In this paper, the tendency of the economic and ground condition improvements that geotextiles laid using the deep-mixing processing method based on the subsidence prediction that the writer suggested was shown. The rupture strength of geotextiles was calculated by the surface friction of geotextiles on the improved part that was equal to the shear strength acting on the geotextiles of the non-improved part. An improved rate and the specifications of geotextiles to become a predetermined subsidence were found. As a result, the laying of geotextiles reduces a construction cost as a predetermined subsidence is smaller, as the shear resistance angle of an embankment is smaller, and as the thickness of an improved layer is smaller.

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While a type of back-to-back reinforced soil wall using geotextile is often applied at approach to the abutment, the seismic behavior and failure mode of the wall are not clear. Authors carried out the shaking table model test for the back-to-back wall to investigate the influence of distance of two opposing walls and overlap length of geotextile. The results of the model tests obtain that the walls behave independently and fail similar to circular slip when they do not intercept each other. When the geotextiles from both sides overlap or contact, the wall deforms due to dynamic settlement. This paper reports the seismic behavior of the wall obtained from the model test and proposes the stability analysis based on the failure mode of the back-to-back reinforced soil wall.

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D・Box construction method has been employed in approximately 2,500 cases for ground improvement in very soft ground and liquefaction mitigation measures, applied to foundations such as buildings, roads, retaining walls, culverts, and box culverts. The increase in ground strength through the D・Box method was confirmed using plate load tests or drop-weight tests. Furthermore, to clarify the compaction effect on the subsoil below the bottom surface of D・Box, three-component electric cone penetration tests (CPT) was conducted before and after D・Box installation in the Tone River riverbed. Comparison between the two tests was made, and the validation of the compaction effect on the underlying ground in a short time through D・Box method.

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Although a concrete block is typically installed at the bends of water supply pipes as thrust protection, the concrete block may be unstable when the surrounding ground liquefies due to earthquakes. This study targeted thrust protection with using buried gabion in the ground outside the bends instead of the concrete blocks. The effects of the buried gabion on increasing the horizontal resistance force acting on the bends were evaluated by model tests. The results showed that the horizontal resistance force was approximately doubled by the installation of the gabion; the horizontal resistance force increased gradually without a clear peak, as the horizontal displacement increased; the gabions were slightly bent by loading and may have distributed the load over a wider area of the ground.

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This paper reports the results of dynamic observations of applying a low-improvement-ratio ground improvement method with gravel foundation reinforcement as a measure against soft ground when constructing a high embankment with a planned height of about 16 m on peat ground. Even when constructing an embankment on peat ground, gravel foundation reinforcement supports the embankment load as if it were a simple beam supported by the improvement, suppressing long-term settlement and deformation of the surrounding ground, which had previously been problematic. Significant fluctuations in groundwater levels were not observed during or after construction of the embankment. The results confirm that this method is highly effective for stabilizing embankments on peat ground and suppressing deformation of the surrounding soil, while having little impact on the groundwater environment around the embankment.

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In this study, we evaluated the erosion prevention effect of a vegetation sheet against surface water flowing down a slope. An erosion test was conducted in which water flowed on the surface of a slope where a vegetation sheet was installed. SfM (Structure from Motion) photogrammetry was adopted as a method for observing erosion scars. The test results confirm that the vegetation sheet has the effect of significantly reducing the amount of erosion and delaying the start of erosion, and clarify that the vegetation sheet spreads the surface water and reduces the flow velocity. In addition, the vegetation sheet promotes the infiltration of surface water into the soil, saturates the soil, and increases the amount of infiltration water discharged from the toe of the slope.

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In this study, we applied the research findings related to mulch-anchored reinforced soil walls and investigated a method to directly measure the pullout resistance of reinforcement during and after construction of geotextile-reinforced soil walls. As a result, by installing small L-shaped retaining walls made of concrete and pullout test rods that can connect geogrid pieces within the reinforced soil wall, it became possible to measure the pullout resistance of the reinforcement in reinforced soil walls covered with inclined steel-framed facing during and after construction, allowing for a comparison with the design values.

