A new composite material which has both the tensile strength of woven geotextile and the compressive strength of expanded polyethlene (EPS) is developed by bonding these two materials.
The laboratory model test of bearing capacity is practiced for verifying the performance of the composite material on soft soil ground, in which the vertical earth pressure, pore water pressure and displacement of soft ground are measured. The effect of the composite materials is compared with the case where only woven geotextile is employed on soft ground.

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The bearing capacity of foundation ground with one layer geogrid is formulated based on the upper bound theorem of plasticity theory. The failure mechanism of reinforced foundation ground is obtained through use of results of model tests. Two reinforcing effects are considered in the proposed formula. One effect is that the failure zone is extended, which is reflected by the enlarged angles of the rigid triangular wedge under the base of footing. Another is that the shear resistance on the two lateral sides of the wedge increses. The calculated results are compared with the loading test results.

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Mattress foundations using geogrids are often used on soil foundations to increase the supporting capability of a mattress-soil foundation system, in which the mattress foundation transmits a point load applied above to a wider area of the soil foundation underneath. To examine this load dispersion capability of the mattress foundation, model experiments were carried out on the lab-floor. Especially, the effects of the thickness of the mattress and the subgrade modulus of the soil foundation on the load dispersion are considered. The load distribution and the energy transmitted to the soil foundation are examined in the paper.

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This paper examines the effects of the stiffness and the shape of geogrid on the stability of reinforced embankment. A series of laboratory model tests on geogrid-reinforced embankment subjected to a uniform surface load were conducted. In the tests, the stability of the reinforced embankment was evaluated from the resultant bearing capacity and the lateral displacements of the slope. Based on the test results, the following results were obtained:
1) there exists an optimum stiffness of geogrid in order to mobilize the maximum reinforcement in the embankment in this test condition.
2) the shape of geogrid, particularly transversal element, have great reinforcing effect on the stability of the embankment.

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Five major geogrids currently in extensive use in Japan were tested for their engineering properties approximately under the same conditions for; 1) tensile strength characteristics, 2) creep characterstics, 3) friction between geagrids and sand determined by pulll-out tests and other characterstics.
Since each brand has several types having different tensile strengths, the properties of the five different geogrids having approximately the same nominal strength of the order of 50KN/m were compared. While all the results showed ultimate tensile strengths exceeding the nominal strength, the strains at failure varied widely between roughly 2 and 15%, each brand exhibiting a consistent rigidity.
Creep tests were conducted for specimens consisting of two or more strands which were subjected to a constant load ranging from 10 to 90% of the nominal load for a period up to more than 1000 hours. The creep strength is a function of the load applied and the resulting strain which appears to have a unique correlation with the short-term tensile test result.
The pull-out test results indicated that the apparent friction angle between the geogrids and sand ranged from about 15 to 30 degrees being considerably smaller than the angle of internal friction of the sand.

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Geotextile are utltized for prevention of soil draw out and filtration material. However testing methods and quality standards have not been established yet in Japen. So, we proposed new test methods for geotextile filtration applicability.
Those methods of testing are; A. O. S (apperent opening size) test, permittivity test and accelerated clogging test.
The test results show that proposed new test methods are effective to estimate geotextile filtration performance. But tepe of A. O. S test method must be carefully selectted according to types of geotextile.

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Soil-Geomembrane interface friction characteristics were investigated using direct shear test apparatuses at a normal stress from 0.036 to 0.6kgf/cm². Two different sizes of interface area were used, which were about 30 and 1000cm². Then Pull-out tests were also carried varing the length of embedded Geomembrane under normal stress of 0.036kgf/cm². Testing materials were kinugawa-river sand of which dry-density was 1.79gf/cm³ and High Density Poly-Ethylen with 1mm of thickness. As a results, a sample with larger interface area gave lower friction factor. The pull-out capacities might be estimated appropriately using a friction factor derived from larger apparatus although they were overestimated using a friction factor from smaller one.

