Kazutaka Otsushi

Experimental Study on Embankment Reinforcement by Steel Sheet Pile Structure Against Tsunami Overflow

This study proposes a new embankment reinforcement using steel sheet piles against tsunami overflow, which has been known as the main cause of the failures of the embankments by the 2011 Tohoku Earthquake Tsunami. Effectiveness of the proposed technique was discussed through a hydraulic experiment. A model of embankment was set in a horizontal open channel, and one or two steel plates are installed into the embankment from the top as vertical walls inside. Temporal variations of the shapes of the embankment and the sheet pile structures were obtained from video images. In most of the cases, the sheet pile structures started to rotate after the erosion of the landward slope of the embankment. However the rotation stopped at about 30° and 10° from the initial location with the single- and double-wall cases. Height of the embankment after overflow was less than 20% with no reinforcement, while more than 70% and 95% of the height were kept with the single- and double-wall structures, respectively. The performance of the embankment with the reinforcement was also discussed in terms of tsunami energy reduction with an additional fixed-bed experiment.

STUDY ON A LIQUEFACTION COUNTERMEASURE FOR FLUME STRUCTURE BY SHEET-PILE WITH DRAIN

Canals are important as lifeline facilities that supply water to urban areas. However, the countermeasure in popular use, such as improvement of entire liquefiable ground of the canal by chemical feeding, is hugely expensive. Against this background, the authors investigated a reasonable liquefaction countermeasure for an existing flume canal using sheet-pile with drain. In this study, several shaking table tests in the 1g gravitational fields were conducted, and the experimental reproducibility of the analysis was checked to confirm the effectiveness of the proposed countermeasure. The results indicated that the proposed method was effective in reducing the deformation (i.e., uplift/sinking dis- placement and inclination) of the canal, and good reproducibility for dynamic effective stress FEM analysis using LIQCA code with respect to the results of the experiment was confirmed.

EXPERIMENTS ON EMBANKMENT REINFORCEMENT USING STEEL SHEET PILES AGAINST TSUNAMI OVERFLOW

In this study, new reinforcement technique of coastal embankment against tsunami overflow is presented, and its performance is discussed through a hydraulic experiment. One or two steel sheet piles are installed into a coastal embankment to have a single or double-wall inside and composite structure of the sheet piles and ground around them is expected to keep the height of the embankment even with severe erosion of landward slope induced by overflow of a huge tsunami. In the hydraulic experiment with 1/50 scale model, the single-wall structure kept about 80 % of the height of the embankment and almost no reduction of the height was observed with the double-wall structure. Introduction Coastal embankments located along the Pacific Coast of Japan were severely damaged by the 2011 Great East Japan Earthquake Tsunami. Local scour behind the embankments induced by tsunami overflow was observed in many places just after the tsunami, and it is considered as one of the main cause of the failures of the embankments (Kato et al. 2012; Tokida and Tanimoto 2012; Mitobe et al. 2014). For designs of new embankments, new reinforcement structures are required to be developed in order to ensure the performance of embankments after overflow of huge tsunamis. In this study, double-wall structure using sheet piles is presented as a new reinforcement structure against tsunami overflow. This structure has been considered as liquefaction countermeasures of embankments (Fujiwara et al. 2013). Composite structure of the sheet piles and ground between them can keep height of the embankment after liquefaction. This structure is expected to keep the height of the 180 16-3-2015

Analytical Study on Mitigation of Liquefaction-Related Damage to Flume Channel Using Sheet-Pile with Drain

Canals are important facilities that serve as lifelines by supplying water to urban areas. However, a budget of staggering proportions would be necessary to apply the usual countermeasures adopted in preventing liquefaction to an entire canal. Against this background, the application of sheet-pile with drain as a reasonable mitigation method to reduce liquefaction-related damage to existing flume channels (i.e., uplift/sinking displacement and inclination) based on performance-based design has been studied by authors. This paper confirms good reproducibility for dynamic effective stress FEM analysis with respect to the results of several shaking table tests in 1g gravitational fields and the effectiveness of the proposed countermeasure for actual-scale structures based on this analysis.