An enormous amount of disaster debris and tsunami deposits were generated by the 2011 Great East Japan Earthquake and Tsunami, and the soil fractions separated from them were required to utilize as geomaterials for disaster reconstruction. However, the utilization had difficulty because the soils contained wood chips that could not have been sufficiently removed in treatment process. In this study, for the purpose to assess applicability of the soils for general earthwork materials, sources of the wood chips in the soils sampled at disaster sites were classified and a series of laboratory tests were conducted to evaluate the influence of wood chip inclusion on compaction and shear strength characteristics. It was clearly seen from the compaction test results that the maximum dry density decreased and the optimal water content increased with the increase in wood chip content. From the results of large-scaled direct box shear tests conducted on the compacted soil specimens, it was seen in some soils that shear strength decreased and dilatancy reduced with increase in wood chip content. Regarding the soils having wood chip content with less than approximately 3 %, the general tendency was that the influence of wood chips on strength and deformation properties did not appear clearly and suggested that they could be used for general geomaterials.

Cement-treated soil specimens were contacted with surrounding soils having different water contents in order to investigate surface strengths affected by calcium leaching. The strength of sound parts of the treated-soils continuously increased until 2 years, the maximum material age in this study. On the other hand, the surface layer of the treated-soils showed lower strength development by contact with the surrounding soils. At the interface between the treated and surrounding soils, the alteration caused by calcium leaching was observed. The altered depth by calcium leaching varied depending on the water contents of the surrounding soils. The lower the water contents of the surrounding soils, the smaller the calcium decreased depth of the treated-soil. However, the relationships between the calcium decrease ratio and the strength decrease ratio of the treated soil showed similar trends regardless of the water contents of the surrounding soils. The higher leaching resistance of the treated soil contacted with the low water content soil could be explained by increase in solid ration at the surface layer, due to transfer of water from the treated soil to the surrounding soil before hardening of the treated soil.

Estimation of water level for the persistent situation or prior to earthquake is crucial for evaluation of seismic performance of road embankments. In this paper, methods of estimating rise velocity and position of water level are proposed based on numerical modeling studies. Validations of these estimation methods are conducted by water level observation data of highway embankments. These validations reveal that rise of the water level in an embankment is expected when the permeability of the embankment is small and rainfall duration is long. On the other hand, short but strong rainfall is required for the water level rise when the permeability of the embankment is large. These suggest that influential rainfall conditions are different depending on the permeability of the embankment. This study also reveals that if the permeability of an embankment is sufficiently large, marked rise of the water level hardly occurs under the typical rainfall condition in Japan.

During the coagulating sedimentation process of a construction sludge conducted in an intermediate treatment plant, polymeric flocculants are frequently used. However, since it is concerned with the toxicity of unreacted monomers included in the polymer coagulant, it is difficult for a construction sludge treated with a polymer flocculant to be accepted at the final disposal site. In order to reduce the amount of polymer flocculants to be added, the gypsum powder is employed as a material to assist the flocculation by combining a polymer coagulant with an inorganic coagulant during the coagulation sedimentation stage. Consequently, it was confirmed that the electric zeta potential of the clay slurry suspension was decreased by the addition of the gypsum powder and the aggregation performance was highly improved. In addition to this, it was confirmed that the addition of a gypsum powder to a sludge generated at a construction site including an arsenic material reduced the elution of an arsenic material originating from nature. It is expected for the employment of a gypsum powder to prevent the elution of naturally derived arsenic material from the soil generated by the underground construction.

The purpose of this study is to investigate the effects of treatment methods on the impermeable ability in order to efficiently and economically make water repellent soils. The two methods of hydrophobic treatment were examined (Case I: silane treatment, and Case II: treatment by coating curing agent for concrete). Considering the characteristics of each method and the cost of production, the most efficient production method was verified. As a result of this study, it was shown that although the silane treatment can achieve the high impermeable ability, the production cost is also increased. On the other hand, in the case of the hydrophobic treatment by the coating curing agent for concrete, the production cost may be lowered, but the impermeable ability is also lowered. From the above results, it is judged that the silane treatment is more suitable as a method of manufacturing the water repellent soil by collectively evaluating the characteristics of both.

In the 2018 Hokkaido Iburi Tobu Earthquake, a large-scale ground disaster caused by liquefaction occurred on embankments filled with volcanic ash soil in the Satozuka area of Sapporo City. Liquefied volcanic ash soil flowed through the ground with a gentle slope, spouted from the end of the slope, and the ground sank up to about 4 m deep. A similar phenomenon has occurred in the 2003 Tokachi-oki earthquake in the Kyowa area, Tanno Town close to Kitami City. In this report, in order to investigate the mechanism of the unique liquefaction damage occurred that the liquefied soil flowed out from the end of the sloping land, the comparison of the landform, the physical properties of the runoff and embankment material, the liquefaction characteristics, etc. of both sites were performed. As a result, it found that the old landform and the damage situation of both sites are very similar. In addition, it was found that the liquefaction resistance of the volcanic ash soil filled in the Satozuka area was very low compared to other volcanic ash soils in Hokkaido.

Monitoring of 2-dimensional displacements at 6 points on the surface of full-scale model slope under multi-step excavation was conducted and monitored data was analyzed to establish the method to evaluate an instability of the slope under excavation. 2-dimensional displacements mean the displacement parallel to the surface of the slope and the displacement perpendicular to the surface. Direction of synthetic displacement which is a root of the sum of square of each displacement was derived from the monitored data. It approached to almost constant value as the displacement parallel to the surface increased at upper part of the slope where creep deformation after the excavation leaded to the failure while it did not converge to constant value at lower part where the slope collapsed during excavation. Direction of synthetic displacement at large displacement means the direction of slip surface. Direction of synthetic displacement can be an indicators of the instability of the slope under excavation in the case that slope collapses after creep deformation.

In recent years, technologies related to 3D surface measurement and 3D printer are spreading rapidly. The use of these technologies is no exception in geotechnical engineering, and many researches have been conducted to understand the mechanical and hydraulic behavior of geomaterials such as cracked and porous media. With the expectation that researchers and engineers involved in geotechnical engineering will have more opportunities to use 3D printer in the future, we review the latest researches on the application of 3D printer to geotechnical engineering.