共查询到18条相似文献，搜索用时 468 毫秒
1.
堆石料三维边界面模型在FLAC3D中的开发与验证 总被引：1，自引：0，他引：1
堆石料三维边界面模型结合了统一非线性强度准则,可以反映三维应力空间堆石料的应变硬化、软化以及体积收缩和剪胀等传统本构模型难以反映的力学特性。基于三维边界面模型的基本理论,通过FLAC3D提供的二次开发平台,在VC++环境下实现了三维边界面本构模型的二次开发,并给出基于FLAC3D程序的边界面本构模型开发的关键步骤、编程要点和调试方法。利用开发的本构模型,开展了三轴压缩试验的数值模拟计算,并与理论值进行了对比分析。结果表明,嵌入在FLAC3D中的三维边界面本构模型能够较好地反映设定试验条件下的材料性能,而且三维边界面本构模型模型参数简单,都可从常规三轴试验获得,从而验证了三维边界面模型二次开发程序的优越性与合理性。 相似文献
2.
砂土液化流动变形的简化方法 总被引：1，自引：0，他引：1
已有的液化砂土流动特性试验结果表明,砂土在液化流动状态下是剪切稀化非牛顿流体,可以用幂函数表示其剪应力-剪应变率的关系,从而建立了砂土液化流动的本构方程。基于FLAC3D程序的二次开发平台,将液化流动本构方程开发到FLAC3D中,建立了液化流动变形的简化分析方法。通过倾斜场地的液化流动变形分析,发现倾斜场地的液化变形曲线可以用正弦函数曲线描述,这与Towhata的理论分析成果一致,验证了本方法的合理性。分析了液化层坡度、稠度系数、流动指数以及弹性参数等变量对液化变形的影响。计算结果表明,液化变形随液化层坡度的增大而逐渐增大,液化砂土的稠度系数和流动指数对液化流动变形有重要的影响,而弹性参数对变形基本无影响,因此,在实际工程分析中,需要对流动模型参数进行深入研究。 相似文献
3.
采用颗粒流软件模拟了饱和砂土在不排水条件下的循环剪切试验,研究了不同因素对液化的影响,并进一步分析了饱和砂土液化后宏观变形的基本规律。在此基础上,从孔隙分布角度解释了砂土液化后的大变形的细观物理机制。通过自编程序对颗粒排列和孔隙分布的演化过程进行定量描述,给出孔隙率标准差作为液化后体积收缩势的度量,并研究了孔隙率标准差与液化后大变形的关系。离散元细观数值模拟再现了室内试验中的宏观现象,证实了室内试验中饱和砂土液化后的有限剪切大变形是客观真实的材料响应。土体体积收缩势的累积所导致的孔隙均匀化以及土颗粒间自由空隙增大正是饱和砂土液化后循环剪应变逐渐增大的细观机制。孔隙率标准差作为孔隙均匀化的量化指标,与循环剪应变各周次幅值有良好的相关性。 相似文献
4.
利用FLAC3D程序提供的二次开发平台UDM在VC++编译环境下实现了一基于修正剑桥模型的简化边界面模型的开发。介绍了边界面模型的基本原理,并给出了开发关键技术和具体实施方法。通过三轴加卸载试验、不排水静三轴试验、不排水动三轴试验等几种数值试验与修正剑桥模型进行了对比研究。计算结果验证了所开发的边界面模型的正确性及相对修正剑桥模型的优越性。 相似文献
5.
《岩土力学》2021,(4)
采用颗粒流软件模拟了饱和砂土在不排水条件下的循环剪切试验,研究了不同因素对液化的影响,并进一步分析了饱和砂土液化后宏观变形的基本规律。在此基础上,从孔隙分布角度解释了砂土液化后的大变形的细观物理机制。通过自编程序对颗粒排列和孔隙分布的演化过程进行定量描述,给出孔隙率标准差作为液化后体积收缩势的度量,并研究了孔隙率标准差与液化后大变形的关系。结果表明,试样初始状态并不会影响液化后的极限状态,仅对初始液化所需循环次数有影响。数值模拟可再现室内试验中的宏观现象,证实了室内试验中饱和砂土液化后的有限剪切大变形是客观真实的材料响应。土体体积收缩势的累积所导致的孔隙均匀化以及土颗粒间自由空隙增大正是饱和砂土液化后循环剪应变逐渐增大的细观机理。孔隙率标准差作为孔隙均匀化的量化指标,与循环剪应变各周次幅值有良好相关性。 相似文献
6.
