Evaluation for Soil Liquefaction Due to Long Duration Earthquakes with Low Acceleration
Past studies show that soil liquefaction due to a long duration earthquake with low acceleration, for example as observed in the Tokyo Bay area in the 2011 Great East Japan Earthquake, is largely affected by liquefaction strength for a large number of loading cycles. It is, therefore, extremely important to know the liquefaction resistance for a large number of loading cycles. This paper describes the results of the hollow cylindrical cyclic torsion shear tests that were conducted to ascertain the effects of grain size distributions on liquefaction resistance for a large number of loading cycles. The test results clearly show that the tendency of a decrease in liquefaction resistance for a large number of loading cycles is influenced by mean grain size, inclination of grain size distribution, and so on. Finally, the effect of liquefaction resistance curve characteristics on the assessment of liquefaction potential is examined using the cumulative damage theory.
Strain Space Plasticity Model for Cyclic Mobility
ABSTRACT The cyclic mobility model proposed in this paper is of a generalized plasticity—multiple mechanism type. The salient feature of the present approach is that the concept of the multiple mechanism, within the framework of plasticity theory defined in strain space, is used as a vehicle for decomposing the complex mechanism into a set of one dimensional mechanisms. The other feature is that the undrained stress path is idealized with the concept of liquefaction front, which is defined in the effective stress space as an envelope of stress points gradually approaching the failure line. Once coded into the finite element program, most of the existing models suffer from serious difficulty in the numerical solution process when effective stress path becomes very close to the failure line. A numerically robust approach is proposed in this paper by introducing a scheme for gradually enlarging scale of shear strain with progress of cyclic mobility.
Undrained Deformation and Liquefaction of Sand under Cyclic Stresses
ABSTRACT The key findings in the previous studies on the deformation of sand are first reviewed to the necessary extent. Then, in summary form, five fundamental postulates are introduced as the bases on which a model of undrained deformation of sand under cyclic loading is to be established. The procedures for assessing pore pressures, shear strains and consequent occurrence of liquefaction during cyclic loading are illustrated on the diagrams based on the above postulates as well as actual data obtained in the static triaxial tests. The undrained performance of sand predicted by the proposed model were compared with several cyclic triaxial test results conducted under various conditions. These include stress and strain controlled tests; static and dynamic tests; and the tests cycled with constant and erratically changing stress amplitude. The comparison disclosed the relevance and applicability of this method of approach.