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In recent years, retrofitting of small earth dams has become an urgent task due to their aging and lack of seismic resistance. In this paper, the stability calculation of the cover soil upstream of the embankment is examined to establish a design method for retrofitting with geosynthetic clay liners, which is on the rise recently. Stability calculations based on the potential slip surface along the sheet surface proposed in a previous study and the circular slip surface slice method were verified in real earth dams in Hyogo Prefecture. As a result, the influence of water level and horizontal seismic intensity on the factor of safety differed depending on the calculation method, and the combination of both methods was found to be important to obtain the minimum factor of safety.

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Geocells are three-dimensional reinforcement materials made of high-density polyethylene. Although geocells are often used to reinforce base course over soft ground, the mechanism of the reinforcement effects are still unclear. Authors investigated the reinforcement effect of geocell by conducting six cases of 300mm plate loading tests. The improved thickness of geocell on base course was determined using the Boussinesq formula. The actual effectiveness of geocell was confirmed in a 750mm plate loading test. The validity of coefficient obtained in the 300mm plate loading test was confirmed. As a results, knowledge about the correction coefficient for geocell base course reinforcement effect are obtained.

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The aim of this study is to investigate settlement in the backfill of geogrid reinforced soil walls (GRSWs) subjected　to earthquakes as an indicator of extent of damage. A series of shaking table tests were performed on model GRSWs　with varying geogrid stiffness and geogrid content. Settlement at the top of the backfill was measured using a LiDAR　camera. Along with settlement, corresponding deformation of facing wall and distribution of maximum shear strain in　the backfill were studied. Typically, larger settlements were observed to occur behind the reinforced soil block.　Regarding the parameters representing settlement, it was observed that the settlement area offers a more consistent　representation of settlement behavior in the backfill and the extent of damage compared to maximum settlement　measured at a particular section. In the experiments, it was observed that the model walls could not withstand excess　shaking when the normalized settlement area reached around 2%.

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In order to widely use of crushed concrete aggregate (CCA) as embankment material, the applicability of geogrid-reinforcing technique was investigated in this study. As a result of various laboratory tests including plane strain compression test, it was confirmed that the mechanical property of CCA can be improved due to geogrid reinforcing. The quality control method based on the degree of compaction Dc can be also applied to CCA as well as natural coarse-grained soil materials. Because the density condition at Dc=90% at standard soil-compaction energy 1Ec is not dense, on the other hand, it is difficult to significantly improve the strength and deformation characteristics of CCA even if applying reinforcing technique. To obtain the effective reinforcing effect, sufficient soil compaction is required.

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It is an important issue to reduce the life cycle cost of asphalt (hereinafter referred to as "As") pavement, which is a huge stock of more than 1.2 million kilometers in Japan, in order to maintain and manage it. In this study, geosynthetics are installed in the base course, and a proposal is made to extend the service life of As pavements by reinforcing the base course. In this report, we begin by capturing the behavior of geosynthetics effects in a homogeneous sandy substrate, where laboratory modeling experiments are feasible. The geosynthetics was then subjected to loading tests using a small soil tank and FEM analysis to investigate the effect of geosynthetics installation on the bearing capacity of the base course from both the model experiment and the analysis. The results showed that the bearing capacity was increased by laying geosynthetics in the soil.

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A reinforced soil retaining wall (RSRW) collapsed due to Typhoon No. 2 that made landfall in May 2011. The cause of the collapse is presumed to be that the water level in the back of the RSRW rose during rainfall, causing excessive water pressure to act on the RSRW, resulting in the reinforcement rupturing and reducing its stability. In this study, the above presumption was verified using a numerical approach. Two-dimensional seepage analysis was conducted to determine the water content of the backfill. Then, the safety factor of the RSRW was calculated by stability analysis. Numerical analysis revealed that the backwater level of the RSRW increased due to the heavy rainfall in May 2011, and that the stability of the RSRW decreased.

