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Genesis and Properties of Collapsible Soils NATO ASI Series Advanced Science Institutes Series A Series presenting the results of activities sponsored by the NATO Science Committee, which aims at the dissemination of advanced scientific and technological knowledge, with a view to strengthening links between scientific communities. The Series is published by an international board of publishers in conjunction with the NATO Scientific Affairs Division A Life Sciences Plenum Publishing Corporation B Physics London and New York C Mathematical and Physical Sciences Kluwer Academic Publishers D Behavioural and Social Sciences Dordrecht, Boston and London E Applied Sciences F Computer and Systems Sciences Springer-Verlag G Ecological Sciences Berlin, Heidelberg, New York, London, H Cell Biology Paris and Tokyo I Global Environmental Change PARTNERSHIP SUB-SERIES 1. Disarmament Technologies Kluwer Academic Publishers 2. Environment Springer-Verlag / Kluwer Academic Publishers 3. High Technology Kluwer Academic Publishers 4. Science and Technology Policy Kluwer Academic Publishers 5. Computer Networking Kluwer Academic Publishers The Partnership Sub-Series incorporates activities undertaken in collaboration with NATO's Cooperation Partners, the countries of the CIS and Central and Eastern Europe, in Priority Areas of concern to those countries. NATO-PCO-DATA BASE The electronic index to the NATO ASI Series provides full bibliographical references (with keywords and/or abstracts) to more than 50000 contributions from international scientists published in all sections of the NATO ASI Series. Access to the NATO-PCO-DATA BASE is possible in two ways: - via online FILE 128 (NATO-PCO-DATA BASE) hosted by ESRIN, Via Galileo Galilei, I-00044 Frascati, Italy. - via CD-ROM "NATO-PCO-DATA BASE" with user-friendly retrieval software in English, French and German (© WTV GmbH and DATAWARE Technologies Inc. 1989). The CD-ROM can be ordered through any member of the Board of Publishers or through NATO- PCO, Overijse, Belgium. Series C: Mathematical and Physical Sciences - Vol. 468 Genesis and Properties of Collapsible Soils edited by Edward Derbyshire (Editor-in-Chief ) Department of Geography, Royal Holloway, University of London, Egham, Surrey, U.K. Tom Dijkstr a and Ian J. Smalley Centre for Loess Research, Department of Civil Engineering, Loughborough University of Technology, Loughborough, U.K. Springer Science+Business Media, B.V. Proceedings of the NATO Advanced Research Workshop on Genesis and Properties of Collapsible Soils Loughborough, U.K. 11-14 April 1994 A C.I.P. Catalogue record for this book is available from the Library of Congress ISBN 978-94-010-4047-1 ISBN 978-94-011-0097-7 (eBook) DOI 10.1007/978-94-011-0097-7 Printed on acid-free paper All Rights Reserved © 1995 Springer Science+Business Media Dordrecht Originally published by Kluwer Academic Publishers in 1995 Softcover reprint of the hardcover 1st edition 1995 No part of the material protected by this copyright notice may be reproduced or utilized in any form or by any means, electronic or mechanical, including photo copying, recording or by any information storage and retrieval system, without written permission from the copyright owner. TABLE OF CONTENTS Preface vii Types and Distribution ofCollapsible Soils C.D.F. Rogers Six DefinableParticleTypes in Engineering Soils and TheirParticipation in Collapse Events: Proposals and Discussions I. Jefferson and I.,J. Smalley 19 A Stress Path Model for CollapsibleLoess R.L. Handy 33 Factors and Mechanism ofLoess Collapsibility V.I. Osipov and V.N. Sokolov 49 Techniques to Examine Microfabric and Particle Interaction ofCollapsible Soils N.K. Tovey 65 On the Development ofMicrostructure in Collapsible Soils J. Locat 93 The Slovak Carpathians Loess Sediments, TheirFabric and Properties A. Klukanova and J. Frankovska 129 Mechanisms ofCollapse ofSoil Structure ~F~a 1@ The Collapse Mechanism ofa Soil Subjected to One-Dimensional Loading and Wetting D.G. Fredlund and J.K.M. Gan 173 TheInfluence ofthe Clay Componentin Loess on Collapse ofthe Soil Structure T.W. Mellors 207 Interpretation and Comparison ofCollapse Measurement Techniques S.L. Houston, W.N. Houston and H.H. Mahmoud 217 Consideration ofthe Possible Contributions ofAmorphous Phases to the Sensitivity of Glaciomarine Clays S.P. Bentley and A.J. Roberts 225 Variation in Collapsibility and Strength ofLoess with Age Z. Lin 247 Collapsible Loess on the Loess Plateau ofChina E. Derbyshire, X. Meng, J.T. Wang, Z. Zhou and B. Li 267 vi Post-Depositional Processes in High-Sensitivity, Fine-Grained, Collapsible Sediments J.K. Torrance 295 Changes in WaterChemistry and Loess Porosity with Leaching: Implications for Collapsibility in the Loess ofNorth China T. Muxart, A. Billard, A. Andrieu, E. Derbyshire and X. Meng 313 Effects ofRock Fragments on the Structural Collapse ofTilled Topsoils During Rain J.W.A. Poesen and B. Van Wesemael 333 Simulation and Modelling ofCollapsible Soils J.D. Nieuwenhuis and M.B. de Groot 345 Collapse Mechanisms and Design Considerations for Some Partly Saturated