In the snowy cold region, a lot of slope surface failure which subjected to freeze-thaw action occurs by melting snow and rainfall at the beginning of spring. As a countermeasure against such collapse, the authors have newly developed a slope stabilizing method using a combination of geocell filled with crushed stone and steel drain pipe, and continue to evaluate the performance by a full-scale experiment. However, among these measurements, it was confirmed that drainage was occurred by rainfall and snowmelt from drainage pipes installed above the groundwater level. In this study, we focused on the drainage pipe installed above the groundwater level in a full-scale experiment at two places, compare in detail the conditions when drainage occur from these pipes.

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Earthquakes tend to cause damage to geogrid reinforced soil wall and appropriate repair method should be decided after the event. This paper focuses on the assessment of seismic stability of geogrid reinforced soil walls using a vertical wall and inclined wall to simulate initial damage. The models were subjected to a stepped sinusoidal wave using a shaking table until full failure occurred. Wall horizontal displacement and shear strain distribution in all models increase with base acceleration and with tilting angle. Slip lines observed in the backfill of the model agree with two-wedge method and slip lines obtained using mobilized pullout resistances are almost similar to those observed in the experiments.

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This study was investigated about the influence of slurry density on strength and deformation property of liquefied stabilized soil (LSS) reinforced with fiber material cured in the laboratory and at the field. The LSS was prepared in the slurry density of 1.280 g/cm3 as criterion and slurry density reduced 5 % from 1.280 g/cm3 mixed with amounts of fiber material, 0, 10 kg/m3, respectively. A series of Consolidated-Undrained triaxial compression tests (CUB tests) were performed on both LSS specimens prepared in the laboratory and trimmed LSS samples retrieved from a model ground by block sampling at curing time of 28 and 56 days, respectively. Based on test results, it is shown that the strength and stiffness of LSS and LSS reinforced with fiber material by low slurry density decrease compared to that prepared by appropriate slurry density.

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In order to confirm the effect of the opening size and laying position of geogrid on the base course, we conducted a box shear test. In the box shear test, two types of geogrids, TX160 and SS2, were used for the case which the distance between the laying position and the shear plane was 0 cm, 3 cm, 5 cm, and 7 cm. Although the restraining effect of TX 160 was demonstrated to about 5 cm from the laying position, it was confirmed that the restraining effect of SS 2 was hardly demonstrated in the range of 3 cm or more from the laying position. As a result, it was found that the range in which the constraining effect is exhibited varies depending on the opening size of the geogrid.

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To investigate the influence of the potential mechanical properties of backfill materials on geogrid reinforcing effects, a series of plane strain compression tests were performed. Differences of reinforcement effects on two types of gravelly soils that have similar grain distributions were investigated in this study. As a result, it was confirmed that the strength-deformation characteristics of compacted gravelly soils did not match even if the gravel soils have the same grains and dry density, and the difference was further increased by the geogrid reinforcing. The reinforcing effect is affected to the dilatancy behavior of the backfill materials. Therefore, the results obtained in the present study indicate that selection of backfill material and well soil compaction leads to construction of soil structure with required stability.

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In order to increase the resistance of river dike against seepage failure and overtopping erosion during flood, we proposed covering the river dike with the air-permeable water-proof geosynthetics as a countermeasure. In this paper, the waterproof performance of the joint part of geosynthetics was evaluated based on the laboratory experiment. The joint part of the geosynthetics can be a weak point during overtopping because it may allow some water infiltrate into the dike and erosion occurs. From the experiment, it was found that the geosynthetics prevented the overtopping water leakage completely when the joint was glued.

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Compound disaster due to earthquake and flood occurred like Fukui Earthquake in 1948 and Kumamoto Earthquake in 2016. However, there are not countermeasure for compound disaster due to earthquake and flood, which are considered separately in planning of river levee. In the present study, a new experimental channel for the compound disaster was used to examine the resistance of reinforced levees like laminar drain reinforced (LDR) levee against earthquake and overflow. The results indicate that the crest settlement of the LDR levee was smaller than those of other reinforcements mainly due to the prevention to increase excess pore water pressure. It should be noted that the LDR levee with cracks and gaps due to earthquake can maintain the cross-sectional shape of the levee under overflow, showing the high performance of the LDR levee against compound disasters.

