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1.
The flow direction is generally different from the gravity direction in geotechnical structures or slopes, the effect of which during suffusion remains unclear. This paper presents a coupled computational fluid dynamics and discrete element method approach to simulate the particle–fluid interaction relevant to this problem. The CFD-DEM approach is first benchmarked by a classic granular system problem, which is then used to investigate the characteristics of suffusion and its impact on the mechanical behavior. Five different angles between gravity and seepage directions for gap-graded soils with two fines contents are examined. Both the macroscopic and microscopic characteristics during suffusion and triaxial loading tests are analyzed. The direction angle is found to play a significant role affecting the erosion process and the mechanical consequence of soils. The results show that the greater the angle is, the harder it is for suffusion to occur and continue. 相似文献
2.
In most marine reclamation projects, sand fill is placed directly on soft marine seabed soils. The sand particles can easily penetrate into the soft marine soils, and the soft soil can also move into the pore spaces inside the sand at the initial contact interface between the sand and the soft marine soil. In this case, the permeability and the volume of the sand above the initial surface are reduced. To avoid this problem, a geotextile separator is often placed on the surface of the soft marine soils before placing the sand. In this study, a two-dimensional physical model is utilized to study the geotextile separator effects. The initial conditions of a clayey soil, sand fill, and surcharge loading were kept the same in the physical model test with the only difference being that a geotextile separator was either placed on the clay surface or omitted. The settlements of the initial interface were recorded and compared for the two cases without or with the geotextile separator. The particle size distribution of the soils taken across the interface zone for different time durations was then measured, analyzed, and compared. Based on an analysis of the results, the sand percolation depth was 40 mm and fine particle suffusion was apparent when the sand was placed directly on the marine slurry surface without a geotextile separator. However, when a geotextile separator was used sand percolation was avoided, and the fine particle suffusion was effectively diminished. A relative fine particle fraction is defined to illustrate the migration of fine particles from the clay to the sand soils. The fine particle percentages of the Hong Kong Marine Deposits–sand mixtures were calculated for the cases with and without a geotextile separator using an empirical formula and micromechanical modeling to obtain a better understanding of the effects of geotextile separators in practice. 相似文献
3.
Granular soils subjected to flow through their soil skeleton can show a behaviour in which fine particles migrate through the pore space between coarser particles. This process is called internal instability or suffusion. This contribution deals with the numerical analysis of the migration of fine particles in a soil column subjected to fluid flow with unresolved coupled computational fluid dynamics–discrete element method (CFD–DEM) with special regards to the used drag force correlation. The contribution investigates the influence of the Schiller–Naumann model and its extension with a voidage term on the migration behaviour of fine particles. The voidage term is further varied with a parameter, which controls the impact of the change of the void fraction on the drag force. It could be observed that the Schiller–Naumann model does not yield in a suffusive behaviour while the extended models show significant particle migration. Thereby, increasing the impact of the void fraction on the drag force results in stronger particle migration. These results reveal the need for good validation techniques. They indicate how the drag force correlation can be adapted to depict the correct particle migration behaviour. 相似文献
4.
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
5.
In India, rural roads are constantly being constructed. To ensure proper design of rural roads, it is desirable to have an appropriate selection of design parameters. The California bearing ratio (CBR) method of pavement design is the most commonly used method employed for the foundation design of rural roads. In the CBR method, the CBR value of the subgrade soil is critical in deciding the overall thickness of the pavement. Additionally, for good drainage, a typical specification for the pavement foundation design requires the value of permeability coefficient of the subgrade material to be specified. Thus, permeability and CBR constitute two important parameters in the design and assessment of long-term performance of the pavement. In this study, laboratory investigation has been carried out on a number of soil samples procured from a roadwork project site. Preliminary tests, such as index tests and particle size distribution tests, useful for soil classification, were followed by light compaction, CBR and variable head permeability tests. Further, observations from the laboratory investigation are statistically analysed to study correlations among various parameters. Because the predominant soil type found in the study area is alluvial, this study also highlights the suitability of alluvial soils as pavement subgrade material. 相似文献
6.
对多个级配不同含水率的粗粒土进行击实试验,研究粗粒土的压实特性和颗粒破碎分形特征。结果表明,粗粒土最大干密度随级配中粗粒含量的增大而增大,当粗粒含量P5=70%时,最大干密度出现最大值;当P5＞70%时,最大干密度又随粗粒含量的增大而减小,粗粒土击实破碎后的粒径分布具有良好的分形特性,破碎分形维数为2.279 0～2.892 2,均大于击实前粗粒土粒度分形维数;相同级配条件下,粗粒土破碎分形维数随含水率的增大而增大,且粗粒含量P5＞50%时,增幅显著;粗粒土破碎分形维数D与破碎率Bg存在良好的线性关系,且击实前后粗粒土粒度分形维数差值能客观表征颗粒破碎的程度;粗粒含量和含水率是影响颗粒破碎率的两个重要因素,但相对于含水率而言,粗粒含量对破碎率的影响更加显著。 相似文献
7.
