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This paper presents a generalised constitutive model for destructured, naturally structured and artificially structured clays that extends the Structured Cam Clay (SCC) model. This model is designated as “Modified Structured Cam Clay (MSCC) model”. The influence of structure and destructuring on the mechanical behaviour of clay can be explained by the change in the modified effective stress, which is the sum of the current mean effective stress and the additional mean effective stress due to structure (structure strength). The presence of structure increases the modified mean effective stress and yield surface, enhancing the cohesion, peak strength and stiffness. The destructuring begins when the stress state is on the virgin yield surface. After the failure (peak strength) state, the abrupt destructuring occurs as the soil–cementation structure is crushed; hence the strain softening. The soil structure is completely removed at the critical state when the yield surface becomes identical to the destructured surface. The destructuring law is proposed based on this premise. In the MSCC model, the yield function is the same shape as that of the Modified Cam Clay (MCC) model. A plastic potential is introduced so as to account for the influence of structure on the plastic strain direction for both hardening and softening behaviours. The required model parameters are divided into those describing destructured properties and those describing structured properties. All the parameters have physical meaning and can be simply determined from the conventional triaxial tests. Thus, the MSCC model is a useful tool for geotechnical practitioners. The capability of the model is verified by the test results of destructured, natural structured and artificially structured clays. 相似文献
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T.A. Newson 《Computers and Geotechnics》1998,23(4):277-287
A non-associated constitutive critical state model is proposed. The yield surface is that of Modified Cam Clay, whilst the plastic potential is an empirical function. The yield and plastic potential surfaces in the octahedral plane vary from circular at low stress ratios, to the Matsuoka-Nakai surface at failure. Assessment of the model has been by comparison with laboratory tests on soft clay. Further validation has been by predicting centrifuge model behaviour using a modified form of the CRISP finite element program. Comparisons of the numerical analyses, using the proposed model and Modified Cam Clay, show improved correlations with the experimental data. © 相似文献
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A new constitutive model for soft structured clays is developed based on an existing model called S‐CLAY1S, which is a Cam clay type model that accounts for anisotropy and destructuration. The new model (E‐SCLAY1S) uses the framework of logarithmic contractancy to introduce a new parameter that controls the shape of the yield surface as well as the plastic potential (as an assumed associated flow rule is applied). This new parameter can be used to fit the coefficient of earth pressure at rest, the undrained shear strength or the stiffness under shearing stress paths predicted by the model. The improvement to previous constitutive models that account for soil fabric and bonding is formulated within the contractancy framework such that the model predicts the uniqueness of the critical state line and its slope is independent of the contractancy parameter. Good agreement has been found between the model predictions and published laboratory results for triaxial compression tests. An important finding is that the contractancy parameter, and consequently the shape of the yield surface, seems to change with the degree of anisotropy; however, further study is required to investigate this response. From published data, the yield surface for isotropically consolidated clays seems ‘bullet’ or ‘almond’ shaped, similar to that of the Cam clay model; while for anisotropically consolidated clays, the yield surface is more elliptical, like a rotated and distorted modified Cam clay yield surface. © 2015 The Authors. International Journal for Numerical and Analytical Methods in Geomechanics published by John Wiley & Sons Ltd. 相似文献
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A critical state model for overconsolidated structured clays 总被引：1，自引：0，他引：1
This paper presents a generalised critical state model with the bounding surface theory for simulating the stress–strain behaviour of overconsolidated structured clays. The model is formulated based on the framework of the Structured Cam Clay (SCC) model and is designated as the Modified Structured Cam Clay with Bounding Surface Theory (MSCC-B) model. The hardening and destructuring processes for structured clays in the overconsolidated state can be described by the proposed model. The image stress point defined by the radial mapping rule is used to determine the plastic hardening modulus, which varies along loading paths. A new proposed parameter h, which depends on the material characteristics, is introduced into the plastic hardening modulus equation to take the soil behaviour into account in the overconsolidated state. The MSCC-B model is finally evaluated in light of the model performance by comparisons with the measured data of both naturally and artificially structured clays under compression and shearing tests. From the comparisons, it is found that the MSCC-B model gives reasonable good simulations of mechanical response of structured clays in both drained and undrained conditions. With its simplicity and performance, the MSCC-B model is regarded as a practical geotechnical model for implementation in numerical analysis. 相似文献
