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It is well known that soil is inherently anisotropic and its mechanical behavior is significantly influenced by its fabric anisotropy. Hypoplasticity is increasingly being accepted in the constitutive modeling for soils, in which many salient features, such as nonlinear stress-strain relations, dilatancy, and critical state failure, can be described by a single tensorial equation. However, within the framework of hypoplasticity, modeling fabric anisotropy remains challenging, as the fabric and its evolution are often vaguely assumed without a sound basis. This paper presents a hypoplastic constitutive model for granular soils based on the newly developed anisotropic critical state theory, in which the conditions of fabric anisotropy are concurrently satisfied along with the traditional conditions at the critical state. A deviatoric fabric tensor is introduced into the Gudehus-Bauer hypoplastic model, and a scalar-valued anisotropic state variable signifying the interplay between the fabric and the stress state is used to characterize its impact on the dilatancy and strength of the soils. In addition, fabric evolution during shearing can explicitly be addressed. Modifications have also been undertaken to improve the performance of the undrained response of the model. The anisotropic hypoplastic model can simulate experimental tests for sand under various combinations of principle stress direction, intermediate principal stress (or mode of shearing), soil densities, and confining pressures, and the associated drastic effect of different principal stress orientations in reference to the material axes of anisotropy can be well captured. 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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Shahid Azam 《Geotechnical and Geological Engineering》2007,25(3):369-381
Soils containing expansive clays undergo swelling that can be both detrimental and beneficial in various applications. In
the Arabian Gulf coastal region, natural heterogeneous soils containing clay and sand (tills, shales, and clayey sands) support
most of the civil infrastructure systems. Likewise, mixes of clay and sand are used for local earthwork construction such
as roads and landfills. A clear understanding of the swelling behaviour of such soils is pivotal at the outset of all construction
projects. The main objective of this paper was to understand the evolution of swelling with increasing clay content in local
soils. A theoretical framework for clay–sand soils was developed using phase relationships. Laboratory investigations comprised
of mineralogical composition and geotechnical index properties of the clay and sand and consistency limits, swelling potential,
and morphology of clay–sand mixes. Results indicated that soil consistency of mixes of a local expansive clay and an engineered
sand depends on the weighted average of the constituents. Mixes with 10% clay through 40% clay capture the transition from
a sand-like behaviour to a clay-like behaviour. Influenced by the initial conditions and soil matrix, the swelling potential
of the investigated mixes correlated well with soil plasticity (SP(%) = 0.16 (I
p)1.188). The parameters sand void ratio and clay–water ratio were found to better explain the behaviour of blended clay–sand soils. 相似文献
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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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隧道围岩中较差的砂土质隧道围岩一般在洞口段较为常见。砂土具有粘聚力是客观事实,该粘聚力会对砂土质围岩稳定性产生较大影响。本文从影响砂土质围岩坑道稳定性因素及围岩稳定性分类的角度出发,探讨了与砂土质隧道围岩稳定性相关的粘聚力的影响因素,发现砂土的密实程度对砂土围岩粘聚力有较显著的影响;细粒(d<0.075mm)含量对粘聚力的影响规律与砂土密实程度有关;采用细粒含水量而不是砂土含水量的方法来评定潮湿砂土的粘聚力的影响是较为合理的方法,并总结了细粒含水量对砂土粘聚力的影响规律。 相似文献
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A hypoplastic constitutive model for clays 总被引：3，自引：0，他引：3
D. Ma&#x;ín 《国际地质力学数值与分析法杂志》2005,29(4):311-336
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
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The paper presents a mechanical model for non‐isothermal behaviour of unsaturated soils. The model is based on an incrementally non‐linear hypoplastic model for saturated clays and can therefore tackle the non‐linear behaviour of overconsolidated soils. A hypoplastic model for non‐isothermal behaviour of saturated soils was developed and combined with the existing hypoplastic model for unsaturated soils based on the effective stress principle. Features of the soil behaviour that are included into the model, and those that are not, are clearly distinguished. The number of model parameters is kept to a minimum, and they all have a clear physical interpretation, to facilitate the model usefulness for practical applications. The step‐by‐step procedure used for the parameter calibration is described. The model is finally evaluated using a comprehensive set of experimental data for the thermo‐mechanical behaviour of an unsaturated compacted silt. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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This paper presents results from a finite element study on the behaviour of a single pile in elastic–plastic soils. Pile behaviour in uniform sand and clay soils as well as cases with sand layer in clay deposit and clay layer in sand deposit were analysed and cross compared to investigate layering effects. Finite element results were used to generate p–y curves and then compared with those obtained from methods commonly used in practice. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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Experimental study of headcut erosion in cohesive soils under different consolidation types and hydraulic parameters 总被引：2，自引：0，他引：2
