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Owing to imperfect boundary conditions in laboratory soil tests and the possibility of water diffusion inside the soil specimen in undrained tests, the assumption of uniform stress/strain over the sample is not valid. This study presents a qualitative assessment of the effects of non‐uniformities in stresses and strains, as well as effects of water diffusion within the soil sample on the global results of undrained cyclic simple shear tests. The possible implications of those phenomena on the results of liquefaction strength assessment are also discussed. A state‐of‐the‐art finite element code for transient analysis of multi‐phase systems is used to compare results of the so‐called ‘element tests’ (numerical constitutive experiments assuming uniform stress/strain/pore pressure distribution throughout the sample) with results of actual simulations of undrained cyclic simple shear tests using a finite element mesh and realistic boundary conditions. The finite element simulations are performed under various conditions, covering the entire range of practical situations: (1) perfectly drained soil specimen with constant volume, (2) perfectly undrained specimen, and (3) undrained test with possibility of water diffusion within the sample. The results presented here are restricted to strain‐driven tests performed for a loose uniform fine sand with relative density Dr=40%. Effects of system compliance in undrained laboratory simple shear tests are not investigated here. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
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Jean H. Prevost 《国际地质力学数值与分析法杂志》1986,10(6):653-665
A procedure is presented which allows site response analyses to be performed with any general multidimensional finite element analysis package. Numerical results which corrorate the theory are presented. Also, as an illustration of the procedure, results of an effective stress analysis for the scismic response and liquefaction of a horizontally layered saturated sand deposit are presented. 相似文献
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The numerical ‘class A’ predictions performed within the framework of the VELACS Project are compared to the experimental results recorded in the centrifuge experiments. The comparisons are made in terms of: (1) the root mean square error of the predictions with respect to the mean of the experimental results; and (2) the size of a confidence interval centered at the predicted value which contains the estimated true value of the experimental results with a 75% probability. An assessment of the capability of various groups of constitutive soil models to predict excess pore pressures induced by dynamic loading is also presented. 相似文献
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Reservoir simulators typically use cell‐centered finite volume schemes and do not model directly the coupling of the flow processes with the geomechanics. Coupling of geomechanics with fluid flow can be important in many cases, but introducing fully coupled geomechanical effects in those simulators is not a trivial issue, because the geomechanics is better done by using the Galerkin vertex‐centered finite element methods by which the solid displacements are computed at the vertices of the cells. This creates difficulties in interfacing cell variables with nodal variables. Uncoupled or loosely coupled models are used by many researchers/practitioners by which a reservoir model is coupled to a geomechanical model by staggering in‐time flow and deformation via a sophisticated interface that repeatedly calls first flow and then mechanics. The method therefore requires projection of the reservoir cell variables onto the nodes of the geomechanics Galerkin finite element mesh. In this note, we attempt to quantify the errors associated with cell to node projection operations. For that purpose, we use a simple model of the pressure equation for a heterogeneous medium in one dimension. We are able to derive the exact analytical solution for this problem for both nodal and cell pressures. This allows us to compute the errors due to projection analytically, function of meshing refinement and permeability field variations. We compute upper and lower bounds for the errors, and analyze their magnitude for a variety of cases. We conclude that, in general, cell to node projection operations lead to substantial errors. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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The model presented in the companion paper is validated in both the linear and nonlinear cases under steady-state single frequency harmonic and transient ground motions. The crest acceleration responses of the Santa Felicia earth dam subjected to the 1971 San Fernando earthquake and of the Long Valley earth dam subjected to the strongest of the 1980 Mammoth Lake earthquakes are computed and compared with the motions recorded at the site. Acceleration time histories for the solid and fluid phases in both horizontal and vertical directions, as well as stress-strain and pore water pressure-strain time histories for points along the height of the dam are presented. The ability of the model to simulate the occurrence of liquefaction in a dam is also demonstrated. 相似文献
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An earlier publication1 considered the properties of circular conical failure surfaces whose axes coincide with the space diagonal in principal stress space. The present work uses a similar approach to analyse conical surfaces that are offset from the space diagonal. It is shown that cones fitted to the Mohr–Coulomb surface in triaxial compression contain a potential singularity. The occurrence and location of the singularity depends on the Mohr–Coulomb friction angle to which the surface is fitted in triaxial extension. It is shown that for a cone fitted to the same friction angle in both triaxial extension and compression, singular conditions occur when that angle reaches \documentclass{article}\pagestyle{empty}\begin{document}$ \sin ^{ - 1} \left({\sqrt 7 - 2} \right)\left({ = 40.22^\circ } \right) $\end{document}. Even cones fitted to smaller friction angles give significant overestimations of material strength for certain stress paths. 相似文献
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In this investigation, the feasibility of earthquake simulation in centrifuge soil experiments is studied. The strong detrimental effect of standing waves for such an endeavour is clearly shown. A modest degree of success toward producing a model earthquake is reported via two devices—a certain kind of physically tuned internal excitor and an effective absorbent material at the walls. 相似文献