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Mattress reinforcement is widely used in Japan to improve bearing capacity and reduce differential settlement when constructing superstructures on soft ground. In recent years, the application of mattress reinforcement methods in narrow areas has been required, and the method of determining the optimum mattress width for the loading width has become an important issue in practice. In this paper, loading tests using aluminum bar laminate were conducted to understand the bearing capacity characteristics of mattress-reinforced ground under the conditions of varying the width and thickness of the mattress for a given loading width. Furthermore, the mechanism of bearing capacity of the mattressreinforced ground was discussed by measuring the tensile resistance of the reinforcement and the deformation behavior in the model ground by image analysis. Finally, the bearing capacity of the mattress-reinforced ground was calculated using a new bearing capacity evaluation method that introduces the concept of the reduction factor of the mattress effect into the conventional design method, and the results were compared with those of the model tests.

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To investigate the effect of soil nails in repairing damaged geogrid reinforced soil walls (GRSWs), a series of model shaking table tests on GRSWs was carries out to simulate earthquake damage by the first shaking, repair with soil nails, and the second shaking to estimate seismic stability of the repaired GRSW. The results showed that the seismic resistance of the damaged GRSW was improved by adding soil nails. Effectiveness of adding soil nails in improving the seismic resistance was found to depend on the length of the soil nails and the degree of damage to the GRSW. Soil nails which were longer than geogrids suppressed the formation of vertical shear plane behind the geogrid reinforced zone. Therefore, seismic stability of the damaged GRSW increased by long soil nails.

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In recent years, a lot of railway embankments have been damaged due to severe rainfall. In the case where the restart of the operation of railway is strictly required, the emergency reconstruction works are conducted, and large-scale sandbags are often used in the works. However, the stability and the characteristics of settlement of the embankments have not been studied efficiently. In this study, the rainfall infiltration and cyclic loading tests of re-constructed embankments were performed. From these studies, it was revealed that the stability of the reconstructed embankments was recovered if the support and drainage of the sandbags was sufficient. Furthermore, the stability of the sandbag could be evaluated by considering balance of earth pressure, so the structures of re-constructed embankment using sandbags were analytically examined.

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Trial calculations and field tests were conducted to understand the effect of the arrangement of geogrids on the stability during construction of the geosynthetics-reinforced soil retaining wall. In addition, the authors proposed a back side construction method in which a formwork for constructing rigid facing is proposed from the back side of the reinforced soil embankment, assuming construction in a confined area. The feasibility of the proposed construction through this field test. The results of the trial calculations and field tests showed that stability could be secured with a vertical spacing of up to 0.6 m, which is one layer less than the standard spacing of 0.3 m. Assuming construction from the back without scaffolding, we developed settlement-allowing components as formwork fixing members.

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In this paper, based on the results of tensile tests conducted on collected samples and samples after accelerated exposure testing, a durability assessment equation using an exponential function model for the degradation prediction of geomembranes is constructed and proposed. In 2009 and 2018, a total of 127 samples were collected from landfill sites where geomembranes had been installed for over 20 years. Additionally, for long-term degradation prediction, a portion of the collected samples was subjected to accelerated exposure testing using a metal halide lamp weathering test apparatus. The proposed evaluation equation reports statistically significant results indicating the accurate assessment of the tensile property retention ratio of geomembranes.

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In order to evaluate hydraulic conductivity normal to the plane of non-woven geotextiles under confining pressure, a new thickness-controlled permeability test apparatus was developed. First, permeability tests were conducted for glass beads and PVA sponges to verify the effectiveness of the new test apparatus. Next, permeability tests were performed for non-woven geotextile specimens which were selected considering their non-uniformity of initial condition. Based on test results, it was clear that the hydraulic conductivity normal to the plane of non-woven geotextiles, kV, under confining pressure can be estimated using only void ratio, e. Furthermore, the distribution of kV during compression process was shown.