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Incorporation of void ratio as a state variable into constitutive models allows, in principle, to use a single set of parameters for soils with different OCRs. Two sets of experimental data on reconstituted clays are used for evaluation of three constitutive models of different complexity (Modified Cam clay model, 3SKH model, hypoplastic model for clays). Although all the models predict the influence of OCR correctly from the qualitative point of view, quantitative comparison using a suitable scalar error measure reveals merits and shortcomings of different models. 相似文献
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A rigorous semi‐analytical solution for undrained cylindrical cavity expansion in critical state soils 
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下载免费PDF全文 Apostolos Vrakas 《国际地质力学数值与分析法杂志》2016,40(15):2137-2160
This paper presents a generalized, rigorous and simple large strain solution for the undrained expansion of a vertical cylindrical cavity in critical state soils using a rate‐based plasticity formulation: the initial stress field is taken as anisotropic, that is with horizontal stresses that differ from the vertical stress, and the soil is assumed to satisfy any two‐invariant constitutive model from the critical state (Cam‐clay) family; no simplifying assumption is made during the mathematical derivation; calculating the effective stresses around the cavity requires the solution of a nonlinear equation by means of the Newton–Raphson method in combination with quadrature. Cavity expansion curves and stress distributions in the soil are then presented for different critical state models (including the modified Cam‐clay model). The solution derived can be useful for estimating the instantaneous response of saturated low‐permeability soils around piles and self‐boring pressuremeters and can serve as trustworthy benchmark for numerical analysis codes. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
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Yannis F. Dafalias Majid T. Manzari Achilleas G. Papadimitriou 《国际地质力学数值与分析法杂志》2006,30(12):1231-1257
SANICLAY is a new simple anisotropic clay plasticity model that builds on a modification of an earlier model with an associated flow rule, in order to include simulations of softening response under undrained compression following Ko consolidation. Non‐associativity is introduced by adopting a yield surface different than the plastic potential surface. Besides, the isotropic hardening of the yield surface both surfaces evolve according to a combined distortional and rotational hardening rule, simulating the evolving anisotropy. Although built on the general premises of critical state soil mechanics, the model induces a critical state line in the void ratio–mean effective stress space, which is a function of anisotropy. To ease interpretation, the model formulation is presented firstly in the triaxial stress space and subsequently, its multiaxial generalization is developed systematically, in a form appropriate for implementation in numerical codes. The SANICLAY is shown to provide successful simulation of both undrained and drained rate‐independent behaviour of normally consolidated sensitive clays, and to a satisfactory degree of accuracy of overconsolidated clays. The new model requires merely three constants more than those of the modified Cam clay model, all of which are easily calibrated from well‐established laboratory tests following a meticulously presented procedure. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Experimental results and simulated behavior of a medium plasticity clay were compared to investigate the performance of an advanced soil constitutive model. The soil model employed for this study was the 3-SKH model. The performance of this model was compared to the performance of two other critical state models; the Cam Clay (CC) and Modified Cam Clay (MCC) models. In addition, the influences of some of the input parameters on the performance of the 3-SKH model were investigated by performing sensitivity analyses. The comparisons demonstrated that the CC model was able to predict normally consolidated compressive behavior of the remolded medium plasticity clay. The compression behavior of overconsolidated clay was better captured by both the 3-SKH and CC models. For extension behavior of the normally consolidated samples, the MCC model performed better than the CC and 3-SKH models in predicting the stress path. The 3-SKH model was found to be very sensitive to varying the exponent in the hardening function. In particular, a difference between the evaluated values as small as 0.01 had a noticeable effect on the predicted stress–strain values for the overconsolidated compression and extension samples. 相似文献
