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1.
超固结粘土的剪切带数值模拟   总被引:5,自引:0,他引:5  
基于中井的子负荷面本构关系模型,采用高精度的隐式应力积分算法,研究了平面应变试验中超固结粘土试样的变形局部化问题。模拟了不同的加载速度和边界约束条件,得到了超固结比为8的藤森粘土土体内部明显可见的X型剪切带和单一型剪切带。结果表明:土体的剪胀特性、孔隙水在土体内的移动规律以及边界约束条件对剪切带的形成和发展起着控制作用。  相似文献   

2.
粘土的双硬化模型   总被引:20,自引:4,他引:20  
本文中建议了一个包含塑性体应变和偏应变两个硬化参数的封闭屈服面模型,可以同时应用于正常固结土和超固结土。该模型沿用了剑桥模型的参数测定方法,而大大拓展其适用范围。通过正常固结试样、超固结试样和应力路线转折条件下计算与试验曲线的对比,说明该模型有较广泛的适应性。  相似文献   

3.
考虑渐近状态特性的超固结土本构模型   总被引:1,自引:0,他引:1  
罗汀  侯伟  姚仰平 《岩土力学》2010,31(3):683-688
基于超固结土的UH模型,结合渐近状态概念,将适用于饱和砂土的渐近状态本构模型推广为考虑渐近状态特性的超固结土本构模型,用于描述土的超固结性和渐近状态特性。通过采用变换应力方法实现了模型的三维化。新提出的本构模型简单、参数较少,与剑桥模型相比,仅增加了一个材料参数,即伏斯列夫面斜率。该模型能够合理反映超固结土的硬化、软化、临界状态、剪缩、剪胀、应力路径依赖性、渐近状态等特性。  相似文献   

4.
王秋生  周济兵 《岩土力学》2019,40(11):4178-4184
基于广义热力学基本理论,通过考虑塑性剪切变形产生的能量一部分以塑性自由能的形式储存,并且该部分自由能与超固结度相关,结合修正剑桥模型的热力学函数形式建立了适用于超固结土的自由能函数和耗散函数。该耗散函数与当前应力状态无关,相关联流动法则仍然适用。由建立的耗散函数和自由能函数,推导了弹塑性本构关系的屈服函数、流动法则、硬化定律。通过4种不同超固结土的试验结果和计算结果进行比较,验证了模型的合理性。  相似文献   

5.
K0固结粘土各向异性不排水剪强度研究   总被引:5,自引:1,他引:5  
在三维各向异性弹塑性本构关系基础上,求解不排水条件和破坏条件,导出各种不同试验条件下K0固结粘土的各向异性不排水剪强度表达式。对常规超固结出定义下的不排水剪强度进行研究,将理论计算结果与试验结果进行比较,验证所提理论的合理性。  相似文献   

6.
刘恩龙  罗开泰  张树祎 《岩土力学》2013,34(11):3103-3109
天然岩土材料具有结构性和各向异性。在岩土破损力学的理论框架下,建立了初始应力各向异性结构性土的二元介质模型。岩土破损力学把结构性岩土材料抽象成由胶结强的胶结块(胶结元)和无胶结的软弱带(摩擦元)组成的二元结构体,变形过程中胶结块逐步破损并向软弱带转化。假定胶结块为横观各向同性的理想弹脆性体,胶结块破损后转化成的软弱带为可用邓肯-张模型描述的非线性弹性体。通过引入考虑各向异性影响的破损率和局部应变系数,建立了初始应力各向异性结构性土的二元介质本构模型,并给出了模型参数的确定方法。最后给出了模型的表现,且通过人工制备初始应力各向异性结构性土的三轴压缩试验结果验证了模型的适用性。计算结果表明,所提出的本构模型可以较好地模拟初始应力各向异性结构性土的应力-应变和体积变形特性。  相似文献   

7.
陈立文  孙德安 《岩土力学》2011,32(10):2922-2928
基于超固结黏土三维弹塑性本构模型,导出水-土耦合部分排水条件下饱和黏土应变局部化的萌生条件,求出在不同应力路径下,单相和水-土耦合条件下超固结土分叉的三维解析解和数值解。理论分析表明,应力罗德角 为-30°、15°和30°时,无论是单相条件,还是水土耦合两相介质条件,该模型均无分叉现象产生;应力罗德角为0°时,单相条件下该模型有分叉现象产生,水土耦合不排水条件下该模型无分叉现象出现,水-土耦合部分排水条件下分叉与否则与参数选取有关;应力罗德角为-15°时,无论是单相条件,还是水-土耦合条件,该模型均有分叉现象产生。利用嵌入了上述本构模型的有限元软件ABAQUS,对单相和水-土耦合条件下的多单元立方体应变局部化分叉现象进行数值分析。分析表明,在应力罗德角为 30°时,单相条件和水土耦合条件下都无分叉现象产生;应力罗德角为15°时,单相条件下有分叉现象产生,水-土耦合不排水条件下无分叉现象出现,水-土耦合部分排水条件下何时分叉则与渗透系数大小有关;应力罗德角为-15°和0°时,单相条件和水土耦合条件下该模型均有分叉现象产生。同一应力路径下数值解相对于理论解更易出现分叉。  相似文献   