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Impermeable sheet (LLDPE, t =3mm or more) is one of the impermeable materials used in the revetment of the leachate-controlled type coastal waste disposal site. By assuming that the impermeable sheet (with double-sided protection mats) is laid directly on the stone materials of about 100kg/piece (grain size of about 40cm, stone angle of 60° or more), we verified the standard of the protection mats to ensure the quality required for the impermeable sheet. In this research, we first investigated the angle shape of stone materials. Furthermore, indoor experiments were carried out to reproduce the process that the impermeable sheet, to be laid directly over the slope formed by the above-mentioned stone materials, was dragged downwards parallel to slope by the crushed stones load and then loaded by the landfill load. As a result, by placing the woven fabric in the protection mat with long-fiber nonwoven fabric (weight per unit area of 1500g/m2), it was confirmed that the impermeable sheet can withstand the vertical load up to 170kPa.

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In bends of pressure pipelines such as agricultural pipelines, unbalanced force called thrust force acts depending on the internal pressure and the bending angle. Although thrust blocks made of concrete are generally placed on the bends to prevent bends from moving, the heavy thrust blocks cause separation of joints during earthquake. In this paper, lateral loading experiments with a lightweight thrust restraint method using gravel and geogrids were conducted in dry sand. As a result, it was revealed that the dimension of the thrust restraint clearly affects the additional resistance in the large displacement. In addition, the shear plane on the passive area could be approximated by a wedge shape.

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The 2011 off the pacific coast of Tohoku earthquake (Mw=9.0) caused great damage to geotechnical structures in the vicinity of the eastern coasts. In contrast, many of reinforced soil walls constructed along the coast were less damaged by the tsunami. In this study, assuming that tsunami overflow force does not have effect on reinforced soil wall, we conducted a model flume test to evaluate the behavior of a reinforced soil wall under strong water flow and water pressure induced by tsunami. It was found that the reinforced soil wall does not have large deformation unless there are some opening in the front panels and the flow out of backfill soils. Furthermore, we present the consideration of seismic evaluation of reinforced soil wall based on the result of experiments.

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In recent years, the usefulness of soil nailing method is reported as earthquake resistance measures of existing embankment. Past studies on the use of small diameter reinforcement materials as soil nailing method in snowy cold environment are proceeding. However, from the new evaluation results of the probability of earthquake occurrence, there is a possibility that the momentum of seismic reinforcement in soil structure in snowy cold environment also increases. In this study, we are conducting observation of the dynamics in cold environments by constructing soil nailing method using large diameter reinforcing material (i.e. dowelling) on test embankment, and conducting test construction of surface work using geogrid. From the results of the pull-out test, it was confirmed that although the resistance to withdrawal had decreased after freeze-thawing, there was no influence on the current design.

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The soil nailing is a typical soil reinforcement method where grouted steel bars that have not been prestressed are arranged in slopes and, thereby reinforces cut and natural slopes. This method is generally applied together with slope protection work. A snowy and cold area like Hokkaido has some reports on damage to the resulting work because frost heaving force acts mainly on the slope. Of them, certain reports show the risk of deteriorating the soundness. In this research, we have minutely worked on how to reduce frost heaving damage to the work by using plastic facing panel featuring relatively small rigidity with heat insulators or continuous fiber reinforced soil.

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Currently, the reinforced earthwork method using band steel reinforcement which is most widely adopted in Japan has many practical achievements even in snowy cold areas such as Hokkaido. However, several cases of deformation due to the frozen embankment have been reported. On the other hand, the detailed mechanism of the deformation of the steel reinforced earth wall has not been clarified. In this study, we constructed Terre-Arrme reinforced soil walls with two embankment materials, frozen and nonfrozen. As a result, a large tensile force and a local strain occurred when the soil behind the wall panel was frozen under the condition that tension force was applied to the reinforcing material installed in the embankment with high frostability material.

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In snowy cold region, many failures of slope occur in beginning of spring. In generally, slope protection works called gabion baskets are widely used against this problem. However, most of them deform or collapse after many years from construction. In this study, we constructed the slope of full scale embankments applied a new slope stabilizing method using geocells with flexibility. On the basis of the freezing and thawing behavior as well as the water level in the embankment, we investigated the various specifications of this method such as the size of geocell and geomaterials in geocell.

