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1.
This paper presents the calibration of an experiment based on filtration tests, able to provide the cumulative constriction size distribution of granular materials. Here, simulations of these tests are performed using a discrete element method. Filters of same density but different thicknesses are created with a poly‐sized spherical material. Lateral periodic boundaries for the samples are used, and their size is calibrated so that a representative elementary volume is obtained. Fine particles are released on the created samples, and the particle size distribution of the collected material that successfully crossed the filters is computed. These particle size distributions are related to the underlying cumulative constriction size distribution (CSD) of the granular material involved in the samples. The CSD is derived using a probabilistic approach for the path length of individual particles through a granular material. We settle all the requisites related to the technique and to the fine particles that are released to allow reaching a correct CSD for the filter. The reference CSD used for the calibration of the experiment is obtained after a radical partition of the void space into Delaunay tetrahedra and a geometrical characterisation of constrictions on each tetrahedron face. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
2.
A particulate model has been developed to analyze the effects of transient and steady state seepage of water through a randomly-packed coarse-grained soil as an alternative to conventional seepage analysis based on continuum models. In this model, the soil skeleton and the pore water are volumetrically coupled in the transient and steady-state conditions. The concept of relative density has been used to define different compaction levels of the soil layers forming a pavement filter system and observe the seepage response to compaction. First, Monte–Carlo simulation is used to randomly pack discrete spherical particles from a specified particle size distribution (PSD) to achieve a desired relative density based on the theoretical minimum and maximum void ratios. Then, a water pressure gradient is applied across one two-layer unit to trigger water seepage. The interstitial pore water motion is idealized using Navier–Stokes (NS) equations with provision to incorporate the drag forces acting between the pore fluid and soil particles. The NS equations are discretized using finite differences and applied to discrete elements in a staggered, structured grid. The model predicted hydraulic conductivities are validated using widely used equations. 相似文献
3.
The model proposed in this article relates permeability to porosity measurements that can easily be performed in the laboratory. The pore size distribution (PSD) curve is updated with strains and damage. The updated volumetric fractions of natural pores and cracks are introduced in the expression of permeability. Contrary to classical permeability models based on PSD integrations, the model proposed in this article accounts for possible changes in the porosity modes: one mode for undamaged samples and two modes for cracked samples. The proposed approach also accounts for varying states of damage, as opposed to classical fracture network models, in which the cracks pattern is fixed. The only material parameters that are required to describe the microstructure are the lower and upper bounds of the pores size for both natural pores and cracks. All the other PSD parameters involved in the model are related to macroscopic parameters that can easily be determined in the laboratory, such as the initial void ratio. The framework proposed in this article can be used in any damage constitutive model to determine the permeability of a brittle porous medium. Drained triaxial compression tests have been simulated. Before cracks initiation, permeability decreases while the larger natural pores are getting squeezed. After the occurrence of damage, permeability grows due to the increase of cracks density. The model performs well to represent the influence of the confining pressure on damage evolution and permeability variations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
4.
Azirou Samira Benamar Ahmed Tahakourt Abdelkader 《Geotechnical and Geological Engineering》2021,39(6):4181-4194
Filters managed in zoned dams are designed according to criteria based on the grain size distribution of both filter and eroded soil. However, the constriction size distribution of the filter is the key parameter which governs the filter retention process of flowing eroded particles. To assess the filter efficiency regarding eroded particles, several filters and base soils are tested in a vertical cell with a configuration coupling erosion and filtration processes. For setting the boundary condition of eroded particles at the filter inlet, hole erosion test (HET) was performed on the base soil. The investigation of the evolution of filter behavior shows that the void ratio and the grain shape are of a great influence on filter efficiency. A new approach of filter clogging was proposed by evaluating a damage index which is affected by various parameters such as the ratio D15/d85 and the size of eroded particles. An approach linking the geometrical parameters (damage index) to the hydraulic conductivity leads to an estimation of the filter performance which provides a more quantifiable and realistic criterion. The results indicate that even existing criteria were not met; the tested filters remain efficient as regards to experimental data. An analytical approach based on constrictions size distribution was used and pore reduction was matched with experimental results.
