Giuseppe Buscarnera Jack Cadigan Donald Cameron Gaylon Campbell Junnan Cao Amy Cerato Uma Chaduvula Lizhou Chen Can Chen Bhaskar Chittoori Mehmet Cil Rodney Collins Jose Andres Cruz Sheng Dai Arghya Das Abhijit Deka Ludmilla Derk Yi Dong Ghada Ellithy David Elwood Matt Evans © ASCE viii Arvin Farid Ashok Gaire Fernando Garcia Lucas Garino Kevin Gaspard Antonio Gens Hande Gerkus Omid Ghasemi-Fare Saswati Ghatak Majid Ghayoomi Amin Gheibi Michael Gomez James Graham Xiangfeng Guo Marte Gutierrez Jumanah Hajjat MD Haque Arash Hassanikhah Kianoosh Hatami Carol Hawk Nathan Hayman Arash Hosseini Sandra Houston Laureano Hoyos Nejan Huvaj Tatsuya Ishikawa Navid Jafari Pegah Jarast Jay Jayatilaka Mohammad Sadik Kahn Edward Kavazanjian Mohammadreza Keshavarz Sadik Khan Morteza Khorshidi Arman Khoshghalb Mohammad Khosravi Ali Khosravi Naji Khoury Charbel Khoury Golam Kibria Wansoo Kim Sihyun Kim S. Sonny Kim Alan Kropp M. R. (Kantha) Lakshmikantha Eng Choon Leong Lin Li Jie Li William Likos Chuang Lin Zhen (Leo) Liu Jose Lizarraga Naresh M Michael Maedo Nariman Mahabadi Emad Maleksaeedi Kalehiwot Manahiloh Ferdinando Marinelli Alejandro Martinez David Mathon John McCartney Marta Miletic Gerald Miller Morteza Mirshekari Debakanta Mishra Shannon Mitchell Rigoberto Moncado Lopez M. Azizul Moqsud Ali Moradi Derek Morris Kimia Mortezaei Hamed Mousavi Masoud Mousavi Sayed Masoud Mousavi Balasingham Muhunthan Kanthasamy Muraleetharan Boo Hyun Nam Soonkie Nam James Nevels Thai Nguyen Wen-Jie Niu PanAm Unsaturated Soils 2017 GSP 300 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Iraj Noorany Hyunjun Oh Olurotimi Victor Ojekunle Austin Olaiz Orlando Oliveira Fatih Oncul Mandeep Pandey Youngjin Park Ujwalkumar Patil Meghdad Payan Aravind Pedarla James Phipps Hariprasad Ponnapu Allison Quiroga Harianto Rahardjo Mehrzad Rahimi Nadarajah Ravichandran Ronald Reed Leonardo Rivera Nick Rocco Breno Rocha Ivo Rosa Montenegro Hakan Sahin Sonia Samir Marcelo Sanchez Sireesh Saride Rajesh Sathiyamoorthy © ASCE ix Gokhan Saygili Sreedeep Sekharan Charles Shackelford Babak Shahbodaghkhan Mohammadreza Shakeri Longtan Shao Sunil Sharma Ajay Shastri Zhenhao Shi Jimmy Si John Siekmeier Greg Siemens Pawan Sigdel Behzad Soltanbeigi Chung Song Xiaoyu Song Timothy Stark Melissa Stewart Richard Sullivan HeMei Sun Amirata Taghavi Nagasreenivasu Talluri Rupert Tart, Jr. Oliver-Denzil Taylor Faraz Tehrani Colby Thrash Martin Tjioe Kala Venkata Uday Florian Unold Farshid Vahedifard Julio Valdes Sai Vanapalli B.V.S. Viswanadham Divya Viswanath Kenneth Walsh Hanlin Wang Kaiqi Wang Shaun Weldon Joshua White Xialong Xia Sudheer Yamsani Xiaoming Yang Yaolin Yi Xinbao Yu Atefeh Zamani Siavash Zamiran Bo Zhang Yida Zhang YouHu Zhang Chao Zhang Xiong Zhang Honghua Zhao Bohan Zhou Yang Zhou PanAm Unsaturated Soils 2017 GSP 300 x Contents Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Keynote Lectures and First Distinguished Pan American Lecture Effect of Initial Conditions on the Interpretation of Soil-Water Characteristic Curves (SWCCs) in Geotechnical Engineering .............................. 1 Delwyn G. Fredlund and Feixia (Cherry) Zhang Generalized Elastic Modulus Equation for Unsaturated Soil .............................. 32 Ning Lu A Mechanical Framework for Modelling Soil Compaction .................................. 49 Bernardo Caicedo Failure Mechanisms of Unsaturated Soil Slopes under Rainstorms in Rio de Janeiro, Brazil: An Overview ...................................................................... 69 Tácio M. P. de Campos, Mariana F. B. Motta, Thiago S. Carnavalle, Eurípedes do A. Vargas Jr., and Antônio R. M. B. de Oliveira Suction-Oedometer Method for Computation of Heave and Remaining Heave .......................................................................................................................... 93 Sandra L. Houston and William N. Houston Use of the Net Partial Wetting Factor (NPWF) Method of Computation of Remaining Heave: A Forensic Study ........................................ 117 Sandra L. Houston, Peter A. Stauffer, Michael W. West, Emma L. Bradford, and William N. Houston Delwyn G. Fredlund Symposium Lectures Numerical Analyses for Assessment of Geobarrier System Performance ........ 132 H. Rahardjo, Q. Zhai, A. Satyanaga, E. C. Leong, C. -L. Wang, and Johnny L. -H. Wong Empirical Approach for the Use of Unsaturated Soil Mechanics in Pavement Design ..................................................................................................... 149 Claudia E. Zapata Spatial Resolution of Degree of Saturation Measurements in Unsaturated Transparent Soil Experiments............................................................................... 