Recently, record-breaking short-duration heavy rainfall has caused extensive damage to soil structures. Reinforced soil walls have also been deformed by heavy rain, and countermeasures are urgently needed. In this study, alternating seepage flow and stability analyses evaluated the time series stability of a reinforced soil wall that collapsed due to Typhoon No. 2 in 2011. The results of the seepage flow and stability analysis revealed numerically that the stability of the reinforced soil wall was reduced by the overflow of water from the surface drainages.

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While the flexible metal facing of a geogrid reinforced soil wall prevents the slipping of backfill soil and confines it by connecting with the geogrid, the earth pressure acting on the facing remains unclear. Authors carried out model test to investigate and model the failure mode of backfill soil when part of the wall’s facing is removed. The results indicate that the backfill soil between the upper and lower geogrids slips out in a wedge shape. Both model test and numerical analysis confirm that local pressure, rather than the active earth pressure typically considered in retaining wall design, acts on the facing. This paper reports on the modeling and verification of local pressure acting on the facing of the geogrid reinforced soil wall.

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In this study, a full-scale reinforced soil wall installing several geogrid pieces was constructed, and pullout tests of the geogrid pieces were conducted from the front side of the wall during and after construction. As a result, it was found that by placing the pullout test rods, which connect the wall panels and the geogrid pieces, into a sheath, the pullout resistance of only the geogrid pieces could be directly measured from the front side of the wall. Additionally, It was found that when the width of the geogrid pieces is small, the pullout displacement required to achieve the specified pullout resistance tends to be underestimated.

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The flexible metal facings installed in the geogrid-reinforced soil wall prevent spilling of the backfill and restrain the backfill. Although the design method of the facings assumes that the horizontal earth pressure acting on the facings is equal to the weight of the arc-shaped backfill, the validation of this method has not been sufficiently verified. In this study, model tests focusing on the behavior of the backfill when the facings were opened were conducted to clarify the earth pressure acting on the facings. The results showed that the backfill slid out in a wedge shape, and the slip surface angles were affected by the internal friction angle of the backfill, not the wall slope or overburden. The calculation method for the horizontal earth pressure was proposed based on the test results.

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In this paper, non-woven filters were installed on a slope in a landslide hazard warning area north of Tokuyama National College of Technology in Shunan City, Yamaguchi Prefecture. Rainfall and volumetric water content were measured in sections with and without the non-woven filters. As a result, the relationship between rainfall and slope failure was clarified. Furthermore, numerical analysis using the rainfall seepage model proposed by Tsubogo et al. confirmed that the results of the numerical analysis agreed well with the measured values when the non-woven filters were installed. On the other hand, in the sections where the bare ground was installed, the results of the numerical analysis agreed with the measured values until the collapse, but the agreement tended to decrease after the collapse.

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Few studies have investigated the infiltration of water into the soil under natural rainfall on slopes covered with non-woven fabric filters. The purpose of this study was to develop a method for observing soil water content on an outdoor experimental slope lined with non-woven fabric filters from the upper to the lower part of the slope. An experimental slope was constructed on the north side of National Institute of Technology, Tokuyama College in Shunan City, Yamaguchi Prefecture, which is Sediment Disaster Special Alert Areas. Soil moisture sensors were then installed in the upper, middle, and lower sections of the slope, and changes of rainfall and volumetric water content were observed.

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In the joining of waterproof sheets for tunnel lining using the NATM method, heat fusion welding is commonly employed. In this process, two sheets are brought into contact with a heat plate of a heat fusion splicer, where they are fused and crimped together. To enhance quality control, thermal imaging remote sensing inspection can be effectively used to assess the quality of the joint by analyzing the relationship between surface temperature and the tensile strength of the welded area. If the heat transfer behavior of the sheets during joining can be accurately modeled, and a threshold temperature for pass/fail determination can be calculated, this method could significantly benefit sheet joining inspections by reducing the need for time-consuming and labor-intensive tensile tests. To address this issue, a heat transfer model of geomembrane seam welding is being developed to derive threshold temperatures for detecting faulty welds, applicable to various materials. To verify the model's accuracy, the vertical temperature distribution of the seam was measured. Temperatures at the jointed part and the surface were obtained using thermocouples while the sheets were welded by a self-propelled heat-welding machine. The model values correspond reasonably well with the experimental data under various conditions.

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When railway embankments are affected by rainfall, emergency restoration using large sandbags is often adopted, but the removal of large sandbags and the reconstruction of embankments when train service resumes are factors that prolong the construction period and increase construction costs. Therefore, in this study, we conducted a watering and loading experiment using a scaled-down model for the purpose of evaluating the subsidence and deformation characteristics of a structure covered with soil on the front without removing large sandbags. From the results, it was found that the proposed structure is sufficiently stable against rainfall, and that the amount of horizontal displacement and subsidence at the top of the embankment that occurs in the sandbags during the loading of the train load is reduced by the soil covering. Furthermore, by osmotic flow analysis that can reproduce the experimental results, it was confirmed that the crushed stone layer in the embankment model has the effect of reducing the water level and saturation in the soil cover and improving the stability of the restoration embankment.