Hossein Babazadeh Masoumeh Ashourian Mahmood Shafai-Bajestan 《Environmental Earth Sciences》2017,76(12):438
Headcut is a change in stream channel elevation, where there is concentrated flow. Most of the past studies focus on non-cohesive soils, although many problems on the streams occur because of cohesive beds and banks. In this study, eight samples of cohesive soils, with a different composition of silt and clay, for different waterfall heights and flow velocity under long- and short-term natural consolidation conditions were tested. In one of the tests, a sand layer was settled on the headcut bed to investigate its impact on headcut erosion. By increasing clay content, the headcut will remain vertical as it moves backward. Result showed that the effect of clay content reduction was more noticeable under the long-term consolidation condition. In general, the effect of clay percentage variation on the measured parameters is much higher than the effects of waterfall height or flow velocity, and the effect of consolidation type and adding a sand layer on the measured values is much higher than the effect of clay percentage variation on the waterfall height and flow velocity. 相似文献
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This paper presents a constitutive model for time‐dependent behaviour of granular material. The model consists of 2 parts representing the inviscid and viscous behaviour of granular materials. The inviscid part is a rate‐independent hypoplastic constitutive model. The viscous part is represented by a rheological model, which contains a high‐order term denoting the strain acceleration. The proposed model is validated by simulating some element tests on granular soils. Our model is able to model not only the non‐isotach behaviour but also the 3 creep stages, namely, primary, secondary, and tertiary creep, in a unified way. 相似文献
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北京平原区地面沉降目前处于快速发展阶段,影响因素十分复杂,其中粘性土体的存在是其赖以形成的物质基础。以北京昌平八仙庄典型地面沉降区为研究对象,采取逐级加荷、逐级卸荷以及反复加卸荷,分析100 m以浅粘性土体在不同加卸载方式下的固结特征。实验结果表明：荷载从25 kPa分级加荷到1 600 kPa,粘土变形量大于粉土,分别为2.822 mm、1.000 mm;荷载从400 kPa分级卸除到50 kPa,粘土的回弹量大于粉土,分别为0.277 mm、0.121 mm;反复加卸荷条件下粉质粘土及粉土较之粘土更容易达到固结状态,蠕变时间效应为粘土>粉质粘土>粉土。建议在制定地面沉降灾害防治措施方案时,应充分考虑沉降区地层土体特征影响。 相似文献
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David Ma&#x;ín Claudio Tamagnini Gioacchino Viggiani Daniele Costanzo 《国际地质力学数值与分析法杂志》2006,30(13):1303-1336
In this paper, the performance of different advanced constitutive models for soils is evaluated with respect to the experimentally observed behaviour of a soft reconstituted clay subject to a wide range of loading directions, see (presented in the companion paper). The models considered include a three‐surface kinematic hardening elastoplastic model; the CLoE hypoplastic model; a recently proposed K‐hypoplastic model for clays, and an enhanced version of the same model incorporating the concept of intergranular strain. A clear qualitative picture of the relative performance of the different models as a function of the loading direction is obtained by means of the incremental strain response envelopes. The definition of suitable error measures allows to obtain further quantitative information in this respect. For the particular initial conditions and loading programme considered in this study, the kinematic hardening and the enhanced K‐hypoplastic models appear to provide the best performance overall. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Hybrid event beds dominated by transitional‐flow facies: character,distribution and significance in the Maastrichtian Springar Formation,north‐west Vøring Basin,Norwegian Sea 
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下载免费PDF全文 Sarah J. Southern Ian A. Kane Michał J. Warchoł Kristin W. Porten William D. McCaffrey 《Sedimentology》2017,64(3):747-776
