This report is a review of utilization of geosynthetics for soft ground. Late Toyotoshi YAMANOUCHI ( Emeritus Prof. Kyushu University) is well-known as a pioneer who had introduced geosynthetics to Japan as materials for earth-reinforcement . Among many achievements, he proposed the Multiple-Sandwich Method as a new method for constructing embankment with soft clay. The author worked on the utilization of the materials at Yamanouchi’s laboratory. This paper describes the author’s experimental experiences for earth-reinforcement in several field works during a half of century at Kyushu , Yamaguchi and Saga Universities.

View full abstract

Impermeable sheet (LLDPE, t =3mm or more) is used in constructing a controlled type coastal waste disposal site with riprap revetment or composite revetment. As a laying method with manpower saving, there is a mechanical sheet laying method, which was originally developed for laying sand prevent sheet. In this paper, this construction method is applied to laying of a impermeable sheet, and good construction results are obtained. In addition, we report the results of laying an impermeable sheet with a high penetration resistance protection mat placed on the lower surface.

View full abstract

In this study, the author took both exposed and buried sheet samples from a landfill after more than 20 years from the time of construction, evaluated the durability and clarified the factors of degradation of geomembrane based on data from microscopy, tensile test, chemical analysis and so on. The result showed that there was certainly some decrease in value in each direction and a big difference in data between the south-facing sheet and the virgin sheet. The buried sheet sample was not degraded compared to exposed sheet. Even in the same direction, surface cracks occurred more on the exposed sheet than on the buried sheet. Moreover, based on the test results, we considered that the total amount of solar radiation is a major cause of degradation.

View full abstract

The barrier performance of the geomembranes against benzene, toluene, xylene, fluorobenzene, trichloroethylene and tetrachloroethylene which are typical organic compounds was evaluated from the continuous batch tests. The process that the organic compounds diffuse into the geomembranes was modeled using the diffusion coefficient and the distribution coefficient, and those parameters were estimated by the model fitting on the experimental results. As the results, the distribution coefficients that mean the adsorbability to the surface of the geomembranes became higher in the order of HDPE, LDPE, and PVC sheet. Therefore, the HDPE sheet exhibited a superior barrier performance. In contrast, the effects of the geomembrane’s thickness on the distribution coefficients were minor. The diffusion coefficient that mean the diffusivity into the geomembranes had 10^-14 to 10^-12 m²/s for any geomembranes according to the results of the continuous batch tests. The diffusion coefficient was increased with the thickness of the geomembrane.

View full abstract

The non-woven fabric is generally used as protection mat in landfills. The non-woven fabric has a laminated structure of fibers, so there is peeling risk between layers of it and peeling phenomena has been reported at the actual landfill site. However, we have no quality control standards to confirm the peel strength. From these points of view, we have examined the method to evaluate peeling strength of the protection non-woven fabric as a quality control test, and confirmed that it is possible by the shear peeling test that used a loop fastener and adhesive tape. Therefore, a slope walking test was conducted to reproduce the actual peeling phenomenon. Then, we confirmed the occurrence of peeling phenomenon and confirmed that it could be quantitatively evaluated by the anti-slip test method for safety shoes and work shoes. In this paper, we report on the evaluation test details and its results of the peeling strength by slope walking tests and anti-slip tests.

View full abstract

This paper proposes the estimation method of seismic fragility curve of unreinforced and reinforced embankment in probabilistic risk assessment. Strong earthquake motion records with seismic intensity 5.5 or more from 1997 to September 2018 are collected as earthquake action and a strong earthquake motion database is made with an index of Arias Intensity. Using this strong motion data and unreinforced and reinforced embankment model with different height according to the railway standard, the fragility curve estimation equation is proposed from the numerical results by the quasi-Monte Carlo method using Newmark method.

View full abstract

By using the method of probalilistic risk asssessment for Geotexile Reinforced soil wall affected by rain fall, this paper shows the damage probability of Multi-anchored Reinforced Soil Wall, which is a type of reinforced soil wall other than Geotexile Reinforced soil wall. As results, we revealed that it is possible to apply the method to the other type of reinforced soil wall and damage probability of the reinforced soil wall which has high allowance of factor of safty is relatively low.

View full abstract

While reinforced soil walls have been widely adopted in practice, some of these structures show unexpected deformation due to big earthquake or heavy rainfall. This paper reports a case study of a collapsed reinforced soil wall due to heavy rainfall. Also, this paper proposes a method of probabilistic risk assessment for the reinforced soil walls subjected to rainfall. The risk of the reinforced soil wall subjected to rainfall is evaluated using a rainfall hazard curve and fragility curve of the reinforced soil walls. The proposed method can estimate the probabilistic performance of reinforced soil walls considering the occurrence probability of rainfall and the variation of soil strength.

