Ryosuke Uzuoka

FEM-FDM coupled liquefaction analysis of a porous soil using an elasto-plastic model

The phenomenon of liquefaction is one of the most important subjects in Earthquake Engineering and Coastal Engineering. In the present study, the governing equations of such coupling problems as soil skeleton and pore water are obtained through application of the two-phase mixture theory. Using au-p (displacement of the solid phase-pore water pressure) formulation, a simple and practical numerical method for the liquefaction analysis is formulated. The finite difference method (FDM) is used for the spatial discretization of the continuity equation to define the pore water pressure at the center of the element, while the finite element method (FEM) is used for the spatial discretization of the equilibrium equation. FEM-FDM coupled analysis succeeds in reducing the degrees of freedom in the descretized equations. The accuracy of the proposed numerical method is addressed through a comparison of the numerical results and the analytical solutions for the transient response of saturated porous solids. An elasto-plastic constitutive model based on the non-linear kinematic hardening rule is formulated to describe the stress-strain behavior of granular materials under cyclic loading. Finally, the applicability of the proposed numerical method is examined. The following two numerical examples are analyzed in this study: (1) the behavior of seabed deposits under wave action, and (2) a numerical simulation of shaking table test of coal fly ash deposit.

FLUID DYNAMICS BASED PREDICTION OF LIQUEFACTION INDUCED LATERAL SPREADING

Abstract This paper presents and verifies a numerical method to predict the lateral spreading of liquefied subsoil based on fluid dynamics. A numerical fluid dynamics code is modified to incorporate the Bingham viscosity with the minimum undrained strength of liquefied subsoil. The numerical method is applied to shaking table tests of a liquefied slope with and without an underground structure and flow failure of a road embankment near Asele in northern Sweden. As the result of simulations, the numerical method is found to reproduce the time history of flow velocity of liquefied subsoil, lateral spreading load to the underground wall and flow failure process of the embankment.

Importance of viscous fluid characteristics in liquefaction induced lateral spreading analysis

Abstract This paper discusses the importance of viscous fluid characteristics in liquefaction induced lateral spreading analysis. A fluid dynamics based numerical method is outlined for the prediction of liquefaction induced ground flow. Pseudoplastic and Bingham models are used to represent the behavior of liquefied soil. A numerical method is used to verify the similitude law for liquefied ground flow. The numerical method reproduced the tendency of the experimental results as well as the proposed similitude law very well. Therefore, the similitude law holds, and thus, can be used as a fundamental information in the formulations of empirical equations for estimating ground displacement during liquefaction induced lateral spreading.

Liquefaction induced lateral spread analysis using the CIP method

Abstract This paper presents a CIP (cubic interpolated pseudoparticle) based numerical method for liquefaction induced lateral spread analysis in the framework of fluid dynamics. Previously, the authors presented similar methods using a SIMPLE-VOF based commercial code but were not able to extend such a code to simulate lateral spread of liquefied ground with an overlaying non-liquefied layer, which is the most common and more practical post liquefaction problem. In this study, the CIP method is used because it is able to treat solid, liquid and gas together, can correctly define the flow behavior at interfaces of multi-fluids and can also be used as a unified scheme for both compressible and incompressible materials. A Bingham model that takes the undrained strength of soils into account is used as the basic constitutive model. A CIP based numerical scheme, which has been successfully used in fluid dynamics problems, is modified by incorporating the Bingham viscosity and an implicit calculation procedure for pressure terms. The Poisson equation is used to compute the pressure over the whole domain. The current numerical method is validated and good agreement is produced in comparison with experimental results. A previously verified similitude for liquefied ground flow is also reproduced by this method. The method is, finally, used to simulate shaking table tests on a liquefied subsoil model with an overlaying non-liquefied layer. From the results of simulations, the numerical method is found to satisfactorily reproduce the time histories of ground surface velocity and displacement and depth distribution of displacement.

