• Proceedings of the KSR Conference
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• 2004.10a
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• pp.1052-1057
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• 2004

Various amplitudes and frequencies of axle loads are applied to the domestic conventional line. Vertical stresses and settlements on the subgrade may be changed depending on the variation of axle loads. This paper introduces the research results to estimate vertical stresses and settlements on the subgrade with numerical analysis(Distinct Element Method), full scale test, and field test.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.03a
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• pp.525-532
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• 2001

In this study, performance of reinforced railroad roadbeds with the crushed stones was investigated through the real scale railroad roadbed tests. Several real scale reinforced railroad roadbeds were constructed in the laboratory with different subgrade conditions and were tested with the estimated actual train loads including the impact loading of train. The affecting factors such as settlement, earth pressure and stress change at the surface of reinforced roadbed, subgrade layers as well as surface of rails were measured. It was found through the actual testing that for the roadbed with the same thickness, the settlement and vibration level (velocity) of reinforced roadbed decreases with the increase of reaction modulus of subgrade. The settlement of reinforced roadbed with the same reaction modulus of subgrade also decreases with the increase of thickness of the reinforced roadbed.

• Journal of the Society of Disaster Information
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• v.2 no.1
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• pp.53-64
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• 2006

This study presents the laboratory properties on the frost heave under various moisture contents and compaction efforts in pavement subgrade soil. Many researches were conducted on the frost heave. However, the researches with the domestic soils have not been so active until now. In particular, the evaluation of the frost heave in pavement subgrade soils was not established by many researchers. The problems relating with the frost heave have been serious causes in the distresses of pavements. The study was performed using an appropriate field simulation. The research results revealed that the drainage conditions in earth work should be treated cautiously.

• Structural Engineering and Mechanics
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• v.3 no.5
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• pp.429-443
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• 1995

The deformational response of plastic board drains installed to accelerate consolidation of soft soils, is examined as a problem of downdrag. The drain is modelled as a beam-column in which the axial load increases nonlinearly with depth. The soil response is represented by the Winkler medium whose coefficient of subgrade modulus increases linearly with depth. The governing equations for the drain-soil system are derived and solved as an eigenvalue problem. The critical buckling loads and the shape of the drain are obtained as functions of the normalized subgrade modulus of the soil at the top, the parameters signifying the variation of axial load along the length of the drain and the increase of subgrade modulus with depth. The derived deformed shapes of the drain are consistent with the observed ones.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.984-996
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• 2009

When evaluating the general subgrade states such as geology, stiffness, underground water, compaction and deformation in the Gyeongbu high speed railway, some applicable testing methods should be selected because lots of trains are currently running. The applicable methods includes not only non-destructive tests such as GPR test, electricity resistivity test, MASW proving, but also standard penetration test (SPT), core test, elastic wave tomography through drilling boreholes and measurements using settlement measuring system or inclinometer, etc. In order for evaluating the subgrade states in the Gyeongbu high speed ralway, this study performed GPR test in several sections and drilling boreholes whose locations were chosen after comparing GPR test results and track maintenance history. Furthermore, the progress of subgrade deformations was analysed by comparing previous and this time GPR test results. The results of this study shall be used to understand the general states of currently operating Gyeongbu high speed railway.

• International Journal of Highway Engineering
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• v.15 no.5
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• pp.57-64
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• 2013

PURPOSES : It is to evaluate lightweight soil as a subgrade material based on mechanical tests and calculation of pavement performance. METHODS : In this research, various contents of cement and air foam are used to make lightweight soil using wasted dredged soil. Uniaxial compressive strength test is conducted to evaluate strength of 7 and 28 day cured specimens. Secant modulus was calculated based on the stress and strain relationship of uniaxial compressive strength test. Resilient modulus test was measured using by repeated triaxial compression test. The measured resilient modulus was used in layered elastic program to predict fatigue and rutting life at a given pavement structure. RESULTS : Uniaxial compressive strength increases as cement content increases but decrease as air foam content increases. Resilient modulus also increases as cement content increases and decrease as air foam content decrease. CONCLUSIONS : It is concluded that dredge clay soil can be used as subgrade layer material using by lightweight treated soil method.

