Motoki Kazama

Thin layer element method for dynamic soil-structure interaction analysis of axi-symmetric structure in submerged soil

The three-dimensional thin layer element method is formulated for the dynamic response analysis of an axi-symmetric structure in submerged soil. Biots wave equation for fluid-filled porous medium is used in the formulation. The three-dimensional thin layer element method computes the wave numbers and their associated mode shapes, for both Rayleigh waves and Love waves in submerged soil, which define the characteristics of the waves. The submerged condition affects the characteristics of the Rayleigh waves in soil. As a result, it alters substantially the soil-structure interaction stresses if the permeability of the soil is relatively large and, to less extent, the response of the structure. The thin layer element method is far more efficient than the finite element method for analyzing the fluid-filled porous medium, yet capable of taking into account a multi-layered inhomogeneous soil.

Dynamic response analysis of submerged soil by thin layer element method

A thin layer element method is formulated to compute the dynamic response of submerged soil. The formulation is based on Biots equation describing the dynamic behavior of fluid-saturated elasto-porous medium. The dynamic response of submerged soil is computed for various cases by using the developed formulation. The effects of submerged conditions are examined for submerged soil deposits with a water level at and above the ground surface. It is found that both submerged conditions and water body above the ground surface can considerably affect the dynamic response of soil deposits.

Density Index for Estimating the Postliquefaction Volumetric Strain of Silty Soils

AbstractThis study examined the liquefaction-induced ground settlement of silty sand ground, in which many nonplastic fines are contained. Investigation determined that if fines were included in the specimen, the minimum void ratio shrank more under water-immersion than dry conditions. In addition, the cyclic minimum void ratio was examined, which was obtained by cyclic liquefaction and drainage testing conducted by assuming earthquake excitation. The results illustrated that the difference between the estimated dry and cyclic minimum void ratios uniquely correlated with fines content. A new density index, the normalized margin of void ratio, was proposed for postliquefaction volumetric strain based on examination of the minimum void ratio of soils containing nonplastic fines. The test results confirmed that maximum and accumulated shear strains are satisfactory indices of loading history. Furthermore, the normalized margin of void ratio performed well as a density index for estimating postliquefaction se...

Progressive Damage Simulation of Foundation Pile of the Showa Bridge Caused by Lateral Spreading During the 1964 Niigata Earthquake

The authors analyze a progressive pile damage of the Showa-bridge caused by post-liquefaction phenomena during the 1964 Niigata earthquake. In the analysis, using time histories of ground displacement and excess pore water pressure calculated, the authors conduct an elasto-plastic analysis of a pile subjected to external force from ground displacement. Simulation results provide a reasonable explanation not only of the observed plastic deformation of the pile, but also the progressive damage of the pile.

Earthquake-Induced Mudflow Mechanism from a Viewpoint of Unsaturated Soil Dynamics

This paper discusses the general liquefaction state of unsaturated soil related to the mudflow type slope failures observed during earthquakes in areas covered with volcanic ash sand deposits. It is found that the volume compressibility of soil structure, the degree of saturation and the confining pressure are key factors governing the liquefaction of unsaturated soils.

The Overflow Model Experiment Using the Waterway for Examining the Countermeasure Effect Against the Tsunami-Induced Tide Embankment Scouring

In this study, the anti-erosion effect of the countermeasure and the erosion extent were considered using the model canal and the model soil ground when the concrete panel with nailing and cement development soil were used as the countermeasure. As the result, the following knowledge were obtained: (1) The erosion depth and extent of the landside ground of the tide embankment decreased markedly due to placing the countermeasure at the landside toe of the tide embankment. (2) The concrete panel with nailing and the cement development soil as the countermeasure had the similar anti-erosion performance. (3) Collapse of the tide embankment due to the Tsunami overflow was caused by the erosion of the landside foundation and the water permeation to the inside of the tide embankment from the seaside.

Subjects of the liquefaction research seen to the liquefaction damage of the Great East Japan Earthquake Disaster

This paper discusses the new subjects of the liquefaction research regarding the liquefaction damage of the Great East Japan Disaster. Specifically, the subject about the liquefaction potential assessment, the subject about the evaluation of ground subsidence caused by liquefaction and the subject seen to generate the liquefaction damage of a river levee, etc. are discussed based on the damage observed or the experimental results. It has been shown that understanding current damage on the extension of the present technology has a limit, and that the prediction and countermeasure technology of the liquefaction damage based on a new concept is necessary.