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1.
This paper presents a three‐dimensional elastoplastic constitutive model for predicting the hydraulic and mechanical behaviour of unsaturated soils. It is based on experimental results obtained from a series of controlled‐suction triaxial tests on unsaturated compacted clay with different initial densities. Hydraulic hysteresis in the water‐retention behaviour is modelled as an elastoplastic process, with the elastic part modelled by a series of scanning curves and the elastoplastic part modelled by the main drying and wetting curves. The effect of void ratio on the water‐retention behaviour is studied using data obtained from controlled‐suction wetting–drying cyclic tests on unsaturated compacted clay with different initial densities. The effect of the degree of saturation on the stress–strain‐strength behaviour and the effect of void ratio on the water‐retention behaviour are considered in the model, as is the effect of suction on the hydraulic and mechanical behaviour. The initial density dependency of the compacted soil behaviour is modelled by experimental relationships between the initial density and the corresponding yield stress and, thereby, between the initial density and the normal compression line. The model is generalized to three‐dimensional stress states by assuming that the shapes of the failure and yield surfaces in the deviatoric stress plane are given by the Matsuoka–Nakai criterion. Model predictions of the stress–strain and water‐retention behaviour are compared with those obtained from triaxial tests with different initial densities under isotropic compression, triaxial compression and triaxial extension, with or without variation in suction. The comparisons indicate that the model accurately predicts the hydraulic and mechanical behaviour of unsaturated compacted soils with different initial densities using the same material constant. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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非饱和土的水力和力学特性及其弹塑性描述 总被引：6，自引：3，他引：3
简单回顾了非饱和土本构模型研究的发展历程,总结了近几年非饱和土弹塑性本构模型最新研究成果,重点介绍了能统一模拟非饱和土水力性状和力学性状耦合的弹塑性本构模型。通过对建立模型过程中的几个核心问题讨论,较详细地说明该类模型的结构、性能以及相关问题。非饱和土水力性状的滞回性用假定存在饱和度弹性区间的弹塑性过程来模拟;该类耦合模型不仅考虑了吸力对非饱和土水力性状和力学性状的影响,还考虑了饱和度对应力-应变关系和强度的影响以及土体变形对土-水特征曲线的影响。用同一套模型参数,耦合模型可统一预测在吸力控制或含水率控制下沿各种应力路径下非饱和土的水力-力学特性,并简单介绍了膨胀性非饱和土的弹塑性本构模型以及耦合模型在有限元数值计算中的应用。 相似文献
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非均匀煤岩渗流-应力弹塑性耦合数学模型及数值模拟 总被引：11，自引：2，他引：9
利用Weibull分布模拟煤岩弹性模量和强度的非均匀性,结合煤岩弹塑性变形理论和瓦斯渗流理论,建立了非均匀煤岩渗流-应力弹塑性耦合数学模型,给出了该数学模型的有限元离散方程,开发了相应的数值计算程序Coupling Analysis。利用建立的模型模拟了辽宁某瓦斯抽放试井瓦斯抽放过程,结果表明,在瓦斯抽放过程中,有效应力变化诱发煤岩局部进入塑性状态,塑性区透气系数增加了约4.9倍,而弹性受压区的透气系数最大减小至22 %,计算实例的瓦斯压、煤岩有效应力和煤岩变形都呈现非对称性,但服从理论规律,表明采用Weibull分布能很好地模拟煤岩力学参数的非均匀性。 相似文献
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In order to understand the mechanical behaviours of the surrounding rocks in the underground caverns of the Wudongde hydropower plant, triaxial tests are performed on a type of dolomite. It is revealed that damage induced by crack development is the main factor controlling the nonlinear plastic deformation and failure behaviour of the dolomite in both pre- and post-peak regimes. Based on this understanding, a coupled elastoplastic damage model is developed for capturing the dolomite’s mechanical behaviours. In the model, the effects of plasticity and damage on rocks is described by introducing plastic hardening and damage softening commonly in the plastic yield surface. Which are both derived from a suitable Helmholtz free energy function. The model is used to simulate the triaxial tests. Comparisons between test results and the numerical modelling show that the developed model is capable of describing the macro mechanical behaviours of the Wudongde dolomite. 相似文献
