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1.
Piping, as one of the critical patterns of internal erosion, has been reported as a major cause for failures of embankment dams and levees. The fundamental mechanism of piping was traditionally investigated through experimental trials and simplified theoretical methods in macroscale. Nevertheless, the initiation and progressive evolution of piping is a microscale phenomenon in its essence. The current understanding of the micro-mechanism of piping erosion is limited due to a lack of quantitative analysis and visualized evidence. And in fact, seepage flows can affect the soil fabrics and the development of contact forces between particles. But how these fabrics and contact forces evolve under a critical hydraulic gradient is still not fully understood. In this paper, the detailed process of piping erosion is investigated by using a coupled computational fluid dynamics and discrete element method (CFD–DEM) approach. The treatment of soil–flow interactions in CFD–DEM is explained by exchanging the momentum between the two phases. During the simulation, the piping erosion process is initiated by incrementally ascending differential water head across the soil samples. The three main stages of piping erosion (initial movement, continuation of erosion and total heave) can be identified from monitoring the particle velocity and positions. In addition, the evolution of contact force, hydraulic force, coordination number and void fraction is inspected to provide insight into the micro-mechanism of piping erosion. Two cases are simulated, one with a uniform particle size and a relatively uniform porosity distribution and the other with specific particle size and porosity distributions. An interesting finding from this study is that piping does not always initiate from the free surface and the evolution of piping depends heavily on the particle size and porosity distribution. 相似文献
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This paper presents a computational method able to effectively model both the simultaneous processes typically observed in backward erosion piping, ie, the pipe tip propagation and the conduit cross-section enlargement. The numerical method is based on the novel formulation of a problem of localized erosion along a line propagating in a multidimensional porous medium. In this line, a conduit with evolving transverse size is embedded, which conveys a multiphase flow. The two systems, porous medium and pipe, are bridged by exchange terms of multiphase fluid mass and by a shared fluid pressure field. On the contrary, different fields are considered to describe flows, which are assumed as Darcian in the porous medium and turbulent in the conduit. These two flows drive pipe propagation and enlargement, respectively, as modeled by means of proper erosion kinetic laws. The corresponding numerical formulation is based on the combination between one- and multidimensional finite elements, to model the erosion conduit and the porous medium, respectively. Several simulations are proposed to demonstrate the ability of the proposed approach in reproducing available experimental data of real-scale tests on levees. Our results point out the crucial role played by the combined influence of pipe propagation and enlargement, as well as of three-dimensional (3D) effects. We also assess the mesh independence of the proposed numerical solution, particularly as concerns the calculated pipe propagation history. 相似文献
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Piping is the main cause of dangerous situations and one of the most serious threats to levees in China. It is unlikely that Darcy’s law is suitable for evaluation of piping zones; therefore, the ordinary seepage computation based method of simply increasing the permeability coefficient of the piping zone is not appropriate. The discrete element method (DEM) may be a promising alternative to the use of Darcy’s law, but the large number of particles hampers its effective application in practice. In this study, a new approach based on combination of pipe flow in the erosion channel and seepage analysis in the remainder of the levee is proposed. Based on the changeable boundary between the two types of computational domains, the element free Galerkin method (EFG) was employed to facilitate the efficiency of coupling iteration. Examples show that this approach can simulate the main characteristics of developing processes in the erosion channel, which implies that this simplified method can be employed practically. 相似文献
