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1.
岩土材料应力路径无关硬化参量的构成方法 总被引：2，自引：0，他引：2
在分析砂土试验结果的基础上,揭示了基本硬化内参量（塑性体积应变、塑性剪应变）变化的应力路径相关性,提出了应力路径无关硬化参量的一般表达式。并指出了塑性功硬化参量及其提出的黏土和砂土统一硬化参量均是所提一般表达式框架下的特例。还将该统一硬化参量直接和修正剑桥模型结合,并与试验结果对比,表现出描述剪胀特性的简单性和有效性。 相似文献
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不同应力路径下砂土的神经网络弹塑性本构模型研究 总被引：3，自引：0，他引：3
基于多种应力路径下砂土的加载、卸载和再加载过程的三轴排水试验数据，研究了三种应力路径对屈服面的影响，其结果表明，不同应力路径对砂土的本构模型有着不可忽视的作用。在此基础上，建立了砂土的弹塑性神经网络模型，对相应路径下的本构关系进行了学习。实例分析表明，该模型能够很好地描述具体应力路径下的本构关系，神经网络建模方法具有方便、容错性强的特点，对岩土力学快速、高效数值方法的进一步发展具有重要的参考价值。同时，在这种弹塑性应力-应变关系中，笔者并没有使用塑性势函数，这在目前的弹塑性本构关系的建模中是一种新的尝试。 相似文献
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G. Y. Sheu 《Geotechnical and Geological Engineering》2009,27(6):729-740
This study presents the recognition of an elastic–plastic constitutive law by a multiobjective evolutionary algorithm (MOEA).
This idea is illustrated by the identification of ellipse aspect ratio and plastic modulus of a reported bounding surface
model. Based on the multi-goals of well predicting all available drained or undrained stress–strain behaviors simultaneously,
the compromising solutions of these two parameters are found by a strength Pareto evolutionary algorithm 2 (SPEA2). Their
fittest values are then determined by additionally introducing the Akaike information criterion. Experimental data for the
Ottawa sand are used to test such processes. The results show that an MOEA is an efficient and automatic tool to identify
the fittest form of an elastic–plastic constitutive law from a large amount of experimental data. However, sufficient data
are required to determine the correct searching range of parameters to be identified. 相似文献
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This paper describes the numerical simulation of two dynamic centrifuge tests on reduced scale models of shallow tunnels in dry sand, carried out using both an advanced bounding surface plasticity constitutive soil model and a simple Mohr–Coulomb elastic-perfectly plastic model with embedded nonlinear and hysteretic behaviour. The predictive capabilities of the two constitutive models are assessed by comparing numerical predictions and experimental data in terms of accelerations at several positions in the model, and bending moment and hoop forces in the lining. Computed and recorded accelerations match well, and a quite good agreement is achieved also in terms of dynamic bending moments in the lining, while numerical and experimental values of the hoop force differ significantly with one another. The influence of the contact assumption between the tunnel and the soil is investigated by comparing the experimental data and the numerical results obtained with different interface conditions with the analytical solutions. The overall performance of the two models is very similar indicating that at least for dry sand, where shear-volumetric coupling is less relevant, even a simple model can provide an adequate representation of soil behaviour under dynamic conditions. 相似文献
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The paper presents a hypoplastic constitutive model for the three-dimensional non-linear stress–strain and dilatant volume change behaviour of sand. The model is developed without recourse to the concept in elastoplasticity theory such as yield surface, plastic potential and decomposition into elastic and plastic parts. Benefited from the non-linear tensorial functions available from the representation theorem the model possesses simple mathematical formulation and contains only four material parameters, which can be easily identified with triaxial compression tests. Comparison of the predictions with the experimental results shows that the model is capable of capturing the salient behaviour of sand under monotonic loading and is applicable to both drained and undrained conditions. 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
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It is well known that the compressibility of crushable granular materials increases with the moisture content,due to the decrease of particle strength in a humid environment.An existing approach to take into account the effect of grain breakage in constitutive modeling consists in linking the evolution of the grain size distribution to the plastic work.But how the material humidity can affect this relationship is not clear,and experimental evidence is quite scarce.Based on compression tests on dry and saturated crushable sand recently reported by the present authors,a new non-linear relationship is proposed between the amount of particle breakage and the plastic work.The expression contains two parameters:(1)a material constant dependent on the grain characteristics and(2)a constant depending on the wetting condition(in this study,dry or saturated).A key finding is that the relationship does not depend on the stress path and,for a given wetting condition,only one set of parameters is necessary to reproduce the results of isotropic,oedometric,and triaxial compression tests.The relationship has been introduced into an elastoplastic constitutive model based on the critical state concept with a double yield surface for plastic sliding and compression.The breakage ratio is introduced into the expression of the elastic stiffness,the critical state line and the hardening compression pressure.Incremental stress-strain computations with the model allow the plastic work to be calculated and,therefore,the evolution of particle crushing can be predicted through the proposed non-linear relationship and reintroduced into the constitutive equations.Accurate predictions of the experimental results in terms of both stress-strain relationships and breakage ratio were obtained. 相似文献
9.
