However the practical uses of Geosynthetics are very diverse, the author has investigated, studied and developed on Crest-reinforcement of highway embankments, Erosion-limitation of earth banks and Unification of Up-cycle Block up to now. This paper introduces the summaries on the above each research subject and shows the lessons obtained and future views on research and development on Geosynthetics.
We developed the multi-layer structure reinforcement geosynthetics for pavement. The reinforcement geosynthetics has a structure bonded in claf to the non-woven of the unit weight lower than usual. In this study, laboratory loading test was carried out used of reinforcement nonwoven. Laboratory test was repeated loading by using a roller compactor testing machine. The state of the reinforcement geosynthetics after an examination was evaluated using 3 method (visual evaluation, breakage rate evaluation using a digital camera and survival rate evaluation using silica sand). These results were compared with the non-woven fabric of conventional products (unit volume mass of 300g/m2 or more). In addition, the water flow capacity in their plane test was also performed in laboratory.
This paper reports the results of field observation and stability assessment for the geotextile-reinforced soil wall which has a double facing system with a vertical layer to absorb the deformation between the facing concrete panels and reinforced backfill during the soil compaction. In the construction of the wall, it was used sandy soil to compact the soil enough, and compressive settlement of embankment and strain of geotextile were measured during and after construction to evaluate the stability of the wall. As the results of the field observation, the compressive strain of the embankment and tensile force of geotextile were sufficiently small. This paper shows the results of evaluation of appropriateness of construction and stability of the wall based on the field observation.
Due to the combination of strong earthquakes and heavy rains, a large number of embankments and existing slopes recently collapsed so that the stability and eventual reinforcement of such earth structures are becoming a major concern. On the other hand, in particular for existing slopes, reinforcement usually become costly due to poor working conditions on inclined environments or troublesome due to limited space available for storage or construction. Therefore a new system of slope reinforcement has been developed with emphasis on the ease of construction and cost-effectiveness. The system consists in combining light weight geocells that provide high workability and soil nails that ensure high stability against earthquakes and heavy rains. In this paper are presented a tentative design approach for this new system along with related experimental results including full scale construction tests, as well as examples of actual constructions.
The large size geotextile sandbags filled with dredged soil are buried along the shore line to protect sea shore erosion. One of the geotextile sandbags at the Ooida coast in Miyazaki city was broken by high waves of the typhoon in 2014. Ministry of Land, Infrastructure, Transport and Tourism (MLIT) investigated the breakage mechanism of the geotextile sandbag. The reason of the breakage was that a concrete brock under the sandbag penetrated the geotextile. In this study, a series of the model tests were carried out to elucidate the breakage mechanism of geotextile sandbag by bending sandbags.
In this paper, reinforcing effect on mixing of a small amount of polymeric fiber in a gravelly soil was investigated by performing a series of laboratory tests including triaxial compression tests. Discrete and flexible linear vinylon fibers that have 0.5 mm in diameter and 30 mm in length were selected in the present study. Strength and deformation property of the fiber-reinforced gravelly soil was compared with the ones of unreinforced gravely soil. The results of triaxial compression tests show that the addition of short fiber in gravelly soil leads increase in peak stress with a slight decrease in volume dilatation behavior. The value of internal friction angle of the gravelly soil can be increase effectively by mixing discrete and flexible short fiber.
Deformation behavior and bearing capacity of geogrid-reinforced sand were investigated through experimental study. Series of cyclic and monotonic loading tests were performed by using a large container, a rectangular footing and two geogrid types: triangular and biaxial. Footing orientation was considered as a parameter to examine the directional confinement effect of the geogrid. Test results showed that this effect was obvious on the development of permanent deformation and on the ultimate bearing capacity of reinforced sand. However, this influence became smaller on the ultimate bearing capacity if a stiffer geogrid was used for reinforcement. Significant reduction in permanent deformation and beneficial improvement in bearing capacity were observed in all geogrid-reinforced tests.
Most soil structures reinforced with geosynthetics have been designed by stability analysis as circular slip surface method. It is difficult to evaluate directly the deformation and stiffness of soil and reinforcement material by the stability analysis. This paper proposes a design procedure which creates the collapse modes similar with conventional stability analysis, and which considers the deformation and stiffness of materials by using FEM, and applies the design procedure to static and dynamic problems of stability of slope, earth pressure against retaining wall, and of bearing capacity reinforced with geosynthetics.