Structural crust is a thin layer formed on the soil surface after a rainstorm. The crust is the result of a physical segregation and rearrangement of soil particles in a way that affects some of the soil properties, such as infiltration, runoff and soil erosion. In practice, there is no rapid, in situ method for monitoring, assessing and mapping crust intensity and quality. In this study, a controlled spectral investigation of the structural crust across the NIR–SWIR spectral region was conducted on three selected Israeli soils, to study the potential of reflectance radiation to detect structural crust in soils. Two major factors served as the driving forces for this study: (1) there is no valid method for in situ assessment of the crust's characteristics in the agriculture field, and (2) the crust might bias thematic remote sensing of soils, because the thin layer of crust blocks photon–matter interaction, which represents the relevant soil body. Through the use of a laboratory rainfall simulator and a sensitive spectrometer, it was revealed that for three selected soils, significant spectral differences occurred between the crust and its bulk soil. The spectral information was found to be related to changes in particle size distribution and texture at the surface of the soil. This conclusion was based on indications of absorption of OH in clay lattice, OH in adsorbed water and CO 3 in carbonates. It was concluded that the structural crust is a phenomenon that should not be ignored by remote-sensing users. In fact, in the field of agriculture, the spectral properties of crust can be used as tools for estimating the crust's intensity. 相似文献
8.
The influence of the stress state on the evolution of suffusion failure is often neglected in the design of sandy gravel foundations containing a partially penetrating cut-off wall. A series of hydro-mechanical coupling experiments on such structures was carried out to investigate the influence using a newly designed apparatus. The results indicate that: (1) The stress state has a significant influence on the evolution of suffusion, which increases the critical suffusion hydraulic gradient dramatically. (2) The critical suffusion hydraulic gradient is linearly related to the confining pressure and to the penetration ratio, and a simple interpolation function for the critical hydraulic gradient was fitted based on the experimental results. (3) The eroded mass in the development of suffusion is nonuniform and intermittent. The evolution of suffusion is a complicated and iterative process involving fine particle migration, pores being clogged, flushing out of the clogged pores, and fine particle remigration. (4) Flow along the interface of sandy gravel and cut-off wall conforms to the piecewise-linear Darcy flow rule. The results will enhance the understanding of the influence of the stress state on the suffusion failure in sandy gravel foundations containing partially penetrating cut-off walls. 相似文献
11.
本文以一个完整的省级行政单元(北京市)为例,进行系统的、大尺度的土壤Cr,Ni含量的空间分布与污染评价研究,通过地统计学方法分析揭示了北京市土壤中Cr,Ni的空间结构与分布特征,并探索其主要成因,为全面了解北京市的土壤环境质量和开展大规模的土壤环境质量评价研究等提供方法学借鉴和参考.结果表明:土壤Cr,Ni含量的空间结构具有较好的可迁性特点;指数模型拟合效果较好,变程分别为174.6km和15km;半变异函数的方向性分析表明,Cr,Ni均为各向同性,土壤中Cr,Ni具有中等程度的空间相关性.土壤中Cr含量的分布特征为空间相关范围较大,从总体趋势来看,土壤Cr含量的分布较为连续,呈明显的东高西低的分布趋势,大致可以分为3个大的斑块,西北方向(太行山山脉)土壤Cr含量较低,而东南方向(冲积平原)土壤Cr含量相对居中,东北部(燕山山脉)的土壤Cr含量最高.土壤Ni含量的空间分布比较零散,其分布大致表现为东北部地区最高,西南部居中,中部地区最低.研究还揭示,北京市土壤中Cr,Ni含量目前仍主要受成土母质的影响,但是个别地区也存在明显的Cr,Ni含量严重偏高现象. 相似文献
12.
The fractal is presented as a method for describing the geometry of particles, with particular reference to the breakdown of granular soils and the formation of loess. The preliminary results are reported: (a) for the extent to which silt due to comminution exhibits a fractal distribution; (b) the tendency of fractal dimension to change with the comminution process; and (c) the relationship between fractal dimension describing particle size distribution and the grinding time. Laboratory simulation confirms the general tendency of fractal characteristics to reflect the size reduction process. 相似文献
13.