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The effects of shape of geogrid-reinforced counterweight fill on seismic stability of existing river levee located on liquefiable ground were investigated. In this study, shape of the counterweight fills as well as its relationship with geological conditions such as thickness of the liquefiable layer were investigated by performed shaking table tests. As a result, it was confirmed that placement of counterweight fill is an effective method for improving the seismic stability of existing levees on liquefiable ground, and is effective in geological conditions where the thickness of the liquefiable layer is thin. Even if the volume is the same, the effects of liquefaction countermeasures depend on the shape of the counterweight fill. Therefore, it is better to place the counterweight fill as to cover the existing levee.

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[in Japanese]

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To address the increasing risk of levee overtopping due to extreme weather events, we propose a new shell net-type erosion control system. This system effectively prevents erosion by combining a crushed shell layer and a capillary barrier soil layer. In this study, a shell net-type erosion control system was laid in a sloping flume, and the tensile strength retention rate of the shell-filled net after 3 hours of overtopping with a flow depth of 0.3 m was measured.Accelerated degradation tests were also conducted under weather conditions and sand abrasion. As a result, it was confirmed that the tensile strength retention rate of the shell-filled net after overtopping and degradation under the specified conditions was 30% or more of the initial tensile strength experimentally demonstrating its practicality.

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The authors conducted experiments and analysis to confirm the deformation suppression effect of a road embankment with a shallow foundation composed of crushed stones and geosynthetics over liquefying ground. Because previous studies were conducted on embankments with heights of 4 m, the authors additionally conducted a 50 G centrifugal experiment on embankments with a height of 6 m. The configurations of embankments with and without the countermeasure after soil liquefaction were compared and the authors confirmed that the countermeasure suppressed deformation and kept the shape of the embankment sufficiently. The dynamic effective stress reproduction analysis was conducted and the analysis was used to examine the deformation reduction effects of embankments even greater than 6 m in height.

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The purpose of this study is to clarify the shear properties of short-fiber reinforced soil after freezing and thawing. Compaction tests were conducted on soil samples with three different short-fiber mixing ratios of 0, 0.1, and 0.3 %, and the maximum dry density decreased as the mixing ratio increased, and the optimum moisture content was almost the same regardless of the short-fiber mixing ratio. Ice lenses were observed in the specimens during the freezing process using a direct box shear test apparatus. Furthermore, the results of direct box shear tests using specimens compacted with various mixing ratios and subjected to freeze-thaw showed that the shear strength was maintained after freeze-thaw as the short-fiber mixing ratio increased.

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Various efforts are being made both in Japan and overseas to move towards a decarbonized society. To achieve carbon neutrality, civil engineers must actively focus on the selection and distribution of materials that can reduce greenhouse gas emissions as much as possible. In this study, we examined the environmental impact reduction effect and shock absorption capacity of rockfall protection reinforced soil walls when the wall facing unit was changed from steel frames to geocells made of high-density polyethylene material. As a result of the verification, it was confirmed that by changing from the steel wall facing unit to geocells filled with single-grain crushed stone, it was possible to reduce emissions and maintain performance in terms of shock absorption capacity.

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Rockfall protection reinforced soil walls have been increasingly constructed in recent years as structures to protect road traffic from falling rocks. This structure uses steel facing unit to maintain the shape of the reinforced soil wall, but we replaced the specifications from the steel facing unit to geocell made of high-density polyethylene to reduce the environmental impact. And We conducted a pull-out test of the geocell and geogrid connections. For the connections, we tried a structure in which the geogrid was simply sandwiched between geocells, and a structure in which fixed piles were inserted. In this paper, we provide an overview of the experiment, provide a detailed description of the structure of the connections, and report on the pull-out strength of the connections obtained in the experiment.

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The authors are investigating geosynthetic soil reinforcement techniques for the construction of emergency and restoration of damaged geostructures in the event of disasters. This paper discusses a geocell reinforcement technique for restoring embankments damaged by hydraulic action. A restoring technique to combine geocell reinforcements and horizontal drainage pipes is proposed. A layout concept of geocell reinforced units is discussed based on the results of the seepage model test of an unreinforced embankment. The results of the seepage model test conducted to verify the proposed technique are presented. It is clarified that the model embankment constructed with the proposed technique showed sufficient stability.

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Geocells are lattice-shaped reinforcement materials used to reinforce the ground, such as to deal with soft ground. Installing geocells in the base course can distribute traffic loads over a wide area and reduce stress. However, a clear design method for geocell installation has not been established. In order to promote the use of geocell-reinforced substrates in the future, it is essential to study the reinforcement mechanism of geocells and propose a design formula that can accurately evaluate the reinforcement effect. In this study, an experiment using a model was conducted to understand the range of stress distribution in the base course when geocells are installed. Based on the results, a base layer thickness calculation formula was proposed, and the accuracy of the proposed formula was examined.

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