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To realize both measures against frost heave and vegetation, a reinforced soil wall is developed. It consists of geocell working as a wall surface material and geogrid used as a reinforcing material. In this research, we have adopted a banking material featuring a wide range of grain sizes in order to construct such a wall and to measure its freezing and melting behavior as well as earth pressure and strains acting on the underground geogrid. Moreover, in consideration of the measurement results and to reduce any frozen banking material load put on the geogrid and wall surface deformation resulting from freezing and melting, we have improved the reinforced soil wall by changing the geocell layout and verified its effects.

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While a type of back-to-back geotextile reinforced soil wall is often applied at approach to the abutment, seismic behavior and failure mode of the wall are not clear. Authors carried out the tilting and shaking model tests for the back-to-back wall and the normal wall in which active earth pressure acts on the behind of reinforced area. The results of the model tests are as follows; 1) residual deformation of the facing of the back-to-back wall is small compared with the normal wall, 2) during the shaking, the both sides of facing forward deforms due to compression of reinforced area, and the shear strain increases in reinforced area at the failure. This paper reports the seismic behavior, failure mode and seismic performance of the back-to-back wall obtained from the model tests.

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In embankment of railway, faced concrete has not been applied to embankment in general because of its poor followability to settling and difficult to eliminate infiltration water. However, in Shinkansen, sinking becomes limited by following the provisions at the time of embankment construction, and it is possible to reduce the infiltration water by adopting a structure combining a concrete roadbed and faced concrete. In this research, in order to apply the faced concrete to the reinforced embankment with a steep gradient 1: 1.2 than before, the peeling test of the slope surface was carried out and examined and evaluated..

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This paper reports the reason of the adaptation and the proceeding of the construction of a gabion soil wall structurally continued with reinforcement applied for high embankment on the sloped ground in expressway construction, and also reports the influence of the damage of the reinforcement due to the rolling compaction of the back-filling material, and the results of observations during construction and after construction. This time, we adopted this reinforced soil wall with gabion as the wall material, expecting the drainage effect of groundwater inside the reinforced soil wall backside and embankment. In construction, it was difficult to hold the shape of the gabion to be used as a wall material. So we solved this problem by using a frame for holding the shape. Regarding the damage of the reinforcing material, the degree of damage was suppressed by installing a nonwoven fabric on the upper surface of the reinforcing material. And we got the results of field observation about the displacement of the wall material was sufficiently satisfying the specified construction control value.

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The impact damage resistance characteristics of geosynthetics used as soil reinforcements are affected by embankment fills and compaction strengths. When on-site generated soils that can contain large rocks, such as tunnel muck, and large-scale rollers are used to induce sustainable and efficient construction projects, the geosynthetics may be severely damaged because their material safety factors are defined using standard fills and rollers. Since long-term damage resistance characteristics of severely damaged geosynthetics are still unknown, a creep test was conducted to determine the effect of the severe damages.

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In this study, we compared the stability of embankments constructed using a composite ground improvement (CGI) technique, we developed and the conventional deep mixing method with an improved ratio of 30%. they were subjected to dynamic centrifugal model test to assess their resistance to level-2 seismic motion. As a result, cracking was found on the crown of the embankment constructed using the conventional method and settlement of the surface was observed. By contrast, cracking and settlement were undetected in the crown of the embankment constructed using the CGI technique. In addition, no lateral flow of the embankment into the adjacent ground was detected. These results indicated embankments built using the CGI technique can withstand level-2 seismic motion.

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There are cases where heavy rain caused some deformations in reinforced soil walls. Probabilistic risk evaluation during rainfall has not been carried out so far. Therefore, in this study, reliability analysis of reinforced soil wall using rain hazard was carried out, which were obtained using the latest AMeDAS data of daily precipitation in Tokyo and Kochi. Fragility of the reinforced soil wall was determined by carrying out the Monte Carlo Carlo simulation. Using the obtained rain hazard and fragility, damage frequency curve of reinforced soil wall during rainfall was obtained. From the obtained damage frequency curve, it was possible to quantitatively show that the probability of damaging the reinforced soil wall increases as the ground water level rises.

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In recent years, the usefulness of surface-wave method has been reported as a method for efficiently evaluation of reinforcing soil walls. It is necessary to evaluation the relevance between the deformation amount of reinforcing soil walls and S-wave velocity, VS from the surface-wave method in the future in order to apply the surface-wave method as the soundness evaluation method of the reinforced soil walls. Therefore, in this study, the surface-wave method, wall panel tilt angle measurement, reinforcement material extraction test, boring survey were performed on geosynthetics reinforced soil wall where deformation exceeding construction control value occurred. In addition, we examined the relevance of various in situ tests results. As a result, when the wall panel tilt angle was large, VS did not monotonically increase with the increase in depth but locally decreased. In other words, we have found the possibility to evaluate the soundness of reinforced soil wall by using VS that can be obtained from the surface-wave method.