相似文献5.
Consequences on water retention properties of double-porosity features in a compacted silt 总被引：2，自引：1，他引：1
The paper deals with an experimental investigation aimed at studying microstructural features and their consequences on water
retention properties of statically compacted unsaturated silt. The evolution of the microstructure of the aggregate fabric
induced by compaction is investigated by studying the pore size distribution changes under different initial conditions (void
ratio and water content). The material used is low plasticity silt from Jossigny near Paris, France. A series of mercury intrusion
porosimetry tests (MIP) were performed at different void ratios and water contents to provide microstructural information.
The arrangement of aggregation/particles and pore network was also investigated with environmental scanning electron microscopy
(ESEM). The MIP data were used to determine the water retention curve on drying for the specific pore network configuration
induced on compaction. The MIP data were used to formulate and calibrate a multimodal water retention model for a specific
pore network configuration, which is obtained by linear superposition of subcurves of a modified van Genuchten type. The study
is then complemented with controlled suction oedometer tests on compacted samples to obtain the water retention properties
of the material at two different void ratios. Finally, we compare the water retention properties obtained by the simulated
progression of the different pore network configurations induced on the hydraulic path with the water retention properties
under suction-controlled conditions. Good agreement between the two methods for the drying path is reached. 相似文献
6.
为研究黄土的孔隙分布(PSD)和土 -水特征曲线(SWCC)与黄土沉积环境的关系,在甘肃榆中县和平镇和正宁县及陕西泾阳县等黄土台塬上部采取原状马兰黄土样,先测定其基本物理指标,再用压汞法测得各土样的PSD曲线,同时用滤纸法测得其SWCC。结果表明:和平镇马兰黄土的PSD曲线为单峰形态,泾阳县马兰黄土的PSD曲线为双峰形态,正宁马兰黄土的PSD曲线具有三峰特点。各土样的SWCC具有与PSD曲线相对应的阶梯状形态。SWCC与PSD曲线之间的对应关系,说明黄土的土水特征受孔隙分布的控制。获取3个原状样扫描电镜图像,微结构显示出这种地域性分异现象。对各采样点的气候环境分析表明,黄土PSD曲线之间的差异主要是由成土作用强弱决定的。将降水量与蒸发量的比值定义为蒸渗系数 (CEI),作为刻画成土作用强弱的指标。发现当CEI≤0.3时,PSD曲线为单峰模式;0.3＜CEI≤0.4时,PSD曲线为双峰模式;0.4＜CEI≤0.5时,PSD曲线为三峰模式,相应的SWCC分别为单拐点、双拐点和三拐点模式。 相似文献
7.
8.
Determination of the critical state line(CSL)is important to characterize engineering properties of granular soils.Grain size distribution(GSD)has a significant influence on the location of CSL.The influence of particle breakage on the CSL is mainly attributed to the change in GSD due to particle breakage.However,GSD has not been properly considered in modeling the CSL with influence of particle breakage.This study aims to propose a quantitative model to determine the CSL considering the effect of GSD.We hypothesize that the change of critical state void ratio with respect to GSD is caused by the same mechanism that influences of the change of minimum void ratio with respect to GSD.Consequently,the particle packing model for minimum void ratio proposed by Chang et al.(2017)is extended to predict critical state void ratio.The developed model is validated by experimental results of CSLs for several types of granular materials.Then the evolution of GSD due to particle breakage is incorporated into the model.The model is further evaluated using the experimental results on rockfill material,which illustrates the applicability of the model in predicting CSL for granular material with particle breakage. 相似文献
9.
The effectiveness of filters to counteract internal erosion in earth structures is particularly related to their ability to capture fine particles moving under seepage flow through the porous material. More precisely, fine particles are likely to be trapped by the narrowest paths between pores: the constrictions. This paper proposes a methodology to compute the constriction size distribution of model granular filters taking into account the relative density of the material. The approach is based upon probabilistic methods which adopt stated simple geometric packing arrangements to represent the solid structure in the extreme density states. Two new models are proposed for the design of the constriction size distribution according to the type of filter grading: continuously graded or gap-graded materials. The models require the usual material characteristics: the grading curve, and the minimum and maximum void ratios for this material. Calibrated on the basis of statistical analyses over numerical assemblies of spheres generated by a discrete element method, the proposed new models constitute a promising tool to significantly improve the modeling of filtration processes in granular materials. 相似文献
10.