View full abstract

This study proposes a roadbed improvement procedure using Geosynthetics for road pavement in which the repair of road surface is repeated at significant frequency due to early deterioration. While the deteriorated road is generally repaired by cutting and overlay of road surface, it is not established the reinforced procedure for roadbed material by Geosynthetics. In order to prolong the life of road pavement, authors propose to reinforce the roadbed material such as asphalt mixture and crushed stone by using Geosynthetics as a new improvement procedure. This paper reports the strength and deformation characteristics of roadbed material and geosynthetics composite structure obtained from the bending test for the geogrid reinforced asphalt mixture and compression test for the geocell confined crushed stone.

View full abstract

Although the maintenance work of pavement is often planned based on MCI and FWD data, the repeated damages of pavement are observed at many places. In order to avoid repeated maintenance works of pavement, the condition of earthfill structure was evaluated by an easy logging technique in this study. Based on the investigated result, the test repair work was planned and carried out for the base course by using several replacement materials, such as crushed stones, geocells with crushed stones, bitumen stabilized material, and bitumen stabilized material with geogrids. In order to confirm the effect of base course improvement, the surface wave exploration and Falling Weight Deflectometer tests were carried out before and after the test construction. The strain distribution of the base course was also monitored by using the optical fiber sensor inserted into the geogrid. This paper summarizes the test construction and the effect of base course improvement.

View full abstract

In this study, cyclic loading tests simulating traffic loads were conducted to verify the reinforcement mechanism of geogrid. Two types of geogrid with rectangular or triangular aperture with different stiffness and two types of granular materials with grain size ranging from, 5-10mm, 10-20mm, for 50cm thick subgrade layer and 20cm thick base course layer respectively were selected. In addition, to find the confinement zone of geogrid, the medium scale direct shear tests were carried out. It was found that vertical deformations of pavement aggregate were reduced by both types of geogrid significantly than those in no-reinforced case. Deformation of aggregate was more when the geogrid was laid at subgrade-base course interface than when it was arranged in the base course layer. The achieved results have proven the mechanical interlocking of material within geogrid sheets. The confinement zone was also estimated through a series of direct shear tests. The test results revealed that the placement of geogrid in the location of 3cm-5cm above the boundary between the subgrade and the base course exhibited better performance due to proper confinement of material movement than other cases.

View full abstract

Laboratory tests were conducted to confirm the differences in tensile strength characteristic depending on the mesh shape of the geogrid. It was confirmed that the triaxial grogrid exhibits tensile rigidity evenly in all directions compared to the conventional biaxial geogrid. In addition, on-site test construction was conducted to confirm the effect of roadbed reinforcement due to differences in geogrid type, subbase thickness, and lying position. It was confirmed that the triaxial geogrid has the effect of reinforcing the granular roadbed. And it is also confirmed that the reinforcement effect is higher as the roadbed thickness is thinner and the elastic modulus of the roadbed layer is improved by about two times compared to the one that is not laid. From this evaluation, we proposed a design index that incorporates the effects of the triaxial geogrid.

View full abstract

In snowy cold region, as an emergency restoration and countermeasure for collapse of the surface layer of slope to the freezing and thawing action, a slope protection work called special gabion baskets is widely used. In this study, we devised a new type slope protection work consisting of two geocell layers which has the function of erosion resistance and water permeability of a geocell filled with crushed stone, and which can be vegetated, as a substitute for special gabion baskets, and conducted field observation by a full scale experiment. In this experiment, the measurement on the sliding force of the geocell layer placed on the slope was also carried out, and the labor saving by the reduction of the long anchor bar driven on the slope was also examined.

View full abstract

Snowy cold regions suffer the failure of many natural, cut, and bank slopes at the beginning of spring. As temporary and recovery measures against this problem, slope protection works called gabion baskets are widely used. In recent years, there have been an increasing number of cases in which a slope protection method is adopted by filling a geocell with crushed stone instead of using the gabion baskets, when there are restrictions on the construction period. However, since forming a stable vegetation base on crushed stone is difficult, there is no established greening method for this slope protection method. Therefore, in this study, we tried to green on crushed stones by using a growth material injection method which enables mixing and injection of seeds, water, and growth material into a baglike mat, and prevent flooding of the vegetation base and prepare a favorable growth environment for plants.

