Based on previous finding that seismically-induced slope displacement δ can be uniquely evaluated from earthquake energy E_eq directed to slope failure, Energy-based Newmark calculations are conducted to determine E_eq from upward wave energy E_u of 10 earthquakes of widely varying irregularity. The energy ratio E_eq/E_u versus E_u correlation has been found to have a clear peak, wherein (E_eq/E_u) _peak and corresponding E_u are correlated with predominant frequencies of the waves. Furthermore, a unified E_eq/E_u/(αβ)~E_u/E_u0* correlation has been developed, overcoming differences in wave irregularities and slope parameters, to uniquely determine E_eq from E_u for arbitrary design earthquake motions. This unified correlation has been applied to evaluate E_eq in numerous slope failure case histories using earthquake records during recent earthquakes. The E_eq-values thus obtained are found 10^-1~10^-2 times or still smaller than the gravity energy E_gr associated with slope sliding. Accordingly, friction coefficients tan ϕ back-calculated from the values E_eq and δ observed in situ tend to be lower with increasing runout distance and smaller than initial slope gradients, tan θ, in most slopes of longer runout distance. These trends indicate that not E_eq but E_gr plays the major role of long-runout slope failures, wherein soil strength has to be drastically reduced due to cyclic loading during earthquakes or subsequent sliding.

In this study, sand specimens with fines were prepared to form different soil structures, and the soil structure of sandy soil was visualized and evaluated using elasto-plastic mechanics. In the visualization of the soil structure, microscopic and microfocus X-ray CT observations indicated that the formation of the soil structure of sandy soil with moderate fine-grain content was strongly influenced by the aggregation of fine-grain fractions. tests and elemental simulations using an elasto-plastic constitutive model showed that the differences in the soil structure could be quantitatively evaluated based on elasto-plastic mechanics. Furthermore, to evaluate the influence of these soil structures on liquefaction, undrained cyclic triaxial tests, 1G small shaking table experiments, and field-scale FEM analyses were conducted to clarify the influence of the degree of soil structure on the degree of liquefaction.

The single-borehole hydraulic tests have been established as a standard by the Japanese Geotechnical Society to be conducted in a specific range, requiring the ratio of the test section length (L) to the hole diameter (D) to be at least 4 (L/D≧4) when there is not an impermeable layer nearby and at least 2 (L/D≧2) when there is an impermeable layer nearby. However, implementing this requirement in the field is often challenging in the loose ground, so it necessitates re-drilling the test hole, which imposes additional labor and costs. That limitation of L/D comes from application ranges of the equations used to calculate hydraulic conductivity, but no discussion of the appropriateness of applying shorter test section length. To solve this problem, the numerical analyses simulating the shape of the single-borehole based on derivation conditions the equation and simulating actual test conditions were used to examine whether the equation could be applied to L/D such that L would be small. As a result, the new range, the lower bound of the ratio, could be reduced to 1.36 when there is not an impermeable layer nearby and 0.68 when there is an impermeable layer nearby was suggested. This proposed adjustment could significantly ease the field conditions for determining hydraulic conductivity by single-borehole test. Relaxing the constraints of the equations holds promise for simplifying and enhancing fieldwork efficiency in permeability assessments.

In the foam shield driving method, it is essential to maintain the plastic flow of the foam mixed soil in the chamber during tunnelling to keep the stable excavation, while maintaining the stability of the cutting face. To maintain plastic flow, it is important to prevent the defoaming and separation phenomena of the excavated soil with foaming additives. Factors that affect defoaming and separation include the water content of the foam mixed soil, the construction environment under high ground water pressure, and the influence of microorganisms. It is important to properly investigate the mixing ratio of the excavated soil ground, foam, and water (water contained in the excavated ground and added water) from the soil water content. The defoaming and separation characteristics of the soil with foaming additives were experimentally investigated and the range of water content to maintain the plastic flow of the soil-foam mixture was indicated. Conclusively the foam shield driving management procedure for the soil-foam mixed in the shield machine chamber was demonstrated.