《岩土力学》2020,(4)
采用颗粒流软件模拟了饱和砂土在不排水条件下的循环剪切试验,研究了不同因素对液化的影响,并进一步分析了饱和砂土液化后宏观变形的基本规律。在此基础上,从孔隙分布角度解释了砂土液化后的大变形的细观物理机制。通过自编程序对颗粒排列和孔隙分布的演化过程进行定量描述,给出孔隙率标准差作为液化后体积收缩势的度量,并研究了孔隙率标准差与液化后大变形的关系。结果表明,试样初始状态并不会影响液化后的极限状态,仅对初始液化所需循环次数有影响。数值模拟可再现室内试验中的宏观现象,证实了室内试验中饱和砂土液化后的有限剪切大变形是客观真实的材料响应。土体体积收缩势的累积所导致的孔隙均匀化以及土颗粒间自由空隙增大正是饱和砂土液化后循环剪应变逐渐增大的细观机理。孔隙率标准差作为孔隙均匀化的量化指标,与循环剪应变各周次幅值有良好相关性。 相似文献
7.
适用于砂土循环加载分析的边界面塑性模型 总被引：1，自引：0，他引：1
基于临界状态土力学框架,建立了一个适用于砂土排水循环加载的边界面塑性模型。采用了考虑虚拟峰值应力比的偏应变硬化准则,初始加载阶段应力点位于边界面上,反向加载阶段以历史最大屈服面作为边界面,同时实现了对密砂软化现象的模拟和对历史所受最大应力的记忆。边界面采用修正的椭圆形,引入考虑密度与应力水平的状态相关剪胀函数,采用非相关联流动法则和以应力反向点作为映射中心的径向映射准则。模型仅有10个参数,通过常规三轴试验即可确定,并且使用一套参数可以模拟不同围压、密度的单调和循环加载情况。分别对饱和砂土的单调、循环排水三轴试验进行模拟,结果表明,该模型能够合理地反映饱和砂土排水条件下的应力-应变特性。 相似文献
8.
采用砂土液化大变形弹塑性本构模型分析可液化砂土,采用模量随应力与应变变化的等效非线性模型增量形式分析碎石桩,应用FLAC3D有限差分软件对地震动力作用下可液化场地碎石桩复合地基进行三维动力响应分析。模拟分析了在地震作用下碎石桩刚度效应和排水效应对加固处理可液化场地的抗液化效果,从初始小变形到液化后大变形的变形发展,超静孔压累积与消散,及桩与土的变形与应力分配变化等。结果表明,所用模型与方法可合理描述可液化场地碎石桩复合地基在地震作用下场地的动力响应特性和抗液化效果;在地震作用下可液化场地中桩周土体与碎石桩体的竖向应力与水平向剪切应力向碎石桩体集中,竖向有效应力比可降至约1/6～1/3;桩周土体与桩体为非协调变形,剪应变比可达7～10;碎石桩抗液化影响范围约为2.5～3倍桩径,对超过3.5倍桩径范围影响较小;碎石桩与砂土渗透系数比大于100时对降低砂土中超静孔隙水压影响明显;碎石桩对场地的加密效应可显著降低超静孔隙水压力,而碎石桩刚度则对超静孔隙水压力变动影响较小,但有助于减低地面加速度响应峰值。 相似文献
9.
饱和砂土爆炸液化特性研究 总被引：3，自引：0，他引：3
基于有效应力动力分析法,在Byrne有效应力弹塑性模型的基础上,提出了一个能够考虑主应力轴旋转、饱和砂土含有少量气体、饱和砂土液化后的应变软化和应力重分布特性的弹塑性模型。将该模型编制成分析模块,并与通用岩土分析软件FLAC接口,进而对饱和砂土分别在单点、两点（微差）和多点（微差）爆炸地震波荷载作用下进行数值模拟分析,分别考虑了水平、微倾以及斜坡场地等3种工况,并且对爆炸地震波荷载与天然地震波荷载作用下饱和砂土的动力特性进行了对比研究。数值模拟结果表明,该模型能够很好地表现饱和砂土的爆炸液化气特性;不同动载和不同场地条件下,饱和砂土表现的动力特性以及液化行为也不尽相同。 相似文献
10.
《岩土力学》2017,(6)
饱和砂土在地震荷载的作用下往往会产生液化变形,包括竖向震陷和侧向扩展。砂土由于液化的作用,其渗透系数会发生改变,而目前描述砂土液化变形的本构模型均采用常量渗透系数,这是造成自由场地的震陷数值模拟结果低于试验观测值的重要原因之一。利用开源有限元平台Open Sees对饱和砂土的自由场地震陷进行模拟分析,对比离心机模型试验,分析了渗透系数对饱和砂土液化震陷的影响。为进一步提高数值模拟的准确性,采用了适合于动力分析及液化模拟的边界面模型。与固定渗透系数模型相比,最终提出的变渗透系数模型允许液化状态的渗透系数升高为初始值的数倍,该模型模拟结果较好,可以作为从渗透模型角度提高数值模拟精度的近似考虑。通过一系列的模拟和分析发现,采用合理的变渗透系数模型,可在一定程度上提高砂土自由场地地震液化震陷的数值模拟精度。 相似文献
11.