Design of embankment constructed on soft ground has been conducted considering with the improved soil strength due to reinforcement use or consolidation. From a view point of construction, a practical safety factor includes some safety margin to adopt geotechnical materials satisfied with design strength. Geomaterial properties have highly variable so that the design parameter in safe side has been often adopted in practice. This paper describes the safety margin defined by a difference of safety factors in design and construction. This paper also reports the embankment stability during construction considering with the safety margins of used geosynthetic strength and improved soil strength due to consolidation.
Many GRS retaining walls, GRS bridge abutments and GRS integral bridges having lightly steel-reinforced full-height rigid (FHR) facing have been constructed due to higher performance and lower life cycle cost than the conventional structures. The facing is constructed fixed to the reinforcement layers for embankment after the deformation of ground and embankment has taken place. Although the construction cost of FHR facing is usually higher than simpler facings (e.g. modular blocks and discrete panels), the ratio of performance to life cycle cost of GRS structures with FHR facing is better due to higher wall stability, narrower crest required for road and railway, the construction of noise/crash barriers, utility poles etc. on the FHR facing. The FHR facing is also used as a bridge abutment.
Sanriku Railway Haipesawa bridge is a new bridge alternative to the old one extensively damaged by the tsunami of the Great East Japan Earthquake. The new bridge is a new type bridge (GRS integral bridges); integral bridge with geosynsetic-reinforced soil (GRS) abatement.??Because of its structural system, i.e. highly statically indeterminate structure, it is concerned that the bridge with longer span may have larger influence on crack occurrence, caused by temperature deformation and shrinkage of concrete.?? This paper describes the measurement results of 2.5-year measurement and the observed knowledge from the measurement results. Considering these results, the timedependent mechanism of resistance of the GRS integral bridge was discussed.
The Kyushu Shinkansen (Nishi-Kyushu route) between Takeo-Onsen station and Nagasaki station, 66km in length, is under construction. The Genshu bridge is placed in a valley between tunnels in Isehaya city (47.263km from Takeo-Onsen station). The bridge structure is adopting a GRS integral bridge using a PC girder. Although, in the past, there were cases of GRS integral bridges using a RC girder or a SRC girder. The structure used for the Genshu bridge is the first case for railway infrastructures. This paper presents the initial railway infrastructure project of the GRS integral bridge with the PC girder.
Hydraulic conductivity and cesium sorption performance of zeolite-amended GCLs were determined by performing batch and column sorption tests. Particularly, the effects of sodium, potassium and calcium ions in waste leachate on both hydraulic barrier and cesium (Cs) sorption performances of the GCLs were evaluated. Batch sorption test results indicated that the Cs distribution coefficient (Kd) of the zeolite was not lowered against the higher concentrations of calcium ions, unlike that of the sodium-bentonite. In the column sorption tests, comparing with a conventional GCL, zeolite amended GCLs maintained excellent cesium sorption performance even when 0.1 mol/L-calcium solution was permeated, while permeation of the waste leachate containing 0.11 mol/L- potassium ion allowed the release of Cs though the GCLs.
We have developed windbreak fence which uses windproof sheet with view and landscape properties, and which has equal or higher benefits than the conventional net type or steel folded plate type. Windproof sheet is made by coating polyester fiber woven fabric (4.8 mm mesh size) with acrylic resin (aperture ratio is 40%, and wind shielding ratio is 60%). In the windbreak fence developed, the windproof sheet is expanded and stretched using special grips. The track record increases gradually in all over the country. This paper reports the basic performance of the windproof sheet such as view, weather resistance, durability, sheltering effect, and the unique deflection restoration property after receiving wind load.
Gas-permeable/waterproof sheets (GPWSs) have been applied as cover sheets for temporary storage sites of decontamination waste due to the Fukushima nuclear accident. In this study, we measured direction and velocity of wind in a real temporary storage site. In the site, tensions of cables that were connected to several points of GPWSs as the cover sheets were also measured to estimate wind-originating tensile force acting on cover sheets. Furthermore, numerical analysis based on these filed measurements was also made to investigate relationship between wind velocity and the tensile force in the temporary storage site with an average shape.
In this study, the experiment at an imitation temporary storage sites was conducted to measure stress distribution of capping sheets using strain gauges and to take aerial photos using drone. Strain of capping sheets increased with elapse time. The experiment results revealed that the strain changed greatly at the edge of the upper part of temporary storage sites where there were water puddles. Thermal stress raised with increasing temperature and solar radiation caused strain of capping sheets to increase. Moreover, damaged parts of capping sheets was precisely verified by analyzing pictures taken by drone equipped a camera at an imitation temporary storage sites.