Three-Phase Seepage-Deformation Coupled Analysis about Unsaturated Embankment Damaged by Earthquake

AbstractThe 2004 Niigata-ken Chuetsu Earthquake in Japan caused serious damage to embankments. Considerable damage occurred in mountainous regions, and the recorded rainfall before this earthquake exceeded the annual rainfall. In this study, numerical simulations were performed to reproduce the damage and to investigate the effect of rainfall on seismic behavior. In the simulations, a three-phase (soil, water, and air) coupled analysis was adopted to consider the behavior of unsaturated soil, and a conventional elastoplastic constitutive model was used for unsaturated soil. The deformation of the embankments was quantitatively reproduced by incorporating rainfall in the seepage analysis before the dynamic response analysis, and it was found that heavy rainfall significantly affected the dynamic behavior. Furthermore, parametric studies of countermeasures showed that the embankments would deform as a result of poor-quality materials even if sufficient drainage or impermeable roadbeds were constructed.

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.

Large Deformation Analysis for Costal Geo-Disasters Using Continuum and Discrete Modeling

Various kinds of geo-disasters have occurred, such as soil avalanches, landslides, failure of river dike, liquefaction and scoring. These disasters have caused serious damage to infrastructures and human activities. Numerical simulations are one of the powerful tools for predicting (1) when the failure will take place, (2) where the failure take place, (3) how far the collapsed soil mass will flow, and (4) how large the impact force to structures will be. In this paper, FEM, CFD, DEM and SPH are introduced as numerical methods for costal geodisasters. Brief explanation of theory of each numerical method will be described in this paper. Based on simulated results, advantages and disadvantages of different methods are discussed.

Shaking Table Test of Embankment on Inclined Ground Affected by Rainfall

During the Nigata-ken Chuetsu Earthquake having occurred in 2004, a number of railway and road embankments collapsed in mountainous regions. It appears that the main reasons of these damages were inclined ground conditions and the rainfall caused by the typhoon just prior to the earthquake. In this paper, the authors performed shaking table tests of embankments on inclined ground affected by rainfall intended for evaluating the adverse effect of rainfall seepage on seismic resistance. We conducted two cases using permeable ground and impermeable one. Rainfall was poured into the embankment until confirming rise of degree of saturation and partial formation of water level. The shaking was conducted until the embankment collapsed with increasing the maximum acceleration. From two cases of shaking table tests; it was revealed that the seepage boundary conditions of the ground affected behaviors of the embankment. In the case without shaping of water level, the response of acceleration at the top of the embankment increased excessively and the embankment deformed to a shape of circular. On the other hand, in the case with shaping of water level, the embankment collapsed with flow, so the response of acceleration decreased during the shaking. Furthermore, the mechanism of stopping of increasing of pore water pressures during shaking was revealed.

General report of TC103 numerical methods in geomechanics

This paper presents a General Report on 46 contributions, including poster presentations, submitted for the parallel sessions organized by TC 103: Numerical Methods in Geomechanics. The authors come from various regions of the world and the topics of the submitted papers are diverse. These contributions are reviewed from the viewpoint of the current research directions in relation to the numerical schemes and their key results. The overview of the latest work is provided in this general report, dividing the broad paper topics into several important subjects.

An Example of the Restoration Method of Levees Damaged by the Great East Japan Earthquake

Following the Great East Japan Earthquake, the aseismatic construction method featuring a combination of sheet pile and drain was adopted as the construction method for recoveries of the levees in Ajiki district along the Tone River. Water seepage and aseismatic effects on the levees in the district by the adopted construction method were evaluated based on the results of the measurements of their observed groundwater level, two dimensional saturate–unsaturated seepage flow analysis, and liquefaction-induced deformation analysis. As a result, it was found that the levels of water infiltration into the bodies following insertion of aseismatic sheet piles along the toes of the back slopes of these levees were reduced by installing drains along the top of the piles inserted. And it was demonstrated that the levees will not be affected by the potential external forces assumed in the post-earthquake flood control plan, if the construction method was used for them. Also, even when the earthquake about the same acceleration scale with the Great East Japan Earthquake occurred, it was also demonstrated that the aseismatic sheet piles inserted along the toes of the back slopes would prevent lateral displacement.