174 G. A. Siemens and R. A. Beddoe © ASCE PanAm Unsaturated Soils 2017 GSP 300 Microstructure and Shear Strength of Widely Graded Soils during Desaturation ............................................................................................................ 185 Hongfen Zhao and Limin Zhang Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Fundamentals of Soil Shrinkage............................................................................ 198 F. A. M. Marinho Simple Approaches for the Application of the Mechanics of Unsaturated Soils into Conventional Geotechnical Engineering Practice ............................... 223 Sai K. Vanapalli and Zhong Han State-of-the-Art and State-of-the-Practice Lectures Desaturation via Biogenic Gas Formation as a Ground Improvement Technique ................................................................................................................ 244 Leon A. van Paassen, Vinh Pham, Nariman Mahabadi, Caitlyn Hall, Elizabeth Stallings, and Edward Kavazanjian Jr. Unsaturated Soil Mechanics in Mining................................................................. 257 L. A. Oldecop and G. Rodari Soil-Atmosphere Interaction in Unsaturated Soils Problem Solving................. 281 G. F. N. Gitirana Jr. Using Principles of Unsaturated Soil Behavior to Design Water Balance Covers for Waste Containment: Case Study........................................................ 306 Craig H. Benson Compaction and Volume Change Behavior of Embankment Soil ..................... 325 Gerald A. Miller State of the Practice in Mexico and Minnesota to Estimate the Effect of Water Content/Suction in Subgrade Soils and Granular Materials .................. 344 P. Garnica, N. Perez, J. Siekmeier, R. Roberson, and B. Tanquist © ASCE xi PanAm Unsaturated Soils 2017 GSP 300 Effect of Initial Conditions on the Interpretation of Soil-Water Characteristic Curves (SWCCs) in Geotechnical Engineering Delwyn G. Fredlund, P.E.1; and Feixia (Cherry) Zhang2 1 Golder Associates Ltd., 1721 8th St. East, Saskatoon, SK, Canada S7H 0T4. 2 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Ph.D. Student, Dept. of Civil and Environmental Engineering, Univ. of Alberta, Edmonton, AB, Canada T6G 2W2. Abstract The test procedure for measuring the soil-water characteristic curve, SWCC, have been largely established within the soil physics discipline over a period of several decades. More recently, these test procedures have been incorporated into geotechnical engineering practice. While there are benefits associated with utilizing past experience, further refinement of the analytical procedures used in soil physics are required when estimating unsaturated soil property functions. The primary assumption that has historically been made is that insignificant volume change occurs as soil suction is increased during the drying process. This assumption may be satisfactory for certain soil types and conditions, but in general, the effects of volume change are significant for many soils and must be taken into consideration when estimating USPFs. The shrinkage curve (SC) of a soil can be effectively used to take volume changes upon drying into consideration. The shrinkage curve can readily be measured but there are also a number of means whereby the curve can be estimated with sufficient accuracy. This paper outlines the steps involved in independently assessing the effects of volume change and desaturation on the calculation of unsaturated soil property functions. The shrinkage curve is used to separate the various volume-mass SWCCs required when dealing with various unsaturated soil mechanics problems. The proposed analytical procedure is described for estimation of hydraulic properties for low to high compressibility soils. INTRODUCTION Research studies on unsaturated soils have repeatedly shown that the relationship between the amount of water in a soil and soil suction (referred to as the soil-water characteristic curve, SWCC, or the water retention curve), is pivotal to the application of unsaturated soil mechanics‟ principles in geotechnical engineering practice. It is unfortunate, however, that there has been numerous inconsistencies with regard to the test and analytical protocols associated with the measured gravimetric water content based SWCC (referred to as w-SWCC). The primary use for the SWCC is for purposes of estimating unsaturated soil property functions, (USPFs), for various geotechnical engineering applications (Fredlund et al, 2012). The measurement of the w-SWCC has become the most common laboratory test performed to obtain insight into unsaturated soil behaviour. A common area of application of SWCCs in geotechnical engineering is the assessment of hydraulic properties required for modeling water movement through unsaturated soils. © ASCE 1 PanAm Unsaturated Soils 2017 GSP 300 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. The SWCC has been widely