In the Tohoku Pacific Ocean Earthquake in 2011, many coastal dykes were destroyed due to overflow of tsunamis which height were higher than the crown heights of coastal dykes. It is shown by previous studies that the GRS coastal dykes covered with crushed stone and panels are strong against overflow of tsunami. In this study, we studied the effects of slope inclination and the water flow inside of the dyke against overflow resistance of dykes. The height of the model dykes were 100 mm. Stepwise increasing water flow rate experiments and bore type water flow experiment with extremely high level of water rate experiments were conducted to the model dykes. The inclinations of slope used were 1:2 and 1:0.5. For performing the water flow through the model dyke, gaps between the panels were made with using paste plastic tapes. Followings were concluded in this study. (1) Effect of slope inclination: To improve the overflow resistance, inclination of seaside slope should be milder than 1:2 and inclination of landside slope should be steep as inclination of 1:0.5. (2) Influence of the water flow through the dyke: The water flow through the dyke has a large effect to the resistance of the dykes against overflow of tsunami, because if the water comes through the dyke, sand or embankment materials will be outflowed from the dyke.

In this study, the 3-dimensional piled embankment reinforced by geo-synthetics models have been developed to observe the difference geo-synthetic-supporting mechanism according to the changes of the spacing and number of the layers. The maximum tensile forces in the geo-synthetics and vertical stress distribution on the soft ground are obtained in each case to compare. When the spacing is increased, the maximum tensile forces transferred through the upper and lower layers become unbalanced. Until the spacing is 20 cm, the greater tensile force acts on the upper layer. If the spacing is increased from 20 cm to 30 cm, the tensile force in the upper layer is sharply decreased. It means the upper geo-synthetic would not receive the vertical stress sufficiently when the upper geo-synthetic placed on the unsuitable position. If the number of geo-synthetic layers are increased, the average tensile force is decreased. The number of geo-synthetics is more than the 4 layers, the imbalance of tensile forces in the each of geo-synthetics are significantly reduced and equalized.

The development of ground improvement technology by means of permeation grouting using recently developed ultra microfine cement has been underway by the authors’ group, especially for mitigating effects of soil liquefaction on existing structures built on liquefiable soil deposits. From the experiences gained from the field tests carried out at the different two sites, this method works well for relatively clean fine sand deposits, though it may still need some refinement for silty sand deposits. Some supplementary methods assisting permeation of cement solutions through silty sand deposits were pursued based on laboratory permeation tests, and one method was found promising. This method employs the injection of water, following infiltration of relatively dense cement solutions which would be terminated by cement particles trapped within micro-scaled silty sand skeletons. In the present study, a series of laboratory one-dimensional permeation tests are conducted to examine this supplementary method in more detail, especially from the viewpoint of cost-effectiveness and performance.

This study investigated the possible development and its application of a honeycomb-shaped, hollow block foundation. By inducing an arching phenomenon in the lower ground, the honey-cell foundation aimed to reduce the transmission of upper load and settlement. Basic theory and numerical verification have been undertaken to establish a basis for proving the hypothesis. In addition, for the field application of the study, a series of soil chamber experiments were performed. The results of the study show that the amount of load to be transmitted to the lower ground reduced significantly due to the honey-cell foundation. Accordingly, a decrease in transmitted stress results in less settlement in comparison to the general shallow footing.

Paper sludge (PS) ash is cinder that is generated when paper sludge (waste of paper manufacturing) is incinerated. We have previously studied application of PS ash in the construction field(improvement of excavated mud etc.)and found that PS Ash had high swelling ability and can be used for environmental clarification of mud. We developed a new soil improvement method and design. However, in late years it comes to be recognized that the improving effect becomes bigger than early stage having curing function and the coverage of PS Ash product spreads out because the property of PS ash changes and some product is manufactured using different PS ash by different processing.In this paper, I examine the improvement function of the present PS ash materials and report the applicability of new PS ash improvement.

In order to investigate the influence of the compaction degree (Dc) of the backfill material and spacing of the transverse members (S) on the pullout resistance of a square-shaped geocell, a series of pullout tests were conducted on small scale models using square-shaped geocells with varying spacing between transverse members at a constant height. The geocells were embedded independently in a sandy backfill material and three gravelly backfill materials, varying the compaction degree (Dc) between 88% and 100%. All the tests were subjected to a 1 kPa surcharge. The results show that a higher compaction degree (Dc) yields a higher pullout capacity of the square-shaped geocell. It was also found that the overall pullout resistance of the square-shaped geocell is affected by the particle size of the backfill material, in which larger soil particles provide a larger pullout resistance. The findings also indicate that the spacing between transverse members becomes crucial when increasing the soil particle size, due to larger spacings can more efficiently accommodate larger soil particles and therefore mobilize its maximum pullout resistance. It is important to note that indefinitely increasing the spacing of the transverse members does not lead to an increment in the overall peak pullout resistance, since each material fully develops maximum pullout resistance at a given spacing, upper limit beyond which a larger spacing will not contribute to the development of larger pullout forces.