Understanding the assemblage of basic grains is essential for predicting many soil properties. X-ray synchrotron microtomography with a high resolution was used for visualisation and quantification of the assemblage of silt grains with a clay phase containing 20% of clays. The 3D computed image was analysed after appropriate segmentation by using: (i) autocorrelation functions which enables anisotropy discussion of the assemblage; (ii) chord distribution which gives information on the size distribution of the void and solid phases; and (iii) the Hoshen-Kopelman algorithm (6-connectivity) in order to label each void with a unique number and thus enabling discussion of the connectivity. Our results show that X-ray synchrotron microtomography enables a more accurate analysis of the assemblage of silt grains with a clay phase than with conventional methods. Thus, it showed the isotropy of the silt-clay assemblage in the studied soil material. The void and solid phase volumes were smaller than 80 and 120 μm in all directions, respectively. The mean distance between two interfaces was 6.9 and 13.4 μm for the void and solid phase, respectively. X-ray synchrotron microtomography of the soil material studied also showed that the voids resulting from the assemblage of the silt grains with the clay phase can be considered as fully connected in the studied dried materials. 相似文献
11.
《Geomechanics and Geoengineering》2013,8(3):197-206
The void distribution of saturated specimens of Ottawa sand is presented. The presence of water inside the sand specimen is detected using the magnetic resonance imaging (MRI) technique. The void distribution of the sample was determined from the image. The specimen was prepared in a non-metallic triaxial cell and was put insie a MRI apparatus to obtain the image. Two sample preparation methods (wet tamping and dry pluviation) were used to illustrate the uniformity of the samples in the initial state. The void distribution along the height of the sample and the three-dimensional orientational void distribution at different locations inside the sample were analysed. The results indicate that the sample generated by the dry-pluviation method is more uniform than the sample generated by the wet-tamping method. When the wet-tamping sample preparation technique is used, the dense sample is more uniform than the loose sample. The development of voids was investigated by a sample loaded inside the MRI device under drained compression condition. The void distribution along the height of the sample at different stages was observed. This work has demonstrated the feasibility of using the MRI technique to examine void distribution in granular material. 相似文献
12.
Micro-Computed Tomography (micro-CT) provides 3D images of the internal structure of sands, allowing quantitative measurements of internal features, including void topology. Methods have already been proposed to measure constriction sizes from idealised particle arrangements or from micro-CT data, however the 3D geometry of constrictions in sands is extremely complex and can be difficult to interpret using existing methods. This paper outlines a new method to measure and visualise void constrictions in sands using micro-CT data, with a view to assessing performance of granular filters. The method is based on watershed segmentation of the void space. Synthetic data obtained from DEM simulations are used to validate the new algorithm and its performance against existing image-based methods is assessed by considering micro-CT data for a representative filter material. 相似文献
13.
Experimental quantification of plagioclase crystal size distribution during cooling of a basaltic liquid 总被引：3，自引：1，他引：2
Elsa Pupier Stéphanie Duchene Michael J. Toplis 《Contributions to Mineralogy and Petrology》2008,155(5):555-570
An experimental study has been conducted to constrain how thermal history controls crystal size distribution (CSD) of plagioclase
in cooling basalts. Data from all experiments are dominated by a log-linear segment of decreasing number density with increasing
crystal size, consistent with observations in many natural rocks. The slope of the CSD is found to be a function of cooling
rate, faster cooling leading to greater slopes. At constant cooling rate the CSDs flatten as temperature decreases, and are
sometimes kinked, characteristics consistent with independent textural observations that crystal agglomeration contributes
significantly to crystal “growth”. A downturn is observed toward small size, which suggests Ostwald ripening. Furthermore,
we find that thermal history above the liquidus has a major influence on CSDs and on the temperatures of phase appearance.