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In this paper, an existing elastoplastic constitutive model, originally developed for granular soils, is adapted to describe the stress–strain behaviour of cemented granular soils. The existing model (CJS), due to its modular formulation, can be easily developed to take into account different supplementary behavioural aspects in soil mechanics. In the present study, the failure mechanism of the CJS model is modified by introducing the essential aspects in the behaviour of cemented granular soils in its formulation. All of the model parameters have clear physical meaning and can be identified using classical laboratory tests. A set of direct relations between model parameters and famous mechanical parameters of soils such as internal friction angle and cohesion at peak and residual states is presented. In order to validate the model, the results of triaxial and uniaxial tests in the compression and extension performed on cemented granular materials are used. The validation results indicate the good capability of the proposed model. 相似文献
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在吸附性气体作用下,煤体将产生吸附应变,吸附应变通过使煤微观结构重新排列从而诱发煤损伤,并使其力学性质劣化。尽管大量试验证实了吸附性气体将会改变煤的力学特性,然而当前描述煤-气相互作用的力学模型并未将吸附诱发的损伤考虑其中,故也无法考虑气体吸附诱发煤强度劣化。基于此,建立一个考虑气体吸附损伤的双重孔隙介质力学模型,揭示气体吸附过程诱发的两个相互作用：一个是游离气体引起的常规弹性力学作用,一个是吸附气体诱发的内部膨胀应力,并在此基础上考虑两个力学作用所带来了煤的附加损伤。研究结果表明：气体吸附诱发煤基质产生细观损伤,以拉伸损伤为主,这使煤的力学性质劣化,表现为弹性模量和强度的降低。吸附能力越强的气体,诱发煤的微观结构改变越大,损伤越明显,甚至会诱发煤样呈现新的破坏形态。超临界CO2会诱发煤更大的损伤和强度劣化。 相似文献
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This paper presents a mechanical analogue which models the response of a rigid circular footing on an ideal elastoplastic half-space to transient loads. In the rational analysis of pile-driving dynamics, the response of soil at the base of a pile is often approximated by a footing on a semi-infinite half-space. Most existing base models employ the well-known Lysmer analogue to model the elastic response of the soil at the pile base, and account for the inelastic soil behaviour through the inclusion of a plastic slider with a slip load equal to the ultimate failure load of the footing. The improved model provides a force response which is significantly closer to the ideal response than existing models. The paper commences with a review of analytical solutions for the dynamic response of a rigid circular footing on an elastic half-space. Existing mechanical analogs for the system are reviewed, and an automatic matching process proposed which improves the accuracy of the analogs under transient loading. The inelastic response is then studied using the finite element method, and the mechanical analogs are modified to allow representation of the observed inelastic behaviour. Examples are presented illustrating close agreement between the proposed models and finite element analyses for a range of Poisson's ratio. The improved models have direct application for one-dimensional models of pile driving, particularly in the back-analysis of data from dynamic testing of piles. They are also applicable to studies of dynamic compaction. 相似文献
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在实际隧道施工过程中,隧道开挖引起地下岩体应力重分布使得围岩的微裂纹扩展损伤,并伴随有塑性流动变形。在地下水环境中对于孔隙和微裂隙围岩介质受到应力作用时,在内部将产生高孔隙水压力影响岩石的力学性质,也改变了围岩的破坏模式。为了研究损伤引起的刚度退化和塑性导致的流动两种破坏机制的耦合作用,从弹塑性力学和损伤理论的角度出发,同时引入修正有效应力原理来考虑孔隙水压力的作用,建立基于Drucker-Prager屈服准则的弹塑性损伤本构模型;针对该本构模型推导了孔隙水压力作用下弹塑性损伤本构模型的数值积分算法-隐式返回映射算法,分别对预测应力返回到屈服面的光滑圆锥面或尖点奇异处两种可能的情况给出了详细的描述,隐式返回映射算法具有稳定性和准确性的特点;大多数弹塑性损伤模型中涉及参数多且不易确定的问题,采用反分析方法获得损伤参数,解决了损伤参数不易确定的难题;采用面向对象的编程方法,使用C++语言编制了弹塑性损伤本构求解程序,并对所建立的弹塑性损伤模型和所编程序进行了试验和数值两个方面的验证;最后将其在吉林抚松隧道工程中进行应用,模拟了塑性区和损伤区的发展变化。研究结果表明：所建立的弹塑性损伤本构模型能够较好地描述岩石的力学性能、塑性和损伤变化趋势,所编程序能够进行实际工程问题的模拟,对现场施工给予一定的指导。 相似文献
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A constitutive model for bonded geomaterials subject to mechanical and/or chemical degradation 总被引：2，自引：0，他引：2
