Peat-based soft ground is widely distributed across the plains of Hokkaido. When constructing structures such as embankments or box culverts on soft peat ground, the preloading method has been used to promote consolidation settlement, address ground settlement and bearing capacity issues, and ensure sufficient allowable vertical bearing capacity through increased strength before constructing the structure. This paper discusses the results of in-situ test construction, dynamic observation results during actual construction, and the results of laboratory model tests conducted to verify the effectiveness of countermeasures, about the culvert foundation reinforcement method on wrapped geogrid developed as the newly shallow ground improvement.

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The corner section of geogrid reinforced soil wall tend to become weak point and may exhibit joint openings of wall facing due to wall deformation. Although the wall has high seismic performance, the mechanism of behavior and deformation of corner section remain unclear. Authors carried out the shaking table model test to investigate the seismic behavior and failure mode of the wall with corner section. The results show that, when sliding failure occurs on one wall face, the adjoining face tends to follow its deformation, leading to noticeable deformation at the corner section. This paper reports the results of model test and numerical analysis aimed at clarifying the wall’s behavior and proposes structural measures to suppress deformation at the corner section.

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　In this paper, in order to obtain basic knowledge on the effect of the tensile stiffness of the geogrid on the deformation of reinforced soil walls, vertical loading model experiments were conducted using three types of geogrids with different tensile stiffness. 　Geogrid with low tensile stiffness reduces the vertical load at yield and increases the ground strain and wall displacement. In this case, the extension of the geogrid was also large. The extensions after yielding were often smaller than the amount of wall displacement. Using geogrid with particularly high tensile stiffness, pullouts of the geogrid were observed. At the yield, the volumetric strain in the reinforced area using medium and high tensile stiffness of the geogrid was almost same. These results suggest that increasing the tensile stiffness of the geogrid may not increase the confining effect of the soil in situations that geogrid pullout occurs.

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　This study proposes a new pipeline uplift countermeasure, the Geocell Shallow-Buried Method, aiming to achieve both reduced construction effort and high uplift suppression performance. Model tests confirmed that this method provides higher uplift resistance compared with unreinforced and conventional methods. Furthermore, the integration ratio, defined as the proportion of uplift resistance mobilized through the integrated behavior of the pipe and surrounding soil, was evaluated, and it was shown that adopting a value of 0.8 for design is reasonable. In addition,an evaluation method for the pullout resistance of the geogrid beneath the geocell was presented. This study provides fundamental insights for the establishment of a rational design method for the Geocell Shallow-Buried Method.

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　The results of dynamic centrifuge model experiments using EPS embankments behind abutments have reported that large forces are generated by the EPS embankments during earthquakes. Analysis of the experimental data showed that these forces are generated as a resistance to the abutment collapsing when inertial forces act on the abutment from its rear side. In this paper, we investigated the relationship between the strain on the abutment in the experiment and the earth pressure and inertial forces acting from the rear, and considered the effects of these forces on the abutment. As a result, we confirmed that the effect of inertial forces on the strain on the abutment is greater than the effect of earth pressure.

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　This paper experimentally evaluated the settlement reduction effect of a new liquefaction countermeasure combining end-constrained geosynthetics using crushed shells (hereinafter referred to as H_GS) and short piles (R=short pile length/liquefaction layer thickness, R< 1) in reducing subsidence. In this study, a new mechanism was added to transmit tensile force to end-fixed body using cylindrical sliding columns. Various experiments were conducted using a 1G-type small vibration table to compare the suppression effects on settlement of the structure and ground settlement. The results revealed that the combination of H_GS and short piles demonstrated a synergistic effect, achieving a greater reduction in settlement than either alone method.

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In road pavements in snowy and cold regions, the fluctuation and phase change of moisture in the pavement structure observed during the freezing and thawing seasons cause various types of structural damage to asphalt pavements. Recently, Wicking Fabric (WF) drainage materials, which have the ability to absorb and drain pore water in the ground, unlike conventional geosynthetic materials, have attracted attention. This study examines the effects of installing WF drainage material, which could improve the stiffness of base course and subgrade layers, and suppress the frost heaving of subgrade materials.

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　To mitigate liquefaction damage to existing houses, it is sometimes more reasonable to take measures to reduce damage to buildings even if liquefaction occurs, rather than improving the ground to prevent liquefaction. This study focused on a measure to mitigate liquefaction-induced deformation of spread foundations by burying gravel-filled geogrid gabions on the sides of the foundations. The effects of this countermeasure for spread foundations subjected to eccentric loads were evaluated through shaking table tests and numerical analysis. The results showed that installing geogrid gabions reduced foundation settlement and inclination regardless of eccentricity, and that extending the dimensions of the gabions on the eccentric side further improved the tilting reduction effect.

