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A non-linear seismic response analysis method for 2-D saturated soil-structure system with an absorbing boundary is presented. According to the 3-D strain space multimechanism model for the cyclic mobility of sandy soil, a constitutive expression for the plane strain condition is first given. Next, based on Biot's two-phase mixture theory, the finite element equations of motion for a saturated soil-structure system with an absorbing boundary during earthquake loadings are derived. A simulation of the shaking table test is performed by applying the proposed constitutive model. The effectiveness of the absorbing boundary is examined for the 2-D non-linear finite element models subjected to random inputs. Finally, a numerical seismic response analysis for a typical saturated soil-structure system is performed as an application of the proposed method.

SUMMARYThe cyclic mobility behaviour of sand by the three-dimensional (3-D) strain space multimechanism model based on the micromechanics of granular material is investigated. The constitutive properties are characterized by the volumetric and shear mechanisms for the initial isotropic soil. The 3-D shear mechanism is decomposed into a number of microscopic plane-strain shear mechanisms in various orientations, each of which in turn consists of a number of microscopic simple shear mechanisms. Using an appropriate summation of mechanisms, the total deformation behaviour can be obtained by evaluating contributions from each mechanism. Based on the some assumptions, the dilatancy model proposed by Iai et al. ' is extended from the two-dimensional (2-D) space to the 3-D space. Comparisons of theoretically predicted results are made with experimental measurements.

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A state-dependent multi-mechanism model for sands in three-dimensional space is proposed within the framework of critical-state soil mechanics. The mechanical deformation behaviour of sands is characterised with a macroscopic volumetric mechanism and a number of one-dimensional equivalent microscopic shear mechanisms (EMSMs) in various orientations. Each one-dimensional EMSM includes a shear deformation and a volumetric deformation due to dilatancy, which are described by a microscopic shear stress-strain relationship and a microscopic stress-dilatancy relationship respectively. The detailed relationships between the macroscopic and microscopic model parameters are established, and all microscopic model parameters can be defined explicitly or implicitly by soil parameters with a clear and easily understandable physical meaning. Moreover, a state parameter, ł, defined by the difference between the current and critical void ratios at the same confining stress is used, relating the dilatancy and peak stress ratios to the critical stress ratio. Successful simulations of the responses of sands under drained, undrained, monotonic and cyclic loading conditions and during rotation of principal stress direction are obtained.Dans le cadre de la mécanique de sol d'état critique, nous proposons un modèle à mécanismes multiples et dépendant de l'état pour des sables dans un espace tridimensionnel. Le comportement de déformation mécanique des sables est caractérisé avec un mécanisme volumétrique macroscopique et un certain nombre de mécanismes de cisaillements microscopiques équivalents (EMSM) unidimensionnels dans diverses orientations. Chaque EMSM unidimensionnel comprend une déformation de cisaillement et une déformation volumétrique dues à la dilatance, qui sont décrites respectivement par une relation contrainte-déformation de cisaillement microscopique et une relation contrainte-dilatance microscopique. Nous établissons les relations détaillées entre les paramètres de modèle macroscopique et microscopique et nous pouvons définir explicitement ou implicitement tous les paramètres de modèle microscopique par des paramètres de sol avec une signification physique claire et facilement compréhensible. De plus, nous utilisons un paramètre d'état, ł, défini par la différence entre les taux de pore courants et critiques à la même contrainte confinante, paramètre lié aux taux de dilatance et de contrainte de pointe par rapport aux taux de contrainte critique. Nous obtenons de bonnes simulations des réponses de sables sous conditions de charge drainée, non drainée, monotone et cyclique et pendant la rotation de la direction principale de contrainte.