共查询到20条相似文献,搜索用时 46 毫秒
1.
In compacted coarse-grained materials, the stress state is largely influenced by the compaction procedure and by the characteristics
of the single grains (mineralogy, shape). In this work, two compacted sandy gravels with the same grading but different grain
properties have been tested in a large soft oedometer to highlight this influence. In the first part of the paper, the effect
of oedometric ring deformability on the stress state is quantified in the framework of elastoplasticity. It is then shown
that, for the adopted apparatus and for the tests carried out, the error in the measurement of the coefficient of earth pressure
at rest K
0 caused by ring deformability is very small. The two tested materials, compacted by wet tamping, behave differently because
of their different grain properties, showing, respectively, small and large grain breakage. In primary loading, the more crushable
material has values of K
0 that compare well with Jaky’s (J Soc Hungarian Archit Eng 355–358, 1944) equation at any stress level and for every tested
soil density. For the material with stronger grains, only very loose specimens that have undergone little or no compaction
have a similar behaviour, while the denser specimens show the typical behaviour of overconsolidated soils, with values of
K
0 initially larger than that suggested by Jaky (J Soc Hungarian Archit Eng 355–358, 1944) for normally consolidated soils,
tending to it only at the largest applied stress values. By considering the complex combined effect of tamping and grain crushing
on the stress state and on the overconsolidation ratio of the soil at the end of compaction, these experimental evidences
have been qualitatively explained. 相似文献
2.
This paper is the first part of a work that aims at developing a mechanical model for the behaviour of propellant‐like materials under high confining pressure and strain rate. The behaviour of a typical material is investigated experimentally. Several microstructural deformation processes are identified and correlated with loading conditions. The resulting behaviour is complex, non‐linear, and characterized by multiple couplings. The general structure of a relevant model is sought using a thermodynamic framework. A viscoelastic‐viscoplastic‐compaction model structure is derived under suitable simplifying assumptions, in the framework of finite, though moderate, strains. Model development, identification and numerical applications are given in the companion paper. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
3.
Studies in the past have tried to reproduce the mechanical behaviour of granular materials by proposing constitutive relations based on a common assumption that model parameters and parameters describing the properties, including gradation of individual grains are inevitably linked. However successful these models have proved to be, they cannot account for the changes in granular assembly behaviour if the grains start to break during mechanical loading. This paper proposes to analyse the relation between grading change and the mechanical behaviour of granular assembly. A way to model the influence of grain breakage is to use a critical state‐based model. The influence of the amount of grain breakage during loading, depending on the individual grain strength and size distribution, can be introduced into constitutive relations by means of a new parameter that controls the evolution of critical state with changes in grain size distribution. Experimental data from a calcareous sand, a quartz sand, and a rockfill material were compared with numerical results and good‐quality simulations were obtained. The main consequences of grain breakage are increased compressibility and a gradual dilatancy disappearance in the granular material. The critical state concept is also enriched by considering its overall relation to the evolution of the granular material. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
4.
5.
Numerical examples are given which illustrate the poor performance of conventional finite elements in problems involving strain localization in frictional materials. In one of the cases investigated, that of granular media subjected to plane strain biaxial loading, isoparametric elements are seen to inhibit localization altogether. With these examples by way of motivation, the performance of a recently proposed finite element method in the context of strain localization in frictional materials is assessed, with particular emphasis on three-dimensional problems. In passing, some issues pertaining to the post-bifurcation response of biaxial specimens are examined. In particular, the numerical simulations suggest that the observed softening is a geometrical effect not attributable to constitutive behaviour. 相似文献
6.
Haifang Wen Justin Warner Tuncer Edil Gingan Wang 《Geotechnical and Geological Engineering》2010,28(4):405-411
In-place recycling of asphalt pavement materials is a sustainable rehabilitation method. Existing hot-mix asphalt (HMA) layer
is pulverized and blended with some or the entire base course and possibly some subgrade to form a broadly graded material
referred to as recycled pavement material (RPM). The RPM is then compacted as the new base course and overlaid by a new layer
of HMA. In some occasions, additives are added to increase the strength of RPM base course, such as cement, emulsion, fly
ash. It is plausible to utilize high calcium high carbon fly ash, as the high level of carbon prevents fly ash from being
used in concrete. A series of laboratory tests were conducted to evaluate the performance of these materials, including crushed
aggregate, untreated RPM, and treated RPM with high carbon fly ash. The tests included compaction, California Bearing Ratio,
resilient modulus, and unconfined compressive strength for treated RPM. The engineering properties of these materials were
compared. 相似文献
7.