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Although the use of geocells around buried pipelines has been shown to increase buoyancy resistance during liquefaction, the degree of soil liquefaction within the geocell has not been fully investigated. This study conducted shaking table tests under normal gravity to examine the liquefaction mitigation effect of geocell-reinforced ground. A sine wave was applied to both unreinforced and geocell-reinforced ground, and changes in pore water pressure and acceleration were measured. Results indicated that while geocell installation did not completely prevent liquefaction, it suppressed ground shear deformation and pore water pressure during shaking. In particular, applying pre-stress to the installed geocells further enhanced the mitigation effect.

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Previously, the authors proposed a subgrade thickness calculation formula based on laboratory tests using geocells placed within a model soil mass. However, since these tests were conducted in small-scale soil troughs, there was a possibility that the proposed formula overestimated the actual subgrade thickness. Therefore, this study investigated the stress dispersion angle using a large-scale soil tank and proposed a new geocell subgrade thickness calculation formula. The stress dispersion angle results confirmed that laying geocells disperses stress over a wider area, with the geocell stress dispersion angle being approximately twice that of the unreinforced stress dispersion angle. Based on the obtained stress dispersion angle, a geocell subgrade thickness calculation formula was proposed.

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The 2024 Noto Peninsula Earthquake with a magnitude of 7.6 occurred on January 1, 2024, at 16:10. In Wajima City, Ishikawa Prefecture, the geogrid reinforced soil wall was deformed as sliding, joint opening of wall facing and pavement crack. Although the critical damage of the wall did not occur, its structural stability remained unclear.Authors conducted the geotechnical investigations such as three-dimensional surveying, standard penetration test and surface-wave method for the wall. This paper reports the assessment of wall’ stability based on the geotechnical investigations.

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In this study, the effectiveness of a method for mitigating levee erosion during flood overtopping by reinforcing riverside slope surfaces with a combination of low-quality soil with high water content generated by river channel excavation and geotextile reinforcement materials was investigated. Centrifugal model tests were conducted to evaluate the effects of the reinforcement material and the water content of the excavated soil on the flood resistance of the levee.The results showed that the combination of excavated soil and reinforcement material increased resilience against flooding, and the river water level was maintained for a longer period, especially under high water content conditions.Furthermore, the reinforcement effect of the reinforcement material was mechanically verified by slope stability analysis.

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This study aimed to clarify the erosion control effects of vegetation sheets and their applicability in snowy coldregions. Observations were conducted on a model embankment during summer, the snowmelt period, and spring.During summer rainfall, the vegetation sheets mitigated raindrop impact and dispersed surface runoff, markedly suppressing erosion compared to bare slopes. Similarly, during the snowmelt period, the sheets demonstrated sufficient erosion control effects against the concentrated flow of meltwater over a short duration. Furthermore, seed-containing vegetation sheets installed in winter exhibited germination and growth in spring after the snowmelt, resulting in a relatively high vegetation cover within a short period.

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Geocells are reinforcement materials with a honeycomb structure when unfolded and are generally filled with crushed stone or local soil upon expansion. Previous studies have reported reinforcement effects of planar geocell applications, such as an increase in ultimate bearing capacity and suppression of settlement. However, the influence of factors such as geocell thickness, variations in the area of individual cells upon deployment, and the presence or thickness of additional reinforcement materials such as nonwoven fabric laid beneath the geocell on the reinforcement effect remain unclear. Therefore, in this study, model tests were conducted by placing a geocell model on a model ground simulating soft soil, focusing on the settlement and deformation shape of the soft ground.

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Growing torrential rain disasters and Eco-DRR initiatives demand construction technologies that balance disaster prevention and the environment. A shell-type capillary barrier (CB) embankment was proposed, which uses a shell-net(crushed seashells restrained in a synthetic net) on river levee back slopes. While previous work clarified the shell-net's stability during overtopping and its residual tensile strength, this study investigates tensile strength changes by comparing outdoor exposure tests with existing data. The research also detailed how contaminated soil particles affect the residual strength ratio. The findings confirm that particle contamination reduces tensile strength, and this effect is predominantly governed by the particle shape.

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This study evaluates the deformation control and seismic performance of a railway embankment restoration method that employs large sandbags as a permanent structure. Static horizontal loading tests showed that constructing a front embankment or increasing sandbag layers significantly reduced deformation. Shaking table tests demonstrated that removing upper sandbags and constructing a front embankment suppressed shoulder collapse and improved seismic performance. When upper sandbags were retained with soil nailing, improvements were evident at 400 gal shaking but were limited at higher accelerations. These results indicate the potential applicability of the proposed method for permanent restoration of damaged railway embankments.

