Toward a decarbonized society, the authors have studied the CO₂ fixation of fly-ash containing Ca²⁺ and propose a plant for CO₂ fixation that reacts CO₂ gas with the fly-ash. In this study, the relationship between the reaction rate and two basic characteristics which are average particle size and the amount of calcium eluted was evaluated to propose an effective index for selecting samples which is suitable for the plant. Three types of fly-ash with different average particle size and Ca²⁺ elution were selected as samples, and the CO₂ fixation reaction rate was calculated from the column test. As a result, the samples with the largest values for mean particle size and the amount of calcium eluted showed the largest reaction rates, and the samples with the smallest values of two characteristics showed the smallest reaction rates. These results suggest that the mean particle size and Ca²⁺ elution have a significant effect on determining the magnitude of CO₂ fixation reaction rates.

In order to investigate the effects of difference between the compaction layer thickness and change in density on liquefaction properties, undrained cyclic triaxial tests and image analysis were performed on well-graded sandy soils used for embankment materials. The change in density in the specimen for preparation was estimated based on the results of the X-ray CT scanning, and the local axial strain during cyclic loading was evaluated by the results of particle image velocimetry (PIV) using the digital image. From the results, it was shown that liquefaction properties of well-graded sandy soils were changed depending on the thickness of compaction. The reason for this is the change of the range of density in the specimen (the non-uniformity of the specimen). In addition, it was found that the liquefaction resistance was lower in cases where lower density zones were formed in the specimen even if the grain size distribution of the materials was different. Based on the test results, an appropriate thickness of compaction layer on the wet tamping method are discussed.

Some of the Neogene sedimentary rocks containing Pyrite holds the risk of heavy metal elution due to acidification. Thus, when reusing the rocks as embankment material, countermeasures for heavy metal leakage and acidification are required. These countermeasures include “roller compaction” and “soil cover using cohesive soil”. Therefore, the authors estimated that it is possible to take rational countermeasures such as reusing the rocks to the road embankment without these countermeasures if it can verify the acidification mechanism inside the embankment. This study conducted the outside exposure test for almost 4 months using 3 types of full-scale size embankment constructed of the Neogene sandstone containing pyrite that rapidly acidified. Thereby, it was inferred that the seepage water supplying the oxygen and heats affects the internal environment and proceeding acidification inside the embankment.

When the ground freezes, the ground expands due to frost heaving. In order to predict this amount of frost heave, in Japan, an empirical formula expressing the freeze expansion rate by the freezing rate is used. In other countries, the amount of frost heave is predicted using an empirical formula that states that the rate of water absorption into the freezing front is proportional to the temperature gradient in the partially frozen region. Here, experiments were conducted with the freezing rate and the temperature gradient as independent parameters, and it was shown that it is difficult to express the frost heaving rate only by the freezing rate and the temperature gradient in the partially frozen region. On the other hand, it was found that the frost heaving rate can be expressed as a linear expression using the freezing rate and the temperature gradient as parameters. A new formula for predicting frost heaving rate is proposed for ground freezing under conditions with various freezing rates and temperature gradients.

In the seismic diagnosis and the aseismic reinforcement design of railway retaining walls, the effects of cohesion in the backfill of the retaining wall are not considered. On the other hand, aseismic design and seismic diagnosis without the consideration of backfill cohesion may lead to too conservative estimation, since the backfill of existing retaining walls sometimes exhibits a certain magnitude of cohesion. Therefore, by considering the effects of backfill cohesion, it is possible to evaluate the seismic active earth pressure more realistically. A formula evaluating the seismic active earth pressure, which considers both the effect of the cohesion along the failure plane generated in the backfill and the adhesive force between the back face of the retaining wall and the backfill, is derived. The validity of the derived equation is verified by comparison with the result of the trial wedge method and the equation derived in the relevant study. In addition, the derived equation is extended so that the derived formulas can be applied even at high seismic intensities by considering the peak and residual strength of backfill soil. Moreover, the simpler method by introducing the apparent frictional angle is also proposed.