热环境控制是城市地下空间安全运行的有力保障,科学预测地下围岩的导热性能是地下空间环控系统热负荷评估的基础。软土是地下空间开发中一类常见土体,现有模型主要适合于预测中低含水率范围内土体导热系数的变化,而对于高含水率软土,合适的导热系数预测模型较少。基于细观模拟,本文提出了一种能有效预测软土导热系数的数值模型。该模型除了能够反映含水率、干密度等常规因素影响外,还可考虑矿物组成以及粒径分布等的影响。最后,通过与苏通GIL管廊工程中20个软土样的实测导热系数进行对比以验证数值模型的可靠性。首先借助激光粒度分析仪和X射线衍射分析测试了矿物组成和粒度分布,代入模型进行数字建模并通过细观导热模拟得到导热系数预测值。导热系数模拟预测值与实测值对比结果显示:模拟预测值基本在实测值±20%范围内,验证了本文模型的可靠性,表明了该模型在预测高含水率软土导热系数方面的潜力。此外,该模型还可以直观地展示土内各处局部热流的分布特征,这为深入认识土体导热行为的机理奠定了基础。本文研究可为软土以及土体导热系数的预测评价提供新的思路和方法。 相似文献
14.
Water retention of clayey soils with wide particle size distributions involves a combination of capillary and adsorbed layers effects that result into suction–saturation relations spanning over multiple decades of matric suction values. The present study provides a physics-based analysis to reproduce the water retention curve of such soils based solely on particle size distribution and porosity. The distribution of inter-particle pore sizes is inferred through a probabilistic treatment of the particle size distribution, which is then used, together with an assigned pore entry pressure, to estimate the inter-particle water volume at a given suction. The contribution to water content from adsorbed layers is also taken into account by considering the balance of electrochemical forces between water and clay material. The total water content is therefore found by summing up the contribution of inter-particle water, as well as adsorbed layers that form around clay particles and around the individual clay platelets. Comparisons with experimental results on nine different soil samples verify the capability of the model in accurately predicting the wide water retention curves without any prior calibration. Additional to capturing the essential features of the water retention curve with remarkable detail, the analytical model also provides insights into the relative contributions of capillary and adsorbed waters to the overall saturation at different suction regimes. Being based upon easily accessible information such as particle size distribution and void ratio, the model can therefore be considered as a substitute for costly and lengthy laboratory and in situ measurements of water retention curve. 相似文献
15.
针对某大型水电站揭露的原状层间错动带试样,模拟现场快速施工可能会产生的不排水边界条件,在围压5～30 MPa的高压力条件下开展了不固结不排水三轴试验,并结合试样物理性质的差异,分析讨论了原状层间错动带的力学特性。试样试验曲线和破坏模式主要由高围压控制：其应力-应变关系曲线均为应变硬化型且破坏后呈腰鼓状为塑性破坏。此外,较湿颗粒发生了大规模的颗粒破碎,其是造成高饱和度试样强度包线的趋势线随围压降低的根本原因。试验结果明显受物理性质影响造成了试验数据离散性,敏感性分析表明,围压P和饱和度 对初始弹性模量 和破坏强度 的影响最大,其次是孔隙比e,颗粒粒径（ ）分布对其影响程度最小。根据试样剪切特性建立的强度特征（ 和 ）初步预测公式可供实际工程参考。 相似文献
16.
土体具有显著的空间变异性,描述土体空间变异性的重要指标是自相关距离。提出基于土体微结构模拟的方法来求解土体的自相关距离。在生成土体的微结构数值模型时,对四参数随机生长法（QSGS法）进行改进,考虑土体的粒径分布信息,使得生成的土体微结构更加合理。改进的四参数随机生长法（MQSGS法）所需的输入参数可以结合土体的扫描电镜试验及粒径分析试验获取。基于生成的土体微结构数值模型,即可计算土体的2点自相关函数,再通过曲线拟合即可求解土体的自相关距离。研究表明：与QSGS法相比,采用MQSGS法生成的土体微结构更加符合自然界的真实土体;基于MQSGS法生成的微结构数值模型计算得到的土体自相关距离略小于QSGS法得出的自相关距离。 相似文献
17.