and Saturated Soils G. Lefebvre 361 Design and Treatment ofLoess Bases in Bulgaria D. Evstatiev 375 Comparison ofResults ofOedometer and Plate Load Tests Performed on Collapsible Soils Y.M. Reznik 383 Post-script 409 Index 411 PREFACE Soil collapse forms a major hazard in large parts ofeastern Canada, the United States, eastern Europe,ChinaandsouthernAfrica.Thesedimentsinvolvedincludeyoung marineclaysand lake sediments,wind-depositedmaterials(loessandsomesands),volcanicash,andsomeresidualsoils. Humanactivitiescontinuetoincreaseinregionsunderlainbycollapsiblesoils,sothatthehazards posed are increasing in both relative and absolute terms. The purpose ofthe NATO Advanced Research Workshop held in Loughborough, England, was to bring together international researchers from several scientific fields (civil engineering, engineering geology, stratigraphy, geomorphology and soil science) that have generally lacked close interaction in addressing this particularprobleminthepast.Theaim was to identifygoalsinthestudyofthe collapseprocess, to propose mutually-acceptable working definitions of "collapse", and to formulate collapse models as a key to soil treatment so as to enhance utilisation and diminish hazard. Collapsiblesoilsare metastable. Agranular material withangularparticles compactedonthe dry side of optimum can form a structure which is capable of further densification. This is a phenomenon known from the full particle size range - from clays to coarse rock aggregates. However, the classic collapsible soils are natural materials in which particle type and sedimentation mechanism combine to produce collapsibility. The collapsing soils problem is exacerbated by a paucity ofdescriptive terms. Collapsiblesoilhasarelativelylowhorizontal-to-verticalstressratioKothatrelatestoelastic deformationandPoisson'sratio, and collapseinvolvingsaturationleads to aliquidorhydrostatic stressconditionwhereby Ko = 1.0.Recentyears haveseenamajoradvance in thequantification ofsoil microfabric, particularly using image processing and analysis techniques. From a micro mechanical viewpoint, collapse occurs by de-bonding, grain crushing, fabric transition, and by temporarykinematicconstraint.Inthemacromechanicalsenseitoccursbyloading,wetting,creep, radialsoftening,andbyexcessporewaterpressures.Soilsasastructuredsystembehaveasallsuch systems: gradual (smooth) development (deformation) is periodically interrupted by collapse events.Inloess,thecollapsephenomenonoccursthroughmicro-shearingatintergranularcontacts, and is influenced by the clay component: it may be explained in terms ofa modified effective stress equation. LoessofPleistoceneageisthemostwidelydistributedcollapsiblesoil.Mostobservedchanges initsmechanicalpropertiesaretheresultofpost-depositionalprocesses,reflectingtheweathering andpedogenesisofthelast3millionyears. However, changewithage(depth) ismuchless than with climatic gradient, as in North China. Here "initial collapsepressure" and "preconsolidation pressure" of saturated samples are technical synonyms. Multiple buried soils are an important sourceofvariation in bulk properties as well as some importantcauses ofvariation in the mode offailure and the collapse potential. Post-depositional processes may both aggravate and alleviate collapse problems in several types ofsediment. Theconsequences ofcollapse are usually moreserious in materials with high sensitivity. Developmentofhighsensitivityis usuallyapost-depositionalprocessarisingfrom (i) decreaseoftheremoulded strength, and (b) increaseofthe undisturbedstrength. Sensitivity may bedecreased by weatheringordiageneticprocesseswhichproduceswellingclaymineralsand/or oxidemineralsand/oragents which increaseparticleinteraction indisturbed material. The fabric ofcollapsiblesoilscanbecharacterisedusingmicromorphologicaltechniques,thesebeingauseful aid in explaining and predicting collapse. The collapse mechanisms may be modelled mathematically. In the case of subaqueous flowslides, comparisons between quantitative simulations and field observations highlight the vii viii influence ofsoil density, slope angle and slope height. Causes and mechanisms ofcollapse can be specified for different soil types including soft sensitive clays, loose unsaturated orsaturated sandsorsilty sands,and loess. Althoughdifferentindetail, the behaviourofthesedifferentsoils has manycommonfeatures andrequiresquitesimilarapproachestodesign. Forstabilityanalysis, theshearstrengthparametersmustbedefinedforthepost-collapseconditiononceanequilibrium has developed between effective stress, voids ratio, and shear stress. The advantages and limitationsofanumberofremedialstrategiestominimisecollapseinloess werediscussed in the final open session in Loughborough. TheWorkshopconcludedwithanew workingdefmitionofsoilcollapsewhichemphasisethe structural strengthofthe grain skeleton as aunifying factor. Given thatcollapse is the transition from an open metastable packing to a closer, more stable packing, then the open structure of quickclays, loess and sands is a unifying entity. Regional views of the collapsibility of loess clearly emerged during the Workshop: eastern European, Chinese and