高等土力学高等土力学 (3).pdf
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1、Development and Application of a Large-Scale Static andDynamic True Triaxial Apparatus for GravelAbstract:To investigate the mechanical characteristics of gravel under general stress conditions,a large-scale static and dynamic truetriaxial apparatus was developed at Tsinghua University.The largest s
2、pecimen was 200?200?400 mm,and the applied pressure canmeet the research requirements of large-scale geotechnical structures.A set of verification experiments with cyclic loadings of differentdirections and frequencies was performed to verify the accuracy of the loading system.Then,a static true tri
3、axial experiment with con-stant mean principal stress,p,and generalized shear stress,q,was carried out to study the deformation characteristics of gravel underchanging Lodes angle,u.The results show that changing Lodes angle,u,causes plastic deformations in all principal stress directions.In additio
4、n,a series of experiments with both axial and lateral cyclic loadings was carried out to study the deformation characteristics of agravel specimen under different lateral dynamic conditions.Resultsfrom the experiments indicate that lateral dynamic loads significantlychange the residual and reversibl
5、e strains in all three principal directions.DOI:10.1061/(ASCE)GM.1943-5622.0001096.2018American Society of Civil Engineers.Author keywords:Large-scale;Truetriaxialapparatus;Gravel;Staticanddynamic;Ovalspecimencap.IntroductionGravel is widely used in earth-rockfill dams,railway and highwaysubgrades,b
6、ridge piers,weak foundation treatments,high backfills,and so forth,because it has low compressibility,high shear strength,andstrongantiliquefactioncapacityunderseismicload(Voznesenskyet al.2013).To date,the static characteristics of gravel have beenextensively investigated using conventional triaxia
7、l experiments(Lade et al.1996;Suwal and Kuwano 2013).However,in practice,thegravelisinatruetriaxialstressstate,andthedirectionofthemajorprincipal stress alternates.In complex stress states,the mechanicalbehavior of gravel is quite different from the results of conventionaltriaxial experiments,showin
8、g inherent and stress stateinduced ani-sotropy.These features are difficult to measure accurately in conven-tionaltriaxialexperiments.Moreover,many large structures made of gravel,such as highearth-rockfill dams,are located in earthquake-prone areas.Projectsdamaged by an earthquake lead to severe co
9、nsequences.At present,the dynamic characteristics of gravel are generally studied usingconventional dynamic triaxial experiments.The cyclic loading isusually applied in one direction and the initial stress state is underconventional triaxial conditions,which is different from actualdynamic loads;hen
10、ce,the obtained experimental results cannotthoroughly represent the dynamic behavior of gravel.Therefore,astudy of static and dynamic characteristics of gravel under complexstress conditions,especially under true triaxial stress states,has sig-nificanttheoreticalandpracticalvalue.As one of the most
11、important instruments used in geotechnicalexperiments,the true triaxial apparatus(TTA)has been signifi-cantly advanced since Kjellman(1936)developed the first one.With the development of the soil constitutive theory,it is urgentthat the more complex stress paths are realized to reveal the stress-str
12、ain relations in soil more systematically and comprehensively;this call for study greatly promoted the development of the TTAandotherexperimenttechnologies.The TTA can be broadly divided into three categories accord-ing to different boundary conditions.The first type is the rigidboundary apparatus,i
13、n which the principal stresses are applied byrigid plates(Ibsen and Praastrup 2002;Matsuoka et al.2002;Ismail et al.2005).One of the most representative apparatus isthe Cambridge TTA(Pearce 1971;Airey and Wood 1988).Thesecond type is the flexible boundary apparatus by which the prin-cipal stresses a
14、re inflicted by flexible bladders(Sture and Desai1979;Yamada and Ishihara 1979;Sivakugan et al.1988;Reddyet al.1992;Mandeville and Penumadu 2004;Choi et al.2008;Voznesensky et al.2013;Hoyos and Macari 2001).Ko and Scott(1967)developed a stress-controlled TTA in 1967,which is themodel of many TTAs of
15、 the flexible boundary type used today.The third type is the mixed boundary apparatus,which is the com-bination of the rigid boundary type and the flexible boundarytype;that is,the principal stresses are applied by the combinationof rigid plates and flexible surfaces.The mixed boundary TTA1Ph.D.Cand
16、idate,State Key Laboratory of Hydroscience andEngineering Dept.of Hydraulic Engineering,Tsinghua Univ.,Beijing100084,China.E-mail:2Professor,State Key Laboratory of Hydroscience and EngineeringDept.of Hydraulic Engineering,Tsinghua Univ.,Beijing 100084,China.E-mail:3Postdoctoral Research Associate,D
17、ept.of Civil and EnvironmentalEngineering,Univ.of Massachusetts Amherst,Amherst,MA 01003(corre-spondingauthor).E-mail:4Professor,State Key Laboratory of Hydroscience and Engineeringand Dept.of Hydraulic Engineering,Tsinghua Univ.,Beijing 100084,China.E-mail:5Senior Engineer,State Key Laboratory of H
18、ydroscience and EngineeringDept.of Hydraulic Engineering,Tsinghua Univ.,Beijing 100084,China.E-mail:6Senior Engineer,State Key Laboratory of Hydroscience andEngineering Dept.of Hydraulic Engineering,Tsinghua Univ.,Beijing100084,China.E-mail:Note.This manuscript was submitted on May 4,2017;approved o
19、nSeptember 26,2017;published online on January 9,2018.Discussion pe-riod open until June 9,2018;separate discussions must be submitted forindividual papers.This paper is part of the International Journal ofGeomechanics,ASCE,ISSN 1532-3641.ASCE04018004-1Int.J.Geomech.Int.J.Geomech.,2018,18(3):0401800
20、4 Downloaded from ascelibrary.org by Yongkang Wu on 01/09/18.Copyright ASCE.For personal use only;all rights reserved.was first invented by Green(1971),and the apparatus designed byLade and Duncan(1973)and Lade(1978)is also very famousbecause of the advantages it has for reducing friction betweentwo
21、 adjoining boundaries and controlling confining pressure eas-ily in the chamber.The mixed boundary apparatus is the one mostwidely used(Lo et al.1994;Lade and Abelev 2003;Shapiro andYamamuro 2003;Alshibli and Williams 2005;AnhDan et al.2006;Leo et al.2008;Yin et al.2010).Although significant progres
22、s has been made on TTAs,most oftheapparatusesarestilllimitedinsize,loadingcapacity,ordynamicperformance,which means they cannot meet the requirements ofthe static and dynamic true triaxial experiment research of gravel ata high-stress state and other complex conditions.To meet theserequirements,theT
23、TAsshouldaddressthefollowingconditions:1.To test gravel of different particle size gradations,largerspecimen sizes are needed.However,the specimen size ofmost available apparatuses ranges between 44?44?44and 102?102?102 mm.Large specimens,necessary forcoarse-grained materials such as gravel,are rare
24、ly tested in athree-dimensional(3D)stress space because of the size limi-tations of the apparatus.2.The height-width ratio of the specimen should be considered.The specimen of some large-scale TTAs designed for gravel arecubic,such as 241?241?241 mm(Choi et al.2008),whichmay affect the formationof s
25、hearbands during the experiment.3.A large confining pressure is needed.The maximum confiningpressure applied by most of the apparatuses is less than1.0 MPa,which cannot meet the stress-state demand of highearth-rockfill dams and other large projects.4.The ability to apply dynamic stresses is require
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