Recently, it was showed by Ministry of Land, Infrastructure, Transport and Tourism that the long-life of infrastructure was important. It is effective that the maintenance is performed in Maintenance-cycle. Therefore construction of Maintenance-cycle for reinforced soil wall is pushed forward in each research organization. In this study, the scenario of degradation were made using an example of the damage of the frost heaving.
In cold, snowy regions, gabion work has been often done as emergency or restoration measures against surface layer failures of cut slopes arising from frost heaving or freezing-thawing. There has been developed a reinforced soil wall that has gabions as walls and is reinforced with woven metallic wires integrated with the gabions. This reinforced soil wall is expected to become popular as a reinforced soil wall suited for the cold regions, due to the high degree of drainage and following capability of the gabions. By constructing the gabion faced reinforced soil wall in a cold, snowy region, this study has conducted a performance evaluation of the reinforced soil wall using permeable heat insulating materials in the cold, snowy environment.
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. Although the work often employs grating crib works by spraying mortar, facing panels made of recycled plastic have recently been developed, for the purpose of reducing environmental burdens and enhancing workability. By executing a soil nailing in a flat ground, this study has precisely examined a displacement of the grouted steel bars and facing panels associated with frost heaving and frost heaving force exerted on the panels made of recycled plastic which, in cold regions, may be more likely to reduce the damage caused by frost heaving.
There are few reports on the effect of ground freezing on the dynamic characteristics of the embankments that deal with experimental research efforts covering the deformation and decomposition of the embankments and their countermeasure constructions. In order to determine the earthquake behavior of the embankments in cold regions and an improvement in earthquake resistance provided by the soil nailing, this study has conducted a vibrating table experiment on an embankment model. Results from the experiment show that the earthquake resistance slightly deteriorated when the natural ground reinforcing materials sustained damage from freezing-thawing.
Numerous liners applied to agricultural pipelines are subjected to internal water pressure. Previous studies on liners focus on their behavior when subjected to external pressure, and the detailed behavior of liners subjected to internal water pressure has not been clarified. Thus, experiments were conducted by applying internal water pressure on a liner (φ1,000 mm) to investigate the influence of a bend, which is a feature of agricultural pipelines, the presence or absence of filling material in a gap between the liner and existing pipe, and deteriorated pipe on the behavior of a liner under internal water pressure. The results reveal that the longitudinal strain of a bend is much greater than that of a straight pipe.Moreover, filling the space decreases the circumferential strain in a straight pipe and longitudinal strains at a bend, and only the liner sustains the internal water pressure when the existing pipe has no strength.
A series of water retention tests were carried out for seven nonwoven geotextiles in different materials and processes of manufacture. The van Genuchten model was applied to the water retention curve obtained from the above-mentioned test and published data. Estimation of the water retention curve using the saturated hydraulic conductivity of nonwoven geotextile was examined. Main conclusions are as follows. The water retention curves in drainage phase of nonwoven geotextiles are S-shaped curve just like that of soil materials. And the curves of nonwoven geotextiles can be estimated by the van Genuchten model. By carrying out only the permeability test of saturated nonwoven geotextiles, it is suggested that the water retention curve in drainage phase can be estimated.
Geosynthetic Clay Liner (GCL) is used as preventive measures against water leakage from bodies of storage reservoirs,ponds of parks and so on. These facilities are generally accompanied with concrete structures such as channels, boxes and/or box culverts. The deformation of these structures by subsidence or skid due to huge earthquake arises gaps in joint part of these structures, leading to water leakage. To understand how the waterproofing properties of GCL changes over time, we measured the amount of leaked water during one year with test structures with artificial opening in joint part covered with GCL. As the result, we confirmed that GCL has equivalent or better waterproofing properties compared with the clay liner as preventive measures of water leakage caused by deformation and/or cracks of concrete structures.
Applying the chemical adhesive waterproof sheetings to tunnel as forward waterproof sheetings, these may not keep the performance when the fracture happened by crack-bridging tension at crack mouth opening or joint surcface expansion regions. To study this problem, the experiments have done that the observation of the deformation on chemical waterproof sheeting at crack opening region by using the tunnel lining model with chemical adhesive waterproof sheeting. Around 3mm of delaminated regions were observed in all specimens until 5mm of opening. Then there was lower crack-bridging tension than fracture. And chemical adhesive waterproof sheetings did not break in 5mm of crack opening under 1.5MPa of high water pressure.
