It is very important to classify soils for investigation and evaluation of residential sites, which can be considered as the reference information for determining the necessity of soil improvement and the selection of soft ground stabilization method. In general, Screw Weight Sounding (SWS) test as a cheap and simple method or Standard Penetration Test (SPT) with high-cost boring is used for the soil classification in private residential sites. SWS testing results depend on the experience of well-trained operators, and it is difficult to accurately discriminate the soil type without individual evaluation variability. Meanwhile, subjective factors in SPT such as the geological background knowledge of the observers for core sampling and their personal characteristics (habits) often cause the differences in the appraisal results, unless the soil samples are collected and laboratory tests for physical properties of soil are conducted. In this study, the four-probe AC impedance method was applied to identify the soil classification by capturing the complex resistivity properties of soil, aiming at newly proposing a simple and quantitative soil classification technique. Specifically, focusing on the frequency characteristics of the complex resistivity for each soil, multivariate analysis that calculates the generalized Mahalanobis distance was carried out based on soil property as the criterion variable (qualitative data) with selecting two variables as explanatory variables (quantitative data). The results showed that the proposing method objectively enabled the soil classification.

Providing a sustainable supply of good-quality soil materials is vital for reliable implementation of earthworks. However, ensuring a sustainable supply is of great difficulty in the present. Therefore, various techniques are deployed in practice, including mixing several types and gradations of soils or mixing with additives such as cement and quicklime. Among other methods, the Rotary Crushing and Mixing technique（RCM） was introduced as a reliable method to modify and control the gradation properties of granular materials²⁾. Through this study, the efficiency of the small type of the RCM series, which is commonly used in practice, is investigated experimentally to elaborate on the role of particle crushing in improving the gradation properties of soil materials. Furthermore, a simple method is proposed considering the single-particle strength for estimating the particle size distribution of a soil material improved using the RCM. The accuracy of the method and its validity were confirmed using several materials, aiming at enhancing the practical efficiency of particle size adjustment methods.

While the problem of neglected bamboo forests is becoming more apparent throughout western Japan, there has been no progress in the utilization of bamboo, which is cut down in large quantities for forest conservation and can be consumed. In our previous studies, we have confirmed that the water absorption and tensile reinforcement effect of bamboo chips in bamboo chip mixed solidified soil increases its strength and shows ductile fracture behavior. It has also been confirmed that as the addition rate of bamboo chips increases, the state of bamboo chips in the specimen shifts from dispersed to a skeleton-formed state. However, the relationship between the toughness effect of bamboo chips due to tensile force and the reinforcing effect of their skeleton formation and the addition rate has not been clarified. Therefore, we investigated the reinforcement effect of the bamboo chip skeletal structure and the toughness effect of the bamboo chip tensile force by using uniaxial compression tests and bending tests on the strength development before and after skeletal formation. The results showed that the reinforcement effect of bamboo chip mixed solidified soil increased with the formation of the bamboo chip skeleton, which affected the strength of the soil. It was also shown that the addition of bamboo chips can provide a toughness effect due to the tensile force between the solidified soil and the bamboo chips.

In this paper, using a sand pile driving equipment that simulates the actual Sand Compaction Pile (SCP) construction method, shaking table tests and cone penetration tests were conducted to confirm the improvement effect of penetration resistance, water pressure and settlement control by preparing the ground by compaction and focusing on the difference of infilling materials of sand piles. From the measurement results of sand pile driving, it was confirmed that the infilling materials used in this study did not affect the increase or decrease of soil pressure and excess pore water pressure during driving, and did not affect the penetration resistance as an improvement effect, i.e., liquefaction strength and the controlling effect of excess pore water pressure. Furthermore, through the shaking table test and the cone penetration test, it was found that the liquefaction strength and excess pore water pressure controlling effect of the improved soil were larger than those of the unimproved soil, even at the same relative density.