The paper offers an analytical determination of the hydraulic properties of an unsaturated soil with reference to its retention curve, which describes the relationship between the volumetric water content and capillarity through matric suction. The analysis combines a particulate approach focused on the physics at the pore scale, including microstructural aspects, with a probabilistic approach where the void space and grain size are considered as random variables. In the end, the soil water characteristic curve of an unsaturated granular medium along a drying path can be derived analytically based on the sole information of particle size distribution. The analysis hinges on the tessellation of a wet granular system into an assemblage of tetrahedral unit cells revealing a pore network upon which capillary physics are computed with respect to pore throat invasion by a non-wetting fluid with evolving pendular capillary bridges. The crux of the paper is to pass from particle size probability distribution to a matching void space distribution to eventually reveal key information such as void cell and solid volume statistics. Making reasonable statistically based assumptions to render calculations tractable, the water retention curve can be readily constructed. Model predictions compare quite favourably with experimental data available for actual soils, especially in the high saturation range. Having a sound scientific basis, the model can be made amenable to address a variety of soils with a wider range of particle sizes. 相似文献
18.
近年来激光粒度分析法在沉积物粒度分析方面的应用得到了进一步扩展。本文利用美国麦克奇公司生产的S3500型激光粒度分析仪开展沉积物粒度分析方法实验,研究表明:S3500型仪器较优的样品用量约为0.2 g;稀释过程会影响样品的粒度分布;样品分取方式会带来不同的随机误差。与薄片图像法和筛析法两种传统粒度分析方法获得的粒度分布参数比较表明:激光法测得的平均粒径较薄片图像法和筛析法偏细;激光法和筛析法的峰度相关性较好。采用Malvern 2000和Micro S3500两种激光粒度分析仪测量结果的比较表明:Malvern 2000测得的平均粒径较Micro S3500测得的平均粒径偏细,但二者的相关性很好(r=0.9574),研究认为这两种粒度仪的测试结果会给岩石粒度定名带来差异。由于各种粒度分析方法存在差异和局限性,在实际工作中粒度分析应尽可能建立在同一测量体系上,以便资料对比。 相似文献
19.
The mining and processing of metal-bearing ores has resulted in contamination issues where waste materials from abandoned mines remain in piles of untreated and unconsolidated material, posing the potential for waterborne and airborne transport of toxic elements. This study presents a systematic method of particle size separation, mass distribution, and bulk chemical analysis for mine tailings and adjacent background soil samples from the Rand historic mining district, California, in order to assess particle size distribution and related trends in metal(loid) concentration as a function of particle size. Mine tailings produced through stamp milling and leaching processes were found to have both a narrower and finer particle size distribution than background samples, with significant fractions of particles available in a size range (?250 μm) that could be incidentally ingested. In both tailings and background samples, the majority of trace metal(loid)s display an inverse relationship between concentration and particle size, resulting in higher proportions of As, Cr, Cu, Pb and Zn in finer-sized fractions which are more susceptible to both water- and wind-borne transport as well as ingestion and/or inhalation. Established regulatory screening levels for such elements may, therefore, significantly underestimate potential exposure risk if relying solely on bulk sample concentrations to guide remediation decisions. Correlations in elemental concentration trends (such as between As and Fe) indicate relationships between elements that may be relevant to their chemical speciation. 相似文献
20.
A significant part of Campania is extensively covered by volcaniclastic soils, deriving from the alteration of airfall-sedimented
formations of layered ashes and pumices that were ejected by Campi Flegrei and Mt. Somma–Vesuvius during explosive eruptions.
Where such soils cover steep slopes cut in carbonate bedrock, landforms depend essentially on the morpho-evolution of such
slopes prior to the deposition of the volcaniclastic soils, because these are generally present only as thin veneers, up to
a few meters of total thickness. Historical records and local literature testify that, in this part of Campania, landslides
that originate on carbonate slopes covered by such soils and terminate at their foot or at gully outlets are frequent, following
critical rainfall events. Such landslides can be classified as complex, occurring initially as debris slides, but rapidly evolving into debris avalanches and/or debris flows. The localization
of the initial sliding areas (i.e. “sources”) on the slopes depends on both the spatial distribution of characters of the
soil cover and the spatial distribution of the triggering rainfall events. It therefore appears reasonable to separate the
two aspects of the problem and focus on the former one, in order to attempt an assessment of soil sliding susceptibility in
the event of landslide-triggering rainfall. In this paper, some results of the application of a method aimed at such an assessment
are presented. The method, called SLIDE (from SLiding Initiation areas DEtection), is based on the concept that, for a spatially
homogeneous soil cover and a spatially homogeneous landslide-triggering rainfall sequence, different values of threshold slope
gradient for limit equilibrium conditions exist, depending on morphological characters of the soil cover, such as its continuity
and planform curvature. The method is based on the assessment of (1) soil cover presence, (2) discontinuities within soil
cover, (3) slope gradients and curvature, by means of good resolution DEMs. It has been applied to sample carbonate slopes
of Campania, where landslides originated either repeatedly or recently. Results are encouraging, and a soil sliding susceptibility
map of a large area, based on a simplified version of method, is also presented. 相似文献
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