In the present study, in order to examine the seismic behavior of small earth dams with a sloping core zone or geosynthetic clay liners (GCLs), full-scale shaking table tests for embankments with 3m high were conducted. When the embankment was subjected to the Level 2 seismic load, large longitudinal cracks have developed at the crest of the embankment with the GCL, although water leakage has not been observed in both the cases. Moreover, the subsidence at the crest as well as the lateral deformation at the bottom of slope were both larger for the upstream side than the downstream side. The results strongly suggest that the presence of reservoir somehow influenced on the seismic performance of embankments.
In this study, in order to examine the seismic behavior of small earth dams with geosynthetic clay liners (GCLs), full-scale shaking table test using an embankment with 3m high was carried out. The GCL was laid in a staircase shape in the embankment. Large longitudinal cracks have developed at the crest of the embankment by level 2 earthquake motion involved with the maximum acceleration of 471Gal. Based on the observation of the cross-section embankment, it was found that the cracks were developed due to the presence of the GCL. The data of the response acceleration revealed that the seismic characteristics between the upstream side separated by the GCL and the downstream side were different from each other.
Short fiber-mixed reinforced soil has been developed by mixing short fiber, 20 mm to 100 mm in length and 2.3 μm to 230 μm in thickness, with soil generated at construction sites and/or processed soil for stabilizing purposes: 1) to enhance strength, toughness and erosion resistance against rain and running water and 2) to promote its effective use as a construction material which is also expected to be conducive to nourishment of vegetation.
This is to report the result of the trial execution in which the short fiber-mixed reinforced soil made of shirasu (white sand) with short fiber and a small amount of cement mixed together in it, was made effective use for strengthening river dike soil on embankment slopes, though shirasu is generally considered prone to erosion and unfit for vegetation, and also to report the result of the follow-up investigation of the status of the short fiber-mixed reinforced soil observed 6 years after its execution.
This study presents a laminar drain reinforced (LDR) levee which may have high resistance against both overflow erosion and infiltration. In the LDR levee, laminar drain laid along the back slope of the levee is connected with surface panels and levee materials by geogrid layer. In this study, we conducted largescale model tests of levees with 1m height against overflow erosion. The results of the model test revealed that: 1) the LDR levee maintained the initial shape of levee even after two hours and a half. 2) Furthermore, the LDR levee can prevent the erosion of the levee body due to the laminar drain at side slope even after the gaps between surface panels exceeded 5 cm.
In the 2011 off the Pacific coast of Tohoku Earthquake, many coastal dykes were destroyed due to overflow of tsunamis. Maximum heights of them were higher than the crown heights of coastal dykes. Previous studies showed that the geotextile reinforced soil coastal dykes covered with crushed stone and panels were strong against overflow of tsunamis. Coastal dykes constructed in such a structure are called GRS coastal dykes. From the results of series of model experiments, it was found that reinforcing coastal dykes with geotexitiles improved the resistance against overflowing tsunamis. In the series of experiment in this study, experimental conditions such as thickness of covered stones, gap between the panels, and way of using geotextiles were changed and conducted overflow experiment with changing flow rate. In the experiments, deformation of the dykes and movement of the soil were observed from the side window of the flume. In this paper, the effect of above mentioned parameters to the resistance against the overflow of tsunamis were discussed.
A measure of riverbed scoring at the front of concrete revetment at the Joganji River, River Bank Protection Works Using Sandbars with Boulders in Rapid and Stony Bed Rivers, which have a flow path control function and preservation and recovery function for sandbank, was implemented and the effectiveness of the works confirmed. However, not many large stones are available in recent years. So, We were tested or become a substitute for stones of small or medium particle sizes were placed in a bag materials for foot protection is large stone. As a result, it was confirmed that it is applicable.
In the temporary coffering method of the river works, large sandbags have been used from the perspective of Workability and Economics. But, during flooding, the large sandbag often can become problematic impact on construction sites and their hinterlands, which becomes a problem. Usually, Large sandbags are made by concatenating the under the weight of their own and ensure the stability of the structure, but large sandbags are separated each other. So, they are prone to unstable by flooding. In this paper, we reports a case study; the continuous collapsible wire mesh frame with non-woven fabric liner of the unitedness was applied to the temporary coffering method in the flowing river for the first time and this method played the role of riverwall without damaging by the reinforcement for the flow by the typhoon. Then, by the analysis of flow based on the result, we confirmed that it has the ability to withstand the current velocity of flooding.