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This paper presents a fracture mapping (FM) approach combined with the extended finite element method (XFEM) to simulate coupled deformation and fluid flow in fractured porous media. Specifically, the method accurately represents the impact of discrete fractures on flow and deformation, although the individual fractures are not part of the finite element mesh. A key feature of FM‐XFEM is its ability to model discontinuities in the domain independently of the computational mesh. The proposed FM approach is a continuum‐based approach that is used to model the flow interaction between the porous matrix and existing fractures via a transfer function. Fracture geometry is defined using the level set method. Therefore, in contrast to the discrete fracture flow model, the fracture representation is not meshed along with the computational domain. Consequently, the method is able to determine the influence of fractures on fluid flow within a fractured domain without the complexity of meshing the fractures within the domain. The XFEM component of the scheme addresses the discontinuous displacement field within elements that are intersected by existing fractures. In XFEM, enrichment functions are added to the standard finite element approximation to adequately resolve discontinuous fields within the simulation domain. Numerical tests illustrate the ability of the method to adequately describe the displacement and fluid pressure fields within a fractured domain at significantly less computational expense than explicitly resolving the fracture within the finite element mesh. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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三相耦合渗流侵蚀管涌机制研究及有限元模拟 总被引：1，自引：0，他引：1
管涌的发生、发展过程是土骨架相在渗流作用下侵蚀为可动细颗粒相,并随水相在孔隙通道中运移流失的过程。在该过程中,渗流与侵蚀相互耦合,相互促进,水相、土相、可动细颗粒相互作用,因此,管涌过程是一个多场、多相耦合的高度非线性的动态过程。现有的管涌试验结果表明,只有当水力梯度大于起始水力梯度时,细颗粒相才会随水相从土体中运移流失,土体才会发生管涌侵蚀,且管涌稳定后土体的孔隙率（稳定孔隙率）和水力梯度之间存在对应关系,根据该结果,提出管涌稳定孔隙率的概念,修正传统的渗流侵蚀本构方程,建立多孔介质中三相耦合的修正的渗流侵蚀管涌控制方程。最后,针对特定应力状态下的土体建立稳定孔隙率和水力梯度之间的对应关系。基于Galerkin有限元法编制有限元程序,在轴对称情况下对该土体的管涌过程进行数值模拟。结果表明,修正后的管涌控制方程能更全面地描述管涌发生、发展直至稳定状态的特性。 相似文献
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缺级粗粒土管涌类型的判别方法 总被引：1，自引：0，他引：1
利用大型渗透变形仪,对不同最大粒径和细粒含量的缺级粗粒土的渗透破坏特性进行了系统的试验研究。研究结果表明,缺级粗粒土在细料含量小于30 %的情况下都发生管涌型渗透破坏,基本符合前人提出的判别流土和管涌的准则。管涌破坏的类型可划分为发展性管涌和非发展性管涌两种,采用刘杰和康德拉且夫对发展性和非发展性管涌的判别方法都不能区分本次试验的管涌破坏类型。在康德拉且夫提出的判别粗粒土管涌类型的方法的基础上,考虑细料对粗料孔隙的填充程度及试样中缺级颗粒百分含量的影响,建立了缺级粗粒土管涌类型的判别式,为缺级粗粒土管涌类型的判别提供了新的思路和方法。 相似文献
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采用三维有限元方法分析了基坑开挖工程在防渗体出现局部失效情况下，引起渗流在失效部位的集中及渗流场空间状况。提出了以一维通道嵌入三维块体的方法模拟管涌发展过程及渗流场变化特征。讨论了管涌通道渗透性对基坑管涌发展规律的影响。 相似文献
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A process called ‘piping’, which often occurs in the soil at dams, levees, and dykes, involves the formation and development of a continuous tunnel between upstream and downstream ends. The hole erosion test is commonly used to quantify the critical stress and the rate of piping erosion progression. The aim of this study is to draw up a model for interpreting the results of this test. A characteristic internal erosion time is defined and expressed as a function of the initial hydraulic gradient and the coefficient of surface erosion. It is established here that the product of the coefficient of erosion and the flow velocity is a significant dimensionless number: when this number is small, the kinetics of erosion are low, and the particle concentration does not have any effect on the flow. This finding applies to most of the available test results. Theoretical and experimental evidence is presented showing that the evolution of the pipe radius during erosion with a constant pressure drop obeys a scaling exponential law. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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对由弱透水黏土层、细砂层和强透水砂砾层组成的三层堤基进行了管涌发展的砂槽模型试验,为了便于观察分析,细砂层由各种颜色的细彩砂依次排列在砂砾石层上表面,通过改变彩砂层的厚度分析研究了不同细砂层厚度对管涌发生、发展机制及过程的影响。试验结果表明,三层堤基细砂层厚度的不同使管涌发生的临界水力梯度、涌砂量和通道发展的速度不同,与双层堤基有很大区别。临界水力梯度是由多种元素决定的,包括破坏土体的性质及其整体性等;细砂层的存在使流量在渗透变形初期对涌砂不敏感;在试验中发生的相同水位下多次间歇性涌砂,其原因一方面是颗粒在运动过程中发生堵塞,另一方面是通道边界的土体失去支撑发生应力释放,抵抗力随着时间逐渐减小。 相似文献
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Zaid Bahaeldeen Vollert Florian Gibmeier Jens Mengel Lena Stelzer Oliver Schneider Achim 《Acta Geotechnica》2023,18(2):865-876
Acta Geotechnica - The hole erosion test (HET) was developed to simulate piping erosion and to study the erosion parameters of cohesive soils. The erosion rate in the HET is evaluated by the... 相似文献
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Pol Johannes C. Kanning Willem van Beek Vera M. Robbins Bryant A. Jonkman Sebastiaan N. 《Acta Geotechnica》2022,17(10):4555-4576
Backward erosion piping (BEP) is a form of internal erosion which can lead to failure of levees and dams. Most research focused on the critical head difference at which piping failure occurs. Two aspects have received less attention, namely (1) the temporal evolution of piping and (2) the local hydraulic conditions in the pipe and at the pipe tip. We present small-scale experiments with local pressure measurements in the pipe during equilibrium and pipe progression for different sands and degrees of hydraulic loading. The experiments confirm a positive relation between progression rate and grain size as well as the degree of hydraulic overloading. Furthermore, the analysis of local hydraulic conditions shows that the rate of BEP progression can be better explained by the bed shear stress and sediment transport in the pipe than by the seepage velocity at the pipe tip. The experiments show how different processes contribute to the piping process and these insights provide a first empirical basis for modeling pipe development using coupled seepage-sediment transport equations.
相似文献13.