• Journal of the Korean Society for Railway
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• v.11 no.1
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• pp.61-68
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• 2008

Resilient modulus has been used for characterizing the stress-strain behavior of subgrade soils subjected to traffic loadings. With the recent release of the M-E Design Guide, highway agencies are further encouraged to implement the resilient modulus test to improve subgrade design. The subgrade design for the trackbed, however, is primarily relying on the static test results such as $K_{30}$ and deformation modulus, Ev. Therefore applicability of the resilient modulus for the design of trackbed needs to be evaluated. In this study, physical property tests, unconfined compressive tests and resilient modulus tests were conducted to assess the resilient and permanent strain behavior of 14 cohesive subgrade soils. A predictive model for estimating the resilient modulus is proposed based on the results of unconfined compressive tests and tangent elastic modulus, unconfined compressive strength, failure strain, secant modulus at peak, and yield strain. The predicted resilient moduli using the predictive models compared satisfactorily with measured ones. Although the permanent strain occurs during the resilient modulus test, the permanent behavior of subgrade soils is currently not taken into consideration.

• Geotechnical Engineering
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• v.14 no.2
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• pp.67-78
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• 1998

Microtunnelling is a technique applied to install a small-size tunnel in a soft cohesionless ground. In microtunnelling, a series of concrete tubular segments are pushed from a starting pit to power-line tunnel under a runway of JFK international airport at New York. During the microtunneling process, bentonite is jetted with very hyh pressure through a nozzle to advance disturbance in the subgrade caused by the pressurized bentonite in the aspects of subgrade stiffness. SASW measurements were performed on the runway above the center line of the shear wave velocity profiles. Besides the change of subgrade stiffness, the change of subgrade strength was also evaluated by the site-specific relationships between shear wave velocity and N value, which was determined by N values. The estimated N values gave a clue to the understanding of the change of subgrade strength.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1228-1236
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• 2006

In soft ground, There are many case that Bridge Abutment is constructed after soil improvement in order to reduce the Negative Friction and prevent from Lateral Soil movements of Bridge Abutment. That section of Horizontal Subgrade Reaction $Modulus(K_h)$ derivation has much important mean due to Horizontal Stability of Abutment. It is come from behavior of Pile and Soil within depth of $1/\beta$. After Soil Improvement, however, If Bridge Abutment was construction, It's not impossible to carry out Field Investigation After Ground of Improved at design stage. Therefore, It's not able to derivate Horizontal Subgrade Reaction $Modulus(K_h)$. Therefore, in this case of study compare with Field Construction Test Data in order to derivation of Horizontal Subgrade Reaction $Modulus(K_h)$ and Reliability in terms of ground of Bridge Abutment by Sand Compaction Pile(SCP) during design of The 2nd Bridge Connection Road of Incheon International Airport. In this paper determine, Soil Property(The rate of strength increase, $c_u$ so on) and Horizontal Subgrade Reaction $Modulus(K_h)$ after soil improvement at design stage.

• International Journal of Highway Engineering
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• v.16 no.6
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• pp.69-78
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• 2014

PURPOSES : The purpose of this paper is showing that the state of pavement sublayers can be evaluated differently according to direction of FWD. METHODS : The concrete pavement slabs above subgrade without anything, subgrade with cavity, and box culvert were modeled by finite element method(FEM). The modeled pavements were analyzed by changing the direction of falling weight deflectometer(FWD). The deflection results obtained from FEM were used to calculate radius of relative stiffness and composite modulus of subgrade reaction using AREA method. Then, the analyzed results were compared to the results of the test performed at the Korea Expressway Corporation(KEC) test road. RESULTS : The composite modulus of subgrade reaction increased with subgrade elastic modulus, while radius of relative stiffness decreased. The pavement sections of pure earth showed the consistent results regardless of FWD direction. In case there was cavity, the radius of relative stiffness was larger and composite modulus of subgrade reaction was smaller when FWD was leaving the cavity than when approaching the cavity. This pattern became clear when the cavity got larger. In case of the section with box culvert, the pattern was opposite to the case of cavity. When the soil cover depth increased, the effect of box culvert got smaller. When the load was applied far from the cavity and box culvert, the effect was also declined. The test performed at the KEC test road showed identical results to those of finite element analysis. CONCLUSIONS : The direction of FWD should be considered in evaluation of the state of pavement sublayers because it can be evaluated differently even under identical condition.