The infinitesimal and finite stages of folding in nonlinear viscous material with a layer-parallel anisotropy were investigated using numerical and analytical methods. Anisotropy was found to have a first-order effect on growth rate and wavelength selection, and these effects are already important for anisotropy values (normal viscosity/shear viscosity) < 10. The effect of anisotropy must therefore be considered when deducing viscosity contrasts from wavelength to thickness ratios of natural folds. Growth rates of single layer folds were found to increase and subsequently decrease during progressive deformation. This is due to interference between the single layer folds and chevron folds that form in the matrix as a result of instability caused by the anisotropic material behaviour. The wavelength of the chevron folds in the matrix is determined by the wavelength of the folded single layer, which can explain the high wavelength to thickness ratios that are sometimes found in multilayer sequences. Numerical models including anisotropic material properties allow the behaviour of multilayer sequences to be investigated without the need for resolution on the scale of individual layers. This is particularly important for large-scale models of layered lithosphere. 相似文献
8.
This paper is devoted to the simulation of large strain compaction process in sedimentary basins. Special attention is paid to the effects of large porosity changes on the elastic and plastic mechanical properties of the sediment material. The latter are introduced in the constitutive behaviour in the framework of a micromechanical reasoning. In particular, the proposed approach avoids the problem of negative porosities that are predicted by classical models under high confining pressures. Some closed‐form solutions are presented in the simplified case of one‐dimensional compaction. While the influence of stiffness increase is shown to be negligible as regards the compaction law, it proves to affect significantly the stress and porosity profiles. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
9.
Pankaj Sharma N. V. Mahure Murari Ratnam 《Geotechnical and Geological Engineering》2011,29(6):1035-1048
Rockfill material is the most readily available and the most flexible material for the construction of dams especially in
the seismic prone regions. The material is obtained either by blasting available rock or is collected from the alluvial deposits
of the river. During construction of the dam, the available rockfill material is compacted to required density layer by layer
using various sophisticated compactors to achieve the required density and slope. Gradually the vertical load on the lower
layers goes on increasing due to placement of subsequent layers of the materials to achieve the desired height. This may result
in variation of grain size distribution of the lower layers due to the breakage of particles. This will certainly influence
the shear parameters. Present studies have been carried out to find the influence of loading the rockfill materials under
two different stress conditions i.e. multistage loading and single stage loading on the grain size distribution and its subsequent
effect on its shear parameters. Consolidated drained triaxial shear tests have been conducted on the materials obtained by
blasting available rock as well as on the materials collected from the alluvial deposits of the river which are generally
used for construction of rockfill dams. Test data have been analyzed to study the breakage factor and corresponding shear
parameters under both conditions. 相似文献
10.
建立颗粒粒径的质量分布分形模型,收集不同堆石坝工程32条堆石料级配曲线,统计分形维数D的分布特性。各堆石坝工程堆石料级配具有良好的分形特性,可考虑将D作为反映和描述堆石料级配特性的新指标,D在2.348~2.699之间,大多数堆石料的分形维数在2.6左右。以古水垫层料为研究对象,设计了6组不同分形维数的级配曲线,采用随机颗粒不连续变形方法(SGDD)研究不同分形维数对堆石料压实性能和宏细观力学特性的影响。分形维数从2.0到2.8,孔隙比呈先减后增趋势,在D =2.7时压实性能最优,而力链的非均匀程度随分形维数的增大而增大。综合考虑试样压实性和力链的非均匀程度,确定D =2.7时的级配为优化级配。 相似文献
11.
12.
黄土在我国西北地区广泛分布,是当地垃圾填埋场封顶覆盖层的主要材料,该材料的气体渗透特性直接影响了覆盖层对填埋气释放的控制效果。利用渗析技术和自制的气体渗透系数测量装置,模拟和测试了干湿气象条件下覆盖黄土服役含水率变化及其对气体渗透系数的影响,并建立填埋气在垃圾体和覆盖层中的一维稳态运移模型,分析了覆盖层气体渗透系数和抽气速率对填埋气释放控制效果的影响。研究结果表明:渗析技术能有效模拟覆盖黄土服役含水率的变化,压实黄土试样的气体渗透系数介于10-17~10-12 m2量级,随服役含水率的增加而降低,且对于压实度比较高的黄土降低得更加明显;覆盖层底部的填埋气压随气体渗透系数的减小而增大,通过覆盖层下部的气体扩散层负压抽气等措施,可有效减小覆盖层底部气压和填埋气的释放量。 相似文献
13.
