Dynamic analysis of strain localization in water‐saturated clay using a cyclic elasto‐viscoplastic model     

B. Shahbodagh Khan  M. Mirjalili  S. Kimoto  F. Oka 《国际地质力学数值与分析法杂志》2014,38(8):771-793

A computational framework is presented for dynamic strain localization and deformation analyses of water‐saturated clay by using a cyclic elasto‐viscoplastic constitutive model. In the model, the nonlinear kinematic hardening rule and softening due to the structural degradation of soil particles are considered. In order to appropriately simulate the large deformation phenomenon in strain localization analysis, the dynamic finite element formulation for a two‐phase mixture is derived in the updated Lagrangian framework. The shear band development is shown through the distributions of viscoplastic shear strain, the axial strain, the mean effective stress, and the pore water pressure in a normally consolidated clay specimen. From the local stress–strain relations, more brittleness is found inside the shear bands than outside of them. The effects of partially drained conditions and mesh‐size dependency on the shear banding are also investigated. The effect of a partially drained boundary is found to be insignificant on the dynamic shear band propagation because of the rapid rate of applied loading and low permeability of the clay. Using the finer mesh results in slightly narrower shear bands; nonetheless, the results manifest convergency through the mesh refinement in terms of the overall shape of shear banding and stress–strain relations. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Modeling the 2D behavior of dry‐stone retaining walls by a fully discrete element method          下载免费PDF全文

James J. Oetomo  Eric Vincens  Fabian Dedecker  Jean‐Claude Morel 《国际地质力学数值与分析法杂志》2016,40(7):1099-1120

The dry‐stone retaining walls (DSRW) have been tipped as a promising solution for sustainable development. However, before recently, their behavior is relatively obscure. In this study, discrete element method (DEM) approach was applied to simulate the plane strain failure of these walls. A commercial DEM package (PFC2D™) was used throughout this study. The authors used a fully discrete approach; thus, both the wall and the backfill were modeled as discrete elements. The methodology for obtaining the micromechanical parameters was discussed in detail; this includes the three mechanical sub‐systems of DSRWs: wall, backfill and interface. The models were loaded progressively until failure, and then the results were compared with the full‐scale experimental results where the walls were loaded, respectively, with hydrostatic load and backfill. Despite its complexity and its intensive calculation time, DEM model can then be used to validate a more simplified approach. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

环渤海区域及邻区现今地壳构造运动形变特征分析     

赵旭坤  张俊  雷前坤  范成成 《大地测量与地球动力学》2019,39(11):1101-1105

将环渤海区域划分为5个次级块体，利用整体旋转与线性应变模型分析2009~2014年中国大陆构造环境监测网络的GPS对地观测速度场数据，得到相对于欧亚板块0.5°×0.5°的水平运动速度场和应变场。分析形变速度场和应变场的空间变化发现，环渤海区域整体上呈现0.25×10^-9/a的NW-SE 111.3°的双向趋势性扩张运动，太行块体、山西块体分别呈NW-SE 116.3°、NW-SE 130°的微弱扩张运动，胶辽块体、冀鲁块体和阴山-燕山块体分别存在NW-SE 144.3°、NE-SW 39.5°和NW-SE 155.6°的微弱压缩运动，其中太行块体的扩张运动量级相对于其他次级块体较大。尽管环渤海区域内部各次级块体的形变在空间上存在以上差异，但整体上环渤海区域主压应变轴方向基本为NEE-SWW，主张应变轴方向为NNW-SSE，且主压应变轴走向为NE 47.70°～89.74°，与利用地球物理方法得到的主压应变轴优势方向大体一致，表明环渤海区域现今地壳运动相对稳定。  相似文献   

Dynamic characteristics of marine soft clay under variable phase difference and initial static shear stress     

Wenqian Dong  Xiuqing Hu  Hongtao Fu 《Marine Georesources & Geotechnology》2020,38(7):770-785

Abstract

Under seismic loading, the soil layer is subjected to multidirectional cyclic shear stress with different amplitudes and frequencies because of the coupling of multiple shear waves and the soil element within a slope or behind a retaining wall is subjected to initial static shear stress before subjected to cyclic loading. Due to the complexity of seismic loading propagation, a phase difference exists between the initial static shear stress and cyclic shear stress. To investigate the influence of the phase difference and initial static shear stress on cyclic shear strain, cyclic modulus, and cyclic strength, a series of laboratory tests are performed on Wenzhou marine soft clay by multi-directional simple shear system, which can simulate the actual state better by controlling the horizontal cyclic stress in the x and y directions simultaneously. As the phase difference varies from 0° to 90°, the dynamic shear modulus increases and cyclic strain accumulation decreases with an increasing number of cycles. The shear strain increases with the initial shear stress.  相似文献   