measured and used in agriculture-related disciplines such as soil physics for several decades, particularly for the estimation of unsaturated hydraulic conductivity (Klute, 1965). Attempts have been made to use similar interpretative procedures in geotechnical engineering as have been historically used in soil physics. There are advantages in being able to utilize the historical protocols and datasets; however, there are also disadvantages and limitations. The primary limitation is related to an assumption related to the amount of volume change that might occur as soil suction is increased during the drying process. While there may be insignificant volume changes that occur for low compressibility soils such as sands, it is clear that large volume changes can occur when testing other materials such as mine waste tailings and other slurries. Geotechnical engineers have attempted to adopt somewhat similar soil testing protocols and analytical data reduction procedures to those historically used in soil physics. It has become apparent, however, that refinements are necessary with regard to the interpretation of the SWCC for some soils. The primary improvement needed to more accurately utilize the SWCC for the estimation of USPFs is an understanding of the effect of volume change as soil suction is increased. The required additional information can be obtained through use of the shrinkage curve, SC, (i.e., the relationship between void ratio change and gravimetric water content change during drying). The objective of this paper is to provide a theoretical basis and associated analytical protocols for the refinements needed when solving unsaturated soil mechanics‟ problems in geotechnical engineering. The refinements focus on the interpretation of laboratory measured soil-water characteristic curves for purposes of estimating unsaturated soil property functions, USPFs. A couple of data sets are presented to illustrate how a measured (or estimated) shrinkage curve can be used to advantage in the interpretation of laboratory measured w-SWCCs. The scope is limited to consideration of the effects of the refined analysis for unsaturated hydraulic property functions. THEORETICAL FRAMEWORK FOR ESTIMATING UNSATURATED SOIL PROPERTY FUNCTIONS There are two independent stress state variables involved in describing unsaturated soil behaviour; namely, i.) net total (along with shear stress) variables with components in three orthogonal directions, [(1 - ua), (2 - ua), and (3 - ua)], and ii.) an isotropic matric suction (or soil suction) component, (ua – uw). The theoretical justification for using independent stress state variables is based on equilibrium considerations of a multiphase system within the context of continuum mechanics (Fredlund and Morgenstern, 1977; Fredlund, 2016). There are also two possible volume-mass properties that can change in response to a change in stress state. The soil state changes are: i.) a potential change in volume recorded as a change in void ratio, (de), and ii.) a potential change in degree of © ASCE 2 PanAm Unsaturated Soils 2017 GSP 300 3 saturation, (dS). There is also a potential for change of gravimetric water content, (dw), however, only two of the volume-mass variables are independent because of the conservation of mass requirement, (i.e., Se = Gsw where Gs is specific gravity of the soil solids). Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Incremental differentiation of the basic volume-mass relationship shows that gravimetric water content change could occur as a result of either a change in void ratio or a change in degree of saturation (Fredlund and Rahardjo, 1993). The stress state variables and volume-mass variables can be combined in a variety of ways to provide constitutive relations useful for the formulation of a variety of unsaturated soil mechanics problems. w  S f e  e f S Gs [1] where: w = gravimetric water content, e = void ratio, S = degree of saturation, and „f‟ = refers to the “final” volume-mass states. The separation of volume changes and degree of saturation changes drying an increase in soil suction can be accomplished through use of a shrinkage curve. The estimation of the permeability function and the water storage function for an unsaturated soil is used in this paper to illustrate the need for refinements in the commonly used estimation of USPFs. In general, commonly used analytical procedures have made the assumption that the soil does not change volume as soil suction is increased. One exception is the Brooks and Corey (1964) empirical procedure that uses the degree of saturation of the soil when estimating hydraulic conductivity. However, overall volume change as soil suction is increased is not commonly measured when performing the laboratory measurements of the SWCC. The intent of this paper