Large post-liquefaction deformation of sand, part I: physical mechanism, constitutive description and numerical algorithm 总被引：4，自引：4，他引：0
This paper presents a theoretical framework for predicting the post-liquefaction deformation of saturated sand under undrained cyclic loading with emphasis on the mechanical laws, physical mechanism, constitutive model and numerical algorithm as well as practical applicability. The revealing mechanism behind the complex behavior in the post-liquefaction regime can be appreciated by decomposing the volumetric strain into three components with distinctive physical background. The interplay among these three components governs the post-liquefaction shear deformation and characterizes three physical states alternating in the liquefaction process. This assumption sheds some light on the intricate transition from small pre-liquefaction deformation to large post-liquefaction deformation and provides a rational explanation to the triggering of unstable flow slide and the post-liquefaction reconsolidation. Based on this assumption, a constitutive model is developed within the framework of bounding surface plasticity. This model is capable of reproducing small to large deformation in the pre- to post-liquefaction regime. The model performance is confirmed by simulating laboratory tests. The constitutive model is implemented in a finite element code together with a robust numerical algorithm to circumvent numerical instability in the vicinity of vanishing effective stress. This numerical model is validated by fully coupled numerical analyses of two well-instrumented dynamic centrifuge model tests. Finally, numerical simulation of liquefaction-related site response is performed for the Daikai subway station damaged during the 1995 Hyogoken-Nambu earthquake in Japan. 相似文献
12.
Based on previous experimental findings and theoretical developments, this paper presents the formulation and numerical algorithms of a novel constitutive model for sand with special considerations for cyclic behaviour and accumulation of large post-liquefaction shear deformation. Appropriate formulation for three volumetric strain components enables the model to accurately predict loading and load reversal behaviour of sand, fully capturing the features of cyclic mobility. Compliance with the volumetric compatibility condition, along with reversible and irreversible dilatancy, allows for physically based simulation of the generation and accumulation of shear strain at zero effective stress after initial liquefaction. A state parameter was incorporated for compatibility with critical state soil mechanics, enabling the unified simulation of sand at various densities and confining pressures with a same set of parameters. The determination methods for the 14 model parameters are outlined in the paper. The model was implemented into the open source finite-element framework OpenSees using a cutting-plane stress integration scheme with substepping. The potentials of the model and its numerical implementation were explored via simulations of classical drained and undrained triaxial experiments, undrained cyclic torsional experiments, and a dynamic centrifuge experiment on a single pile in liquefiable soil. The results showed the model’s great capabilities in simulating small to large deformation in the pre- to post-liquefaction regime of sand. 相似文献
13.
Triaxial tests on the fluidic behavior of post-liquefaction sand 总被引：2，自引：1，他引：1
Yu Huang Hu Zheng Wuwei Mao Maosong Huang Guanghui Li 《Environmental Earth Sciences》2012,67(8):2325-2330
Liquefaction-induced ground deformation is a major cause of structural damage during earthquakes. However, a better understanding of seismic liquefaction is needed to improve earthquake hazard analyses and mitigate structural damage. In this paper, a dynamic triaxial test apparatus was employed to investigate the fluidic characteristics of post-liquefaction sand. The specimens were vibrated to the point of liquefaction by dynamic loading, and then the liquefied sand was further sheared by triaxial compression in an undrained manner. It was found that a non-Newtonian fluid model can accurately describe the shear stress and the shear strain rate of post-liquefaction sand during undrained triaxial compression. The apparent viscosity, a major parameter in a constitutive model of a non-Newtonian fluid, decreases with an increase in the shear strain rate. 相似文献
14.
DEM study of fabric features governing undrained post-liquefaction shear deformation of sand 总被引：3，自引：3，他引：0
In an effort to study undrained post-liquefaction shear deformation of sand, the discrete element method (DEM) is adopted to conduct undrained cyclic biaxial compression simulations on granular assemblies consisting of 2D circular particles. The simulations are able to successfully reproduce the generation and eventual saturation of shear strain through the series of liquefaction states that the material experiences during cyclic loading after the initial liquefaction. DEM simulations with different deviatoric stress amplitudes and initial mean effective stresses on samples with different void ratios and loading histories are carried out to investigate the relationship between various mechanics- or fabric-related variables and post-liquefaction shear strain development. It is found that well-known metrics such as deviatoric stress amplitude, initial mean effective stress, void ratio, contact normal fabric anisotropy intensity, and coordination number, are not adequately correlated to the observed shear strain development and, therefore, could not possibly be used for its prediction. A new fabric entity, namely the Mean Neighboring Particle Distance (MNPD), is introduced to reflect the space arrangement of particles. It is found that the MNPD has an extremely strong and definitive relationship with the post-liquefaction shear strain development, showing MNPD’s potential role as a parameter governing post-liquefaction behavior of sand. 相似文献
15.
