共查询到20条相似文献，搜索用时 78 毫秒
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为了真实地描述饱和密砂在循环加载过程中的变形行为,需要引入考虑剪胀阶段组构变化的宏观参量。在已有的基于状态参量的本构模型基础上,引入反映组构变化的剪胀内变量,简称组构-剪胀内变量z。以相变线PTL作为参考线,采用基于相变的状态参量判断砂土在初始时刻和任意时刻体积变形的变化趋势,并通过z对剪胀比d的影响,考虑反向加载过程中塑性变形的累积,建立了一个针对饱和密砂的循环加载的弹塑性本构模型。该模型根据试验现象将已有模型中的塑性剪切模量区分为首次加载模量与再加载模量,能较好地模拟排水情况下砂土循环加载的胀-缩变化过程。最后,针对密砂的三轴排水情况,利用文中模型进行预测,并把预测结果与试验结果进行比较,结果表明该模型能够总体反映砂土循环加载的变形行为。 相似文献
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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
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Hypoplastic model for sands with loading surface 总被引：3，自引：3，他引：0
Although the hypoplastic models for sands have exhibited good predictive capability in monotonic loading, they are not able to reproduce memory effects and predict excessive plastic accumulation under cyclic loading. To overcome these issues, a loading surface has been incorporated into a hypoplastic model. This surface is capped and has two hardening variables. Notions from the bounding surface plasticity were borrowed in order to formulate the hardening functions. With this novel model, some salient features can be described: the model can account for the accumulation of plastic deformation, a memory effect is provided by the new surface, and stress-induced anisotropy effects observed in sands are successfully simulated. A short calibration guide of the parameters is given, and some simulations for Hostun RF loose sand and Toyoura sand are presented. 相似文献
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Alexandros L. Petalas Yannis F. Dafalias Achilleas G. Papadimitriou 《国际地质力学数值与分析法杂志》2019,43(1):97-123
SANISAND is the name of a family of bounding surface plasticity constitutive models for sand within the framework of critical state theory, which have been able to realistically simulate the sand behavior under conventional monotonic and cyclic loading paths. In order to incorporate the important role of evolving fabric anisotropy, one such model was modified within the framework of the new anisotropic critical state theory and named SANISAND-F model. Yet the response under continuous stress principal axes rotation requires further modification to account for the effect of ensuing noncoaxiality on the dilatancy and plastic modulus. This modification is simpler than what is often proposed in the literature, since it does not incorporate an additional plastic loading mechanism and/or multiple dilatancy and plastic modulus expressions. The new model named SANISAND-FN is presented herein and is validated against published data for loading that includes drained stress principal axes rotation on Toyoura sand. 相似文献
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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
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马露 《水文地质工程地质》2021,48(4):72-77
我国南海神狐海域海底沉积物主要由钙质砂与无黏性土组成,其力学性质对海洋工程的稳定性具有显著影响。无黏性土的压缩特性是研究其力学性能的重要内容之一,为分析不同荷载作用下土样的压缩特性,利用高压三轴仪试验系统,开展了不同砂含量及不同初始孔隙比下无黏性土样的等向压缩试验。试验结果表明:在试验采用的高有效应力下,无黏性土具有显著的过渡土性质,初始组构难以被改变;随多孔易碎钙质砂含量的增加,土样可压缩性和压缩曲线的收敛度均增加,钙质砂的破碎显著改变了初始组构。提出可以描述含砂无黏性土压缩特性的数学模型,所含参数物理意义明确且易于确定。与不同砂土压缩试验数据对比发现,该模型对其他种类土同样具有较好的拟合度,验证了本模型的广泛适用性。与已有压缩模型的对比,验证了本模型的实用性,为无黏性土应力-应变关系的理论研究提供基础。 相似文献
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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
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地震波是一种多维的随机荷载,一般在参数测定中应将其转化为等效循环荷载。采用有限元模拟多向地震荷载作用下的砂土动力响应,介绍了弹塑性边界面模型及其参数的含义,阐述了确定参数的方法,选取涵盖大震、中震、近场、远场及不同土质条件的155组多向地震输入时程进行单向、多向加载。利用混合效应回归分析法,建立了多向地震荷载作用下等效循环周数计算模型,分析验证了该模型的准确性。提出了基于等效循环周数比的多维地震荷载作用下等效循环周数计算方法。研究表明：模型预测值能较好地反映等效循环周数实际值的变化趋势;震级和震中距对等效循环周数比影响不明显;砂土特性对等效循环周数比的影响具有主导作用, 在不同震级范围内,等效循环周数比均随着相对密度的增大而增大,对应于相对密度为45%、60%、80%、100%的砂土,等效循环周数比分别近似为1.60、1.85、1.90和2.05。 相似文献
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Modelling cyclic behaviour of granular soils under both drained and undrained conditions with a good performance is still a challenge. This study presents a new way of modelling the cyclic behaviour of granular materials using deep learning. To capture the continuous cyclic behaviour in time dimension, the long short-term memory (LSTM) neural network is adopted, which is characterised by the prediction of sequential data, meaning that it provides a novel means of predicting the continuous behaviour of soils under various loading paths. Synthetic datasets of cyclic loading under drained and undrained conditions generated by an advanced soil constitutive model are first employed to explore an appropriate framework for the LSTM-based model. Then the LSTM-based model is used to estimate the cyclic behaviour of real sands, ie, the Toyoura sand under the undrained condition and the Fontainebleau sand under both undrained and drained conditions. The estimates are compared with actual experimental results, which indicates that the LSTM-based model can simultaneously simulate the cyclic behaviour of sand under both drained and undrained conditions, ie, (a) the cyclic mobility mechanism, the degradation of effective stress and large deformation under the undrained condition, and (b) shear strain accumulation and densification under the drained condition. 相似文献
