1、 GEOTECHNICAL SPECIAL PUBLICATION NO. 184PAVEMENTS ANDMATERIALSMODELING, TESTING, AND PERFORMANCEPROCEEDINGS OF THE SYMPOSIUM ON PAVEMENT MECHANICS ANDMATERIALS AT THE INAUGURAL INTERNATIONAL CONFERENCE OFTHE ENGINEERING MECHANICS INSTITUTEMay 18-21, 2008Minneapolis, MinnesotaSPONSORED BYThe Pavemen
2、ts Committee of the Geo-Instituteof the American Society of Civil EngineersTask Committee on Mechanics of Pavements, Granular Materials Committee,and Inelastic Committee of the Engineering Mechanics Instituteof the American Society of Civil EngineersEDITED BYZhanping You, Ph.D., P.E.Ala R. Abbas, Ph
3、.D.Linbing Wang, Ph.D., P.E.Published by the American Society of Civil EngineersASCELibrary of Congress Cataloging-in-Publication DataSymposium on Pavement Mechanics and Materials (2008 : Minneapolis, Minn.)Pavements and materials, 2008 : modeling, testing, and performance : proceedings of theSympos
4、ium on Pavement Mechanics and Materials at the inaugural International Conference of theEngineering Mechanics Institute : May 18-21, 2008, Minneapolis, Minnesota / sponsored by thePavements Committee of the Geo-Institute of the American Society of Civil Engineers . et al. ;edited by Zhanping You, Al
5、a R. Abbas, Linbing Wang.p. cm. - (Geotechnical special publication ; no. 184)Includes bibliographical references and index.ISBN 978-0-7844-1008-01. PavementsCongresses. 2. Road materialsCongresses. 3. PavementsPerformanceCongresses.4. Pavements, AsphaltCongresses. I. You, Zhanping. II. Abbas, Ala R
6、. III. Wang, Linbing, 1963-IV. Engineering Mechanics Institute. International Conference (2008 : Minneapolis, Minn.) V.American Society of Civil Engineers. Geo-Institute. Pavements Committee. VI. Title.TE250.S924 2008625.8-dc22 2008045728American Society of Civil Engineers1801 Alexander Bell DriveRe
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12、prints Department, Publications Division, ASCE, (address above);email: permissionsasce.org. A reprint order form can be found athttp:/pubs.asce.org/support/reprints/.Copyright 2009 by the American Society of Civil Engineers.All Rights Reserved.ISBN 978-0-7844-1008-0Manufactured in the United States
13、of America.Geotechnical Special Publications1 Terzaghi Lectures2 Geotechnical Aspects of Stiff and HardClays3 Landslide Dams: Processes, Risk, andMitigation7 Timber Bulkheads9 Foundations tutumlueuiuc.eduABSTRACT: The main objective of this paper is to present the state-of-the-art in theanisotropic
14、characterization of unbound aggregate layers to support the developmentof the next generation of highway as well as airport pavement infrastructure byemploying advanced technology and detailed knowledge gathered within the last oneand a half decades in characterization of the actual stress- and dire
15、ction- (anisotropic)dependent aggregate behavior. From advanced triaxial tests conducted in thelaboratory, unbound aggregate materials are clearly shown to have greater modulus inthe vertical direction, which can be adequately modeled using cross-anisotropic,stress-dependent modulus characterization
16、 models. Field validations of the anisotropicaggregate layer behavior have involved comparing measured full-scale pavement testsection responses with the predicted ones using the anisotropic aggregate moduluscharacterization. A simplified approach of obtaining level of anisotropy as anaggregate qual
17、ity indicator is summarized to indicate use of high quality aggregateswith superior properties, including size, gradation and shape, critical to successfulpavement designs. Recent efforts as well as the need to develop simplified design andanalysis methodologies that will enable optimized use of eng
18、ineered aggregatestructural layers for improved performance and increased use in flexible pavementsare also discussed in detail.INTRODUCTIONMore than three billion tons of aggregates (or 2.95 billion metric tons) wereproduced in 2006 at a value of approximately $21 billion, contributing nearly $40bi
19、llion to the gross domestic product of the United States (www.nssga.org). A verylarge quantity of this material goes into the construction of pavements. In flexiblepavements, and especially for the most common applications of thinly surfaced low tomoderate volume roads, unbound aggregate layers serv
20、e as major structuralcomponents of the pavement system. With increasing demands being placed onhighways and airfields through heavier and increasing number of loads, it is criticalthat the unbound aggregates component of these transportation facilities are properly1PAVEMENTS AND MATERIALScharacteriz
