Internal erosion is a complex phenomenon which represents one of the main risks to the safety of earthen hydraulic structures such as embankment dams, dikes or levees. Its occurrence may cause instability and failure of these structures with consequences that can be dramatic. The specific mode of erosion by suffusion is the one characterized by seepage flow-induced erosion, and the subsequent migration of the finest soil particles through the surrounding soil matrix mostly constituted of large grains. Such a phenomenon can lead to a modification of the initial microstructure and, hence, to a change in the physical, hydraulic and mechanical properties of the soil. A direct comparison of the mechanical behaviour of soil before and after erosion is often used to investigate the impact of internal erosion on soil strength (shear strength at peak and critical state) using triaxial tests. However, the obtained results are somehow contradictory, as for instance in Chang’s study (Chang and Zhang in Geotech Test J 34(6):579–589, 2011), where it is concluded that the drained strength of eroded soil decreases compared to non-eroded soil, while both Xiao and Shwiyhat (Geotech Test J 35(6):890–900, 2012) and Ke and Takahashi (Geotech Test J 37(2):347–364, 2014) have come to the opposite conclusion. A plausible explanation of these contradictions might be attributed to the rather heterogeneous nature of the suffusion process and to the way the coarse and fine grains are rearranged afterwards leading to a heterogeneous soil structure, a point that, for now, is not taken into account, nor even mentioned, in the existing analyses. In the present study, X-ray computed tomography (X-ray CT) is used to follow the microstructure evolution of a granular soil during a suffusion test, and, therefore, to capture the induced microstructural changes. The images obtained from X-ray CT reveal indeed that fine particles erosion is obviously not homogeneous, highlighting the existence of preferential flow paths that lead to a heterogeneous sample in terms of fine particles, void ratio and inter-granular void ratio distribution.
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The ability of discrete element models to describe quantitatively (and not only qualitatively) the constitutive behaviour of a dense sand is assessed in this paper. Two kinds of 3D discrete models are considered. Both consider spheres as elementary particles. Nevertheless, the first model implements a contact law with rolling resistance whereas the second takes into account clumps made of two spheres. The discrete models are calibrated and validated from mechanical tests performed on a dense Hostun sand with a true triaxial apparatus. The calibration is carried out from axisymmetric drained compression tests, while the validation is discussed from monotonic and cyclic stress proportional loading paths and from a circular stress path in the deviatoric stress plane. The quality of the predictions of the discrete models are evaluated by comparison with the predictions given with advanced phenomenological constitutive relations, mainly an incrementally non-linear relation. Predictions given by the discrete models are remarkable, particularly when it is put in perspective with respect to the very few number of mechanical tests required for their calibration. However, these results and conclusions were reached in enabling conditions, and some limitations of such discrete models should be kept in mind. 相似文献
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The problem is considered of the slow outflow of gas from a Close Binary System with subsequent formation of a shell or cloud of matter around the whole system. It appears that with a small change of velocity introduced to the most external parts of the gaseous ring around one of the components the gas particles can flow out from the binary system leaving it through the external Lagrangian point. This process can lead to the formation of a shell around the binary star. The change in kinetic energy of a gas particle corresponding to the perturbation in its motion leading to the escape through the adjacent external Lagrangian point can be smaller than 10% of the total kinetic energy of the considered particle for the case of a ring around a component with mass equal to or larger than the mass of the companion. 相似文献
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Experimental investigation of microstructural changes in soils eroded by suffusion using X-ray tomography 总被引：1，自引：0，他引：1
Nguyen Cong Doan Benahmed Nadia Andò Edward Sibille Luc Philippe Pierre 《Acta Geotechnica》2019,14(3):749-765
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A. Daouadji F. Darve H. Al Gali P. Y. Hicher F. Laouafa S. Lignon F. Nicot R. Nova M. Pinheiro F. Prunier L. Sibille R. Wan 《国际地质力学数值与分析法杂志》2011,35(16):1731-1773
This paper presents a synthesis of the works performed by various teams from France, Italy and Canada around the question of second‐order work criterion. Because of the non‐associative character of geomaterials plastic strains, it is now recognized that a whole bifurcation domain exists in the stress space with various possible modes of failure. In a first part these failure modes are observed in lab experimental tests and in discrete element modelling. Then a theoretical study of second‐order work allows to establish a link with the kinetic energy, giving a basis to explain the transition from a prefailure (quasi)static regime to a postfailure dynamic regime. Eventually the main features of geomaterials failure are obtained by applying second‐order work criterion to five different constitutive rate‐independent models—three being phenomenological and two micromechanical. As a whole this paper tries to gather together all the elements for a proper understanding and use of second‐order work criterion in geomechanics. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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F. Sibille Ph. Merlin I. Vauglin F. Billebeaud P. O. Lagage R. Jouan F. Lacombe P. Drossart J. Ph. Bernard 《Experimental Astronomy》1994,3(1-4):175-176
This paper presents the general features of the C10 camera, now in routine operation at the CFHT, with initial results on CVF observations of the C2H2 and C2H6 bands and the continuum in the atmospher e of Saturn. 相似文献
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In this article, we present a numerical method to deal with fluid–solid interactions and simulate particle–fluid systems as encountered in soils. This method is based on a coupling between two methods, now widely used in mechanics of granular media and fluid dynamics respectively: the discrete element (DE) method and the lattice Boltzmann (LB) method. The DE method is employed to model interactions between particles, whereas the LB method is used to describe an interstitial Newtonian fluid flow. The coupling presented here is a full one in the sense that particle motions act on fluid flow and reciprocally. This article presents in details each of the two methods and the principle of the coupling scheme. Determination of hydrodynamic forces and torques is also detailed, and the treatment of boundaries is explained. The coupled method is finally illustrated on a simple example of piping erosion, which puts in evidence that the combined LB–DE scheme constitutes a promising tool to study coupled problems in geomechanics. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
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The question of diffuse failure in granular media such as soils is treated by numerical modelling with a discrete element
model. Two numerical samples are considered, one dense and the other loose. A criterion based on the sign of the second-order
work is applied to the numerical model to detect bifurcation points related to diffuse failure. The notions of loss of controllability
and loss of sustainability are taken into account to simulate diffuse failure at bifurcation points detected. Therefore, the
failures predicted based on the second-order work criterion are numerically verified. 相似文献
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