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Fabric and its evolution need to be fully considered for effective modeling of the anisotropic behavior of cohesionless granular sand. In this study, a three‐dimensional anisotropic model for granular material is proposed based on the anisotropic critical state theory recently proposed by Li & Dafalias [2012], in which the role of fabric evolution is highlighted. An explicit expression for the yield function is proposed in terms of the invariants and joint invariants of the normalized deviatoric stress ratio tensor and the deviatoric fabric tensor. A void‐based fabric tensor that characterizes the average void size and its orientation of a granular assembly is employed in the model. Upon plastic loading, the material fabric is assumed to evolve continuously with its principal direction tending steadily towards the loading direction. A fabric evolution law is proposed to describe this behavior. With these considerations, a non‐coaxial flow rule is naturally obtained. The model is shown to be capable of characterizing the complex anisotropic behavior of granular materials under monotonic loading conditions and meanwhile retains a relatively simple formulation for numerical implementation. The model predictions of typical behavior of both Toyoura sand and Fraser River sand compare well with experimental data. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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循环加载方式与应力路径对砂土的抗液化强度有很大的影响。利用GDS空心圆柱扭剪仪对南海珊瑚砂进行了一系列复杂加载条件下均等固结不排水循环试验,探讨了90°突变应力路径下主应力方向角对珊瑚砂抗液化强度的影响。试验结果发现：以循环应力比（CSR）作为应力水平指标,当不控制中主应力系数b的变化时,主应力方向角 对珊瑚砂的抗液化强度并无显著影响;当控制b始终保持0.5时,珊瑚砂的抗液化强度随着 的增加呈现出先减小后增大的趋势,且在 45°时的抗液化强度最低。基于分析循环荷载引起的土单元大、小循环主应力 、 变化,定义了单元体循环应力比（USR）作为一个新的物理指标,发现不同循环加载方式与应力路径条件下施加于珊瑚砂试样的USR与引起液化所需的循环次数NL存在事实上的唯一性关系。通过引自文献的4种无黏性土原始试验数据的再处理,独立地验证了以USR表征砂类土液化强度的适用性。 相似文献
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亚塑性模型为模拟颗粒材料的非线性力学行为提供了一条新途径,特别是CLoE亚塑性模型在模拟应变局部化时具有一定的优势。然而该模型在模拟小幅应力-应变循环时表现出一定的锯齿效应。为了克服该效应,基于颗粒间应变张量的概念发展了修正的CLoE亚塑性模型以正确模拟循环荷载下密砂的力学行为。此外,为保证单调荷载作用下修正模型与原模型预测结果的一致性,改进了颗粒间应变率及颗粒间最大应变的定义。数值算例表明:（1）修正模型保留了克服锯齿效应的优点。（2）修正模型能够反映不同振幅条件下的卸载刚度。（3）在大振幅循环条件下,滞回圈的面积随着循环次数增加而增大。（4）修正模型能够保证单调加载条件下所得结果与原模型的一致性。（5）修正模型可以反映材料的疲劳破坏机制。 相似文献
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A three-dimensional (3D) soil–structure interface model is proposed within the two-mechanism constitutive theory and bounding surface theory originally established for soils. The proposed model has two main characteristics: first, the model is formulated based on two different and superposed deformation mechanisms. The first mechanism is due to the stress ratio increment, and the second is due to the normal stress increment. Each mechanism induces a shear strain component and a normal strain component. The proposed model can be reduced to the conventional single-mechanism interface model. Second, the plastic modulus and stress dilatancy are defined using the bounding surface theory. The plastic flow rule under cyclic loading is modified and assumed to be dependent on both the stress state of the mapping point and the stress reversal loading direction. The proposed model was validated against the available 3D interface tests and was found to satisfactorily reflect the salient features of the interfaces under monotonic and cyclic loading paths with different normal boundaries. The problem in which the elastic normal stiffness in conventional single-mechanism interface models is often underestimated to enhance the simulation performance under varying normal stress conditions is solved by incorporating the second mechanism. And the effect of the second mechanism on the modeling behavior is discussed. The modified plastic flow direction accurately simulates the 3D cyclic shear response, and the difference between the model simulation and test result increases with the number of cycles by use of the plastic flow direction defined in conventional bounding surface theory. 相似文献
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基于临界状态土力学框架,建立了一个适用于往返循环荷载作用的砂土边界面本构模型。采用无纯弹性域假设,认为受到反向荷载的瞬时土体就产生塑性变形,砂土的弹性区域退化为一个点。屈服面为倒子弹头型,由于砂土孔隙比与压力之间不存在惟一对应的关系,使得屈服面大小无法与体积应变直接耦合,故采用塑性偏应变而不是剑桥模型那种塑性体应变作为硬化参数。流动法则采用加入状态参数的修正的Rowe应力剪胀关系,体现了依赖状态的剪胀思想。屈服面大小的比值 反映了塑性模量的演化,并推导了 的表达式。只用1套参数,该模型就能合理地模拟砂土在不同密度和固结压力下循环荷载的应力-应变关系曲线。 相似文献
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A sand constitutive model accounting for elastic–plastic coupling is presented. To this aim, general constitutive equations describing an elastic–plastic coupling effect are developed first. Afterwards, a modified critical state plasticity model for granular soils is introduced accordingly. Several examples are presented to show the achieved improvements compared to the existing approaches. Comparing directly with experimental data, it is shown that the proposed model provides realistic simulations for pore pressure built-up under undrained cyclic loadings. 相似文献