21、ed by incorporating recent advances into our solutions for a more accuratepavement analysis and improved field performance.A recent Federal Highway Administration (FHWA) International Scanning Programreport nicely captured some of the pavement technology best practices of foreigncountries in the are
22、a of long life flexible pavements built on unbound aggregatestructural layers and strong pavement foundations (Beatty et al. 2002). Thesepavements generally consist of deep subbase and deep base sections with a thin, high-quality wearing course to provide a good riding surface and moisture protectio
23、n for thebase. For example, a typical Australian pavement section serving high volume trafficconsists of a 152-mm lower gravel subbase, overlain by an 203-mm upper crushedrock subbase, overlain by an 203-mm of high quality crushed stone base and only awearing surface of two coat chip seal. Factors c
24、ritical to the success of such pavementdesigns and construction alternatives included a willingness to invest in qualityaggregates with superior properties along with paying significant attention to size andgradation. As a national priority, the FHWA report recommended buildingdemonstration projects
25、 with deep subbase and deep base designs in different regionsof the United States to determine the effectiveness of this design strategy for 30- and40-year pavement design lives (Beatty et al. 2002).The main objective of this paper is to present the state-of-the-art on the anisotropiccharacterizatio
26、n of unbound aggregate layers in flexible pavements and thereforesupport the development of the next generation of highway and airport infrastructureby (i) employing advanced technology and detailed knowledge gathered within the last15 years in characterization of the actual stress- and direction- (
27、anisotropic) dependentaggregate behavior and (ii) developing simplified design and analysis methodologiesthat will enable optimized use of engineered aggregate structural layers for improvedperformance and increased use in flexible pavements. The laboratory and fieldvalidations of the anisotropic ap
28、proach has proven this ability to more accuratelyanalyze pavement structures and predict the expected performances of pavements withunbound aggregate layers for incorporation into mechanistic-empirical pavementdesign procedures.NONLINEAR, CROSS-ANISOTROPIC AGGREGATE BEHAVIORElastic behavior of granu
29、lar particles is generally determined in the small strainrange during static unloading and/or repeated load triaxial tests for resilient responseafter shakedown is reached. Under the repeated application of traffic loads, most ofthe pavement deformations are recoverable and thus considered elastic.
30、It has beencustomary to use resilient modulus (MR) for the elastic stiffness of the pavementmaterials. MR is defined as the repeatedly applied wheel load stress or deviator stress,Od, applied in repeated load triaxial tests divided by the recoverable specimen axialstrain, 6 r, and given by MR=Od/er.
31、 The resilient response has been shown to benonlinear elastic, with a dependency of MR upon the stress state (Boyce 1980; Ladeand Nelson 1987; Uzan 1985; Uzan et al. 1992). Any irreversible axial strainaccumulated due to wheel loading in the vertical direction will undoubtedly create ananisotropic s
32、tructure leading to an anisotropic elastic domain and an anisotropic elasticlaw (Biarez and Hicher 1994).2PAVEMENTS AND MATERIALSThe behavior of a granular medium at any point depends on the arrangement ofparticles which is usually determined by aggregate characteristics, constructionmethods, and th
33、e loading conditions. In the case of unbound aggregate bases inflexible pavements, an apparent anisotropy is induced during construction byaggregate placement, loading from the compaction equipment and subsequently bytraffic loading. As the material stiffens, the deformability decreases with a highe
34、relastic modulus attained in the vertical wheel loading direction. This vertical loadtransfer is achieved through compression and shear forces between the particlesoriented in a chainlike manner (Dobry et al. 1989). Tensile forces, however, cannot betransferred from grain to grain. When such forces
35、act in the horizontal direction, thebehavior of the base course is significantly affected by a directional dependency ofmaterial stiffnesses. An anisotropic approach can adequately accommodate suchdirectional variation of granular material stiffnesses (Tutumluer 1995; Tutumluer andThompson 1997a-b;