北部湾地区海砂填料的动力特性分析     

王家全  陈胜前  唐毅  黄世斌  黄钦政 《海洋工程》2020,38(5):149-155

为研究北部湾地区海砂填料的动力特性，采用高级动态三轴测试系统开展循环荷载下的动三轴试验，研究不同围压及不同动应力幅值对海砂动力特性的影响规律。试验结果表明：轴向累计应变随围压增加而减小，围压150 kPa时振次10 000后应变仅为3%；随着动应力幅值的增大轴向累积应变随之增大，且达到破坏标准的时间越短。动弹性模量随着动应力幅值和围压的增加而增大，不同围压下动弹性模量随动应变的增加出现先骤减再略减后稳定的发展趋势，ε_d>0.3%后开始趋于稳定；不同动应力幅值下动弹性模量出现先增后减直至稳定的趋势，其中动应力幅值对动弹性模量有明显的影响，围压影响相对较小。孔压比随动应力幅值增加而减小，随围压增加而增加。  相似文献   

Reaction softening by dissolution–precipitation creep in a retrograde greenschist facies ductile shear zone,New Hampshire,USA          下载免费PDF全文

R. J. McAleer  D. L. Bish  M. J. Kunk  K. R. Sicard  P. M. Valley  G. J. Walsh  B. A. Wathen  R. P. Wintsch 《Journal of Metamorphic Geology》2017,35(1):95-119

We describe strain localization by a mixed process of reaction and microstructural softening in a lower greenschist facies ductile fault zone that transposes and replaces middle to upper amphibolite facies fabrics and mineral assemblages in the host schist of the Littleton Formation near Claremont, New Hampshire. Here, Na‐poor muscovite and chlorite progressively replace first staurolite, then garnet, and finally biotite porphyroblasts as the core of the fault zone is approached. Across the transect, higher grade fabric‐forming Na‐rich muscovite is also progressively replaced by fabric‐forming Na‐poor muscovite. The mineralogy of the new phyllonitic fault‐rock produced is dominated by Na‐poor muscovite and chlorite together with late albite porphyroblasts. The replacement of the amphibolite facies porphyroblasts by muscovite and chlorite is pseudomorphic in some samples and shows that the chemical metastability of the porphyroblasts is sufficient to drive replacement. In contrast, element mapping shows that fabric‐forming Na‐rich muscovite is selectively replaced at high‐strain microstructural sites, indicating that strain energy played an important role in activating the dissolution of the compositionally metastable muscovite. The replacement of strong, high‐grade porphyroblasts by weaker Na‐poor muscovite and chlorite constitutes reaction softening. The crystallization of parallel and contiguous mica in the retrograde foliation at the expense of the earlier and locally crenulated Na‐rich muscovite‐defined foliation destroys not only the metastable high‐grade mineralogy, but also its stronger geometry. This process constitutes both reaction and microstructural softening. The deformation mechanism here was thus one of dissolution–precipitation creep, activated at considerably lower stresses than might be predicted in quartzofeldspathic rocks at the same lower greenschist facies conditions.  相似文献   

Contrast in stress–strain history during exhumation between high- and ultrahigh-pressure metamorphic units in the Western Alps: Microboudinage analysis of piemontite in metacherts     

《Journal of Structural Geology》2016

Our analyses of microboudinage structures of piemontite grains embedded within six samples of metachert, one collected from an ultrahigh-pressure (UHP) metamorphic unit at Lago di Cignana in Italy of the Western Alps, and the other five from surrounding high-pressure (HP) metamorphic units in Italy and France, have revealed that the structures are all symmetrical in type, and were presumably produced in coaxial strain fields. Stress–strain analyses of the microboudinaged grains revealed significant contrasts in the stress and strain histories of the UHP and HP metamorphic units, with the differential stress recorded by the UHP sample being unequivocally lower than that recorded by the five HP samples. In addition, our analyses showed that the UHP sample underwent stress-relaxation during microboudinage, whereas the five HP samples did not. On the basis of these observations and analyses we discuss the mechanical decoupling of the UHP and HP units that led to different histories in differential stress between the units during exhumation of the Western Alps.  相似文献   

Modification of strain wedge method for lateral soil-pile interaction in sandEI北大核心CSCD     