The frequent use of soils and earth materials for hydraulic capping and for geo‐environmental waste containment motivated our interest in detailed modelling of changes in size and shape of macro‐pores to establish links between soil mechanical behaviour and concurrent changes in hydraulic and transport properties. The objective of this study was to use finite element analysis (FEA) to test and extend previous analytical solutions proposed by the authors describing deformation of a single macro‐pore embedded in linear viscoplastic soil material subjected to anisotropic remote stress. The FEA enables to consider more complex pore geometries and provides a detailed picture of matrix yield behaviour to explain shortcomings of approximate analytical solutions. Finite element and analytical calculations agreed very well for linear viscous as well as for viscoplastic materials, only limited for the case of isotropic remote stress due to the simplifications of the analytical model related to patterns and onset of matrix‐yielding behaviour. FEA calculations were compared with experimental data obtained from a compaction experiment in which pore deformation within a uniform modelling clay sample was monitored using CAT scanning. FEA predictions based on independently measured material properties and initial pore geometry provided an excellent match with experimentally determined evolution of pore size and shape hence lending credence to the potential use of FEA for more complex pore geometries and eventually connect macro‐pore deformation with hydraulic properties. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
14.
Manuela Cecconi Antonio DeSimone Claudio Tamagnini Giulia M.B. Viggiani 《国际地质力学数值与分析法杂志》2002,26(15):1531-1560
A constitutive model for granular materials is developed within the framework of strain–hardening elastoplasticity, aiming at describing some of the macroscopic effects of the degradation processes associated with grain crushing. The central assumption of the paper is that, upon loading, the frictional properties of the material are modified as a consequence of the changes in grain size distribution. The effects of these irreversible microscopic processes are described macroscopically as accumulated plastic strain. Plastic strain drives the evolution of internal variables which model phenomenologically the changes of mechanical properties induced by grain crushing by controlling the geometry of the yield locus and the direction of plastic flow. An application of the model to Pozzolana Nera is presented. The stress–dilatancy relationship observed for this material is used as a guidance for the formulation of hardening laws. One of the salient features of the proposed model is its capability of reproducing the stress–dilatancy behaviour observed in Pozzolana Nera, for which the minimum value of dilatancy always follows the maximum stress ratio experienced by the material. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
15.
16.
Kannan K. R. Iyer Jeevan Joseph Bruna C. F. L. Lopes D. N. Singh Alessandro Tarantino 《Geomechanics and Geoengineering》2018,13(2):88-103
The soil–water retention (SWR) characteristics of the clays play an important role in controlling their engineering behaviour, particularly, in the unsaturated state. Although, researchers have attempted to understand the water retention characteristics of the clays in their reconstituted or remoulded state, such studies are rare for the clays in their intact state. In this context, it becomes important to understand the influence of initial state of compaction, which would create different pore and fabric structure (viz., microstructure), on the water retention characteristics of the clays. With this in view, SWR behaviour was experimentally determined for the swelling clays (dried from different compaction states, viz., intact, reconstituted and remoulded) by employing Dewpoint PotentiaMeter (WP4C®). The changes in the pore size distribution of the clays at different stages of drying cycle were also studied by employing the Mercury Intrusion Porosimetry. The study reveals that the SWR curves for the intact and reconstituted specimens of the clays converge beyond a certain stage of drying. Also, a critical analysis of changes in the pore structure of the swelling clay specimens, during drying, indicates that the progressively deforming pore structure plays an important role in controlling its water retention characteristics to a great extent. 相似文献
17.
Micromechanical Modelling of Granular Materials: Effect of Particle Size and Gradation 总被引:4,自引:0,他引:4
In this paper the effects of maximum particle size, particle gradation/sorting and fabric on bulk mechanical behaviour of granular materials such as coarse grained soils and rockfills are investigated" from micromechanical considerations starting from the grain scale level, using numerical" simulations based on Discrete Element Modelling (DEM). Hydrostatic compaction and biaxial tests on 2-dimensional assemblies of discs with varying particle sizes and gradations were modelled using DEM. An examination of the constitutive behaviour of granular media considering" the particulate nature of the medium has been attempted to explain the effect of particle size and gradation. Simulation results on perfectly parallel graded assemblies indicate that with increase in the size of the particles, a marginal increase (or no increase) in the angle of internal friction is observed during biaxial loading conditions. A change to a wider gradation (keeping the minimum grain size the same) results in a decrease in the angle of internal friction and an increase in volumetric strain to a considerable extent. Based on micromechanical force and fabric parameters, the basis for the physical behaviour was established. This helps in understanding the physics of parallel gradation techniques. 相似文献
18.