Weathering is a natural phenomenon that involves physical and chemical changes. Changes in its chemical properties may result in the formation of smectite, a type of clay mineral group. Although there are examples of sampling weathered soft rock and evaluating its swelling behavior based on laboratory test results, the authors do not find studies which evaluate the swelling behavior from the perspective of the degree of weathering progress in the depth direction. In this study, we clarify the physical and chemical properties of weathered soft rocks containing smectite, which are classified into three types depending on the degree of weathering progress in the depth direction, and we present the results of evaluating swelling behavior depending on the degree of weathering progress in the depth direction. We found that the swelling behavior of weathered soft rock is related to the increase in smectite content and the decrease of dry density depending on weathering progress, and the moisture content and the type of exchangeable cations depending on the surrounding environment, and the effect of solidification depending on undisturbed state.

To establish an evaluation method for the leaching behavior of heavy metals and metalloids from geomaterials exposed to a reducing environment, we simulated a reducing environment by adding 0.01 mol/L sodium ascorbate (chemical method) and 0.17 – 0.34 mol/L organic carbon (biological method), and examined changes in Eh, pH and the leaching concentration of heavy metals. In the excavated rock, the average Eh was −50 mV in the chemical method and −154 mV in the biological method, which was lower than non-additive system (249 mV). Under these conditions, significant increase in leaching concentration of arsenic was not observed. Coal ash mixed material and concrete exhibited Eh values lower than 0 mV with the chemical method, but did not necessarily fall below 0 mV with the biological method regardless of conditions. Since the leaching behavior of heavy metals and metalloids are affected by pH and bacterial activity as well as Eh, these chemical indexes should be carefully evaluated under simulated reducing conditions.

In designing pile foundations against lateral forces, the coefficient of lateral subgrade reaction is evaluated by considering the influence of pile group effects. The influence of these effects is generally expressed as a reduction factor, known as pile group efficiency. However, studies of pile group efficiency are typically conducted under conditions where the piles don’t project from the ground surface. In contrast, pile foundations with a single pile-single column configuration, such as for over-track buildings or pile-bent bridges, lack foundation beams or footings. Consequently, these structures exhibit behavior like that of projecting piles due to the combined action of the pile and the column. This study aims to investigate the impact of projection on pile group effects through centrifugal tests and three-dimensional elasto-plastic finite element analysis. Results indicate that projection reduces pile group effects, and the mechanisms behind this phenomenon are clarified by examining the deformation modes of piles and the stress distribution in the surrounding soil.

In this study, small-scale river embankment model tests and two-dimensional seepage analyses were conducted to verify the effects of surface covering work and drains installed as overtopping countermeasures for levees. For a uniform embankment, it was clarified that levee failure occurs owing to erosion at the toe of the slope caused by overtopping and soil absorption caused by seepage through the embankment, which triggers piping beneath the surface covering works. The results demonstrated that toe protection and drainage work were effective. Furthermore, it was shown that in the case of a river embankment on a highly permeable foundation ground, piping beneath the surface covering works progresses rapidly during overtopping, shortening the time to failure, and clarifying that drain works are highly effective in that case.

There is a unique relationship between the dry density ρ_d of the rock, the unconfined compressive strength q_u, and the deformation coefficient E₅₀. Using this relationship, we proposed the "ρ_d method" for evaluating and estimating the disturbances in q_u and E₅₀ due to rock sampling, etc. The applicability of the ρ_d method was examined for 32 samples obtained by rotary tube sampling and percussion wireline sampling. On the other hand, there is a method for evaluating rock disturbance using the stiffness recovery rate SRR, however since SRR focuses on the change in the ratio of deformation coefficient in each stress σ to the initial deformation coefficient, the value of SRR will be small if the relationship between σ and strain is linear even in a disturbed sample. The ρ_d method is effective as a disturbance assessment method for rock drilling, sample collection, etc.

