In this study, seismic hazard assessment was conducted to calculate the probability of earthquake occurrence in Japan using the strong-motion network observed since 1996. Then, a fragility assessment was conducted to calculate the limit state exceedance probability using the past proposed regression equation. Finally, the seismic probabilistic risk assessment of railway embankments was carried out using the above hazard and fragility assessment results, and the seismic risk was mapped on the national map in Japan.

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Long-term shaking table tests of unreinforced and reinforced retaining walls were conducted using a permanent magnet shaking table to investigate the effect of reinforcement installation and the effect of reinforcement length. The results showed that the unreinforced retaining wall collapsed brittleness at relatively small vibration energy due to yielding of the supporting ground, while the reinforced soil retaining wall did not yield due to the lack of stress concentration at the toe of the footing and did not deform significantly even at relatively large vibration energy. In the shaking test of the reinforced soil retaining wall with short reinforcement length, the reinforcement tension continuously decreased during shaking due to the reduction of the reinforcement area.

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The 2018 Iburi eastern earthquake caused a traffic obstruction due to bumps of up to 0.3 m caused by sliding deformation due to liquefaction and compressive settlement of the embankment due to seismic motion on the residential road in the Tsukisamu Higashi district of Toyohira-ku, Sapporo. As an effective restraint method for such bumps, the development of countermeasures suitable for residential roads using geocells that can be easily removed and reconstructed is underway. In this paper, a full-scale model test using a large crane is described in detail, which was carried out to obtain the optimum geocell size, non-woven fabric installation method, and optimal compaction method to satisfy the standard value.

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Geogrid reinforced soil double facing wall consists of the outer wall built of concrete panels, the inner wall of geogrid reinforced backfill and vertical drainage layer between outer and inner walls. Because the wall is often constructed on steep slope and becomes large scale, it affects the road traffic and neighboring structure when the wall deforms due to disaster. Repairability of the wall is influenced by scale of the wall, construction condition and deformation level. Additionally, the frequency of occurrence of heavy rainfall increases so that it needs to define the repaired procedure for the reinforced soil wall. This paper proposes the repaired procedure for the reinforced soil wall appropriate for damage level based on actual repair works for damaged wall due to rain infiltration and earthquake.

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The aim of this study is to investigate the seismic behavior of the reinforced soil walls that are geogrid reinforced soil walls (GRSW) with soil nails. Reinforced soil wall models were made using geogrids and soil nails. Shaking tests were conducted to investigate the difference in seismic behavior of reinforced soil walls. It was found that the addition of soil nails to GRSW improved seismic resistance. It was also observed that seismic resistance was high even if the geogrids were not fixed to the facing panels. From this study, it was found that seismic resistance of GRSW, whose geogrids were damaged by the earthquake, can be restored by adding soil nails to it.

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It has been reported that a buried flexible pipe excessively deformed due to the sheet-pile extraction after backfilling. Many studies have been conducted on the design method in consideration of the influence of sheet-pile extraction. However, studies for the aim of establishing methods of reducing pipe deformation are scarce. In this study, a sheet pile pullout tests were conducted to verify the effect of the backfill material integrated using geogrids to prevent the horizontal earth pressure from rapid decreasing, thus suppressing the pipe deformation during sheet-pile extraction. In addition, the separate integration of the base and upper area of the pipe was more effective in suppressing pipe deformation.

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A ground improvement method combining low improvement rate ground and gravel foundation reinforcement has been proposed as a method for controlling lateral flow and uneven subsidence when constructing embankments on soft peaty ground. In that method, adding cement does not easily strengthen soft peaty ground; therefore, in order to realize more economical designs, there is need to clarify the stress-sharing ratios on improved and unimproved ground. Accordingly, this study uses a 1/20 scale model to examine in detail the effects of sand mat, the thickness of gravel foundation reinforcement, and other factors affecting the stress-sharing ratio when using this ground improvement method. The results show that, in comparison with laying only geotextile, the stress-sharing ratio is decreased by installing a sand mat and increased by constructing gravel foundation reinforcement on the target of improvement.

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It has been confirmed by sprinkling model tests and full-scale slope tests that the slope protection work composed of two layers of geocell with different filling geomaterials has seepage control function of rainwater. However, the effect of the non-woven fabric laid between the two layers on the seepage control function of this protection work has not been clarified. In this study, we conducted two types of sprinkling model tests using non-woven fabrics with different thickness and mass per unit area. As a result, it was confirmed that the non-woven fabric is indispensable for maintaining the seepage control function for a long period of time, and that the function is not enhanced even if the non-woven fabric is thickened.

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When the reinforced soil wall applies as approach embankment to abutment, it has to consider the experimental verified interacting force in the design of abutment. However it is not clear the effects of reinforced soil wall to abutment so that authors carry out the shaking model tests for normal embankment and reinforced soil wall constructed behind the abutment to confirm the behavior of the approach embankment and earth pressure acting on abutment. The results of the tests, the earth pressure acting on abutment tends to active and passive state during bridge axis shaking, and active state during bridge cross axis shaking. This paper reports the seismic behavior of approach embankment and earth pressure acting on the abutment obtained from the shaking model tests.

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The authors investigated a temperature-accelerated creep test under confining pressure conditions on a single-rib geogrid placed in a soil layer. A basic study was conducted on the fixing method of the geogrid to the loading device, the applying method of creep load considering the friction between soil and geogrid, and the adjusting method of the soil temperature. In this paper, the outline of the testing device is explained, and usefulness of fixing of geogrid to the device with adhesive, loading method considering the friction angle by monotonic-tensile tests under soil confinement, temperature-controlling method with the electronic heaters set in water and soil are shown based on laboratory tests.