Batch leaching experiments of arsenic contained in mudstone samples and a hydrothermally altered rock sample were conducted with and without an immobilizer such as calcite, periclase, and half-burnt dolomite. The results showed that the immobilizers reduced the leaching concentrations of arsenic from the rock samples although the removal ratio depended on the immobilizer. The leaching concentrations of calcium and magnesium as major components in the immobilizers primarily depended on pH, and not the existence of rock samples. The calculated results of calcium and magnesium leaching concentrations by PHREEQC agreed with the results obtained by the experiments. This means that the solubility of calcium and magnesium is mainly controlled by leachate pH, and not coexisting ions. This indicates that the lifetime of the calcium- or magnesium-bearing immobilizers can be evaluated by their leaching concentrations controlled by their solubilities, assuming that the performance of those cases when all of the major components are leached out. The calculated lifetime of the immobilizers ranged from several thousand years to tens of thousands, which are significantly longer than the life of structures. This implies that the lifetime of an immobilizer can reasonably be estimated using the method based on the solubility of major components in it.

The simplified CU test is a test to determine the strength of seabed clay soil, and is a triaxial CIU test in which a clay sample is isotropically consolidated at 2/3 of the in-situ effective overburden pressure σ_v0’. From a series of laboratory test, of Tokyo Bay marine clay with overconsolidation ratio of 1.00-2.77, the internal friction angle φ’_SCU obtained with c’ = 0 in the simple CU test was compared with the internal friction angle φ’_NC obtained by the triaxial CIU test consolidating to the normal consolidation state. Regarding the representative valueφ’_NC(AVG.), the relationships φ’_NC(AVG.)=(0.75-0.95)φ’_SCU and φ’_NC(AVG.)=(0.85-1.05) φ’_SCU were obtained for the highly plastic clay layer with a liquidity limit of 100% or more and for the low-plasticity clay with a liquidity limit of 60% or less, respectively.

The Kumamoto Earthquakes in April 2016 caused extensive damage to residential land, such as sliding failure of residential area ground and the failure of retaining walls, in Nishihara village, located above the hypocenter in the Futagawa Fault Zone. The embankments of residential area ground consist mainly of Kuroboku soil, with Akaboku soil in the lower part of the embankments. Sliding failure occurred mainly in these Kuroboku soil embankments and Akaboku soil. The present study examined the reduction in strength of Kuroboku soil embankments and Akaboku soil under cyclic seismic loading to identify the causes of sliding failure of residential area ground. We analyzed the physical and mechanical properties of such embankments and soil, compared undrained shear strength and shear strength under cyclic loading, and conducted a simulation analysis by the circular slip method using the decreasing rates of horizontal seismic coefficient and strength parameters as a case study. The results indicated that the strength parameters of Kuroboku soil embankments and Akaboku soil with high water content decreased to about 50%-60% under cyclic seismic loading, which presumably caused the sliding failure.

Saturated and unsaturated cyclic shear tests were conducted on six types of volcanic ash coarse-grained soils distributed in Japan to determine cyclic shear deformation characteristics and liquefaction characteristics with decreasing saturation. The test results showed that the liquefaction resistance increased with decreasing saturation except for the bora, which is a pyroclastic fall deposit. However, the increasing tendency is insensitive in relation to the medium density Toyoura sand, and liquefaction resistance due to reduced saturation does not increase as much as in the medium density Toyoura sand. Shikotsu pumice flow deposit and Shirasu, which is the pyroclastic flow deposits, the tendency of increasing liquefaction resistance in the 80% to 70% saturation range was sensitive to the pyroclastic fall deposits in the pyroclastic flow deposits, and the increase in liquefaction resistance with decreasing saturation was greater in the pyroclastic flow deposits with higher initial fine-grained content than in the falling pyroclastic deposits. Bora showed little change in liquefaction resistance with decreasing saturation and no clear increasing tendency.

Small displacements of Shinkansen viaducts can be fatal for running safety. Therefore, not only ultimate bearing capacity but settlement is an important verification index of the foundation structures. The plain area at Omura city in Nagasaki prefecture, located between Takeo-onsen and Nagasaki station of the Kyushu Shinkansen, is composed of unusual soil, that is sandy gravel with coble stone, and the Shinkansen viaducts have not been constructed on such type of the soil. In addition, the soil in Omura was not simply considered as a bearing stratum for the shallow foundations because N-values from the standard penetration test varied widely, and the minimum was 20. However, shallow foundations have a cost advantage over other foundation types like pile foundations. Therefore, the authors examined the application of shallow foundations in this site with the in-situ test, self-boring typed in-situ friction tests, plate loading tests, and triaxial tests using the specimens sampled by gel push method. As a result, the design values of the soil were suggested, and the performance required for shallow foundations was verified with the proper management method.