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Hiroyoshi Hirai 《国际地质力学数值与分析法杂志》1987,11(5):503-520
The constitutive model of sands is proposed to describe the characteristics of plastic behaviour for cyclic loadings. A non-associated flow rule is used and both yield function and plastic potential are generalized forms of the Modified Cam clay model. The hardening parameter is represented by the plastic work related to different portions of volumetric and deviatoric changes. The boundary surface is employed to describe the plastic strain within the yield surface. The directional independency of yield condition in triaxial compression and extension tests is extended to that in general stress states. Several drained and undrained cyclic tests are predicted and the comparison is made with experimental results. The proposed model is capable of representing the monotonic and cyclic behaviours of sands with reasonable accuracy. The simulation is performed for both included and excluded membrane penetration effects and it is suggested that the membrane penetration causes the significant influences on the results of undrained cyclic tests. 相似文献
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The performance of several soil constitutive models was evaluated by comparing experimental results and simulated behavior of a medium plasticity clay. Input parameters for the soil constitutive models were obtained from triaxial compression and extension tests on normally and overconsolidated medium plasticity clay. The soil models employed for this study were the Cam Clay, Modified Cam Clay, 3-SKH, and S-CLAY1 models. In order to investigate the influence of some of the input parameters on the performance of the models, sensitivity analyses were also performed. The comparisons demonstrate that the Cam Clay model was able to predict the normally consolidated compressive behavior of medium plasticity clay. Both 3-SKH and Cam Clay models were able to produce acceptable predictions for stress?Cstrain and stress path behavior for overconsolidated compression of the soil. The 3-SKH model did not perform satisfactorily for predicting pore pressure variations, while the Cam Clay model demonstrated fairly acceptable predictions. For the normally consolidated reduced extension test, the Modified Cam Clay and S-CLAY1 models performed better than the Cam Clay and 3-SKH models in predicting the stress?Cstrain curve, pore pressure variations, and stress path. 相似文献
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原状土的结构性和初始应力状态对土的力学效应影响比较显著,在应力水平较小的情况下,原状土的力学行为与重塑土有很大的差异。目前,在描述土体应力应变的本构模型中,绝大多数模型都是基于重塑土在实验的基础上构建的,没有充分考虑土的结构性和初始应力状态的影响。本文在经典的弹塑性理论的大框架下,以桂林岩溶区分布的饱和软黏土为研究对象,结合室内试验的成果,依据前人已建的模型,考虑了土的结构性和初始应力的影响,在充分发挥修正剑桥模型优点的基础上对其进行改进,构建了一种新的饱和软黏土的弹塑性本构模型,并对模型作了分析和比较,初步表明了模型的合理性和有效性,进一步的工程验证研究还在进行之中。该模型的构建可使桂林岩溶区分布的饱和软黏土的应力应变计算更加趋近于实际,并且,对于桂林岩溶区高速公路饱和软基填土过程中,控制加荷速率和控制分级荷载的大小具有重要的现实意义。 相似文献
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Tsutomu Namikawa 《国际地质力学数值与分析法杂志》2001,25(6):605-627
A delayed plastic model, based on the theory of plasticity, is proposed to represent the time‐dependent behaviour of materials. It is assumed in this model that the stress can lie outside the yield surface and the conjugate stress called static stress is defined on the yield surface. The stress–strain relation is calculated based on the plastic theory embedding the static stress. Thus, the stress–strain relation of the model practically corresponds to that of the inviscid elastoplastic model under fairly low rate deformation. The delayed plastic model is coupled with the Cam‐clay model for normally consolidated clays. The performance of the model is then examined by comparing the model predictions with reported time‐dependent behaviour of clays under undrained triaxial conditions. It is shown that the model is capable of predicting the effect of strain rate during undrained shear and the undrained creep behaviour including creep rupture. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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A large proportion of the constitutive models currently employed in Geomechanics are based on the theory of plasticity. Owing to the limitations of the data obtained from conventional testing equipment, arbitrary assumptions are often made about the behaviour of the material in generalized stress space. In this paper it is shown that the Lode angle of the stress state at failure in plane strain deformation is dependent on the shape adopted for the plastic potential. The influence of the shape of the plastic potential in the deviatoric plane on the predicted behaviour of two boundary value problems both prior to and at failure is then considered. In both cases a form of the Modified Cam Clay model is employed to describe the soil behaviour, and numerical predictions are obtained using a finite element computer code. For drained situations it is shown that the Lode angle of the stress state at failure has a dominating influence on the predicted behaviour. However, for undrained cases the effects are not so important as long as the correct undrained strength at failure is enforced. 相似文献