is to explain how the shrinkage curve can be used to compute the instantaneous void ratio of a soil and thereby determine all volume-mass variables related to soil suction changes. It should also be noted that different volume-mass properties may be required when estimating other unsaturated soil property functions. EFFECT OF INITIAL CONDITIONING ON SWCCS The soil testing protocols for the measurement of the SWCC have largely been adopted from soil physics. The laboratory SWCC test is always commenced by establishing a zero matric suction condition. In other words, the soil specimen is brought to a near saturated condition by allowing the soil specimen to have free access to water. The initial degree of saturation is generally greater than 90% but may be lower for some coarse-grained soils. © ASCE PanAm Unsaturated Soils 2017 GSP 300 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. From a geotechnical engineering standpoint it would appear preferable to always use undisturbed soil samples, and attempt to re-establish a stress state closer to field conditions. It would also appear to be preferable to follow a stress path that would be similar to the stress path likely to be followed in the field when simulating a particular physical process under consideration. While these conditions would appear to be preferable, consideration must also be given to the: i.) costs associated with such a refined approach to unsaturated soil property determination, and ii.) long history of empirical experience that has been gained through using protocols that have been used in other disciplines. Practicing geotechnical engineers should have standardized protocols for the measurement and interpretation of laboratory SWCCs. This paper attempts to detail engineering practice procedures that can yield adequate solutions to commonly encountered unsaturated soil mechanics problems. There are a number of aspects that should be taken into consideration when estimating USPFs, one being consideration of the initial state of the soil specimen. Initial soil state There are three main initial states that can be used when studying the SWCCs of soils. The soil may initially be: i.) prepared in a slurry state, ii.) prepared in an initially compacted state, or, iii.) sampled in an undisturbed sample state. The initial state depends largely on the desired application of the test results in engineering practice. The soil may initially be in a slurry condition such as is encountered when dealing with mine waste tailings. It is also possible that the soil sample is from a compacted fill or from an undisturbed unsaturated soil deposit. The shrinkage or volume change of the soil (i.e., the shrinkage curve, SC) can be introduced to quantify the effect of initial state conditions on the measured SWCC. Much of the original research on shrinkage curves was performed on looselystructured remolded soils for agricultural science applications (Haines, 1923). Haines (1923) proposed three different phases for the drying of agricultural soils; namely, i.) structural shrinkage where a few large pores are initially emptied, ii.) normal shrinkage where the volume of the soil decreases by an amount equal to the water lost, and iii.) residual shrinkage where essentially no volume change occurs as the soil is dried to zero water content. All of the above phases of drying may or may not be of interest in a particular geotechnical engineering application. Leong and Wijaya (2015) provided a summary of equations that can be used for various shrinkage paths. While there are a variety of possible shrinkage paths, the commonly used pathway for measuring the SWCC involves first bringing the soil to near saturated conditions. There may be hysteresis effects between drying and wetting that need to be taken into consideration. © ASCE 4 PanAm Unsaturated Soils 2017 GSP 300 5 Slurry condition Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Initially slurry samples start the drying process from a near saturated condition and generally follow the normal shrinkage phase where the volume change is equal to the loss of water from the soil. Eventually the soil dries to the point where air begins to enter the largest voids of the soil. Desaturation usually commences when the gravimetric water content approaches the plastic limit of the soil (Fredlund et al, 2012). The drying of the soil then moves towards the residual phase and continues until zero water content is reached. The shrinkage limit of the soil is a fictitious water content based on the assumption that a completely dried soil (i.e., zero water content) could have all the voids filled with water while undergoing zero volume change. Figure 1 illustrates the relationship of the shrinkage limit of a soil to the shrinkage curve of a soil. The shrinkage limit of a soil