P. S. Theocaris 《Rock Mechanics and Rock Engineering》1999,32(4):267-290
Summary Experimental evidence from true triaxial tests on dense rocks are analysed with emphasis on the failure modes of these materials
under multiaxial loading, ambient temperature and external pressure. The strong dependence of the modes of fracture on the
secondary components of applied stresses, and especially on the intermediate principal stress, indicated that the failure
surface of these brittle materials may be appropriately described by a failure tensor polynomial criterion. As such, the elliptic
paraboloid failure criterion was found to conveniently describe their mode of failure, by considering also the severe influence
of anisotropy of the material.
For this purpose, a method developed recently (Theocaris and Panagiotopoulos, 1995a, 1995b) was applied, defining anisotropic
hardening plasticity through an appropriate sequence of anisotropic elasticity problems. Assuming a particular path of loading
or unloading, we measured the instantaneous tension and compression yield stresses along the transient principal-stress directions.
These parameters completely define the instantaneous state of anisotropy of the body for the corresponding loading step, by
applying the theory of the elliptic paraboloid failure locus (EPFS) (Theocaris, 1989a). A parameter identification problem was formulated on the constitutive expressions for this most general failure criterion. Then, by applying convenient constraints
derived from the EPFS theory, which serve as filters throughout the whole procedure, the characteristic values of terms defining
the variable components of the failure tensor polynomial were calculated, as the material was continuously loaded from the
elastic into the plastic region and up to the ultimate failure load. Accurate simple tests in uniaxial tension and compression
provided sufficient data for the definition of the yield loci of the material, at the considered loading step. These tests
may be complemented with biaxial and triaxial modes of loading of the specimens. The results improve the accuracy and sensitivity
of the method. All such data were used as input values, for establishing the mode of plastic deformation of the body during
particular loading paths.
Moreover, the method employed allows the complete definition of the components of the failure, H, and the strength differential effect, h, tensors at each loading step. These quantities define completely the failure tensor polynomial for each material. Therefore,
it presents the important advantage over other experimental methods by clearly indicating the parts contributed to the failure
mode (either by plasticity, or by the strength differential effect) and their evolution during plastic deformation.
As convenient prototype materials for testing the method, specimens of metamorphic rocks such as Westerly granite (G), or
quartzite (Q) were selected. Interesting results concerning the mechanical and especially the failure modes of such materials
were obtained. Furthermore, the mechanical tests indicated clearly some basic properties of these materials as concerns the
mode of their structure. 相似文献
19.
A numerical technique, based on a mathematical programming algorithm, is presented for the solution of geotechnical problems where elastic-plastic material behaviour is considered. The proposed approach can be adopted for geotechnical media characterized by any suitable yield condition, accounting, if necessary, for workhardening behaviour. The loading process is subdivided into a series of steps applied to a finite element mesh with geometry and material properties constant along each step, but with possible changes between subsequent steps. As an application some typical geotechnical problems are analysed by means of the proposed algorithm and a comparison is made between the available in situ measurements and the numerical results. 相似文献
20.
Existing solutions to Mandel's problem focus on isotropic, transversely isotropic, and orthotropic materials, the last two of which have one of the material symmetry axes coincide with the vertical loading direction. The classical plane strain condition holds for all these cases. In this work, analytical solution to Mandel's problem with the most general matrix anisotropy is presented. This newly derived analytical solution for fully anisotropic materials has all the three nonzero shear strains. Warping occurs in the cross sections, and a generalized plane strain condition is fulfilled. This solution can be applied to transversely isotropic and orthotropic materials whose material symmetry axes are not aligned with the vertical loading direction. It is the first analytical poroelastic solution considering mechanical general anisotropy of elasticity. The solution captures the effects of material anisotropy and the deviation of the material symmetry axes from the vertical loading direction on the responses of pore pressure, stress, strain, and displacement. It can be used to match, calibrate, and simulate experimental results to estimate anisotropic poromechanical parameters. This generalized solution is capable of reproducing the existing solutions as special cases. As an application, the solution is used to study the responses of transversely isotropic and orthotropic materials whose symmetry axes are not aligned with the vertical loading direction. Examples on anisotropic shale rocks show that the effects of material anisotropy are significant. Mandel-Cryer's effects are highly impacted by the degree of material anisotropy and the deviation of the material symmetry axes from the vertical loading direction. 相似文献