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Prediction of stresses and strains around model tunnels with adjacent embedded walls in overconsolidated clay 总被引：1，自引：0，他引：1
This paper presents the results of finite element analyses carried out using different constitutive models for overconsolidated clay: the Modified Cam clay model and the Three-Surface Kinematic Hardening (3-SKH) model. These analyses are evaluated against data from an extensive series of physical model tests examining the influence of an embedded wall placed near a tunnel on ground movements and tunnel stability. It is shown that for heavily overconsolidated soils reasonable predictions of both deformations and failure can be obtained from kinematic hardening models such as the 3-SKH model, which allow plastic deformation inside a Modified Cam clay state boundary surface. 相似文献
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The mechanical behavior of natural clays is affected by their inherent anisotropy and metastable soil structure. A simple hierarchical model that considers initial anisotropy and destructuration was formulated within the framework of critical state soil mechanics. In the proposed model, stress sensitivity and a destructuration index were introduced to account for the degree of bonding and the rate of destructuration, respectively. An inclined yield surface was used to incorporate the effect of the initial anisotropy. The proposed model can be degenerated to the Modified Cam Clay model by setting the initial stress sensitivity equal to unity and using a horizontal yield surface. Reasonable agreement between the model simulations and the experimental results on a variety of stress paths demonstrated that the proposed model can capture well the deformation behavior of natural clay and reconstituted soil. The model was implemented into the finite element program for the numerical analysis of an embankment on soft clay improved with prefabricated vertical drains. The numerical predictions were compared with the field-measured data in terms of embankment settlement. Additionally, the numerical simulations were analyzed in terms of horizontal displacements, excess pore water pressure, mean effective stress and volumetric strain. All of the simulations and comparisons indicate the importance of considering the effects of plastic anisotropy, interparticle bonding and destructuration caused by loading beyond yield stress and field disturbance in analyzing the behavior of an embankment on natural soft clay. 相似文献
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In this paper, a study is made of the generalization of constitutive models for geomaterials from two‐dimensional stress and strain states to three‐dimensional stress and strain states. Existing methods of model generalization are reviewed and their deficiencies are highlighted. A new method is proposed based on geometries of the model imprints on two normal planes. Using the proposed method, various three‐dimensional failure criterions suitable for geomaterials are implemented directly into a two‐dimensional model and the generalized model is identical to its original form for the axially symmetric condition. To demonstrate the application of the proposed method, the Modified Cam Clay model is extended using the Matsuoka–Nakai failure criterion. Simulations of soil behaviour for loading in the principal stress space are presented and analysed. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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A two-surface plasticity model for stiff clay 总被引：1，自引：1，他引：0
This paper presents a constitutive model for describing some important features of the behavior of natural stiff clay evidenced experimentally such as the limited elastic zone, the presence of strain hardening and softening, and the smooth transition from elastic behavior to a plastic one. The model, namely ACC-2, is an adapted Modified Cam Clay model with two yield surfaces: similarly to bounding surface plasticity theory, an additional yield surface—namely Inner yield surface—was adopted to account for the plastic behavior inside the conventional yield surface. A progressive plastic hardening mechanism was introduced with a combined volumetric-deviatoric hardening law associated with the Inner yield surface, enabling the plastic modulus to vary smoothly during loading paths. The main feature of the proposed model is that its constitutive equations can be simply formulated based on the consistency condition for the Inner yield surface, so that it can be efficiently implemented in a finite element code using a stress integration scheme similar to that of the Modified Cam Clay model. Furthermore, it is proved to be an appropriate model for natural stiff clay: the simulations of a set of tests along different mechanical loading paths on natural Boom Clay show good agreement with the experimental results. 相似文献