• Structural Engineering and Mechanics
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• v.61 no.5
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• pp.593-603
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• 2017

A high-efficiency simplified modelling approach is proposed for investigating the nonlinear responses of reinforced concrete linings of shield tunnels. Material and geometric nonlinearities are considered in the analysis of the lining structures undergoing large deformation before ultimately losing the load-carrying capacity. A beam-spring element model is developed to capture the force-transfer mechanism between lining segments and radial joints. The developed model is validated by comparing analyzed results to experimental results of a single-ring lining structure under two loading conditions: the ground overloading and the lateral unloading respectively. The results show that the lining structure under the lateral unloading due to excavation on the both sides of the tunnel is more vulnerable compared to the case of ground overloading on the top of the tunnel. A parameter study is conducted and results indicate that the lateral pressure coefficient has the greatest influence on the behaviour of the lining structure.

• Journal of the Korean Geotechnical Society
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• v.24 no.10
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• pp.5-15
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• 2008

The purpose of this study is to examine the validity of recycled aggregates (RAs) as a substitute for Sand-Mat material for soft ground improvement in the housing site development. To evaluate the possibility of RAs as a substitute for sand mat material, first of all, the criteria and regulations related with the quality of lateral drain layer were collected and checked. Secondly, both of the properties of RAs were compared with the properties of natural sand for the lateral drain layer. The material properties related to coefficient of permeability, pressure at-rest state and so on satisfied most standards. On the basis of the test results, RAs were used to the construction site as lateral drain layer. Accordingly, if the quality of RAs can be managed well, the application of these RAs as lateral drain layer to replace natural sand was highly effective. Also, based on cost analysis of two materials, RAs are proved to be very competitive.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.703-710
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• 2002

In the design of cut and cover tunnels, the structural analysis has been used for its simplicity. Contrarily to the geotechnical analysis, this technique could not account for the geological and geometric factors. In this study, the dominant factors influencing the behavior of cut and cover tunnel such as interface element, cut slope, distance between cut slope and tunnel lining, berm, coefficient of lateral earth pressure, were investigated and compared by geotechnical numerical analysis. Based on the results, the variations of earth pressure, bending moment, shear stress, axial load, and displacements were evaluated and analyzed for each factor.

• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.1
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• pp.116-127
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• 1996

This paper dealt with FEM analysis of foundation improved with pack drain. The theory on pack drain was scrutinized and observed values in the field were compared with numerical results. Work site of Kwangyang container pier was selected as a ease study in which measurement of settlement and pore water pressure was accurately carried out. Biot's consolidation equation was selected as governing One, coupled with modified Camclay model as constitutive one. Christian and Boehmer's numerical technique was adopted. Behavior of foundation with pack drain is not simple but very complicated. Discontinuity resulted from rigidity difference between adjacent materials, smear effect and complicated boundary conditions should be considered in the behavior analysis of foundation behavior. The results of numerical analysis were influenced by smear zone. In relevant to this effect, finite element analysis was carried out using the reduced horizontal coefficient of permeability in the smear zone; The numerical results were compared with observed values in surface settlement. including pore water pressure. However only lateral di5plaoement by numerical ana1Ysis was shown since its measurement was not performed in the field. The predication of settlement to be developed later can be effectively employed for the obtimization of construction. The predication of residual settlement using the data measured in the field was made by Hoshino, Asaoka and hyperbolic method. Among them, the hyperbolic method proved best one. Settlements accorded well between numsrical and observed values while pore pressure showed a slight difference. Lateral displacement showed largest values at constant distance from ground surface. The validation of foundation analysis improved with pack drain by computer program employed in this study selecting modified Cam-clay model was satisfactorily secured.

• Geomechanics and Engineering
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• v.23 no.1
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• pp.71-83
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• 2020

Cantilever sheet pile walls are subjected to surcharge loading located on the backfill soil and at different distances from the top of the wall. The response of cantilever sheet pile walls to surcharge loadings at varying distances under seismic conditions is scarce in literature. In the present study, the influence of uniform surcharge load on cantilever sheet pile wall at varying distances from the top of the wall under seismic conditions are analyzed using finite difference based computer program. The results of the numerical analysis are presented in non-dimensional form like variation of bending moment and horizontal earth pressure along the depth of the sheet pile walls. The numerical analysis has been conducted at different magnitudes of horizontal seismic acceleration coefficient and vertical seismic acceleration coefficients by varying the magnitude and position of uniform surcharge from the top of the wall for different embedded depths and types of soil. The parametric study is conducted with different embedded depth of sheet pile walls, magnitude of surcharge on the top of the wall and at a distance from the top of the wall for different angles of internal friction. It is observed that the maximum bending moment increases and more mobilization of earth pressure takes place with increase in horizontal seismic acceleration coefficients, magnitude of uniform surcharge, embedded depth and decrease in the distance of surcharge from the top of the wall in loose sand.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.8
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• pp.728-733
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• 2008