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A series of shaking table tests were carried out to investigate the effect of reinforcement vertical spacing and size on seismic performance of reinforced soil retaining walls. In addition to consider similarity rule on reinforcement rigidity, modulus of rigidity and friction angle of soil and a reinforcement. A method to measure the tensile force of the selected polyester reinforcement was also examined. As a result, even if reduce the number of laying, seismic performance when extended the length of reinforcement is equal to or greater than conventional arrangement of reinforced soil retaining walls. Because it is related to the rigid facing and connection strength are high. Similarly, segmental wall structure and reduce the number of laying was degrade the performance of seismic and different failure condition.

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In EPS embankment, RC slabs are generally installed at a vertical interval of about 3 m. When EPS embankment is constructed on the back of the abutment, a big acting force is reportedly generated by the collision of the slabs against the abutment during earthquakes. A shaking table experiment was conducted to confirm such behavior and investigate countermeasures to reduce the acting force of the intermediate slab. As a result of the shaking table experiment, it was confirmed that such acting force was generated when the inertial force was directed toward the back side of the abutment. As a measure to reduce the acting force, we confirmed the effectiveness of the method of replacing a part of the slabs with EPS material.

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In recent years, the technology to create a strong soil cement by mixing the in-situ clay and cement has been developed. If the frictional properties between the clay and the soil cement reinforcement can be properly evaluated, it will be possible to design combined reinforced structures with geosynthetics. In this study, the frictional properties between clay and acrylic plates with different surface roughness were investigated by a ring shear test, and the effect of the relationship between clay particle size and surface roughness on the frictional properties was examined. Furthermore, the relationships between the particle size of mother clay and the surface roughness of soil cement columns were also investigated. From the test results, a method to determine the frictional resistance of soil cement was discussed.

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A utilization method of excavated soil that leads to improvement of the seismic stability of the river levee founded on saturated sandy ground was proposed. This method is arrangement the geogrid-reinforced counterweight fill upon the existing embankment, expects to 1) stabilization of the embankment, and 2) increment of the liquefaction resistance of the ground due to increasing of the confining stress level. As the results of shaking table tests, it was confirmed that the proposed method can be contributed to the improvement of seismic stability of the existing embankment.

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In the construction of a soil dumping site, impervious sheeting and soil covering are sometimes used. In order to protect the impervious sheet and to prevent the roots of native trees from growing on the soil, weed control sheets are sometimes placed. In this study, we examined the relationship between the damage to the weed barrier sheets and the critical height of trees using a larch tree that was found to be growing naturally in the soil dumping site of the Tohoku Shinkansen line between Hachinohe and Shin-Aomori. As a result, it was confirmed that the weed prevention sheet was safe enough and that the tree height obtained from past results was smaller than the calculated limit height.

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Recently, LLDPE geomembrane has been applied for liner system of coastal waste disposal sites. In this study, samples of LLDPE geomembrane were installed in a real disposal site which has been fully operational since March 2011, and several tests were conducted to evaluate their water barrier performances after 10 years from 2011. Some of the geomembrane samples were buried under the condition similar to those practically applied at the site, while other samples were placed directly on the slope, with and without the protection of geomembranes. As a result, no degradation was observed in both tensile strength and elongation at break for the buried samples. In some samples placed directly on the slope, UV-induced surface degradation was observed, but the depth of degradation was supposed to be limited within a thin surface layer, whereas the original thickness was more than 3 mm. In addition, it was demonstrated that all the samples maintained their water impermeability. These results indicate that the geomembrane can be expected maintain sufficient durability for a longer period of time.

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Geosynthetic sorption sheet is one of the recently developed countermeasures for geogenic contaminated soils and rocks. This study focused on a geosynthetic sorption sheet containing hydrotalcite. Batch tests and column tests using arsenic solutions were conducted to evaluate the effect of contact time with leachate and overburden pressure anticipated from the load of contaminated soils and rocks. The batch test showed that the arsenic attenuation performance of the sorption sheet significantly increased after the first hour of contact. The column test demonstrated that the compressive stresses slightly contributed to the arsenic attenuation performance. Furthermore, the breakthrough curve showed a step-like behaviour.

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When soils and rocks that contain toxic geogenic metals and metalloids are excavated in construction works, infiltration of soluble metals and metalloids is sometimes prevented by underlying the geosynthetic sheet with adsorption capacity. In this study, based on water retention properties of two types of the geotextile sheets carrying calcium/magnesium (Ca/Mg) oxides agent as an adsorbent, unsaturated water flow around the geotextiles sheet underlying the excavated soil were numerically modeled and water retention periods in the geotextile sheets were estimated under various conditions. Next, a series of batch adsorption tests was conducted to evaluate arsenic adsorption behavior of the geotextile sheets under the short periods of contact and the effect of the pre-hydration on Ca/Mg oxide on the adsorption performance.

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Geomembranes used in bottom of waste containment facilities are required to have good barrier performances against water and chemical substances in order to prevent pollution of the surrounding environment due to leakage. Previous studies on the barrier performance against chemical substances has been carried out on organic compounds with hydrophobicity and low molecular weight, and it has been found that the permeation rate for the organic compounds passing through the geomembranes became higher as their hydrophobicity became stronger. Even if the substances are highly hydrophobic, however, it is difficult for the substances having large molecular size to pass the geomembranes in short duration. For geomembranes used in waste containment facilities, it is necessary to construct a theory to quantitatively calculate the shieldable periods against such chemical substances. This paper presents the effects of the apparent molecular size, considering hydration, and the pore size of the geomembranes on the diffusion coefficients using molecular dynamic simulations.

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