Hanifi Missoum Mostefa Belkhatir Karim Bendani Mustapha Maliki 《Geotechnical and Geological Engineering》2013,31(1):279-296
In a number of recent case studies, the liquefaction of silty sands has been reported. To investigate the undrained shear and deformation behaviour of Chlef sand–silt mixtures, a series of monotonic and stress-controlled cyclic triaxial tests were conducted on sand encountered at the site. The aim of this laboratory investigation is to study the influence of silt contents, expressed by means of the equivalent void ratio on undrained residual shear strength of loose, medium dense and dense sand–silt mixtures under monotonic loading and liquefaction potential under cyclic loading. After an earthquake event, the prediction of the post-liquefaction strength is becoming a challenging task in order to ensure the stability of different types of earth structures. Thus, the choice of the appropriate undrained residual shear strength of silty sandy soils that are prone to liquefaction to be used in engineering practice design should be established. To achieve this, a series of undrained triaxial tests were conducted on reconstituted saturated silty sand samples with different fines contents ranging from 0 to 40 %. In all tests, the confining pressure was held constant at 100 kPa. From the experimental results obtained, it is clear that the global void ratio cannot be used as a state parameter and may not characterize the actual behaviour of the soil as well. The equivalent void ratio expressing the fine particles participation in soil strength is then introduced. A linear relationship between the undrained shear residual shear strength and the equivalent void ratio has been obtained for the studied range of the fines contents. Cyclic test results confirm that the increase in the equivalent void ratio and the fines content accelerates the liquefaction phenomenon for the studied stress ratio and the liquefaction resistance decreases with the increase in either the equivalent void ratio or the loading amplitude level. These cyclic tests results confirm the obtained monotonic tests results. 相似文献
16.
Developing the pore water pressures in loose to medium sands below the water table may lead to liquefaction during earthquakes. The simulation of liquefaction (cyclic mobility and flow liquefaction) in sandy soils is one of the major challenges in constitutive modeling of soils. This paper presents the simulation of sand behavior using a critical state bounding surface plasticity model (Dafalias and Manzari’s model, 2004) during monotonic and cyclic loading. The drained, undrained, and cyclic triaxial tests were simulated using Dafalias and Manzari’s model. The simulation results showed that the model predicts behavior of sand, reasonably well. Also, for CSR?<?0.2, number of cycles for liquefaction is significantly increased. The residual strength of Babolsar sand is produced when it is deformed to an axial strain of 20 to 25%. 相似文献
17.
Liquefaction is associated with the loss of mean effective stress and increase of the pore water pressure in saturated granular materials due to their contractive tendency under cyclic shear loading. The loss of mean effective stress is linked to loss of grain contacts, bringing the granular material to a “semifluidized state” and leading to development and accumulation of large cyclic shear strains. Constitutive modeling of the cyclic stress-strain response in earthquake-induced liquefaction and post-liquefaction is complex and yet very important for stress-deformation and performance-based analysis of sand deposits. A new state internal variable named strain liquefaction factor is introduced that evolves at low mean effective stresses, and its constitutive role is to reduce the plastic shear stiffness and dilatancy while maintaining the same plastic volumetric strain rate in the semifluidized state. This new constitutive ingredient is added to an existing critical state compatible, bounding surface plasticity reference model, that is well established for constitutive modeling of cyclic response of sands in the pre-liquefaction state. The roles of the key components of the proposed formulation are examined in a series of sensitivity analyses. Their combined effects in improving the performance of the reference model are examined by simulating undrained cyclic simple shear tests on Ottawa sand, with focus on reproducing the increasing shear strain amplitude as well as its saturation in the post-liquefaction response. 相似文献
18.
A modification to the nonlinear Pastor–Zienkiewicz–Chan (PZC) constitutive model without any change in the number of model parameters is introduced in order to simulate stiffness degradation of dense sands at dynamic loading. The PZC model is based on generalized plasticity and was verified by good prediction of liquefaction and undrained behavior of saturated sand. The PZC is a robust model that can predict drained dynamic behavior of sands, especially stiffness increase in loose sand at reloading of dynamic loading. Yet, this model does not show stiffness degradation of dense sand at reloading. The modification is made through modifying the stress memory factor, H DM, which is multiplied by the plastic modulus, H L. This modification does not influence reloading behavior of loose sand. The modified PZC model is verified via results of drained cyclic tests. Two cyclic triaxial tests on loose and dense specimens, along with two cyclic plane strain tests on dense sand are utilized for validation. The model simulation shows that the modified PZC model is able to predict the stiffness degradation of dense sand at reloading well. 相似文献