高等土力学高等土力学 (6).pdf
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1、Simulated Crack and Slip Plane Propagation in Soil Slopeswith Embedded Discontinuities Using XFEMAbstract:Tosimulatetheonsetandgrowth ofstrongdiscontinuities(cracks orslipplanes)andthefailure mechanism insoil slopeswith rea-sonable accuracy,a program was developed based on the existing extended fini
2、te-element method(XFEM).This program consists of a newanalytical algorithm for strong-discontinuity initiation and propagation in soils considering the stress concentration and redistribution aroundthe discontinuity tip and an integration scheme for the XFEM enriched discontinuities.Two different ty
3、pes of interfacial contact constitutivemodels areused todescribe theinterfacebehavior ofthecracksor slip planes.Analyses of twoslope failure examples arepresented to demon-strate the reliability of this program and the reference values for engineering measurements.DOI:10.1061/(ASCE)GM.1943-5622.0001
4、290.2018AmericanSocietyofCivilEngineers.Author keywords:Extendedfinite-elementmethod(XFEM);Slopefailure;Strong-discontinuitygrowth;Slipplane;Crack.IntroductionSlope failure is one of the most common geotechnical and geologichazards.However,the failure mechanism and the simulation of thefailureproces
5、sarehighlycomplexandneed tobestudiedfurther.Ingeneral,soilsontheslip planedonotreachthestateoflimitequilib-rium simultaneously;instead,one or more local weak points start topropagate,and eventually all connect to form a run-through slipplane(Skempton 1964;Bjerrum 1967).Many different induce-ments,su
6、ch as gradual excavation of a slope toe,multistage heaploading,andrainfallandseepage,wouldresultinslopefailureswithan obvious slip plane development(Yang et al.2012;Leonardosand Terezopoulos 2003).Reasonable simulations of the initiation,growth,and run-through process of the slip plane could further
7、 theunderstanding of the failure mechanism of specific soil slopes orearth structures,help to locate dangerous sites,aid in more accurateevaluation of the safety of specific areas,and assist in recommend-ingprotectionmeasures.Currently,the limit-equilibrium method(LEM)is still widelyused for conserv
8、atively predicting the potential instabilities of soilslopes due to the large amount of accumulated research results andengineering experience(Janbu 1954;Bishop 1955;Baker andGarber 1978).However,therigid-plastic constitutiveassumption inthe LEM is far from the nonlinear and elastoplastic stress-str
9、ainrelationship of actual soil;furthermore,the LEM cannot describethe initiation or propagation process of slip planes.The strength-reduction method(SRM),which represents a large improvement inslopestabilityanalysis,definesarun-throughslip failureasthenon-convergence of the finite-element solution o
10、r the coalescence of theplasticity area(Zienkiewicz et al.1975;Ugai 1989;Griffiths andLane 1999;Khosravi et al.2013).Compared with the LEM,theSRM is more theoretically complete.Nonlinear constitutive rela-tionships can be applied in an SRM solution to reflect the stress-strain process in the slope a
11、nd do not require assumptions on the in-ternal force distribution or the shape of the sliding surface.However,the SRM assumes a simultaneous reduction of shearstrength in the whole slope,so the computed stress and strain distri-butions cannot representthe general condition.Thus,theSRM doesnot convin
12、cingly capture the progressive formation of a slip planein an actual state,especially in cases of stress-redistribution-inducedlandslides.Skempton(1964)proposed a conceptual model for analyzingthe propagation process of a shear band.This model considers thestrain-softening characteristics of soil an
13、d the stress concentrationin the shear band tip.However,the assumed tangential propagationdoes not represent the true slip direction in the soil.Furthermore,the model lacks an efficient method for describing a discontinuousdisplacementfield,resultinginatheoreticalmodelthat isnotpracti-cal for analyz
14、ing complex conditions.Experimental and theoreticalstudies of the stress concentration and redistribution at the tip of ashear band reveal that theevolutionconditions of theshearband aremainly controlled by only part of the tip area,not the whole tip area(Yu et al.2010a,b);thus,these are area-select
15、ive conditions.Therefore,selecting the direction of the discontinuity propagationaccording to the stress state of the tip area would be more preciseandeasiertoapplyinprogramsfortwo-dimensional(2D)analysis.In addition to the propagation analysis,considerable attentionhas been paid to establishing an
16、appropriate method for describingthe discontinuous displacement field using finite-element methods,such as the Cosserat theory and the gradient plasticity theory(Zervos et al.2007;Liu et al.2012).The methods that simulate thefailure process of soil slopes typically use shear-zone or weak-discontinui
17、ty detection in an elastoplastic constitutive model,and1Ph.D.Candidate,State Key Laboratory of Hydroscience andEngineering,Dept.of Hydraulic Engineering,Tsinghua Univ.,Beijing100084,China.Email:2Ph.D.Candidate,State Key Laboratory of Hydroscience andEngineering,Dept.of Hydraulic Engineering,Tsinghua
18、 Univ.,Beijing100084,China.Email:3Senior Engineer,China Renewable Energy Engineering Institute,Beijing 100120,China.Email:4Professor,State Key Laboratory of Hydroscience and Engineering,Dept.of Hydraulic Engineering,Tsinghua Univ.,Beijing 100084,China(corresponding author).Email:5Senior Engineer,Sta
19、te Key Laboratory of Hydroscience andEngineering,Dept.of Hydraulic Engineering,Tsinghua Univ.,Beijing100084,China.Email:Note.This manuscript was submitted on October 9,2017;approved onMay 21,2018;published online on October 3,2018.Discussion periodopen until March 3,2019;separate discussions must be
20、 submitted for indi-vidual papers.This paper is part of the International Journal ofGeomechanics,ASCE,ISSN 1532-3641.ASCE04018170-1Int.J.Geomech.Int.J.Geomech.,2018,18(12):04018170 Downloaded from ascelibrary.org by TSINGHUA UNIVERSITY on 01/02/19.Copyright ASCE.For personal use only;all rights rese
21、rved.the soil strain-softening behavior is accounted for by reducing thestrength parameters with increasing plastic strain(Troncone 2005).In these methods,the inherent length scale of the shear band or anyother type of localization leads to mesh dependence,and the com-puting convergence is affected.
22、One possible strategy would be totreat the width of the shear band as zero,that is,to use a strong dis-continuity(displacement discontinuity)to replace a weak disconti-nuity(strain discontinuity)(Oliver et al.2006;Sanborn and Pr?evost2011).With the reasonable embedment of a strong discontinuity,ashe
23、ar band is reduced to a slip plane,thus avoiding a complex con-stitutive model or mesh refinement.The extended finite-elementmethod(XFEM)(Belytschko and Black 1999;Zi and Belytschko2003)constructs a discontinuous displacement field based on nodeenrichment.The XFEM offers a clear difference between t
24、he nonli-nearity of material constitutive behavior and the nonlinearity ofmoving internal boundaries,which are mutually independent of themesh.Thus,different types of interface constitutive models can beused to describe the mechanical properties of the strong-discontinuity interface(Dolbow etal.2001
25、;ZhouandCheng 2017).For the unenriched elements,traditional elastoplastic governingequations ensure the continuous deformation of the uncracked do-main.Obviously,theXFEMhasitsownadvantagesinusingmacro-scopic constitutive models to simulate discontinuity.However,existing criteria for crack initiation
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