Unsteady aerodynamic analysis of an air-pressure-levitated high-speed ground vehicle moving over the nonplanar ground surface are performed using the boundary-element method. The potential flow solution is included in a time-stepping loop and the wake is captured as part of the solution. When the vehicle moving inside the channel, the lift coefficient and the pitching moment coefficient of the vehicle are increased further because the air trapped by the channel increases the ground effect. In other words, the nonplanar ground surface such as the channel decreases further the longitudinal stability of the vehicle. On the other hand, there is little difference between the ground and the channel in the lateral stability of the vehicle because the lift increment due to the nonplanar ground surface such as the channel takes place on both sides of the wing with the same rate of increase.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.163-171
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• 2001

It is important to pay careful attention to the backfill construction for the structural integrity of concrete box culvert. To increase the structural integrity of culvert good compaction by the dynamic compaction roller with big capacity is as effective as good backfill materials. However structural distress of the culvert could be occurred due to the excessive earth pressure by great dynamic compaction load. In this study, two box culverts were constructed with change compaction materials and construction methods. Two type of on-site soils such as subbase and subgrade materials were used as backfill materials. In most case, dynamic compaction rollers with 11 to 12 ton weights were used and vibration frequency were applied from 2000 to 2500 rpm for the great compaction energy. Backfill compactions with good quality soils were carried out to examine the effect of cushions on dynamic lateral soil pressure. Expanded polystyrene (EPS) and rubber of tire were adapted as cushion materials and they are set on the culverts before backfill construction. This paper presents the main results on the characteristics of dynamic earth pressures. Test result indicates that the amounts of increased dynamic pressures are affected with backfill materials, depth of pressure cell, and compaction condition. The earth pressure during compaction can give harmful effect to box culvert because the value of dynamic earth pressure coefficient $(\DeltaK_{dyn}=\DeltaK\sigma_h\DeltaK\sigma_v)$ during compaction is greater than that of static condition. It was observed that cushion panels of EPS(t=10cm) and rubber(t=5cm) are effective to mitigate dynamic lateral pressure on the culverts.

• Geomechanics and Engineering
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• v.9 no.5
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• pp.547-567
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• 2015

This study investigates the behavior of group of tapered and cylindrical piles. The bearing capacities of groups of tapered and cylindrical piles are computed and compared. Modeling of group of piles in this study is conducted in sand using three-dimensional finite element software. For this purpose, total bearing capacity of each group is firstly calculated using the load-displacement curve under specific load and common techniques. Then, the model of group of piles is reloaded under this calculated capacity to find group settlements, stress states on the lateral surfaces of group block, efficiency of group and etc. In order to calculate the efficiency of each group, single tapered and cylindrical piles are modeled separately. Comparison for both tapered and cylindrical group of piles with same volume is conducted and a relation to predict tapered pile group efficiency is developed. A parametric study is also performed by changing parameters such as tapered angle, angle of internal friction of sand, dilatancy angle of soil and coefficient of lateral earth pressure to find their influences on single pile and pile group behavior.

• Structural Engineering and Mechanics
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• v.46 no.1
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• pp.53-73
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• 2013

Prediction of prestressed concrete girder integral abutment bridge (IAB) load effect requires understanding of the inherent uncertainties as it relates to thermal loading, time-dependent effects, bridge material properties and soil properties. In addition, complex inelastic and hysteretic behavior must be considered over an extended, 75-year bridge life. The present study establishes IAB displacement and internal force statistics based on available material property and soil property statistical models and Monte Carlo simulations. Numerical models within the simulation were developed to evaluate the 75-year bridge displacements and internal forces based on 2D numerical models that were calibrated against four field monitored IABs. The considered input uncertainties include both resistance and load variables. Material variables are: (1) concrete elastic modulus; (2) backfill stiffness; and (3) lateral pile soil stiffness. Thermal, time dependent, and soil loading variables are: (1) superstructure temperature fluctuation; (2) superstructure concrete thermal expansion coefficient; (3) superstructure temperature gradient; (4) concrete creep and shrinkage; (5) bridge construction timeline; and (6) backfill pressure on backwall and abutment. IAB displacement and internal force statistics were established for: (1) bridge axial force; (2) bridge bending moment; (3) pile lateral force; (4) pile moment; (5) pile head/abutment displacement; (6) compressive stress at the top fiber at the mid-span of the exterior span; and (7) tensile stress at the bottom fiber at the mid-span of the exterior span. These established IAB displacement and internal force statistics provide a basis for future reliability-based design criteria development.

• Journal of Aerospace System Engineering
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• v.13 no.5
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• pp.32-38
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• 2019

The flying wing configuration with high sweep angles and rounded leading edge represent a complex flow of structures by the leading edge vortex. For control of the tailless flying wing configuration with unstable directional stability, flaperon is used. In this study, we conducted numerical simulations for a non-slender flying wing configuration with a rounded leading edge and analyzed the effect of the sideslip angle and flaperon. Through aerodynamic coefficient analysis, it was found that the effect of AoS on lift and drag coefficient was minimal and the side force and moment coefficient were markedly influenced by AoS. As the sideslip angle increased, the pitch break, which is related to the pitching moment coefficient, was delayed. Through stability analysis, the directional and lateral static stability of the flying wing configuration were increased by flaperon. Also, the structure and behavior of the leading edge vortex were analyzed by observing the contour of the pressure coefficient and the skin friction line.