The applicability of DAS (Distributed Acoustic Sensing), a vibration-type optical fiber measurement method for detecting the soil particle movement accompanied with seepage flow in a river embankment and deformations caused by erosion of the embankment due to overflow, was verified in laboratory experiments. First, the characteristics of vibration waveforms during soil particle movement were investigated from elemental experiments using a small soil tank, and then the elongation of optical fiber caused by soil particle movement was calculated from the vibration waveforms after waterlogging using a large embankment model with a full cross section of the embankment in an overflow break test. As a result, it was found that the vibration waveform measured by the DAS could be regarded as a single-amplitude spike waveform, i.e., the amount of displacement of the optical fiber cable elongation, and that this displacement occurred within a short period of 5 to 10 ms.

It has been about half a century since the first reinforced soil wall was constructed in Japan, and it is now widely used in the general public. However, with the increase in the number of construction results, deformation of the wall panels has been reported in some of the reinforced soil walls constructed in Hokkaido. Therefore, we have organized the actual situation of reinforced soil walls constructed by the Hokkaido Development Bureau, and established a forum (hereinafter referred to as “Reinforced Soil Wall WAKATTEN-KAI”) where people involved with reinforced soil walls in Hokkaido (client, design consultants, contractors, reinforced soil wall manufacturers, Kitami Institute of Technology, and the Civil Engineering Research Institute for Cold Region) can share their awareness of each other's work. As a result of discussions at the Reinforced Soil Wall Checklist Meeting, the effectiveness of the reinforced soil wall checklist was confirmed in the work and construction of reinforced soil walls ordered by the Hokkaido Development Bureau (hereafter referred to as the Development Bureau) based on the recognition that the checklist is effective in ensuring quality, in which items that should be shared by both contractors and receivers are mutually verified. This paper describes the background of the reinforced soil wall checklist as a tool for building cooperative relationships and encouraging dialogue between the client and the contractor.

In the land development by cutting and embanking, it is basic to balance the cutting and the embanking within the project area, including not only the commercial land but also the construction of the regulating reservoir for disaster prevention, which is an attached facility. The embankment soil to construct the regulation reservoir was planning to use the excavated soil from the embankment foundation and the reservoir area, but the strength required to ensure the embankment slope stability was insufficient, so it was decided to use after improving the excavated soil by cement. This paper presents that the compaction and strength characteristics of cement-improved soil investigated by laboratory cement mixing test, the determining method of the effective stress strength parameters of cement-improved soil necessary for the stability analysis, the determining method of the cement amount to achieve the required strength on site, the strength quality controlling method of the cement-improved soil, and the results of confirming the applicability of these method to an actual construction site.

In this study, we conducted basic investigations on improvement effects of mixing solidifying materials to soil unsatisfied the standard for judging embankment materials in geotechnical investigations of an agricultural reservoir renovation project in Oita Prefecture. From the obtained results, it was showed that permeability coefficient k=5×10^-8m/s for impervious materials was satisfied under mixing conditions of 90 kg/m³ for cement-based solidifying material, 30 kg/m³ for lime-based solidifying material, and 60 vol%/m³ for slag-based solidifying material at the curing period of 28 days. Also, it was clarified that the concentration of hexavalent chromium elution was 0.022 mg/L at 90 kg/m³ for cement-based solidifying material and was satisfied sufficiently with the soil environmental standard value (0.05 mg/L) from the results of the hexavalent chromium elution test at the curing period of 28 days.

In this study, a detailed examination of the results of water content tests conducted on recycled gypsum and recycled gypsum stabilized soil by the JIS method was carried out. Also, the influence of the apparent water content determined by the JIS method on compaction properties of the gypsum was investigated. From the obtained results, it was found that when reagent gypsum and recycled gypsum without / with addition of water were oven-dried for 24 hours at a furnace drying temperature of 110°C using the JIS method, obtained water content were those in which the form of the gypsum changed from gypsum dihydrate to hemihydrate or anhydrate, and gypsum hemihydrate changed to gypsum anhydrate, and the apparent water content was greater than the true water content. It was also shown that the apparent optimum water content and the apparent maximum dry density of recycled gypsum obtained by the JIS method and the true optimum water content and the true maximum dry density obtained by calculation were significantly different. Furthermore, it was found that the difference between the true water content and the apparent water content of gypsum stabilized soils increased with increasing gypsum addition ratio.