In the Great East Japan Earthquake of March 11, 2011, liquefaction was not observed in areas where sand compaction piles (SCP) had been used for soil improvement, confirming the effectiveness of the compaction method. Recently, energy-based liquefaction determination methods have been developed for liquefaction determination in the design of SCP methods. In this study, hollow torsional shear tests were conducted under isotropic and anisotropic stress conditions with different fine-grain content and density. Then, liquefaction determination was conducted using both the FL and energy methods, and the validity of the obtained experimental results and the improvement effects were discussed from an energetic viewpoint. The results showed that the liquefaction strength ratio and the normalized cumulative loss energy increased with an increase in coefficient of earth pressure at rest. The liquefaction determination results suggest that the energy method may be more sensitive than the FL method in considering the improvement effect.

Soil-cement walls with H-shaped steels used as retaining walls can be used as piles to support vertical loads of buildings by extending the pile tip (H-shaped steel tip) into the bearing layer and controlling soil-cement strength. On the other hand, the lateral resistance, especially in-plane resistance, may cause the H-steels to break apart into strips and rapidly reduce the lateral rigidity. Therefore, cyclic lateral loading tests were conducted on the in-plane walls of the soil-cement with H-shaped steels. The initial stiffness was the shear stiffness of the entire soil-cement wall. However, at a deformation angle of about 0.5/1000 rad, the lateral bearing capacity determined by the adhesion strength between the H-steel and soil-cement was reached, after which the stiffness dropped rapidly. It was also found that the lateral bearing capacity increased when stud connectors were attached to the H-steel. After the adhesion reached the ultimate resistance, the lateral stiffness became the stiffness of the H-steels only, and the behavior was stable until about 10/1000 rad, when the steel yielded.

As a measure to increase the acceptance capacity of disposal pond for dredged clay in operation, the accelerated consolidation method, in which PVD is installed vertically, was adopted in Shinmoji-oki disposal pond. In this study, the issues of setting up the geotechnical model at the time of PVD installation and the effective period of PVD itself were focused. The validity of the method using the reclamation analysis with monitoring results proposed as a method to solve these problems and the effective period of the PVD itself were examined.

The advantage of gabion structures is that they are simple, cost-effective, and quick to construct, and they are used in a wide variety of applications in Japan and abroad. However, despite the fact that wire mesh comprising the gabion has been used for a long time, there are few studies on its basic mechanical properties. Therefore, the design and construction of gabion structures are mostly based on experience due to the lack of established design methods. In this study, large triaxial compression tests on the stones for filling into gabion boxes and a series of compression tests on miniature gabions were carried out in order to understand the basic mechanical properties of the structures. From the tests, the compressive properties of the miniature gabions were found to be varied depending on the difference of geometry of the stone and the combination of the shape and direction of the wire mesh. These results suggest that an understanding on deformation mechanism of gabion structures is necessary for their reasonable design and construction.

In cold and snowy regions such as Hokkaido, there are many examples of conventional anti-frost heaving measures on the cut slope by laying special gabion boxes to cover the slope surface, and this has become a common practice against frost heaving. However, do not prevent freeze penetration due to cold weather into the ground on the mountainside and it causes wavy deformation of special gabion boxes. Conventional special gabion boxes also require manual labor on slopes and at high elevations, complicating maintenance/management and causing lower workability and safety after the special gabion boxes have been installed. Therefore, we have researched and developed one-pack heat insulator gabions as a new anti-frost heaving measure on the cut slopes. In this study, countermeasures were test installed in winter and fall. The results of the test construction clarified that frost heaving may occur in case construction is performed in winter due to freezing penetration into the backside ground, even when a countermeasure against frost heaving is being taken. It was also confirmed that avoiding winter construction would fully demonstrate the effectiveness of the one-pack heat insulator gabions as a countermeasure.

This study investigates the effects of bagasse addition on the activity of alkane-degrading bacteria derived from waste oil. Bagasse, a fibrous residue of sugarcane after juice extraction, has potential as a substrate for various microbial process. In this experiment, alkane-degrading bacteria were isolated from waste oil samples in Okinawa, Japan and their activity in tetracosane and triacontane, which are alkanes constituting machine oils, was evaluated in the presence of dried bagasse, bagasse ash, and carbonized bagasse. The results indicate that addition of dried bagasse and bagasse ash significantly enhances the activity of the bacteria, leading to improved alkane degradation of tetracosane and triacontane. The findings suggests that bagasse can serve as a promising co-substrate for enhancing the efficiency of microbial remediation of oil-contaminated environments.