Scheperboer I. C. Suiker A. S. J. Bosco E. Clemens F. H. L. R. 《Acta Geotechnica》2022,17(11):4769-4798
Acta Geotechnica - A coupled hydro-mechanical erosion model is presented that is used for studying soil piping and erosion void formation under practical, in-situ conditions. The continuum model... 相似文献
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提出了一种由平面三角网格自动生成三维空间四面体单元网格的方法,其基本思路是将含水层平面分成三角形单元网格,将每个三角形沿垂直方向对应一个三棱柱,作为最初的三棱柱;依次将每个三棱柱按照潜水面位置和分层信息划分成不同数目的四面体,从而生成三维空间四面体单元网格。剖分结果表明,此方法综合考虑了潜水面的位置和各含水层顶底板的起伏情况,能够简洁地生成层面起伏的空间四面体网格,特别适用于刻画潜水面波动、含水层顶底板起伏和存在透镜体或岩性缺失等含水层结构复杂的情况下,自动地剖分并生成单元信息,为三维计算的实现奠定了基础。 相似文献
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X. S. Zhang H. Wong C. J. Leo T. A. Bui J. X. Wang W. H. Sun Z. Q. Huang 《Geotechnical and Geological Engineering》2013,31(2):479-492
The present paper describes a model of internal erosion of earth structures, based on rigorous thermodynamic principles and the theory of porous media. A particular focus of this paper is concerned with the initial stage of internal erosion, when the pore volume forms a continuous network, without the formation of macroscopic cavities or channels. The continuum approach is applicable in this case. The soil skeleton saturated by a pore fluid is treated as the superposition of three continua in interaction, with independent velocity fields. The pore fluid itself consists of a mixture of water and eroded particles. The erosion kinetics is based on the shear stress developed at the solid–fluid interface. The applicability of the model is illustrated by numerical simulations based on the finite element method. These simulations show how the phenomenon of piping can progressively arise, and preferentially in regions where hydraulic gradients are critical. Effects of mechanical degradations due to internal erosion are at the same time demonstrated. 相似文献
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Acta Geotechnica - Backward erosion piping is an important failure mechanism in both dikes and dams where uniform silts and sands are covered by a cohesive layer. It is an internal erosion... 相似文献
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Acta Geotechnica - Backward erosion piping is an important failure mechanism for water-retaining structures. It results in the formation of shallow pipes at the interface of a sandy or silty... 相似文献
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Acta Geotechnica - Backward erosion piping is an important failure mechanism for cohesive water-retaining structures which are founded on a sandy aquifer. This paper studies the effect of the... 相似文献
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Analysis of development and depth of backward erosion pipes in the presence of a coarse sand barrier
Akrami Sepideh Bezuijen Adam van Beek Vera Rosenbrand Esther Terwindt Jarno Förster Ulrich 《Acta Geotechnica》2021,16(2):381-397
Backward erosion piping (BEP) is a failure mechanism that can affect the safety of water-retaining structures. It can occur when a local anomaly on the downstream side of an embankment causes a concentration of seepage flow at that location. Shallow pipes may then form, progressing in the upstream direction and leading to a collapse of the water-retaining structure. A novel and economically appealing measure against BEP is the coarse sand barrier (CSB), which is now being developed in a multiscale experimental programme in the Netherlands. The method involves placing a trench filled with coarse sand below the blanket layer on the downstream side of the embankment. The CSB prevents the upstream progression of the pipe and significantly enhances resistance to BEP. This paper presents medium-scale laboratory tests involving a range of sands, barrier depths and relative densities. The piping process and the observations of pipe progression in the presence of a CSB are presented, followed by a conceptual model. The presence of a CSB changed the erosion pattern. It resulted in pipe formation perpendicular to the flow direction over the entire width of the barrier before the barrier was damaged. The findings also demonstrate the effect of material properties on pipe initiation, progression and pipe depth. Measurements of the pipe depth are presented and analysed, revealing the significance of pipe depth for understanding the piping process. This analysis shows considerable erosion in the downstream background sand and demonstrates that erosion profiles and measured pipe depths are significantly larger than in BEP tests without a CSB.
相似文献20.
细砂层埋深对堤基管涌影响的试验研究 总被引：1，自引：0，他引：1
不同土层结构的堤基,其管涌发生和发展的情形不同。以前的研究多集中于双层堤基的情况。事实上,含夹砂层堤基中,位于砂砾石层内的细砂层会对堤基管涌的发生产生重大影响,并且这些影响随细砂层在砂砾石层中的位置不同而不尽相同。利用室内砂槽试验,模拟当细砂层位于砂砾石层内部不同深度时含夹砂层堤基管涌的发展过程,研究细砂层埋深对 堤基管涌的影响。试验结果表明,细砂层埋深存在一个临界深度,当细砂层埋深较浅时,堤基的临界水力梯度较小,易于发生管涌,且管涌发生以后,堤基被侵蚀的速率较大,出砂较多;堤基破坏的临界水力梯度随着细砂层埋深的增加而增大,当细砂层埋深大于临界埋深时,堤基的临界水力梯度基本不变,同时堤基抵抗管涌破坏的能力较强,其破坏形式与双层堤基 相类似。 相似文献