H. S. Yu 《国际地质力学数值与分析法杂志》1998,22(8):621-653
The purpose of this paper is to present a simple, unified critical state constitutive model for both clay and sand. The model, called CASM (Clay And Sand Model), is formulated in terms of the state parameter that is defined as the vertical distance between current state (v, p′) and the critical state line in v–ln p′ space. The paper first shows that the standard Cam-clay models (i.e. the original and modified Cam-clay models) can be reformulated in terms of the state parameter. Although the standard Cam-clay models prove to be successful in modelling normally consolidated clays, it is well known that they cannot predict many important features of the behavior of sands and overconsolidated clays. By adopting a general stress ratio-state parameter relation to describe the state boundary surface of soils, it is shown that a simple, unified constitutive model (CASM) can be developed for both clay and sand. It is also demonstrated that the standard Cam-clay yield surfaces can be either recovered or approximated as special cases of the yield locus assumed in CASM. The main feature of the proposed model is that a single set of yield and plastic potential functions has been used to model the behaviour of clay and sand under both drained and undrained loading conditions. In addition, it is shown that the behaviour of overconsolidated clays can also be satisfactorily modelled. Simplicity is a major advantage of the present state parameter model, as only two new material constants need to be introduced when compared with the standard Cam-clay models. © 1998 John Wiley & Sons, Ltd. 相似文献
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This paper presents a finite element approach to analyse the response of shallow foundations on soils with strain-softening behaviour. In these soils, a progressive failure can occur owing to a reduction of strength with increasing the plastic strains induced by loading. The present approach allows this failure process to be properly simulated by using a non-local elasto-viscoplastic constitutive model in conjunction with a Mohr–Coulomb yield function in which the shear strength parameters are reduced with the accumulated deviatoric plastic strain. Another significant advantage of the method is that it requires few material parameters as input data, with most of these parameters that can be readily obtained from conventional geotechnical tests. To assess the reliability of the proposed approach, some comparisons with experimental results from physical model tests are shown. A fairly good agreement is found between simulated and observed results. Finally, the progressive failure process that occurs in a dense sand layer owing to loading is analysed in details, and the main aspects concerning the associated failure mechanism are highlighted. 相似文献
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黏土的应力路径本构模型 总被引：2，自引：0，他引：2
根据黏土应力-应变曲线的特点及其应力路径的相关特性,将作者所建立的砂土应力路径本构模型扩展用于黏土,建立了黏土的应力路径本构模型,利用变换应力方法将SMP准则用于黏土的应力路径本构模型,使模型得到了合理的三维化。黏土的应力路径模型与修正剑桥模型相比,在双向加载A区和卸载D区二者完全相同;在单向加载B区和F区,两种模型均可计算塑性应变;特别是在C区和E区,黏土的应力路径模型可计算塑性应变,而修正剑桥模型的塑性应变为0。通过与修正剑桥模型比较和对藤森黏土试验结果的预测,反映了黏土应力路径本构模型描述黏土在不同应力路径条件下应力-应变特性的优越性。 相似文献
13.
Selection of sand models and identification of parameters using an enhanced genetic algorithm 
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下载免费PDF全文 Numerous constitutive models of granular soils have been developed during the last few decades. As a consequence, how to select an appropriate model with the necessary features based on conventional tests and with an easy way of identifying parameters for geotechnical applications has become a major issue. This paper aims to discuss the selection of sand models and parameters identification by using genetic algorithm. A real‐coded genetic algorithm is enhanced for the optimization with high efficiency. Models with gradually varying features (elastic‐perfectly plastic modelling, nonlinear stress–strain hardening, critical state concept and two‐surface concept) are selected from numerous sand models as examples for optimization. Conventional triaxial tests on Hostun sand are selected as the objectives in the optimization. Four key points are then discussed in turn: (i) which features are necessary to be accounted for in constitutive modelling of sand; (ii) which type of tests (drained and/or undrained) should be selected for an optimal identification of parameters; (iii) what is the minimum number of tests that should be selected for parameter identification; and (iv) what is the suitable and least strain level of objective tests to obtain reliable and reasonable parameters. Finally, a useful guide, based on all comparisons, is provided at the end of the discussion. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
14.