is useful in estimating the shrinkage curve for a soil. 1.4 1.2 S = 60% S = 40% 1.0 Void ratio S = 80% S = 20% 0.8 Line of saturation 0.6 Shrinkage curve 0.4 emin eo= SL x Gs/So 0.2 Gs == 2.68 2.68 Gs S = 98.0 % Shrinkage limit 0.0 0 10 20 30 40 Gravimetric water content, % 50 60 FIG. 1. Relationship of the shrinkage limit to the shrinkage curve. Compacted conditions Compacted soils usually have an initial degree of saturation in the order of 70% to 85%. The primary purpose for measuring the shrinkage curve of a compacted soil is to provide assistance in interpreting the results of a laboratory measured soil-water characteristic curve, w-SWCC. The generally accepted testing protocol for measuring the drying SWCC of a soil first involves the saturation of the soil specimen. It is also reasonable to commence the shrinkage curve test from similar (near-saturated) conditions. Compacted soils may or may not exhibit the initial structural shrinkage conditions referred to by Haines (1923). Undisturbed conditions Undisturbed soil samples may have a wide range of initial degrees of saturation. For example, in situ sands and silts may be relatively dry with degrees of saturation less than 20%. On the other hands, undisturbed clays and soft shales may have high © ASCE PanAm Unsaturated Soils 2017 GSP 300 6 initial soil suctions and still have a degree of saturation approaching 100%. Consequently, there can be a wide range of initial volume-mass and stress state conditions for soil samples that are brought into the laboratory for unsaturated soil testing. The primary purpose of a measured shrinkage curve is to assist in interpreting the results of a laboratory measured soil-water characteristic curve, (i.e., w-SWCC). Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. Since the w-SWCC is measured starting from an initial near-saturated condition, it is reasonable to also start the shrinkage curve test from similar conditions. An undisturbed sample of sand may have had a low initial degree of saturation, however, the specimens are subsequently wetted towards saturation prior to commencement of the shrinkage curve test. The test result may show essentially no volume change as water is removed throughout the drying process or there may be a slight overall volume change. In other words, both structural shrinkage and normal shrinkage may occur as referred to by Haines (1923). Volume change upon wetting to establish initial conditions for soil specimens The three initial state conditions listed above undergo different amounts of overall volume change as the soils is wetted to establish the initial state when measuring the drying w-SWCC. Volume change associated with the initial wetting of the soil is not part of the laboratory w-SWCC measurement. In each case, the w-SWCC test and the SC test are conditioned to a near saturated state as shown in Figure 2. The initial conditioning (i.e., wetting of the soil to near saturation), for a low compressible soil such as a dense silt or sand appears as a horizontal line which represents zero change in void ratio. However, a swelling soil shows an increase in void ratio upon wetting and a collapsible soil may show some decrease in void ratio upon wetting. It is also possible that a collapsible soil may not show a decrease in void ratio upon wetting since no surcharge is applied to soil during the initial wetting for the w-SWCC and SC. 1.4 S = 80% S = 20% 1.2 S = 40% S = 60% Void ratio 1.0 Collapsible soil 0.8 0.6 Drying from slurry Line of saturation Sand Swelling Swellingsoil soil 0.4 0.2 0.0 0 10 20 30 40 Gravimetric water content, % 50 60 FIG. 2. Initial conditioning in preparation for the SWCC and SC laboratory tests © ASCE PanAm Unsaturated Soils 2017 GSP 300 In each of the above cases the soil is prepared for the SWCC and SC laboratory test by allowing the soil to come as close as possible to the saturation line. As a result, all shrinkage curves will start near saturation and continue to follow a constant nearsaturation line until the air-entry value of the soil is reached. Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. The overall volume changes during the measurement of the w-SWCC have been shown to have a significant effect on the interpretation of the SWCC. Consequently, the effect of volume change is carried over to the estimation of unsaturated soil property functions (Zhang and Fredlund, 2015). The measurement or the estimation of the shrinkage curve has been used to assist with the interpretation of the w-SWCC. Soil type and classification The SWCC and the SC are related to the character of the grain-size distribution curve and are referred to as “pedo-transfer functions”. However, it is difficult to fully rely on “pedo-transfer functions” for the prediction of the SWCC and the SC (Fredlund et al., 1997). Acceptable