The mechanical behaviour of bonded geomaterials is described by means of an elastoplastic strain‐hardening model. The internal variables, taking into account the ‘history’ of the material, depend on the plastic strains experienced and on a conveniently defined scalar measure of damage induced by weathering and/or chemical degradation. For the sake of simplicity, it is assumed that only internal variables are affected by mechanical and chemical history of the material. Despite this simplifying assumption, it can be shown that many interesting phenomena exhibited by weathered bonded geomaterials can be successfully described. For instance, (i) the transition from brittle to ductile behaviour with increasing pressure of a calcarenite with collapsing internal structure, (ii) the complex behaviour of chalk and other calcareous materials in oedometric tests, (iii) the chemically induced variation of the stress and strain state of such kind of materials, are all phenomena that can be qualitatively reproduced. Several comparisons with experimental data show that the model can capture the observed behaviour also quantitatively. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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Granular soils subjected to seepage flow may suffer suffusion, ie, a selective internal erosion. Extending the classical approach of poromechanics, we deduce a new form of the Clausius-Duhem inequality accounting for dissipation due to suffusion, and we deduce restrictions on the constitutive laws of the soil. We suggest (a) a possible coupling between the seepage forces and the suffusion kinetics and (b) an extension of an existing elastoplastic model for the skeleton mechanical behaviour. Numerical integrations of the elastoplastic model are carried out under drained axisymmetric triaxial and oedometric conditions. As a result, we prove that the extended model is able to qualitatively reproduce the suffusion induced strains and the strength reduction experimentally observed. Predictions on the oedometric behaviour of suffusive soils are also provided. 相似文献
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The Barcelona basic model cannot predict the mechanical behaviour of unsaturated expansive soils, whereas the Barcelona expansive model (BExM) can only predict the stress–strain behaviour of unsaturated expansive soils without the water‐retention behaviour being incorporated. Moreover, the micro‐parameters and the coupling function between micro‐structural and macro‐structural strains in the BExM are difficult to determine. Experimental data show that the compression curves for non‐expansive soils under constant suctions are shifted towards higher void ratios with increasing suction, whereas the opposite is true for expansive soils. According to the observed water‐retention behaviour of unsaturated expansive soils, the air‐entry value increases with density, and the relationship between the degree of saturation and void ratio is linear at constant suction. According to the above observation, an elastoplastic constitutive model is developed for predicting the hydraulic and mechanical behaviour of unsaturated expansive soils, based on the existing hydro‐mechanical model for non‐expansive unsaturated soil. The model takes into consideration the effect of degree of saturation on the mechanical behaviour and that of void ratio on the water‐retention behaviour. The concept of equivalent void ratio curve is introduced to distinguish the plastic potential curve from the yield curve. The model predictions are compared with the test results of an unsaturated expansive soil, including swelling tests under constant net stress, isotropic compression tests and triaxial shear tests under constant suction. The comparison indicates that the model offers great potential for quantitatively predicting the hydraulic and mechanical behaviour of unsaturated expansive soils. