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Instability of liquefaction is one of the major reasons which results in the failure of earth structure such as dam. The present study focuses on the simulation of static liquefaction behavior for granular materials such as sand and sand-silt mixtures. Based on micromechanical analysis of inter-particle behavior, a simple one-scale model is proposed to simulate the stress-strain response of sand; then the proposed model is extended to simulate the sand-silt mixtures using the mixture theory combining the properties of sand and silt according to their proportions. Empirical expressions are introduced to fit the critical state strength and the location of the critical state line for each mixture. Parameters of the model can be divided into two categories: the first seven parameters have the same values either with pure sand or pure silt for silt-sand with any given fines content; the other three parameters are the function of fines content and three more parameters are required to estimate their values. The predicted results of triaxial test of sand and sand-silt mixtures with different fine content, which has a good agreement with the results of laboratory tests, suggest that the proposed model can simulate static liquefaction behavior of sand and sand-silt mixtures.

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This paper presents a method of eigen analysis to evaluate the accuracy of the time integration method in the structural dynamic analysis of both transient and steady state responses. Accuracy measure for transient response is evaluated by period elongation and amplitude decay after a complete cycle of response of an undamped system. The proposed method is a unique measure, independent of the initial conditions. Accuracy measure for steady state response is evaluated by the amplitude decay and phase angle of a frequency response. The accuracy measure proposed by this method can be applied to all ranges of Δt/T. The significance of the large range Δt/T is discussed. The proposed method is used to evaluate the accuracy of three commonly used time integration methods: the Wilson method, the Newmark method and the Houbolt method. ffimmtimmtpmmMftmzmmftVx £^l*ft#T^K«B8lfIK«S 5SM£ Mmmw±m±*JLmm&

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