geotechnical engineering practice appears to have found it acceptable to use “pedo-transfer functions” for preliminary design purposes in engineering practice. However, the laboratory measurement of the SWCC is required for “final” design purposes (Fredlund and Houston, 2009). The present paper focuses on the measurement of soil-water characteristic curves and its acceptable interpretation. Laboratory tests can readily be performed for both the w-SWCC and the SC. Geotechnical engineers must be able to characterize the physical behaviour of a wide range of materials ranging from natural soils to the coarse (waste rock) and fine streams (mine tailings) associated with mining operations. The materials encountered can range from gravels sizes to clay sizes. The air-entry values can range from less than 1 kPa to a value in excess of 1000 kPa (i.e., ~ 5 orders of magnitude). The SWCCs can often be best-fit with a sigmodal type of curve; however, that is not always the case (Fredlund and Xing, 1994). A nest of two sigmodal SWCC curves can be used in cases where high volume changes occur when measuring the drying SWCC (Zhang et al., 2014). Likewise, nested sigmodal SWCCs can be used when bimodal behaviour is encountered (Stianson and Fredlund, 2014). In some cases of bimodal behaviour it may also be necessary to use a modified form of the shrinkage curve when analyzing the test results. LINKAGE OF VOLUME-MASS VARIABLES THROUGH SHRINKAGE CURVES A triaxial test cell can be modified such that volume change is measured while suction is applied to a soil. The costs associated with converting a triaxial apparatus for this purpose might be justifiable for research purposes; however, the costs are prohibitive for commercial, consulting engineering practice. For this reason, it becomes more acceptable in geotechnical engineering practice to perform two tests; namely the w-SWCC test and the SC test and combine the results in a theoretically © ASCE 7 PanAm Unsaturated Soils 2017 GSP 300 8 Downloaded from ascelibrary.org by RMIT UNIVERSITY LIBRARY on 01/03/19. Copyright ASCE. For personal use only; all rights reserved. justifiable manner. The various volume-mass SWCCs can then be used to calculate unsaturated soil property functions. Pressure plate apparatuses have also been developed that use Ko loading (1-D loading) while varying the applied suction (Fredlund et al., 2012). The apparatus has the limitation that an increase in suction may cause the soil specimen to pull away from the sides of the containment ring. At this point, overall volume change of the soil specimen can no longer be measured. Shrinkage curves, SCs, can readily be measured in the laboratory by using a small specimen about 12 mm thick and 37 mm in diameter as shown in Figure 3. The soil specimens are confined in a metal ring and can be prepared in a slurry state, a compacted state or an undisturbed state. The initial conditioned state should be the same for both the SC test and the independently run SWCC test. The mass and the volume of the soil specimen for the SC can be measured periodically as the soil is allowed to dry while being exposed to room temperature conditions. The challenge has been to find a reliable means of measuring the volume of the soil specimen each time the mass is measured. ASTM (1998) describes a standard procedure for measuring the volume of a shrinkage limit soil specimen through use of the mercury immersion technique; however, the use of mercury in laboratories is now prohibited and the volume of shrinkage curve soil specimens is more commonly measured using micrometer calipers. Shrinkage curve equation for gravimetric water content versus void ratio M. Fredlund et al., (2002) proposed a mathematical equation to best-fit measured shrinkage curve data. The emphasis is on characterizing the drying SC with the suggestion that the effects of hysteresis can be handled independently once the drying behaviour is quantified. The M. Fredlund et al., (2002) equation has the form of a hyperbole which can be used to best-fit the SC.   w  c sh  e  w   a sh     1   b sh     1 c sh [2] where: ash = minimum void ratio upon complete drying, bsh = variable related to the slope of the drying curve calculated as: bsh = (ash ×So)/Gs, and csh = variable related to the sharpness of curvature as the soil desaturates, and So = initial conditioned degree of saturation. Equation [2] can be applied for shrinkage from any initial degree of saturation and the equation is based on the assumption that the shrinkage curve starts asymptotic to a degree of saturation line on the shrinkage curve plot. Since the measurement of the SWCC starts near the saturation of the soil specimen, the initial degree of saturation will be near 100% (e.g., S = 98%). © ASCE
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