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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In the last decades, a number of hydro-mechanical elastoplastic constitutive models for unsaturated soils have been proposed. Those models couple the hydraulic and mechanical behaviour of unsaturated soils, and take into account the effects of the degree of saturation on the stress–strain behaviour and the effects of deformation on the soil–water characteristic response with a simple reversible part for the hysteresis. In addition, the influence of the suction on the stress–strain behaviour is considered. However, until now, few models predict the stress–strain and soil–water characteristic responses of unsaturated soils in a fully three-dimensional Finite Element code. This paper presents the predictions of an unsaturated soil model in a Three-dimensional Framework, and develops a study on the effect of partial saturation on the stability of shallow foundation resting on unsaturated silty soil. Qualitative predictions of the constitutive model show that incorporating a special formulation for the effective stress into an elastoplastic coupled hydro-mechanical model opens a full range of possibilities in modelling unsaturated soil behaviour. 相似文献
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为了给电磁辐射预测矿井冲击地压灾害提供理论依据,采用电磁波和损伤力学理论初步分析了电磁辐射能和加载机械能的关系;采用试验和能量理论研究了单轴压缩条件下煤体变形破坏产生电磁辐射能与受载煤体能量积聚、耗散的耦合关系。研究结果表明：加载机械能与煤体变形破坏产生的电磁辐射能成系数为m正线性关系,m与煤体的弹性模量成0.107 4的比例关系;受载煤体峰值弹性应变能与电磁辐射能成正对数关系,煤体的弹性能指数与峰值累积电磁辐射能、总累积电磁辐射能均成正线性关系,电磁辐射信号反映了能量聚集和耗散的状态,表征了煤体冲击破坏的难易程度。因此,电磁辐射能够预测矿井冲击地压灾害的发生。 相似文献
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We present a numerical modelling of elastoplastic damage due to drying shrinkage of concrete in the framework of mechanics of partially saturated porous media. An elastoplastic model coupled with isotropic damage is first formulated. Two plastic flow mechanisms are involved, controlled by applied stress and suction, respectively. A general concept of net effective stress is used in take into account effects of capillary pressure and material damage on stress‐controlled plastic deformation. Damage evolution depends both on elastic and plastic strains. The model's parameters are determined or chosen from relevant experimental data. Comparisons between numerical simulations and experimental data are presented to show the capacity of model to reproduce mains features of concrete behaviour under mechanical loading and during drying shrinkage of concrete. An example of application concerning drying of a concrete wall is finally presented. The results obtained allow to show potential capacity of proposed model for numerical modelling of complex coupling processes in concrete structures. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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The Barcelona Basic Model (BBM) is an extension of the Cam clay model that has become popular in applications involving unsaturated soils and, in particular, in simulations using the finite element method. Partially saturated soils can be loaded in different ways, for instance, mechanically and/or hydraulically. In addition, cycles of loading and unloading can be applied. The present work introduces a modification of the BBM in order to simplify its computer implementation and also to allow the simulation of elastoplastic behaviour during cycles of both mechanical and hydraulic loading. A unique smooth yield surface is introduced and a two-yield surfaces concept is applied in order to represent the cyclic behaviour. The influence of the intermediate principal stress on the strength is also accounted for. Finally, the numerical integration (stress update) of the extended BBM is briefly discussed. 相似文献
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针对特厚煤层大采高工作面,将超前支承压力作用的煤体分为破裂区、塑性区和弹性区。考虑支架护帮阻力等因素,建立了支承压力作用的煤体变形破坏及煤壁片帮分析力学模型。通过摩尔-库仑准则和非关联弹塑性分析,推导出了煤壁水平位移量及破裂区和塑性区半径解析表达式,分析了影响煤壁片帮的主要因素。理论结果与现场实测结果误差仅为15.6%,验证了模型的正确性。研究表明,随支承压力集中系数的增大、机采高度的增加以及支架护帮阻力的减小,煤壁水平位移量明显增大,煤壁片帮程度严重。工程实践表明,提高支架工作阻力,减缓煤壁处压力,控制合理采高以及增大支架护帮阻力,可有效缓解大采高综放工作面煤壁片帮程度。 相似文献