Yang Xiao-feng  Zhang Chen-rong  Huang Mao-song  Yuan Ju-yun 《岩土力学》2016,(10):2877-2884

A modified strain wedge (SW) method for analyzing the behavior of laterally loaded single piles in sand is proposed. The modified model assumes that the lateral displacements of a pile behind the three-dimensional passive soil wedge are nonlinear, which makes the horizontal soil strain variable with depths instead of a constant value in the original strain wedge model, and also employs two different hyperbolic models, one for describing horizontal stress increment-strain behavior of soil in the wedge, and the other for describing the shear stress-displacement property at the interface between soil and pile shafts. An example is analyzed to demonstrate the effectiveness of the modified method, and a good agreement is obtained. Finally, the effects of modifications on the lateral bearing capacity of pile shafts are discussed. The results show that the problem of overestimating the lateral bearing capacity of piles with strain wedge method can be ameliorated by introducing the assumption of nonlinear lateral displacements of piles. It makes the SW method more convenient and effective in analyzing the behavior of laterally loaded piles by introducing the new relationships of horizontal stress increment-strain and shear stress-displacement.  相似文献   

华北克拉通基底花岗质片麻岩变形和流变学研究——以辽西寺儿堡地区为例   总被引：2，自引：0，他引：2  

李婧  刘永江  李伟民  金巍  梁琛岳  温泉波  张媛媛 《大地构造与成矿学》2016,(5):891-907

辽西寺儿堡镇新太古代花岗质片麻岩内发育的宏观、微观构造变形特征表明该地区曾遭受了强烈的韧性变形改造。花岗质岩石变形程度在初糜棱岩–糜棱岩之间,岩石经历了SWW向左行剪切作用改造。岩石中石英有限应变测量判别结果表明,构造岩类型为L-S型,为平面应变。岩石的剪应变平均值为1.43,运动学涡度值为0.788~0.829,指示岩石形成于以简单剪切为主的一般剪切变形中。此外,石英颗粒以亚颗粒旋转重结晶和颗粒边界迁移重结晶作用为主,长石颗粒塑性拉长,部分发生膨凸式重结晶作用;石英组构特征(EBSD)揭示石英以中–高温柱面滑移为主;石英颗粒边界具有明显的分形特征,分形维数值为1.151~1.201,指示了中高温变形条件。综合石英、长石的变形行为、石英组构特征以及分形法Kruhl温度计的判别结果,推断辽西寺儿堡镇新太古代花岗质片麻岩经历过480~600℃的中高温变形,其同构造变质相为高绿片岩相-低角闪岩相。花岗质岩石的古差异应力为10.62~12.21 MPa,估算的应变速率为10~(–11.67)~10~(–13.34) s~(–1),即缓慢的变形,可能记录早期中高温、低应变速率的韧性变形过程,反映华北克拉通基底中下部地壳变形特征。  相似文献   

构造物理模拟和PIV有限应变分析对构造裂缝预测的启示   总被引：1，自引：0，他引：1       下载免费PDF全文

沈礼  贾东  尹宏伟  魏东涛  陈竹新  孙闯  崔键 《高校地质学报》2016,22(1):171

油气储层中构造裂缝发育与有限应变状态关系密切,为了探索有限应变分析与构造裂缝预测的新技术方法,此次研究设计完成了一组单侧挤压收敛模型的物理模拟实验,并引入粒子图像测速(PIV,Particle Image Velocimetry)技术对实验过程进行了定量化分析。实验模型在垂向上为含粘性层的多层结构,实验结果形成了一个肉眼可见的箱状褶皱。通过PIV技术可以获取实验模型变形演化过程中各阶段的位移场数据,计算出各阶段的增量应变,实现从初始状态到褶皱形成之后整个变形过程的有限应变分析,探讨构造裂缝成因机制和分布规律,进行定量化裂缝预测。挤压变形过程初期,应变分布范围很广,有限应变较弱(约4%~8%),在挤压方向上的线应变表现为弱压应变,在垂向上的线应变表现为弱张应变,这种现象是褶皱和断层产生前平行层缩短和层增厚的纯剪变形结果,也是区域型张裂缝和剪裂缝形成的主要机制。褶皱和断层即将发育之时至发育之后,应变局限在断层发育的剪切带及附近区域,有限应变表现为较强(达20%)的剪切应变和剪切张应变,是断层面附近简单剪切变形作用的结果,也是局部型剪裂缝和张剪裂缝形成的主要机制。  相似文献