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Under the two successive gigantic earthquakes which struck the Kumamoto area of Japan in 2016, damaged was the local EPS road founded on the active fault. Fortunately, only part of the embankment collapsed and it did not fail completely. Therefore, the road surface was remediated temporarily and was maintained as it was for the opening of traffic. Most importantly, the collapsed EPS road was put into practical use as a temporary road for the everyday life of local residents. Based upon the investigation of why the road was not completely demolished, future issues to be considered not only at the local government level but also at engineering institutions are disclosed for preparation for future great earthquakes.

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The back-fill of abutment was eroded and a road collapse occurred due to Hokkaido heavy rain disaster in 2016. In this study, the open channel experiment was conducted to observe the basic erosion process of the back fill of the abutment during flowing water condition. In addition, From the results of the model test, the erosion of the embankment advanced at the boundary of the structure of the abutment and the embankment. In the two countermeasures using the geosynthetics material adopted in this experiment, no collapse of the road surface occurred.

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In this study, centrifugal model experiments and dynamic response analysis were conducted for elucidating the effectiveness of seismic retrofitting method of aged pond due to joint use of masonry block and reinforced earthwork method commonly used in the forest of the law did. In the model experiments, we investigated the dynamic behavior of the cut-off body. In the analysis by the finite element method, we investigated the position of the slip surface obtained in the experiment and the vibration characteristic of the settlement amount of the cut-off wall and clarified the effect of the reinforced portion. As a result, it was found that the stability of the cut-off wall method front part is improved by the masonry block and the reinforcing net on the back side, so that destruction of the upper part of the cut-off wall is suppressed, and it is found that it is effective for deterring the cut-off wall deformation.

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To consider the stability of heavy equipment such as crawler crane at construction work, this study investigates the effects of geogrid reinforcing on the bearing capacity behaviors of strip footing under eccentric loading. A series of laboratory model loading tests on rigid shallow foundation that was simulated a crawler of mobile crane were performed. In the present study, a) Changing of load-deformation relations of the strip footing and failure mode of the model ground due to eccentric loading and b) the effects of geogrid reinforcing on the bearing capacity behavior were investigated. As the results of model loading tests, the ultimate stress of the footing significantly reduces due to eccentric load concerned with changing failure mode of the ground. Moreover, it was found that the ultimate strength of the footing under eccentric loading can be increase by arranged a geogrid layer in the ground.

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For the purpose to evaluate the effects of dimension and rigidity of plastic bearing plate for soil nailing on the shearing resistance, a series of direct shear tests were conducted on reinforced slope models that were made in a shear box. Using plastic bearing plates with different sizes and stiffness as model slope protection works, the experiment results showed that the bearing pressure induced by plates applied as vertical pressure to the soil block that lead to increase in shear resistance, and that the shear resistance increased with the increase in covering ratio and rigidity of bearing plate. Also, a linkage frame connecting nail heads was found effective due to the increase in covering ratio and the overall stiffness of the slope works.

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The small-scaled model tests have been carried out at laboratory to improve the stability of EPS embankments undergoing such gigantic earthquakes as Tohoku Great earthquake in 2011 and Kumamoto earthquake in 2016. In particular, an attempt was made to ensure whether the newly developed Joint Metal Binder (JMB) for enabling uniformity of each EPS block for embankments is eligible for attaining the purpose stated above. It is found out not only from lab. Tests but also from numerical analysis that the new JMB is available for increasing the stability of EPS embankments even under gigantic earthquakes.

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In order to study the effects of combined use of EPS (block of expanded polystyrene) and geogrid to improve seismic stability of a retaining wall, a series of 1g shaking table tests are conducted on a reduced-scale model of a cantilever type retaining wall and its backfill soil. It could be observed from experiment results that the base sliding and tilting of the wall can be further reduced by replacing partly the backfill soil with blocks of EPS in combination with the use of the middle-height geogrid. Moreover, the relative settlement of the backfill soil at the interface with the wall could be reduced by the combined use of EPS and geogrid. The resultant normal force and rotational moment acting on the wall from the backfill soil during excitation also became small for the reinforced wall with both EPS and geogrid.

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