• Journal of the Korean Geotechnical Society
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• v.21 no.10
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• pp.73-83
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• 2005

Recently, foundation designs based on piled raft concept have been increasing, where the piles are required not to ensure the overall stability of the foundation but to act as settlement reducer. When a concrete track is constructed on soft ground, excessive settlements may occur, while it rarely has bearing capacity problems. In this case, the settlement of the concrete track may be effectively reduced by arranging a small number of small-diameter piles beneath the track. This paper presents the effect of pile installation on the reduction of concrete track's settlement. A 3D finite difference method was employed to model the piled concrete tracks. A parametric study was carried out to assess the effect of varying soil condition and pile arrangements. From the analysis results, it is verified that the effect of the pile installation is significant to effectively reduce the settlement of concrete track. Optimal number of pile rows and pile spacings was proposed for the economical design of a piled concrete track. The bearing mechanism of piles was also investigated by analyzing load sharing characteristics of pile according to soil conditions and pile arrangements.

• Journal of the Korean Geotechnical Society
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• v.20 no.2
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• pp.107-113
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• 2004

A new innovative prestressed support (IPS) earth retention system has been developed and introduced. The IPS is a wale system prestressed by steel wires. The IPS consists of wale, wires, and H-beam support. The IPS provides a high flexural stiffness to resist the bending by earth pressures. The IPS earth retention system provides a larger spacing of support, economical benefit, construction easiness, good performance, and safety control. This paper explains basic principles and mechanism of new IPS system and presents a design method of IPS earth retention system. In order to investigate applicability and safety of new IPS system, field tests were performed in a trench excavation. The new IPS system applied in a trench excavation was performed successfully. The measured performances of IPS system were presented and discussed.

• Journal of the Korean Geotechnical Society
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• v.20 no.3
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• pp.85-96
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• 2004

The ultimate bearing capacity of surface foundations on a sand layer overlying clay has been theoretically investigated. First, a review of previous studies on the bearing capacity problems for this type of foundation was performed and a discussion was presented concerning the practical application. Second, the kinematic approach of limit analysis was used to calculate the upper bound of the true ultimate bearing capacity. The kinematic solutions are upper bounds and their accuracy depends primarily on the nature of the assumed failure mechanism. This approach makes it convenient to create design charts, and it is possible to trace the influence of parameters. Third, the commercial finite element program ABAQUS was applied to obtain the ultimate bearing capacity based on the elasto-plastic theory. Results obtained from the kinematic approach were compared with those from the program ABAQUS and the limit equilibrium equations proposed by Yamaguchi, Meyerhof and Okamura et al. Finally, the validities of the results from the kinematic approach, the results from the program ABAQUS and the limit equilibrium equations were examined.

• Geotechnical Engineering
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• v.13 no.4
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• pp.177-198
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• 1997

Since decomposed granite soil shows various characteristics of shear behavior dependent on initial conditions such as weathering degree and grain breakage, it is nacessary to invert ligate stress -strain relationship and changes of shear characteristics for different initial conditions. Associated with abovefnentioned view, direct shear tests, and triaxial compression tutsts(Ef, CD) were carried out in this study for undisturbed and disturbed compacted weathered granite samples obtained from 4 construction work sites with the various weathering degree and components of parent rocks. The deformation behavior of undisturbed samples under small confining stress shows hardening to softening, which is similar to that of over nsolidated clay whereas disturbed weathered granite soils do hardeningfonstant regardless of weathering degree, which is also similar to sedimentary clay. Conventional direct shear-tests for undisturbed samples show a tendency to overestimate cohesion. It is possidle to approximate stress ratio(q/p') and volumetric increment ratio(dv/ds) in the triaxital compression tests by an equation, ($dv/d\varepsilon,=\alpha(M-\eta))$ irrespective of moisture content, weathering degree and disturbance.

• Geophysics and Geophysical Exploration
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• v.9 no.3
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• pp.193-206
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• 2006

Among various borehole seismic testing techniques for determining body wave velocity, crosshole seismic method has been known as one of the most suitable technique for evaluating reliably geotechnical dynamic properties. In this study, to perform successfully the crosshole seismic test for rock as well as soil layers regardless of the groundwater level, multi-purposed spring-loaded source which impact horizontally a subsurface ground in vertical borehole was developed and applied at major facility sites in Korea. The geotechnical dynamic properties were evaluated by determining efficiently the body wave velocities such as shear wave velocity and compressional wave velocity from the horizontally impacted crosshole seismic tests at study sites, and were provided as the fundamental parameters for the seismic performance evaluation and seismic design of the target facilities.