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Nonwoven geotextiles specimens were selected considering non-uniformity in initial condition, and long-term compression tests for 30 days were conducted under the constant compression stress, p. The range of p was set to be 4–533 kN/m2. Based on test results and the previous results of compression tests under incremental loading, the longterm compression properties of non-woven geotextiles were formulated considering the confidence intervals. Using the results, the e-log p curve in the long-term compression process was shown. And the change in the distribution of void ratio during long-term compression process was also shown.

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The authors have studied geosynthetic basal reinforcement techniques for emergency and rehabilitation roads in the event of disasters. In this paper, the authors report the physical model tests of the geocell-reinforced ground under moving load conditions. The results of model tests of unreinforced and geocell-reinforced ground whose relative density is 50 % are presented, including wheel settlement, horizontal loads acting on the wheels, and vertical loads acting on the model ground. The visualized displacement field of the model grounds by PIV method is also shown. It was revealed that the geocell can reduce the wheel settlement of the foundation by constraining the horizontal deformation of the infilled soil in the moving wheel loads condition.

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Advanced geosynthetic reinforced soil (GRS) structures are widespread in Japanese high-speed railways. High-performance geogrids are commonly employed to meet strict requirements. However, current design practices often rely on simpler in-isolation stiffness, potentially leading to underestimated costs. To showcase the benefits of pullout stiffness, this study tested geogrids using in-isolation and pullout methods at similar displacement rates. Results consistently demonstrated that pullout stiffness surpasses in-isolation factors like confining pressure and geogrid stiffness were also explored, indicating positive effects on pullout stiffness. Prioritizing pullout stiffness can lead to more cost-effective designs and enhanced structural stability.

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Geocell that forms a structure with lateral binding force by confining infill material in the cells can reduce the stress on the subgrade layer. Therefore, it is expected to be used for the reduction of the stress of the load transferred to the road base. However, there are still many factors unknown about the strengthening mechanism. In this study, we conducted a loading test using a ground model made with EPS boards in order to identify the impact of Geocell on the changes to the stress distribution range. After the test, the deformation behavior of the EPS board was measured to determine the stress distribution range and to analyze the effect of Geocell installation on the ground.

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In recent years, the effective utilization of excavated soils and rocks has gained importance. A proposed method for reusing soils containing heavy metals is to underlay geosynthetic materials with adsorption capacity beneath the excavated materials. This study evaluated the adsorption performance of arsenic and lead using batch tests and column tests on non-woven modified geotextile. Factors such as contact time, hydration reaction, compaction effects, and overburden pressure were found to significantly influence the adsorption performance. Comparing with the batch test results with column test results, it can be found that the conventional batch sorption test has a risk of overestimating the adsorption performance.

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There are many different types of materials in geosynthetics. Their functions include reinforcement, drainage, separation, filtration, imperviousness, shape stability, and space reservation, and material test methods exist for each function and type. To evaluate the function of geosynthetics, some test methods have been established in international standards, but some test methods have not been standardized in Japan. This report presents a summary and analysis of domestic and foreign geosynthetics standards and future strategies for domestic standardization.

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This paper presents the implementation of the first application of RRR embankment (Embankment of Reinforced Railroad with Rigid Facing Wall) in the Philippines. This project is one of Official Development Assistance (ODA) project (Special Terms for Economic Partnership’s project), and the RRR-B method as the advanced Japanese technology is applied to the embankment of the main line under the existing expressway, the branching line connecting the depot and the main line, and the embankment around the depot partially. The paper introduces the study considered before construction, reports on the record of implementation using photographs, and provides future improvement and request points.

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The purpose of this study is to confirm the supporting performance of the pillars in the photovoltaic generation base mat construction method by a full-scale experiment and to reflect it in the design. The solar power generation base mat construction method is a construction method that replaces the conventionally used pile foundation and concrete block foundation when installing a solar power generation system on a slope. Through experiments, we were able to confirm the setting of the withstand load by a static load test on the column.

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