Liquefaction happened in a wide area along Pacific Ocean coastal area during the Eastern Japan Great Earthquake. The influence of repeated long-time earthquake followed by a quiet consolidation period has been investigated carefully in this study. The calculation is conducted with soil-water coupling finite element-finite difference analyses based on the cyclic mobility model. From the analysis, it is known that some small sequential earthquakes, which might not affect the liquefaction of the ground anyhow in an independent vibration, cannot be neglected for their impact to the liquefaction if they vibrate the ground after a major vibration. In order to predict correctly the ground behavior in such repeated earthquake vibration that may occur in future, it is necessary to deal with this geotechnical engineering problem based on sophisticated numerical analysis proposed in this paper. From the work in this paper, it is possible to understand the dynamic behaviors of soil such as, increasing and dissipation of excessive pore water pressure during or after earthquake, the development of stress-induced anisotropy, liquefaction and consolidation etc.

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It has been confirmed that the tsunami debris from the Northeastern Japan Pacific Offshore Earthquake consists of a massive amount of mud with woodchips, concrete chips and plastic wastes (estimated to be approximately 13–28 million tons) after relatively large-size wreckage had been removed. In some cases, mud contains a mixture of small- and large-size debris. According to Ministry of the Environment’s guideline for the treatment of tsunami deposit from the Great East Japan Earthquake, the priority is to make the best use of what can be effectively utilized; what cannot be utilized should be properly processed. The authors have long been involved in the effective utilization of industrial by-products and the processing of illegally dumped materials, using the Crushing and Diffusive Mixing Technique. In the face of the Great East Japan Earthquake, the authors experimentally processed the actual tsunami deposits from the Earthquake using Crushing and Diffusive Mixing Method, and succeeded in efficiently separating debris from soil with improved contents. This is a report on successful separation of and utilization of improved soil.

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Preventing global warming has been one of the anurgent issues require imminent attention. The authors propose the use of wood as a construction material to contribute towards effectively reducing the emission of CO₂. A practical example of the usage is log piles for improving soft ground. Although log piling have been widely adopted in the past, it is rarely found in modern constructions. Due to this reason, the engineering properties of log piles are not well understood. To investigate this, the authors conducted a field experiment using full-scale cedar logs piled into the artificial soft ground. As a result, settlement of the area with small pile interval is approximately half of those with large pile interval as well as the non-improved ground. The foundation strength of all area increased one year later. Especially, the foundation strength of the area with small pile interval experienced the highest increment. Furthermore, the safety factor of skin resistance increased twice as large compared to the initial value.

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The Noto Hanto Earthquake in 2007 caused large-scale landslide failures of embankments in NOTO YURYO road. The landslide mainly occurs in the embankment on inclined ground after the earthquake, not on horizontal ground. In this study, seismic deformation behavior of embankments both on horizontal and on inclined ground are simulated by the soil-water coupled finite deformation analysis code, GEOASIA, and the simulation revealed a mechanism of landslide of embankment on inclined ground after earthquake. The main conclusion is shown as follows (1) The behaviors of the embankment materials are reproduced by SYS Cam-clay model. (2) The analysis shows that the embankment on horizontal ground does not fail due to earthquake like actual behavior. The main reason is that the embankment stabilizes by consolidation after the earthquake. (3) The embankment on inclined ground fails after the earthquake through analysis. After the earthquake generates the negative pore pressure in the embankment, the embankment swell by dissipating the pore pressure, and finally the embankment failed. During swelling, loss of over consolidation and upgradation of structure occurs with plastic swelling in the embankment.

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