• Journal of the Korean Geotechnical Society
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• v.20 no.9
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• pp.5-15
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• 2004

It is worthwhile to verify the vertical stress distribution in soil mass for rigorous design of foundation. A series of laboratory model tests were performed to investigate the Boussinesq's theory on vertical stress increment in sandy soil mass caused by surface loading. The test results were also compared with Boussinesq's theoretical values. The Boussinesq's theoretical values were always smaller than test results under the footing regardless of depth. Outside of the footing the values were larger than the measured stress at the depth of just footing width. The theory and the test showed similar results when the depth reached two and three times the footing width. The vertical stress decreased as the applied load increased. These trends were confirmed to be valid for the considered range of the relative density of sand and/or the width of footing. More accurate values can be acquired by correcting the theoretical values using these results when Boussinesq's theory is used.

• Geotechnical Engineering
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• v.4 no.1
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• pp.7-16
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• 1988

The safety factor has been used widely and uniquely at present to check the safety of the structure . However, probability of failure would be logically attempted to check the reliability of the structure in future Coulomb's theory or Rankine's theory has been applied in practice to retaining earth structure in spite of the fact that the lateral earth pressure, which is the primary factor in the determination of wall structure, depends on the modes of wall movement . This study is concentrated on the two modes of , wall movement (active case rotation about bottom(AB) , active case rotation about top(AT)) of the overturning'failure of vertical wall with horizontal sand backfill . The static active earth pressure is determined by applying each of Coulomb's theory, Dubrova's redistribution theory and Chang's method The earthquake active earth pressure is determined by adding Seed and Whitman's earthquake pressure to the static earth pressure , On the condition that design variables are fixed with each of the above earth pressure, reliability is analyzed using the recently developed method of AFOSM (Advanced First Order Second Moment)

• Journal of the Korean Geotechnical Society
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• v.21 no.7
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• pp.43-54
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• 2005

Tunnelling in a water bearing soil may cause draw-down of ground water table. Modelling of this problem requires considering the change of phreatic surface including the stress constitutive relationship for an unsaturated soil. However, it is normally assumed that ground water is confined. Numerical formulation of coupled behavior considering phreatic surface is described and implemented into computer program. Influence of unconfined flow on tunnel and ground is thoroughly investigated and compared with that of confined flow condition. It is identified that ground and lining behaviour below phreatic surface is almost the same as that under confined flow conditions, however, there is considerable difference in ground behaviour above phreatic surface. It is generally concluded that the assumption of confined flow is acceptable in terms of lining design.

• Journal of the Korean Geotechnical Society
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• v.21 no.8
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• pp.55-61
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• 2005

Mononobe-Okabe method is generally used to evaluate dynamic earth pressure for the seismic design of retaining walls. However, Mononobe-Okabe method does not consider the effects of dynamic interactions between backfill soil and walls. In this research, shaking table tests on retaining walls were performed to analyze the phase and magnitude of dynamic earth pressure. The unit weight of walls, the amplitude of input acceleration and the base friction coefficient of walls were varied to analyze the influence of these factors on the dynamic earth pressure. Test results showed that the dynamic earth pressure was 180 degrees out of phase with the wall inertia force for the low sliding velocity of the wall, whereas small peaks of the dynamic earth pressure, which are in phase with the wall inertia force, were developed for the high sliding velocity of the wall. The amplitude of dynamic earth pressure was proportional to that of wall acceleration and the unit weight of the wall. In addition, the dynamic earth forces calculated by the Mononobe-Okabe method were the upper limit of the dynamic earth pressures.

• Journal of the Korean Geotechnical Society
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• v.28 no.6
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• pp.5-17
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• 2012

The moment responses of electric pole foundations for a railway were investigated using real-scale load tests. Large overturning moments were applied to two circular rigid piles with a 0.75 m diameter and a 2.5 m embedded depth; the circular rigid piles were installed in an actual railway embankment fill. Two different loading directions-toward the fill slope and toward the track -were applied to evaluate the influence of the fill slope on the moment capacities of the foundations. It was found that the failure of the foundations that were constructed according to Korean railway practices exhibited a sudden overturning pattern without any significant pre-failure displacement. The moment capacity toward the fill slope was less than the moment capacity toward the track by 30%. From the test results, the geometry factor (K), which accounted for the reduction of the moment capacity, due to the fill slope, was 0.7. Moment capacities determined from the load tests were compared with those predicted from three existing design methods, and their applicability was discussed.