Hybrid event beds comprising clay‐poor and clay‐rich sandstone are abundant in Maastrichtian‐aged sandstones of the Springar Formation in the north‐west Vøring Basin, Norwegian Sea. This study focuses on an interval, informally referred to as the Lower Sandstone, which has been penetrated in five wells that are distributed along a 140 km downstream transect. Systematic variations in bed style within this stratigraphic interval are used to infer variation in flow behaviour in relatively proximal and distal settings, although individual beds were not correlated. The Lower Sandstone shows an overall reduction in total thickness, bed amalgamation, sand to mud ratio and grain size in distal wells. Turbidites dominated by clay‐poor sandstone are at their most common in relatively proximal wells, whereas hybrid event beds are at their most common in distal wells. Hybrid event beds typically comprise a basal clay‐poor sandstone (non‐stratified or stratified) overlain by banded sandstone, with clay‐rich non‐stratified sandstone at the bed top. The dominant type of clay‐poor sandstone at the base of these beds varies spatially; non‐stratified sandstone is thickest and most common proximally, whereas stratified sandstone becomes dominant in distal wells. Stratified and banded sandstone record progressive deposition of the hybrid event bed. Thus, the facies succession within hybrid event beds records the longitudinal heterogeneity of flow behaviour within the depositional boundary layer; this layer changed from non‐cohesive at the front, through a region of transitional behaviour (fluctuating non‐cohesive and cohesive flow), to cohesive behaviour at the rear. Spatial variation in the dominant type of clay‐poor sandstone at the bed base suggests that the front of the flow remained non‐cohesive, and evolved from high‐concentration and turbulence‐suppressed to increasingly turbulent flow; this is thought to occur in response to deposition and declining sediment fallout. This research may be applicable to other hybrid event bed prone systems, and emphasizes the dynamic nature of hybrid flows. 相似文献
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A hypoplastic constitutive model for debris materials 总被引：1，自引：1，他引：0
Debris flow is a very common and destructive natural hazard in mountainous regions. Pore water pressure is the major triggering factor in the initiation of debris flow. Excessive pore water pressure is also observed during the runout and deposition of debris flow. Debris materials are normally treated as solid particle–viscous fluid mixture in the constitutive modeling. A suitable constitutive model which can capture the solid-like and fluid-like behavior of solid–fluid mixture should have the capability to describe the developing of pore water pressure (or effective stresses) in the initiation stage and determine the residual effective stresses exactly. In this paper, a constitutive model of debris materials is developed based on a framework where a static portion for the frictional behavior and a dynamic portion for the viscous behavior are combined. The frictional behavior is described by a hypoplastic model with critical state for granular materials. The model performance is demonstrated by simulating undrained simple shear tests of saturated sand, which are particularly relevant for the initiation of debris flows. The partial and full liquefaction of saturated granular material under undrained condition is reproduced by the hypoplastic model. The viscous behavior is described by the tensor form of a modified Bagnold’s theory for solid–fluid suspension, in which the drag force of the interstitial fluid and the particle collisions are considered. The complete model by combining the static and dynamic parts is used to simulate two annular shear tests. The predicted residual strength in the quasi-static stage combined with the stresses in the flowing stage agrees well with the experimental data. The non-quadratic dependence between the stresses and the shear rate in the slow shear stage for the relatively dense specimens is captured. 相似文献
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This paper presents a fabric tensor-based bounding surface model accounting for anisotropic behaviour (e.g. the dependency of peak strength on loading direction and non-coaxial deformation) of granular materials. This model is developed based on a well-calibrated isotropic bounding surface model. The yield surface is modified by incorporating the back stress which is proportional to a contact normal-based fabric tensor for characterising fabric anisotropy. The evolution law of the fabric tensor, which is dependent on both rates of the stress ratio and the plastic strain, rules that the material fabric tends to align with the loading direction and evolves towards a unique critical state fabric tensor under monotonic shearing. The incorporation of the evolution law leads to a rotational hardening of the yield surface. The anisotropic critical state is assumed to be independent of the initial values of void ratio and fabric tensor. The critical state fabric tensor has the same intermediate stress ratio (i.e. b value) and principal directions as the critical state stress tensor. A non-associated flow rule in the deviatoric plane is adopted, which is able to predict the non-coaxial flow naturally. The stress–strain relation and fabric evolution of model predictions show a satisfactory agreement with DEM simulation results under monotonic shearing with different loading directions. The model is also validated by comparing with laboratory test results of Leighton Buzzard sand and Toyoura sand under various loading paths. The comparison results demonstrate encouraging applicability of the model for predicting the anisotropic behaviour of granular materials.
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