We conclude that near the liquidus heterogeneous nucleation typically dominates.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
14.
击实黄土孔隙结构对土水特征的影响分析 总被引：1，自引：0，他引：1
土水特征曲线是非饱和土的基本土物理-力学关系,即将含水率这一物理参数转化为土粒间力的作用,土水特征曲线受土的结构控制。为了探讨击实黄土孔隙结构对土水特征曲线的影响,本文在3种不同的初始含水率（小于最优含水率8%、最优含水率17%和大于最优含水率19%）下制备不同结构的击实黄土试样,分别用压汞试验测其孔隙分布曲线,用滤纸法测其土水特征曲线,并用扫面电镜获得其微观结构图像。对以上测试结果的分析表明,3种击实土样的孔隙分布曲线在相应的大孔径范围内相差较大,在小孔径范围内趋于一致;土水特征曲线在低吸力区差异较大,小于最优含水率的击实黄土土水特征曲线最陡;在高吸力区,3种击实土样的土水特征曲线趋于一致,这与孔隙分布特征一致。对比孔隙密度分布曲线与土水特征区曲线发现,土的土水特征受孔隙分布的控制,孔隙密度越大,土水特征曲线的斜率越陡。SEM图像也显示出3种击实土样的结构特点,小于最优含水率的土样有较多架空孔隙,优势孔径最大;高于最优含水率的土样,大孔隙减少,小孔隙增多,优势孔径最小。而最优含水率的击实黄土的孔隙分布较均匀,优势孔径覆盖范围大。 相似文献
15.
最小孔隙比是确定岩土体的密实程度与孔隙特征的有效物理指标,如何快速有效地确定岩土体的最小孔隙比,可为岩土体的固结与稳定提供可靠参数。多数估算细粗混合材料最小孔隙比的模型参数与细粗粒径比一一对应,导致估算困难。在分析尾矿粒度组成、沉积规律和固结稳定的基础上,以8种不同粗细粒径,7～9种不同细粒含量尾矿为试验对象,拟合得到不同粒组尾矿最小孔隙比分布模型参数的函数关系;基于混合尾矿颗粒的粒组特征,给出了确定参数幂函数关系的指数值。分别采用模型参数要求粒组范围内的其他6组岩土材料和非粒组范围内的3组岩土材料进行验证。结果表明,考虑粒组分类影响下的模型,参数简单,对不同材料的最小孔隙比估算准确率较高,给出的最小孔隙比的分布规律合理,可为岩土工程领域最小孔隙比估算提供可靠的计算方法。 相似文献
16.
Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization 总被引：2，自引：5，他引：2
Bruce D. Marsh 《Contributions to Mineralogy and Petrology》1988,99(3):277-291
Crystal-size in crystalline rocks is a fundamental measure of growth rate and age. And if nucleation spawns crystals over a span of time, a broad range of crystal sizes is possible during crystallization. A population balance based on the number density of crystals of each size generally predicts a log-linear distribution with increasing size. The negative slope of such a distribution is a measure of the product of overall population growth rate and mean age and the zero size intercept is nucleation density. Crystal size distributions (CSDs) observed for many lavas are smooth and regular, if not actually linear, when so plotted and can be interpreted using the theory of CSDs developed in chemical engineering by Randolph and Larson (1971). Nucleation density, nucleation and growth rates, and orders of kinetic reactions can be estimated from such data, and physical processes affecting the CSD (e.g. crystal fractionation and accumulation, mixing of populations, annealing in metamorphic and plutonic rocks, and nuclei destruction) can be gauged through analytical modeling. CSD theory provides a formalism for the macroscopic study of kinetic and physical processes affecting crystallization, within which the explicit affect of chemical and physical processes on the CSD can be analytically tested. It is a means by which petrographic information can be quantitatively linked to the kinetics of crystallization, and on these grounds CSDs furnish essential information supplemental to laboratory kinetic studies. In this three part series of papers, Part I provides the general CSD theory in a geological context, while applications to igneous and metamorphic rocks are given, respectively, in Parts II and III. 相似文献
17.