8.
热黏弹塑性本构模型是描述土在温度(热)和时间(黏)耦合作用下的应力-应变关系的本构模型。在一些新型岩土工程诸如高放核废料地质处置、地热资源开发与贮存的建设中,需要同时考虑温度和时间对土的影响,所以建立一个热黏弹塑性本构模型具有理论和实际意义。将温度变化对黏土体积和强度参数的影响引入笔者之前提出的超固结土等向应力-应变-时间关系,建立了一个等向应力条件下的应力-应变-时间-温度关系。随后,基于该关系推导了屈服面硬化定律,并将其与超固结土统一硬化模型的屈服方程和流动法则结合,建立了超固结土的热黏弹塑性本构模型。最后,使用新模型预测室内试验,证明新模型能够反映时间和温度对土体积、一维压缩曲线和前期固结压力的耦合影响。  相似文献   

9.
结构性粘土的堆砌体模型   总被引:50,自引:18,他引:50  
天然粘土一般都具有结构性, 其变形过程必然伴随着结构的破坏。 提出了一种新型的堆砌体模型, 用以描述这种结构破坏现象。 这一模型把变形过程中的结构性土看作不同大小土块的集合体, 总的变形将由土块的弹性变形、土块之间滑动引起的塑性变形和土块破碎引起的损伤变形三部分组成。 塑性变形常用屈服函数描述, 损伤变形则可以引入一种类似的损伤函数加以描述。推导了相应的应力应变关系式并提出了模型参数的测定方法。  相似文献   

10.
软粘土的各向异性和小应变条件下的本构模型(ASM)   总被引:7,自引:5,他引:7  
以能量方程为基础推导出各向异性和小应变条件下弹塑性的本构方程,并将屈服面与修正桥模型和试验测得的屈服面进行了对比,表明新的屈服面比修正剑桥模型更接近试验结果,采用从初始应力到状态边界面的距离为参数的系数来修正硬化准则以模拟土体小应谱条件下的应力-应变特征。将新的本构模型编入有限元程序,对小应变试验进行了计算分析,计算结果表明,新的模型比修正剑桥模型能更好地反映土体的主要力学特性。  相似文献   

11.
In dynamic geotechnical problems, soils are often subjected to a combination of sustained static and fast cyclic loading. Under such loading conditions, saturated and normally consolidated clays generally experience a build-up of excess pore water pressure along with a degradation of stiffness and strength. If the strength of the soil falls below the static stress demand, a self-driven failure is triggered. In this paper, a constitutive model is presented for the analysis of such problems, based on a general multisurface plasticity framework. The hardening behavior, the initial arrangement of the surfaces, and the nonassociated volumetric flow rule are defined to capture important aspects of cyclic clay behavior. This includes nonlinear hysteretic stress-strain behavior, the effect of anisotropic consolidation, and the generation of excess pore water pressure during undrained cyclic loading along with a degradation of stiffness and strength. The model requires nine independent parameters, which can be derived from standard laboratory tests. A customized experimental program has been performed to validate the model performance. The model predictions show a good agreement with test results from monotonic and cyclic undrained triaxial tests, in particular with respect to the strain-softening response and the number of loading cycles to failure. A procedure for a general stress-space implicit numerical implementation for undrained, total stress-based finite element analyses is presented, including the derivation of the consistent tangent operator. Finally, a simulation of the seismic response of a submarine slope is shown to illustrate a possible application of the presented model.  相似文献   

12.
This paper presents a new generalized effective stress model, referred to as MIT-S1, which is capable of predicting the rate independent, effective stress–strain–strength behaviour of uncemented soils over a wide range of confining pressures and densities. Freshly deposited sand specimens compressed from different initial formation densities approach a unique condition at high stress levels, referred to as the limiting compression curve (LCC), which is linear in a double logarithmic void ratio, e, mean effective stress space, p′. The model describes irrecoverable, plastic strains which develop throughout first loading using a simple four-parameter elasto-plastic model. The shear stiffness and strength properties of sands in the LCC regime can be normalized by the effective confining pressure and hence can be unified qualitatively, with the well-known behaviour of clays that are normally consolidated from a slurry condition along the virgin consolidation line (VCL). At lower confining pressures, the model characterizes the effects of formation density and fabric on the shear behaviour of sands through a number of key features: (a) void ratio is treated as a separate state variable in the incrementally linearized elasto-plastic formulation: (b) kinematic hardening describing the evolution of anisotropic stress–strain properties: (c) an aperture hardening function controls dilation as a function of ‘formation density’; and (d) the use of a single lemniscate-shaped yield surface with non-associated flow. These features enable the model to describe characteristic transitions from dilative to contractive shear response of sands as the confining pressure increases. This paper summarizes the procedures used to select input parameters for clays and sands, while a companion paper compares model predictions with measured data to illustrate the model capability for describing the shear behaviour of clays and sands. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