Perfluorooctane sulfonate (PFOS) contamination in groundwater and soil has become a global problem. Although evaluating the sorption performance of soils against PFOS is essential for considering the proper countermeasures, limited research has been conducted in Japan. This study investigated the sorption kinetics and isotherms using local Japanese soils. In addition, the relation between the sorbed amount of PFOS and the basic properties of local Japanese soils was evaluated. The results of sorption kinetics were well fitted to the pseudo-first-order or pseudo-second-order models, except for the case using silica sand at the initial PFOS concentration of 1 mg/L. Sorption equilibrium against PFOS was achieved after approximately 24 hours. The Langmuir model can well describe PFOS sorption isotherms for four soils. A positive correlation was obtained between sorbed amount and soil properties such as Organic Carbon (OC), fines content, and aluminium oxide (Al₂O₃) content. Results implied that the soil properties should be carefully examined when we discuss the sorption performance against PFOS.

Downward-flow column percolation tests were conducted for hydrothermally altered rock with a high acidification potential, with and without treatment by two different magnesium oxide (MgO)-based agents to limit the generation of acid drainage and leaching of heavy metals and metalloids with natural origins. Particularly, the effects of the physicochemical properties of the MgO-based agents, such as hydration rate, chemical composition, and specific surface area, on the treatability were evaluated. When the additive content of the MgO-based agent is 5% in dry-mass basis, the agent is consumed in the neutralization reaction for the acid drainage generated by the oxidation of the sulfide minerals, as well as the release of soluble Mg out of the system. Accordingly, immobilization of the arsenic is adversely affected, particularly in the cases in which the soft-burnt granular agent with a low hydration rate is adopted. Whereas, it is confirmed that when the additive content of the MgO-based agent is 10% in dry-mass basis, consumption of Mg is greatly suppressed by maintaining a pH in which the hydration reaction of MgO can occur sufficiently over the long term, and arsenic leaching concentrations are effectively decreased until the cumulative flow volume reaches 50 mL/g. However, in the cases of the agents containing a certain amount of calcium, the initial solubilization of Ca raises the pH to a level close to the isoelectric points of MgO, resulting in the lowered arsenic immobilization effect.

This paper reports on the chemical behavior of the C-A-S-H, tobermorite, and zeolite,. C-A-S-H, zeolite and tobermorite blend gel were prepared with different temperature (80℃ and 120℃) and characterized by Ca/Si ratio. As a result, the formation of zeolite structure was suppressed and the formation of C-A-S-H was more likely to occur as the amount of Ca added increased at both temperatures. In addition, the three-dimensional network bonding of SiO₄ and AlO₄ tetrahedra caused by zeolite was more likely to occur at high temperatures than at low temperatures, and the zeolite framework structure was more likely to be maintained. In addition, regardless of the temperature conditions, when the Ca/Si ratio in the system was 0.4, the bonding states of the products, SiO₄ tetrahedrons, and AlO₄ tetrahedrons in the system were similar.

Sedimentary soft rocks are one of the foundations of large and important constructions. Because the mechanical properties of the soft rocks control the behavior of the foundations, it is necessary to understand the consolidation characteristics of the sedimentary soft rocks. Particularly, the anisotropy of mechanical property is important, therefore, the relationship between these properties to bedding planes and the stress environment should be considered. In this study, consolidation tests were conducted in three directions using four block samples of Neogene to Quaternary sedimentary soft rocks from the western part of the Boso peninsula, central Japan: orthogonal to the bedding plane (σ₃direction) and two directions within the bedding plane defined by paleo-stresses (σ₁ and σ₂). In comparison with other fundamental physical properties, elastic wave velocity measurements and tensile strength tests were also conducted to investigate their anisotropy. The results show that the consolidation yield stresses in the three directions are almost the same or larger in the past principal stress direction than others, suggesting that they reflect the tectonic stress history experienced in the past. In addition, the anisotropic degree of consolidation yield stress is almost the same as that of tensile strength and higher than that of P-wave velocity. As the degree of anisotropy of consolidation yield stress increases, tensile strength increases negatively. Anisotropy of the internal structure due to lateral compressive stress increases with the action of lateral compressive stress, while anisotropy of the internal structure due to the sedimentation process decreases.