Large deformation of an embankment on the box culvert was discovered at the Tamasaka tunnel in Kobe city. The deformation at the parapet of the tunnel had steadily accumulated since August 2012. Based on the observations, a contingency plan was demanded to avoid carefully any serious hazardous events. Therefore, a scheme to stabilize the embankment with aseismic reinforcements was considered in order to improve the seismic safety against the Level-2 earthquake. In this paper, a series of geotechnical investigation, numerical analysis, the aseismic design and the counter-measures associated with this case study is in detail described.
April 14, 2016 at 21:26 foreshock of magnitude 6.5 occurred at the depth of 11 km and the epicenter was located in the Kumamoto district. 28 hours after that, i.e. at 1:25 on April 16, main shock of magnitude 7.3 with the earthquake center at depth 12 km and epicenter in Kumamoto district occurred. In this earthquake, earthquakes of seismic intensity 5 and above occurred more than 19 times and geotextile reinforced soil walls were repeatedly subject to large seismic movements. After the main shock, we investigated the damage condition geotextile reinforced soil walls at 271 places located on seismic intensity 5 and above. This paper presents the reports the results of investigation for health and danage of reinforced soil walls using reinforced soil chart proposed by Ohta et al.
Urayasu City had a big damage due to the great Eastern Japan Earthquake in 2011. In the survey results after earthquake, the particle size distribution of the sand boil contained a lot of silt. Therefore, this research is focused on the effect of silt contents on the liquefaction suppression behavior of short fibers mixed soil. This study carried out undrained monotonic and cyclic shear test using a short fiber mixed decomposed granite soil with different fine friction contents. As a result, the liquefaction strength of short fiber mixed decomposed granite soil was found to be strongly affected by changes in the skeleton void ratio due to the fine fraction contents.
Five years have passed since the disaster by the Great East Japan Earthquake of 11 March 2011. While restoration revival projects at the damaged area were being in progress, a series of large-scale natural disasters took place consecutively, including heavy rain at Kanto-Tohoku areas in September 2015 and an earthquake at Kumamoto in April 2016.As quickly as possible recovery from the breakdown of the transportation system caused by disasters is required. In this research, we confirm the applicability of the restoration technology using large sandbags and grid reinforcements by real scale experimental test.
To reduce differential settlement between bridges or culverts and their approaches due to earthquakes, the confined-reinforced earth (CRE) method was introduced in subgrade layer, at the bottom of paved road. The method consists of granular material, geogrid layers and confining tie-rods. In order to investigate the effects of geogrid length of CRE on its behavior under differential settlement, two tests with two lateral boundary conditions, i.e., one fixed condition corresponding to long geogrid and one free condition corresponding to short geogrid, were carried out to investigate the effects. The results show that the length of CRE significantly reduces differential settlement and the deformation of long CRE case is much smaller than that of short CRE case.
Small scale shaking table tests in a 1-g gravity field were carried out to evaluate effectiveness of a deformation mitigation method for road embankment during liquefaction by using gyosynthetics sandwiched between gravel. The gravel layer could dissipate an excess pore water pressure during liquefaction immediately, and restrained a shear deformation under the embankment because of its high permeability. Furthermore, the composite layer which consisted of the gravel with geosynthetics could perform as a rigid plate with high permeability. As a result, the improved layer could restrain the deformation of embankment, and this effect could keep shape of embankment.
The present design criteria for irrigation pressure pipelines prescribes that the thrust force acting on the bend section of the pipe is supported by the passive earth pressure. However, a decrease of the resistance force due to liquefaction has not been considered for the design, and rational aseismic design method has not been developed. In the present study, we conduct lateral loading tests for the buried pipe model under different hydraulic gradient, and try to verify the mechanical characteristics of several countermeasures which use gravel and geogrid. From the experimental results, we clarify that the shear resistance of the gravel bed decreases due to liquefaction of the sand bed surrounding the gravel zone. On the other hand, when the geogrid is combined with the gravel, the tensile force of the geogrid is given to the lateral resistance force, and sufficient strength is obtained.
Due to climate change caused by global warming or increase in an earthquake, disaster risk of infrastructures increases in Japan. Reinforced soil retaining walls and embankments have high stability against earthquake or heavy rain so that construction results have increased continuously. However, there exist damaged reinforced soil retaining walls and embankments due to heavy rainfall or earthquake. This paper describes the damage, its cause and counter measure of damaged such structures. This paper also makes clear about the issue of conditions prone to deformation of such structures due to heavy rain or earthquake from the collected case studies.
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