Kazuhiro Miyazaki 《Contributions to Mineralogy and Petrology》1991,108(1-2):118-128
This paper presents a theoretical formulation of Ostwald ripening of garnet and discusses the importance of the process during
high pressure and low temperature (high P/T) metamorphism. The growth rate of garnet due to Ostwald ripening is formulated for the system consisting of minerals and
an intergranular medium. Crystal size distribution (CSD) of garnets are examined and compared with the theoretical distribution
for Ostwald ripening. Two types of CSDs are recognized. One is consistent with the theoretical prediction of size distribution
while the other is wider than the theoretical distribution. The former CSD applies to samples in which garnets show homogeneous
spatial distributions. The latter CSD applies to samples in which garnets show heterogeneous spatial distributions such as
in clusters or layers. These relations suggest that the heterogeneity of spatial distributions results in a heterogeneity
of concentration of garnet, causing the wide distributions. The mean diameter (dg) has a large variation in samples having narrow distributions. Ostwald ripening explains well the similar patterns of CSD
in these samples with different dg because of a scaling law. Compositional profiles of garnets with different size are consistent with Ostwald ripening rather
than nucleation and growth kinetics. This suggests that the CSDs result from Ostwald ripening. Magnitude of heating rate will
determine which mechanism controls CSD. Nucleation and growth kinetics are dominant when heating rate is large. On the other
hand, Ostwald ripening is dominant when heating rate is small. CSDs of garnets in high P/T metamorphic rocks are consistent with the latter case. 相似文献
18.
The mid-subtropical forest is one of the biggest sections of subtropical forest in China and plays a vital role in mitigating climate change by sequestering carbon. Studies have examined carbon storage density (CSD) distribution in temperate forests. However, our knowledge of CSD in subtropical forests is limited. In this study, Jiangle County was selected as a study case to explore geographic variation in CSD. A spatial heterogeneity analysis by semi-variogram revealed that CSD varied at less than the mesoscale (approximately 2000–3000 m). CSD distribution mapped using Kriging regression revealed an increasing trend in CSD from west to east of the study area. Global spatial autocorrelation analysis indicated that CSD was clustered at the village level (at 5% significance). Some areas with local spatial autocorrelation were detected by Anselin Local Moran’s I and Getis-Ord G*. A geographically weighted regression model showed different impacts on the different areas for each determinant. Generally, diameter at breast height, tree height, and stand density had positive correlation with CSD in Jiangle County, but varied substantially in magnitude by location. In contrast, coefficients of elevation and slope ranged from negative to positive. Based on these results, we propose certain measures to increase forest carbon storage, including increasing forested area, improving the quality of the current forests, and promoting reasonable forest management decisions and harvesting strategies. The established CSD model emphasizes the important role of mid-subtropical forest in carbon sequestration and provides useful information for quantifying mid-subtropical forest carbon storage. 相似文献
19.
作为黄土的关键水力参数之一,土-水特征曲线(SWCC)受到了土体孔隙结构特征的影响;然而目前还缺乏基于黄土沉积过程的孔隙演化对其土-水特性影响分析。本文在陕西泾阳县泾河南塬黄土剖面自上至下取L1、L2和L6黄土,通过扫描电镜定性分析黄土孔隙结构随沉积过程的演化特征,通过孔隙分布(PSD)曲线量化分析各层黄土的孔径分布特征;在此基础上,利用滤纸法测定黄土SWCC曲线,对比分析黄土SWCC随埋深的变化规律。通过Young-Laplace方程将孔径转化为对应的吸力值,将PSD与SWCC曲线采用同一吸力坐标放置一起,分析黄土孔隙结构分布与SWCC的对应关系。结果表明:随埋深的增大,黄土优势孔径及其分布密度减小;相应地,黄土SWCC的饱和段增长,进气值增大,过渡段变缓,持水能力增强。同时,在各层黄土取样位置取重塑土样,在确保制样含水率和干密度与对应原状土一致的情况下,对比分析重塑与原状黄土的孔隙结构与土-水特性,发现随着土层埋深的增大,两者之间孔隙结构差异增大,SWCC的差异也随之增大。 相似文献