36、Tutumluer 1998). A special type of anisotropy, known as cross-anisotropy, is commonly observed in pavement granular materials due to stratification,compaction, and the applied wheel loading in the vertical direction.An isotropic model of the unbound aggregate layer has the same resilient materialpro
37、perties in all directions. A cross-anisotropic representation, however, has differentresilient properties (i.e., MR and Poissons ratio) in the horizontal and verticaldirections. Figure 1 illustrates the five cross-anisotropic material properties needed todefine an anisotropic material under conditio
38、ns of axial symmetry as given byZienkiewicz and Taylor (1989): resilient moduli in vertical and radial directions, MRZand MRr; shear modulus in vertical direction, GR; Poissons ratio for strain in thevertical direction due to a horizontal direct stress, vz; and Poissons ratio for strain inany horizo
39、ntal direction due to a horizontal direct stress, vr. The variables, n and m,commonly substituted for horizontal modulus and shear modulus (GR in z direction) inthe formulation, represent the ratios of horizontal modulus to vertical modulus andshear modulus to vertical modulus, respectively. Pickeri
40、ng (1970) studied for positivestrain energy the bounds of the elastic parameters in a cross-anisotropic material.FIG. 1. Stratified cross-anisotropic material under axial symmetry.3PAVEMENTS AND MATERIALSSummary of Research Efforts in Aggregate Structural Layer CharacterizationEarly work in characte
41、rizing the anisotropic modulus properties of unboundaggregate layers used in flexible pavements was carried out at the Georgia Institute ofTechnology and the University of Illinois (Tutumluer 1995, Tutumluer and Thompson1997a). An anisotropic modeling of a typical flexible pavement resulted in thema
42、gnitudes of both the horizontal and shear stiffnesses throughout the base being onlysmall fractions of the vertical stiffness (Tutumluer 1995; Tutumluer and Thompson1997a). Unlike isotropic type analysis, the horizontal stiffnesses were found to bemuch lower when compared to the vertical values. The
43、se stiffnesses were notassumed in the base layer, but predicted by the nonlinear stress dependent modelsobtained directly from the triaxial specimen behavior. Both the important effects ofload-induced directional stiffening and the dilative behavior of granular materialsunder applied wheel loading w
44、ere successfully modeled using a cross-anisotropicapproach (Tutumluer 1995; Tutumluer and Thompson 1997a).Tutumluer and Thompson (1997b) modeled conventional flexible pavements usingthe GT-PAVE finite element (FE) program. The results of this analysis were ofsignificance since three stress dependent
45、 MR models were used successfully for thefirst time in a nonlinear cross-anisotropic base to completely define the resilientgranular material behavior in vertical, horizontal and shear planes as follows:where MR is resilient modulus, Ii = 01 + 02 + 03 = 6 = first stress invariant or bulkstress, Toct
46、 = l/3(ai-a2)2 + (ai-as)2 + (c-as)2172 = octohedral shear stress or fortriaxial conditions (02=03), Toct = 0.47lad (oa = 01-03 = deviator stress), pa =atmospheric pressure (100 kPa or 14.7 psi) and KA, KB, Kc = material constantsobtained from repeated load triaxial tests. The three cross-anisotropic
47、 moduli, eachmodeled by the same stress dependent functional form similar to the models proposedby Lade and Nelson (1987), Uzan (1985) and Uzan et al. (1992), have, therefore, thefollowing model parameters:where KI to Kp are model parameters obtained from advanced triaxial tests foranisotropic prope
48、rties. Unlike isotropic type analysis, a certain set of aggregate typesand properties used in the granular layer typically resulted in horizontal stiffnessesvarying between 3 to 21% of the vertical, and the shear stiffnesses between 18 to 35%of the vertical throughout the base. As shown in Figure 2,
49、 the horizontal stiffnessratios (MRh/MRv) were low under the wheel load, 0.08 to 0.12 from the contour linesnear the centerline, and increased radially away from the centerline to reach a value of1 at about 6 load radii, which corresponds to the isotropic case. These stiffnesses were4CoefficientKiK4K7IiExponentK2K5K8ToctExponentK3K6K91. Horizontal Resilient Modulus, MRh:2. Vertical Resilient Modulus, MRV:3. Resilient Shear Modulus, GR:PAVEMENTS AND MATERIALSnot assumed in the base layer, but pr
