• International Journal of Highway Engineering
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• v.6 no.3 s.21
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• pp.65-77
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• 2004

Deformational characteristics of subbase materials are important parameters in the mechanistic design of pavement. The subbase materials are mostly unbound granular materials in Korea, and seven representative subbase materials were collected for testing from the pavement construction sites. To evaluate the deformational characteristics of subbase materials, RC/TS, TX and FF-RC tests were performed. The effects of various variables on modulus were studied. The variation in the modulus with number of loading cycles and loading frequency are very small and can be ignored in a practical sense. The modulus of subbase materials were significantly affected by confining pressure and strain level. The representative modulus reduction curve and constitutive models for Korean subbase materials were suggested.

• Journal of the Korean Society for Railway
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• v.3 no.2
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• pp.68-76
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• 2000

Such traditional construction methods as the interchange or improvement of railway subbase maintenance and reinforcement have many problems in the matters of construction period, constructive and economical efficiency aspects. This paper will describe the alternative railway subbase reinforcement method based on geosynthetics system. It is presently very popular in Germany and Japan. In summary it is to say, that geosynthetics used at fine grained subsoils to a strong improvement of the whole railroad system.

• International Journal of Highway Engineering
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• v.17 no.1
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• pp.69-75
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• 2015

PURPOSES : The objective of this study is to evaluate the effectiveness of a geogrid reinforced subbase of permeable flexible pavement structures with respect to permanent deformation. METHODS : Experimental trials employing a repeated triaxial load test scheme were conducted for both a geogrid reinforced subbase material and a control specimen to obtain the permanent deformation properties based on the VESYS model. Along with this, a finite element-based numerical analysis was conducted to predict pavement performance with respect to the rutting model incorporated into the analysis. RESULTSAND CONCLUSIONS : The results of the experimental study reveal that the geogrid reinforcement seems to be effective in mitigating permanent deformation of the subbase material. The permanent deformation was mostly achieved in the early stages of loading and then rapidly reached equilibrium as the number of load applications increased. The ultimate permanent deformation due to the geogrid reinforcement was about 1.5 times less than that of the control specimen. Numerical analysis showed that the permeable, flexible pavement structure with the geogrid reinforced subbase also exhibits less development of rutting throughout the service life. This reduction in rutting led to a 20% decrease in thickness of the subbase layer, which might be beneficial to reduce construction costs unless the structural adequacy is not ensured. In the near future, further verification must be conducted, both experimentally and numerically, to support these findings.

• International Journal of Highway Engineering
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• v.2 no.2
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• pp.149-161
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• 2000

The stiffness of the subbase materials is represented by the resilient modulus, $M_R$, which are very important properties in the mechanistic design of flexible pavement system. However, the cyclic $M_R$ testing method is too complex, expensive, and time consuming to be applicable on a production basis. In this study, the alternative $M_R$ testing technique for subbase materials was developed using a free-free resonant column (FF-RC) test considering deformational characteristics of subbase materials. To estimate the deformational characteristics of subbase materials, effects of strain amplitude and mean effective stress on modulus of subbase materials were investigated. The $M_R$ values determined by alternative testing procedures matched well with those determined by standard $M_R$ test, showing the capability of the proposed methods being used in determining $M_R$ values.

• Magazine of the Korean Society of Agricultural Engineers
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• v.43 no.3
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• pp.77-84
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• 2001

A few study has been performed on the durability of subbase treated with geo-cement for the farm road although many papers for the road treated with soil-cement were published. The objectives of the study are to develop the stabilizing method of subbase using additives of cement groups and 2nd additives such as gypsum and MgO, etc. A series of test was performed to investigate possible mixing ratios with geo-cement A, B, C, D and 2nd additives on the various soft soils from the rice paddy. Based on test results, durability index was greatly affected by geo-cement D which was mainly composed with gypsum. Compressive strength of clayey soil such as Soil I was less than threshold strength(30kgf/$\textrm{cm}^2$) but the strength was increased as addition of gypsum and MgO. It is recommended that geo-cement for soil stabilization has to be carefully chosen because strength characteristics of subbase are varied not only with soils but also with addition of geo-cement and 2nd additives. The developed method in this study can be used subbase treatment of low-cost agricultural roads.

• International Journal of Highway Engineering
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• v.11 no.2
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• pp.85-98
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• 2009

The in-situ Compaction test using sand cone (RC) and Plate Bearing Capacity Test (PBT) has been widely used for evaluating the subgrade and subbase condition on the pavement system. However, because the in-situ RC and PBT test are expensive and take plenties of time for operation, these are very difficult to figure out the in-situ characteristics of subgrade and subbase strength in detail. Therefore, for faster and economical operation, this study is to compare the Light Falling Weight Tests and propose the LFWD test as the in-situ Compaction test. This study suggests the relationship between in-situ RC value, $K_{30}$, $M_R$ and $E_{LFWD}$ of the subgrade and subbase materials in Korea using the laboratory and in-situ testing.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.89-98
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• 2010

Recently, many researches on bottom ash which is produced in the burning process of power plant are actively performed for its utilization for soil-subbase materials. In this paper, bottom ashes from 5 different power plants are prepared and several tests including compaction, CBR, and tri-axial compression are carried out for mixed bottom ash and weathered soil considering 3 replacement ratio of 30%, 50%, and 70%. Through the tests, CBR result over 20 are evaluated without plastic property, which shows availability of subbase material. With higher increase in replacement ratio of bottom ash, CBR of mixed soil increases due to the higher mechanical performance of bottom ash. However, replacement effects of bottom ash on friction angle and cohesion are evaluated to be little since bottom ash plays a little role in rearrangement of mixed soil. Bottom ash with a good mechanical property is evaluated to have reasonable bearing capacity which shows a good property for subbase materials.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3D
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• pp.331-338
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• 2008

Road pavements consist of layered structure and each layer is made of various materials. The load responses of pavement structures are very sensitive to properties of subbase materials. Successful pavement design, therefore, depends on the method and the accuracy of measuring material properties, and it requires realistic description of the behavior of layered materials. Resilient modulus ($M_R$) is widely used properties representing pavement structure materials. In this study, we collected data for mechanical characteristics of subbase materials that were used in domestic construction and adopted them to form a constitutive equation of subbase $M_R$ value. Proposed model was evaluated through the finite element analysis.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.11a
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• pp.657-664
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• 2000

Weak and soft compressible clay deposits are commonly found in natural subgrade soils. These Soils need to be stabilized for using the subbase materials of highway constructions. This paper presents that a chemical treatment using chemical additives comprised of sulfate(SO$_4$) and chloride(Cl) is evaluated for stabilizing soft clay deposits and lime. The physical and mechanical characteristics of soil-lime and additives are described by means of a laboratory study. The study results indicate that the presence of chlorides encouraged the efficiency of lime stabilization, and the use of calcium chloride with quicklime is the best additive for improving soil behavior. The treated soil with lime-calcium chloride can have the adaptability to the subbase materials of highway constructions.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.11c
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• pp.117-128
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• 1999

Geosynthetics have been studied especially Korean Railway earth works from the outset and have proved successful in both technical and economic terms. Hitherto Geosynthetics have been given consideration chiefly in dimensioning the requisite track subbase thickness, but have not been considered when calculating the thickness of the frost protection layer. this often made it impossible to reduce the thickness of the subbase. The article therefore puts forward a proposal for considering the German Geosynthetics in dimensioning the requisite thickness of the frost protection layer.