View full abstract

In recent years, vegetation work has been preferentially adopted as slope protection work, in consideration of ecosystems and the natural environment. Of the various types of vegetation works, an erosion control blanket protects the slope surface from rainfall until the plants grow, enabling maintenance of a soil environment suitable for vegetation. In this study, in order to clarify the anti-erosion effect of the erosion control blanket with plant seed, an erosion resistance test method using a soil specimen in which the erosion control blanket is laid was carried out. An erosion test apparatus using a commercially available sprayer was manufactured. After the erosion resistance test, X-ray CT scans were performed to determine the depth of erosion. In addition, X-ray CT scans were also used to observe how the specimens eroded.

View full abstract

For drainage pipes with slits installed in the soil, it is generally known that drainage from the pipe will not occur unless the soil around the pipe approaches saturation and the pore pressure becomes positive. However, it has been found that in a slope stabilizing method using a geocell filled with crushed stones and a steel drainage pipe with slits, drainage from the pipe occurs with rainfall and snow melting, even though the pipe is installed above the groundwater level. Therefore, in this study, two types model tests were carried out focusing on geocell layers filled with crushed stones placed on the slope surface, and the role of geocell layers and the conditions for occurring drainage from pipes were examined in detail.

View full abstract

To realize both measures against frost heave and vegetation, a reinforced soil wall which consists of geocell working as a wall surface material and geogrid working as a reinforcing material is developed. It is possible to prevent the maximum freezing depth from reaching the geogrid by changing the number of geocell in order to avoid a local strain on the geogrid when banking material in reinforced soil walls freezes. In this research, we examined the function between the outside air temperature and the surface temperature which is required to estimate the maximum freezing depth in the 2D heat conduction analysis software. Using this, we examined the thickness of wall surface (the number of geocell) that can cover the maximum freezing depth corresponding to the freezing index of constructed region.

View full abstract

The Liquefied Stabilized Soil (LSS) is easy to occur brittle failure with the increase of cement content and it was found that the addition of fiber content might improve the brittle property of the LSS. In this study, a series of triaxial compression tests were conducted with LSS specimens prepared in different slurry densities of 1.216, 1.280 g/cm³, cement content of 80, 100 kg/m³ and the fiber content of 0, 10 kg/m³ . Based on the results of the triaxial test, the influence of changing in slurry density, as well as added amount of fiber on the triaxial shear properties of the LSS with different cement contents, is discussed.

View full abstract

Few studies have been conducted regarding the effect of multiple reinforcement stiffness along the geosynthetics reinforced soil wall (GRSW) height. This type of reinforcement arrangement can be used for reduction in the total construction cost of GRSW structures maintaining an adequate seismic stability. In order to investigate its behaviour, a series of shaking table tests was conducted on segmental geogrid reinforced soil wall reinforced with two different reinforcement stiffness in different location along the wall height. Results showed that shear deformation in the backfill was strongly dependent on the location of weak geogrid and despite the application of different reinforcement stiffness along the wall height, the failure surfaces remained almost the same.

View full abstract

It is quite difficult for nonwoven filters to suppress clogging while achieving sufficient filtering characteristics for fine fraction suspended in turbid water. But filtering characteristics of whole filter layer can be improved without clogging under the specific sites, such as Interim Storage Facilities (ISF) for removed soil, where the period and amount of turbid water supplied to filter layer are limited and the drainage process can be continued for a certain period even after stopping the supply of turbid water. In this study, we experimentally made a nonwoven and 5 types of nonwoven-based geocomposites to carry out turbid water permeability tests. In addition, cumulative capture rates of fine fraction were estimated in case that nonwoven-based geocomposites were partially applied as filers for drainage pipes in ISF for removed soil.

View full abstract

In previous researches, it was found that reinforced earth wall composed of anchored gabions (hereafter referred to as anchored gabion wall) has higher stiffness than steel flat panel wall and its reinforced soil has apparent cohesion. However, the tolerance of anchored gabion wall against seismicity has not yet been evaluated. Thus shaking tests on lab scale model of multiple stacked anchored gabions were conducted. In conclusion, anchored gabion wall showed its highly tough properties.

View full abstract

This paper presents the results of a full-scale shaking table experiment conducted to evaluate the earthquake resistance of a new type joint metal for the civil engineering method (EDO-EPS method) using polystyrene foam. At the same time, considering the influence of rocking of EPS embankment, which is a top heavy structure, we are studying countermeasures to reduce the deformation caused by this. As a result of the test, it was confirmed that the new type this can suppress the deformation compared to the old type metal joint. In addition, it was found that deformation due to rocking can be reduced by arranging the metal joints and providing steel plates in the floor slab.

