Liquefaction engineering covers a broad range of issues that apply to level to sloping ground with consequences including settlement, lateral spreading, flow slides, and seismically-induced deformations. In this seminar, the speaker will focus on three recent advances related to these evaluations. Historically, different liquefaction triggering evaluations have evolved for non-plastic to low plasticity sandy soils (sand-like behavior) and low plasticity silty and clayey soils (clay-like behavior). Having separate procedures (that often yield very different consequences) can be quite confusing for practitioners. Here, the speaker will present a recently developed cone penetration test (CPT)-based procedure that better characterizes soil type behavior, particularly for overconsolidated soils. Using this new characterization method, the speaker will introduce a universal method to evaluate liquefaction triggering in sandy and clayey soils, avoiding the need for separate procedures. Next, liquefaction triggering analysis commonly involve performing using a peak acceleration at the ground surface derived from code-based amplification factors or from total stress-based equivalent linear or nonlinear site response analysis. The motion then is propagated back into the ground using a depth reduction factor that is consistent with the liquefaction triggering curves being employed. This technique uncouples the site response analysis (performed in a total stress environment) from the actual soil behavior (where excess porewater pressure can be generated). Here, the speaker will present recent work to develop and validate a nonlinear, effective stress-based site response analysis procedure that can be used to directly judge level-ground liquefaction triggering. Next, the speaker will describe newly developed methods to evaluate shaking-induced settlement of sandy soils, both in the free-field and below structures. Current methods to evaluate settlement largely are focused on liquefaction-induced settlement, and there are very limited methods available to evaluate building settlement. The proposed procedure incorporates both loose (liquefiable) and dense (nonliquefiable) soils and can be used to evaluate settlement for either free-field conditions or for buildings.

Rapid development of urban areas originated from plains and lowlands towards hills in the suburbs poses increasing risks in geo-hazards. The potential geo-hazards include soil liquefaction during earthquakes, collapse of artificial cut-and-fill, and slope instability. A series of strategic measures are required for mitigating these geo-hazards and establishing higher performance of geotechnical works. Various approaches are adopted for achieving these objectives, such as nonlinear effective stress analysis of soil-structure systems constructed on saturated sandy deposits, global modeling of geo-hazards based on the use of GIS and urban geo-data base, experimental studies through geotechnical centrifuge. Such as study on combined disaster induced by rainfall, earthquake and tsunami etc. To understand the ground and structure behaviour under different external forces with time difference such as earthquake after rainfall, rainfall or tsunami after earthquake. To develop dynamic numerical analysis of various structures on saturated/unsaturated ground based on porous media theory with finite deformation. To improve reliability of numerical simulation based on uncertainty quantification (UQ) with Verification & Validation (V&V) method. One of his specialty is numerical solution development, he and his co-workers derived the governing equations for the dynamic response of unsaturated poro-elastic solids at finite strain. They obtained simplified governing equations from the complete coupled formulation by neglecting the material time derivative of the relative velocities and the advection terms of the pore fluids relative to the solid skeleton, leading to a so‐called us − pw − pa formulation. They also imposed the weak forms of the momentum and mass balance equations at the current configuration and implement the framework numerically using a mixed finite element formulation. They verified the proposed method through comparison with analytical solutions and experiments of quasi‐static processes. They used a neo‐Hookean hyperelastic constitutive model for the solid matrix and demonstrate, through numerical examples, the impact of large deformation on the dynamic response of unsaturated poroelastic solids under a variety of loading conditions. In the respect of application of his developed numerical tool, he did many field validation, for example; during the 2011 off the Pacific coast of Tohoku earthquake, liquefaction at the bottom of embankments extensively damaged river levees in the Tohoku and Kanto areas. They conducted numerical simulation of liquefaction in a river levee on soft cohesive ground along the Eai River during the earthquake. Static analysis reproduced the initial state of stress and moisture in such an embankment before the earthquake. Static analysis showed a decrease in mean effective stress and an increase in water content at the bottom of the embankment due to the settlement of soft cohesive ground. The effect of initial stress and moisture conditions on the seismic responses of the river levee are discussed through dynamic three phase coupled analysis with an initially deformed configuration and moisture distribution. Numerical results showed that stress relaxation in the embankment caused an increase in settlement at the crest of embankment.

Site response analysis is commonly used to account for local site effects and to estimate the surface ground motion. The pioneering work of H. B. Seed and I. M. Idriss during the late 1960’s introduced modern site response analysis techniques. Since then significant efforts have been made to more accurately represent the non-linear behavior of soils during earthquake loading. Recent advances in the field of non-linear site response analysis mainly focus on 1-D site response analysis commonly used in engineering practice. The improvement includes developments of material models for both total and effective stress as well as the challenges of capturing the measured small and large strain damping within these models. Moreover, recent development also considers the shear strength of soil under large strains, which avoid the overestimation or underestimation of ground response under strong shaking. Those advance make the site response analysis be potentially used for soil liquefaction assessment and ground response evaluation of a liquefied site. This presentation will introduce the time domain nonlinear site response analysis program, DEEPSOIL, which has been widely used in the world. Moreover, the coupling effect between pore water generation and soil stiffness degradation can be accounted for in the time domain nonlinear analysis, namely effect stress analysis. The effect stress analysis can be potentially used for soil liquefaction assessment and ground response evaluation of a liquefied site.

The Great East Japan (Tohoku) Earthquake, with a magnitude of Mw=9.0, occurred in the Pacific Ocean about 130 km off the northeast coast of Japan’s main island on March 11, 2011. Soil liquefaction occurred in a very wide area from the Tohoku region to the Kanto region, including the Tokyo Metropolitan Area, because the earthquake was huge (Yasuda et al., 2012). In Japan, a similar huge earthquake is predicted to occur in the near future along the Nankai Trough in the Pacific Ocean, causing liquefaction in a wide area. Liquefaction occurred in Hiroshima City during the 1946 Nankai Earthquake (Mj=8.0), though its epicenter was very far from the city. Another worry is a strong earthquake occurring in the Tokyo Metropolitan Area. Seismic zoning for liquefaction-induced damage to wooden houses in Hiroshima City and the Kita-Senju area of Tokyo were carried out based on soil profile models and seismic response analyses. Furthermore, a recent study is carried out regarding to hazard maps for liquefaction-induced damage to wooden houses during future supposed earthquakes in Hiroshima City and the Kita-Senju area of Tokyo were estimated. Representative soil profile models in a mesh size of 250 m × 250 m in plan constructed by the Japanese Geotechnical Society were used to estimate the liquefaction strength ratio (CSR). The cyclic shear stress ratio (CSS) was evaluated by seismic response analysis. The damage to wooden houses was evaluated based on a new method proposed by the MLIT of Japan that combines the liquefaction potential, PL, and the thickness of the non-liquefied layer, H1,. It is estimated that liquefaction-induced damage would occur in many meshes during future earthquakes in both Hiroshima City and the Kita-Senju area. Hazard maps estimated by PL only and by PL and H1 coincide for the Kita-Senju area but differ for Hiroshima City because of the effect of the depth of the water table. The latest development of the liquefaction hazard maps is kept being executed in the following 3 years.