North American, in particular. The main communication "gap" appears to lie between the micromorphologists (soil scientists) and the remainder. Strategies for future research into the collapse phenomenon were discussed and some broad avenues agreed. Longer-tenn research objectives requiring interdisciplinary collaboration also emerged. It was agreed by the group that, in future, special attention will begiven to (1)detennininganddescribingsoilandsedimentstructures; (2)finding waystodetenninechangesinstructure;(3)improvingmineralogicaldescription;and(4)mapping collapsible soils. This volume contains 21 ofthe 27 papers presented at the Loughborough meeting. As the Director of the Workshop, I am acutely aware of the debt of gratitude lowe to a number of organisationsandindividuals.First,IampleasedtoacknowledgetheScientificandEnvironmental Affairs DivisionoftheNorth AtlanticTreatyOrganisation whosecontractualgrantARW931148 provided the means of organisation the meeting and compiling this book. I would like, in particular,tothankLuigiSertorio,fonnerDirectoroftheARWProgrammeforhisencouragement and support in the early days oforganising this event. Special thanks are also due to Drs. Tom Dijkstra for his very practical help immediately before and during the Workshop, to Meng Xingmin and Justin Jacyno for computercartography, and to Kathy Roberts at Royal Holloway (University of London) for exceeding the secretarial speed limit and withstanding deadline pressures without complaint. Itis a pleasure to thank ourcolleagues in the Department ofCivil and Building Engineering ofLoughborough University ofTechnology for making all workshop contributors so welcome. Maryon Derbyshirestoically tookontheonerous taskofcompilingthe index, and my co-editors Tom Dijkstra and Ian Smalley are gratefully acknowledged for their influenceonthewaytheWorkshopwasshapedandfortheirevaluationofearlyversionsofsome papers.Finally,Iwarmlyapplaudthedistinguished,livelyandgood-humouredgroupofscientists who, by theirprofessionalism, made this meetingamostrewarding intellectualexperience. They were the Workshop, and they made the book. It is dedicated to them. Edward Derbyshire Editor-in-Chief March 1995 MainirrigationpiperupturedbysubsidenceinhighlycollapsibleloessonGaolan Mountain,Lanzhou, north-centralChina. TYPES ANDDISTRIBUTIONOFCOLLAPSmLESOILS C.D.F. ROGERS SeniorLecturerinGeotechnics DepartmentofCivilandBuildingEngineering LoughboroughUniversityofTechnology Leicestershire, UnitedKingdom ABSTRACT. Collapsiblesoilsaremetastableandmusthavean open structure,that isthesoil particles must be in an open packing which is capable of becoming a (significantly) closer packing. Agranularmaterial withangularparticles compactedonthedry sideofoptimum can form astructurewhich iscapableofsignificantfurther densification, buttheclassic collapsible soilsarenaturalmaterialswherethecombinationofparticletypeandsedimentationmechanism combinetogivecollapsibility. Thereisafiercedebateaboutwhatsoilsshouldbeconsideredas collapsible and this has spawned several definitions ofa collapsible soil, all ofwhich are in some way limiting. The debate is advanced hereafter by consideration, from a geotechnical viewpoint, of what is not a collapsible soil. Thereafter a simple hierarchical, systematic classification can be produced which allows both compacted and natural materials to be included. Ageographicalclassificationwhichplacesalltypesofnatural collapsiblesystemson a convenient base map is also required. This paper aims to address both ofthese issues by consideringcollapsiblesoilsintheirwidestpossiblesense. 1. Introduction This paper was written primarily to form a good starting point for discussions on the genesis and properties ofcollapsible soils, the paper constitutingthe first keynote talk toa NATOworkshoponthistopic [I). Theaimofthepaperwas toproduce a critique, from a geotechnical engineering viewpoint, of the various attempts to classify collapsible soilsinorderthat the typesofcollapsible soil encountered in practice could bedefined. Inconsideringthevarioustypesofcollapsiblesoil that occurit is necessary to consider the genesis ofthese soils, which results in turn in a consideration ofthe distributionofthe majordepositsofcollapsiblesoilsworldWide. In order to meet these primary aims, it was important that collapsible soils should be considered in their widest sense. It rapidly became clear that the subject is one which is addressed by researchers from numerous academic disciplines ranging from geotechnical engineers through engineering geologists, geologists, geomorphologists andsedimentologiststo soil scientists. It is necessarily the casethat the boundaries of study ofthese disciplines will limit the subject definition and that each will form a subsetofthewhole. Itequallybecameapparentthatgeotechnical engineeringprovided the bestvantage point from which to view these various subsets since it must become involved, at some point, in all natural and man-made soils. Nevertheless full 1 E.Derbyshireeta1.(eds.),GenesisandPropertiesofCollapsibleSoils, 1-17. ©1995KluwerAcademicPublishers.
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