View full abstract

In order to study the effects of combined use of EPS (block of expanded polystyrene), geogrid, and soil nailing to improve seismic stability of a bridge abutment, a series of 1g shaking table tests are conducted on a reduced-scale model of the abutment with girder and its backfill soil. It could be observed from experiment results that the horizontal displacement and tilting of the abutment and the relative settlement of the backfill soil at the interface with the abutment can be effectively reduced by setting the geogrid at the upper level of backfill and blocks of EPS at the middle level of backfill respectively. Moreover, the combination of soil nailing, geogrid and EPS can improve the seismic stability of abutment.

View full abstract

After the recent big earthquakes, it is an urgent task to improve the aseismatic performance of block retaining walls. However, it is difficult to reconstruct a new aseismatic retaining wall and to install aseismatic reinforcements because of high-cost and small space between structures, so simple and low-cost reinforcing methods are required. In this study, we carried out a series of shaking table tests of the model block retaining walls to elucidate their dynamic behaviors and deformation characteristics during sine wave shaking. The soil nailing methods, nailing with top plates and vertical soil nailing methods were applied for the block retaining walls. Deformations of blocks and embankment were measured after the shaking table tests until the block retaining walls had collapsed. As a result, the soil nailing method was effective to improve the aseismatic performance of the block retaining walls, also nailing with top plates prevented from dropping the blocks. The vertical soil nailing method prevented from the top block collapse.

View full abstract

In this paper, a case study on estimating the stability of a large GRRW during the construction by means of observational method is in detail described. The embankment having the total height of 45m (n.b., 25m thick embankment on 20m high GRRW) exhibited substantially large wall deformation when the lower part of GRRW was just completed. Accordingly, a countermeasure by using a series of anchored concrete panels on the deformed portion of the wall was adopted. As a result, is was observed that the deformation of the embankment on the GRRW was successfully restrained by showing no sign of any harmful tension force in the geotextile. The tension force of the anchors developed was slightly lower than that of the design value, suggesting the effectiveness of this deformation restrained method.

View full abstract

In the design of geosynthetic reinforced wall (GRW) using geotextiles, countermeasures against possible liquefaction of the foundation are usually considered beforehand. In this paper, however, a new concept of design in which ground displacement in the event of liquefaction due to level-two earthquakes is considered without any ground improvement in the foundation. The designed facility was an approximately 7m high tsunami seawall behind the revetment, which was constructed to prevent flood due to tsunami and tidal wave bearing Nankai megathrust earthquakes in mind. In this paper, at first, we set the allowable inclination angle of the 1m-thick concrete slab placed underneath the GRW. Second, we predicted the inclined angle of the base slab due to level-2 earthquake by means of 2D effective stress analysis using program “FLIP”. Moreover, in this numerical simulation, we designed the deck as well as the arrangement of geotextiles.

View full abstract

There is still a need to investigate effective methods of improving bearing capacity on soft grounds in Japan as constructions on soft soils are gradually increasing especially in urban areas. Improvement by substituting crushed stones or crushed gravels is widely used for retaining walls and box culverts, however large excavation area and surplus soil management remain an issue. To solve these issues and further reduce labor work, it is proposed to improve supporting ground by using geocells, which have been already widely employed as a roadbed improvement. A first series of full-scale foundation load tests have been performed to confirm the ease of construction, the effects on bearing capacity as well as to investigate the effects of geocell type and geocell mattress dimensions. Test results could confirm a significant improvement of bearing capacity by using geocells, while differences observed between the two types of geocells used were relatively small.

View full abstract

This study was intended to clarify the compressive property of soils mixed with deformable particles. Generally, in the case of soil mixed with deformable particles such as rubber, it is thought that two more compression components, one is compression of the deformable particle themselves and the other is the following reduction of pore space, are added to the ordinary volumetric compression. Therefore, a series of one-dimensional compression tests was executed using rubber and aluminum tips to estimate these compression components, then the calculation method of these compression amount was examined from a geometrical viewpoint. As a result, it was found that each compression components of the mixture can be predicted almost well, only when the specimen is in the densest state and there is no disordered movement of the skeletal particles.

View full abstract

This study focuses on the structural conditions of geogrid that affects the reinforcing effects of sand. A series of plane strain compression tests were performed to investigate the influence of connection strength of geogrid between strand and rib on the strength-deformation properties of sand. The connection strength is a factor that greatly influences the reinforcing effect, and the influence becomes stronger as the aperture shape of geogrid increases. In order to improve reinforcing effects efficiently, therefore, it is important not only maintain the high rupture strength and surface friction of the strands but also sufficient connection strength of geogrid.

View full abstract