In this paper, the novel concept of probabilistic yielding is used for 1‐D cyclic simulation of the constitutive behavior of geomaterials. Fokker–Planck–Kolmogorov equation‐based probabilistic elastic–plastic constitutive framework is applied for obtaining the complete probabilistic (probability density function) material response. Both perfectly plastic and hardening‐type material models are considered. It is shown that when uncertainties in material parameters are taken into consideration, even the simple, elastic‐perfectly plastic model captures some of the important features of geomaterial behavior, for example, modulus reduction with cyclic strain, which, deterministically, is only possible with more advanced constitutive models. Furthermore, it is also shown that the use of isotropic and kinematic hardening rules does not significantly improve the probabilistic material response. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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Numerous attempts have been made to modify the generalized constitutive model and to introduce new constitutive models in the framework of generalized plasticity. The modified models can predict the behavior of sand fairly well, however, such models require many parameters and are difficult to calibrate. Moreover, it is highly desirable for a model to be able to reproduce soil behavior using a single set of parameters. In this paper, the constitutive model by Pastor and Zienkiewicz is further developed based on critical state and bounding surface models. The model is used to simulate the behavior of three types of sands under monotonic and cyclic loadings. 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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The mechanical behavior of granular materials is characterized by strong nonlinearity and irreversibility. These properties have been differently described by a variety of constitutive models. To test any constitutive model, experimental data relative to the nature of the incremental stress–strain response of the material is desirable. However, this type of laboratory data is scarce because of being expensive and difficult to obtain. The discrete element method has been used several times as an alternative to obtain incremental responses of granular materials. Crushable grains add one extra source of irreversibility to granular materials. Crushability has been variously incorporated into different constitutive models. Again, it will be helpful to obtain incremental responses of crushable granular materials to test these models, but the experimental difficulties are increased. Making use of a recently introduced crushing model for discrete element simulation, this paper presents a new procedure to obtain incremental responses in discrete analogs of granular crushable materials. The parallel probe approach, previously used for uncrushable discrete analogs, is here extended to account for the presence of crushable grains. The contribution of grain crushing to the incremental irreversible strain is identified and separately measured. Robustness of the proposed method is examined in detail, paying particular attention to aspects such as dynamic instability or crushing localization. The proposed procedure is later applied to map incremental responses of a discrete analog of Fontainebleau sand on the triaxial plane. The effect of stress ratio and granular state on plastic flow characteristics is highlighted. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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A unified constitutive model for unsaturated soils is presented in a critical state framework using the concepts of effective stress and bounding surface plasticity theory. Consideration is given to the effects of unsaturation and particle crushing in the definition of the critical state. A simple isotropic elastic rule is adopted. A loading surface and a bounding surface of the same shape are defined using simple and versatile functions. The bounding surface and elastic rules lead to the existence of a limiting isotropic compression line, towards which the stress trajectories of all isotropic compression load paths approach. A non‐associated flow rule of the same general form is assumed for all soil types. Isotropic hardening/softening occurs due to changes in plastic volumetric strains as well as suction for some unsaturated soils, enabling the phenomenon of volumetric collapse upon wetting to be accounted for. The model is used to simulate the stress–strain behaviour observed in unsaturated speswhite kaolin subjected to three triaxial test load paths. The fit between simulation and experiment is improved compared to that of other constitutive models developed using conventional Cam‐Clay‐based plasticity theory and calibrated using the same set of data. Also, the model is used to simulate to a high degree of accuracy the stress–strain behaviour observed in unsaturated Kurnell sand subjected to two triaxial test load paths and the oedometric compression load path. For oedometric compression theoretical simulations indicate that the suction was not sufficiently large to cause samples to separate from the confining ring. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
19.
Wei Wu 《国际地质力学数值与分析法杂志》1998,22(11):921-940
The paper presents a constitutive model for the three-dimensional deformation–strength behaviour of inherently anisotropic sand. Based on non-linear tensorial functions, the model is developed without recourse to the concepts in plasticity theory such as yield surface and plastic potential. Benefited from the fact that no decomposition of strain into elastic and plastic parts is assumed, a unified treatment of anisotropic behaviour of deformation and strength is achieved. Anisotropy is characterized by a vector normal to the bedding plane. The extension of the constitutive model is furnished by incorporating the vector under consideration of the principle of objectivity and the condition of material symmetry. Distinct features of the model are its elegant formulation and its simple structure involving few material parameters. Model performance and comparison with experiments show that the model is capable of capturing the salient behaviour of anisotropic sand. © 1998 John Wiley & Sons, Ltd. 相似文献
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This paper presents a simple concept which can be used for simulating a range of soil mechanics problems. The study is motivated by the observation that many experimental results are commonly described in terms of lines or curves according to a phenomenological approach. Frequently, these relations are based on rather different formulations from one application to another, and in complex forms for some cases. This leads to complications for the calibration of parameters as well as constitutive modelling. Thus, a general framework referred to as “reference curves” has been developed. This framework provides a unique treatment of the macroscopically observed behaviour of clays, sands, and structured materials under isotropic compression, as well as the water retention characteristics of granular materials and geotextiles. Several examples are provided illustrating the good accuracy of models developed with this concept. The proposed framework may be equally applied to any other behaviour where reference lines are easily identifiable from a macroscopic scope, such as some non-linear failure envelopes for granular materials. In addition, we show that the incorporation of the proposed equations into constitutive models is quite straightforward. 相似文献