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In Japan, reinforced soil walls are extensively utilized and are recognized for their excellent seismic performance. On the other hand, there have been reported cases in which frictionally reinforced soil walls were damaged during earthquakes under high groundwater conditions, due to a decline in drainage performance within or around the reinforced soil walls. However, the seismic deformation behavior of strip-type reinforced soil walls using frictional reinforcement materials under groundwater conditions remains poorly understood. Therefore, in this study, a　series of　centrifuge model tests were conducted to investigate the seismic behavior of frictionally reinforced soil walls under　groundwater conditions.

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In this study, the authors experimentally investigated effective aperture patterns to ensure high permeability of sheetshaped and tubular geosynthetics such as geocells and geopipes. A variable head permeability test apparatus developed by the authors, to evaluate the permeability of geomaterials under a wide range of hydraulic gradient conditions, was used in the series of experiments. In this paper, the influence of the periodic arrangement of circular apertures on the permeability of the soil-geosynthetic system is first demonstrated. A new aperture pattern is proposed based on the observation results of the pore structure of a soil sample using a μX-ray CT device. Finally, the effectiveness of the proposed aperture pattern is discussed based on the results of variable head permeability tests.

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This paper discusses a preventive maintenance technique using geosynthetics to mitigate the risk of deformation and collapse in embankments prone to seepage action. Results from seepage model experiments revealed that nonreinforced embankments show progressive failure deformation from the toe due to seepage actions. Based on these findings, the effectiveness of a preventive maintenance technique using geotextile bags and drainage pipes was evaluated. Test results show that the investigated method can protect the toe of the embankment using geotextile bags and reduce the seepage water height using drainage pipes.

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During Typhoon Hagibis in 2019 (Reiwa 1), 142 levee breaches occurred across Japan, with 86% attributed primarily to overtopping. While conventional flood prevention methods such as sandbag barriers and water bags have been widely implemented to prevent overtopping, the effectiveness of post-overtopping countermeasures— specifically, erosion resistance of protective sheets applied to the landside slope—has not been sufficiently verified. In this study, a flood protection sheet designed to delay levee failure after overtopping was developed. The erosion resistance of the flood protection sheet was evaluated through large-scale levee model experiments under controlled overtopping conditions.

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In this study, in order to investigate a method for evaluating the integrity of reinforced soil walls using reinforcement connected at the wall surface before and after shaking, pull-out tests were conducted using a model geotextile reinforced soil wall with reinforcement pieces installed for pull-out tests. Shaking table tests were conducted using three types of wall materials. As a result, it was found that the L-shaped retaining wall can be vertically stacked and has a certain level of seismic resistance to shaking, and that the stair-step stacking method contributes to improving the overall stability of the reinforced soil wall during shaking. The results of the pull-out test of the reinforcement pieces showed that its test can be useful even after shaking to assess pull-out resistance behind the assumed slip surface.

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In recent years, road washouts have frequently occurred in sections adjacent to rivers. In the field of river management, the concept of resilient river levees has been discussed as one of the disaster mitigation measures for crisis management. In this study, the breaching mechanism of earthen levees due to overflow erosion was examined. In addition, a levee structure was proposed in which the crest of the levee is covered with a road base course and reinforced with geosynthetics: geonets placed horizontally. The effectiveness of this structure was verified. The experimental results suggested that pavement covering the levee crest suppresses the occurrence of localized longitudinal erosion, and that reinforced embankments with multiple horizontal layers of geosynthetics are effective in improving erosion resistance.

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In recent years, on national roads and expressways with heavy traffic, in addition to damage to the surface layer due to long-term use, fatigue cracks from the underside of asphalt pavement and weakening of the subbase have been confirmed. In such cases, replacing or improving the roadbed layer would be effective, but this is often difficult in terms of construction time and cost. Therefore, it is important to reinforce the underside of asphalt pavement, which is the starting point of fatigue cracks, and we are developing a reinforcing sheet made of geosynthetics.

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The ballast generated during the removal of existing railway lines, among other activities, has a single grain size and cannot be compacted; therefore, it is not suitable for use as embankment material in its original form. However, if it can be reused as embankment material through particle size adjustment, it is possible to reduce CO₂ emissions generated during disposal, making this approach effective for reducing environmental impact. In this study, with the aim of reusing removed ballast as reinforced embankment soil, we examined a simple particle size adjustment method focusing on the construction steps of railway elevation projects. Various tests were conducted using full-scale test embankments to evaluate the applicability of the material as reinforced embankment soil, and, based on the evaluation results, the method was applied to actual construction.

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