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An encapsulated soil by a geotextile such as a soil-bag increases its strength due to the confining effect of deformation. In order to investigate the mechanical properties of its multi-layered system, several laboratory model tests were carried out in terms of compressibility, shear resistance, slope stability, and friction of geotextile-interfaces. As the results, it was found that the compressibility of fine gravel was smaller than that of sand. A higher compressibility was observed in loose, dry and cubic packing conditions for both sand and fine gravel. The shear strength has a relation to the density of soil but not the soil type. The optimum frictional stability of the multi-layerd system was obtained at 60 to 80% of the relative density of a soil-bag.

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There are thousands of landslies induced by rains during rainy seasons and melting snow. The author is proposing a preventive measure by covering ground surface of landslide area with with geomembranes, which are placed about 1 to 2 meters below the ground surface. The soil cover allows to grow plants and to construct light houses.
If the ground surface is steep and the cover soil has possibility of sliding, the slope is built in tiers.
Subsurface drainages such as drainage wells and drainage tunnels are widely used to prevent landslides. But those methods are not always effective. It seems that those methods are too expensive to drain rich percolated water by heavy rain in a short time.
The geomemrane method is far more economical than other methods.
There are some problems left for future study.
(1) Is it necessary to cover the whole area?
(2) Quality of geomembrane.
(3) Seams and overlapping.
(4) Combination of other methods.
(5) Prediction of rain or melting snow landslides.

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For reinforcing procedure of retaining wall using Geogrids, Geogrids, in general, are wrapped around successive lifts of sandbags. This procedure, however, may result in changes in the slope of wall facings, etc. for the settlement due to consolidation and/or extrusion of soils by the compaction. In addition, many labours are required for this procedure.
To cope with this problem, a new frame-type procedure has been developed and been put to practical use. This report summerizes its background and procedure.

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Slope-covering with geotextiles has been frequently used to improve the resistance of slope. However, it was difficult to plant grasses on slopes which were reinforced with the spunbonded nonwoven fabrics. New method, which is able to plant grasses on the slope, was developed. The method is to spray the liquidised mixture of seed, cement, organic material and adhering material on the slope surface. As a result of erosion test and plant growing test under the outdoor environment the effectiveness of the new method is confirmed.

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At the engineering development of improvement method on artificial extremery soft clayey ground using horizontal board drains, application of Barron's theory, permeability capacity of drain and loading effects of vacuum consolidation were researched.
The horizontal board drain method was recongnized as the useful method by the results of these researches and the data of field executions and managiments are taken at the three actual works.
This paper describes outlines of foundamental studies and applications of actual improvement works using horizontal geosynthetics board drains.

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This paper deals with the results from stability analyses of geogrid reinforced road embankment that remains without any damage during Kushiro Offshore Earthquake (Jan. 15 1993; M_j=7.8) in Japan. The earthquake's epicenter was located approximately 33km from the embankment, and the horizontal acceleration at the embankment site is estimated more than 310gal. The embankment under study has the following features: height: 5.5m, face slope: 73.3°, reinforcement: geogrids of type SR-55, wall face material: expanded metal, height of upper unreinforced embankment section: 1.2m. The analyses are conducted according to the seismic design method of Public Works Research Institute compared with Geogrid Research Boad's method.

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Abutments of the intercross between the Hokuriku and the Banetsu highways (Niigata Chuo IC) were constructed on very soft ground. The intercross consists of three stories roadways. Formerly it was planned to construct those abutments on the 8-13m height embankment. However, since the soft ground exerted huge lateral pressure on the piles, very big caissons were required. In order to reduce the lateral pressures and keep low construction's cost, new construction method along with the using of the geosynthetic were adopted. For caisson A1, light-weighted foam was used in EPS method and for caisson A2, the geogrid was used to reinforce the embankment. The results and efficiency of the new method were confirmed.

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