13.
A hypoplastic constitutive model for clays   总被引:3,自引:0,他引:3  
This paper presents a new constitutive model for clays. The model is developed on the basis of generalized hypoplasticity principles, which are combined with traditional critical state soil mechanics. The positions of the isotropic normal compression line and the critical state line correspond to the Modified Cam clay model, the Matsuoka–Nakai failure surface is taken as the limit stress criterion and the non‐linear behaviour of soils with different overconsolidation ratios is governed by the generalized hypoplastic formulation. The model requires five constitutive parameters, which correspond to the parameters of the Modified Cam clay model and are simple to calibrate on the basis of standard laboratory experiments. This makes the model particularly suitable for practical applications. The basic model may be simply enhanced by the intergranular strain concept, which allows reproducing the behaviour at very small strains. The model is evaluated on the basis of high quality laboratory experiments on reconstituted London clay. Contrary to a reference hypoplastic relation, the proposed model may be applied to highly overconsolidated clays. Improvement of predictions in the small strain range at different stress levels is also demonstrated. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

14.
A numerical model capable of performing deformation analysis of a medium containing discontinuity surfaces is presented. The discontinuity can be either a crack, which can be open or closed, or a shear band. The model consists of two separate numerical algorithms, which are coupled together by means of the principle of superposition. In particular, an integral equation scheme based on the theory of dislocations is adopted for modelling the discontinuity, while a finite element discretization is used for the continuous medium. In this paper the discontinuity modelling is illustrated in detail, together with the specific formulation of the principle of superposition adopted, and some simple examples of application are presented. The well-known modelling approach based on Fracture Mechanics theory is also briefly discussed. The two models are compared and some advantages and drawbacks of each are pointed out, comments are made regarding their applicability in the specific case of soil mechanics, and conclusions are drawn as regards the conditions under which one or the other is appropriate. Finally, a full-scale example of deformation analysis using the proposed model is presented. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

15.
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   

16.
魏星  黄茂松 《岩土力学》2007,28(9):1811-1816
剑桥模型只适用于正常固结软黏土,不能描述不等向固结土的应力-应变行为的各向异性特性。基于剑桥模型,在其椭圆屈服面中引入各向异性张量和一个形状参数,建立了一个各向异性屈服面,提出了一个适用于等向和不等向固结软黏土的本构模型。各向异性张量的初始值由初始固结应力状态确定,其演化过程由一个与塑性剪应变和塑性体应变都有关的硬化法则描述。形状参数的引入保证了各向异性屈服面的灵活性和适应性。通过对Boston Blue黏土、高岭土和Otaniemi黏土的三轴试验结果的模拟,验证了模型的模拟能力。  相似文献   

17.
This paper presents an advanced thermomechanical model – TEAM in the framework of two‐surface plasticity for saturated clays, with emphasis put on some important thermomechanical features of natural clays evidenced experimentally such as the limited thermomechanical elastic zone, the smooth transition from elastic to plastic behavior. Two plastic mechanisms are introduced in the model: one is to reproduce the thermoplasticity involving thermal expansion and contraction observed at high over‐consolidation ratios and the second one describes the temperature effect on the yield behavior. The model adopts additional yield surfaces, namely inner yield surfaces that are associated with the two proposed plastic mechanisms to account for the plastic behavior inside the existing conventional thermomechanical yield surface namely yield surfaces. The general expressions of the yield surfaces and plastic potentials in p′–q–T space are introduced. A progressive plastic hardening mechanism associated with the inner yield surface is defined, enabling the plastic modulus to vary smoothly during thermomechanical loadings inside the yield surfaces. Several tests on natural Boom clay along different thermomechanical loading paths have been simulated by TEAM, and results show its relevance in describing the thermomechanical behavior of saturated clays. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

18.
王琛  彭越 《岩土力学》2006,27(Z2):191-194
提出了一个考虑超固结黏土应变软化特性的应力-应变-时间关系,其应变-时间关系采用幂函数,应力-应变关系采用双曲线方程的改进模式。该方程的试验参数引入了脆性指数和超固结比,不仅能模拟应变硬化型应力-应变-时间关系,而且能模拟应变软化型应力-应变-时间关系,是应变硬化型应力-应变-时间方程的推广。并针对常应变率试验结果进行预测,证明了该方程的合理性。  相似文献   

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