• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.6C
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• pp.239-247
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• 2012

Some methods were proposed to predict lateral flow due to embankments for road constructions on soft grounds, in which vertical drains were placed. In order to investigate the prediction methods of lateral flow, 200 field monitoring data for embankments in thirteen road construction sites at western and southern coastal areas of the Korean Peninsula were analyzed. For analyzing the relationship between the safety factor of embankment slope and the horizontal displacement in soft grounds where horizontal drain mats were placed, it was reliable to apply the maximum horizontal displacement in soft ground instead of the horizontal displacement at ground surface. The maximum horizontal displacement was developed less than 50mm in fields where the safety factor of slope was more than 1.4, while the one was developed more than 100mm in fields where the safety factor of slope was less than 1.2. In safe fields where the maximum horizontal displacement were developed within 50mm, lateral flow would not happen since shear deformation was not appeared. On the other hand, shear failure would happen in the fields where the maximum horizontal displacement were developed more than 100mm. In such fields, embankments might be continued after some appropriate countermeasures should be prepared. Safe embankments can be performed on soft grounds, in which the stability number is less than 3.0 and the safety factor for bearing is more than 1.7. However, if the stability number is more than 4.3 and the safety factor for bearing is less than 1.2, shear deformation would begin and even shear failure would happen.

• Magazine of the Korean Society of Agricultural Engineers
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• v.42 no.5
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• pp.133-143
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• 2000

A large scale field test of prefabricated vertical drains was performed to anayze the effect of parameters of the very soft clay at a test site. compression index and the coefficient of horizontal consolidation obtained by back-analysis of settlement data were compared with those obtained by means of laboratory tests. Hyperbolic method, Asaoka meoth and curve fitting method were used to compute final settlement of coefficient of consolidation. The relationships of settlement measurement(Sm) versus design settlement(St) and the measurement consolidation ratio(Um) versus design consolidation (Ut) were shown as Sm=(1.0~1.1) St , Um=(1.13~1.17) Ut at 1.0m spacing of drain and Sm=(0.7~0.8)St, Um= (0.92~0.99) Ut at 1.5 m spacing of drain, respectively . The relationships of the field compression index(CcField) and virgin compression index(vcc lab) were shown as Ccfield =(1.0~1.2)vcc lab . But it was nearly within the same range when considering the error factor with the determination method of virgin compression index and the prediction back-analysis of the settlement data was larger than the coefficient of vertical consolidation, and the ratio of consolidation coefficient (Ch/Cv) was Ch =(2.4~2.9) Cv , Ch=(3.4~4.2) Cv at 1.0m and 1.5m spacing of drain, respectively.

• Magazine of the Korean Society of Agricultural Engineers
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• v.42 no.4
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• pp.115-123
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• 2000

This study compared the degree of consolidation by hyperbolic, curve fitting , Asaoka's and methods using values measured with a theoretical curve in consideration of smear effect and well resistance. The degree of consolidation by the Hyperboilc method was underestimated than the degree of consolidation by Curve fitting. Asaoka's , and Monden's methods. The typical range of the coefficient of horizontal consolidation was Ch=(2-3)Cv in the case considering smear effect and well resistance, and Ch =(0.5-2.1) Cv in the case disregarding smear effect and well resistance. The degree of consolidation obtained by ground settlement monitoring was nearly the same value when the coefficient of smear zone permeability by back analysis was shown to be half that of in-situ and the diameter of the smear zone was shown to be double that of mandrel. By increasing the diameter reduction ratio of the drain, the time of consolidation was delayed. The effect of well resistance showed that the case of a small coefficient of permeability was much more than in the case of a large coefficient of permeability . It was recommended that when designing diameter reduction of a drain, well resistance should be considered.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.11a
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• pp.89-92
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• 2007

In the present study, the flow field in a square container with various comer rounding is studied to investigate drain flow characteristics. An attempt has been made to understand the mechanism that is responsible for vortex suppressing by the different radius of rounding at the comer. For this purpose, flow visualization studies using PIV (Particle Image Velocimetry) are employed to determine the flow patterns in a square tank. Results are obtained when there is no draining and with draining. The flow field is visualized both in horizontal and vertical planes.

• Journal of Electrical Engineering and information Science
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• v.2 no.3
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• pp.132-138
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• 1997

Electrical characteristics of split-gate flash EEPROM with triple polysilicon is investigated in terms of effects of floating gate and offset gate. In order to search for t the effects of offset gate on programming characteristics, threshold voltage and drain current are studied with variation of control gate voltage. The programming process is believed to depend on vertical and horizontal electric field as well as offset gate length. The erase and program threshold voltage are found to be almost constant with variation of control gate voltage above 12V, while endurance test indicates degradation of program threshold voltage. With increase of offset gate length, program threshold voltage becomes smaller and the drain source voltage just after program under constant control gate voltage becomes higher.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.313-316
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• 2007

In the present study, the flow field in a square container with various corner rounding is studied to investigate drain flow characteristics. An attempt has been made to understand the mechanism that is responsible for vortex suppressing by the different radius of rounding at the corner. For this purpose, flow visualization studies using PIV (Particle Image Velocimetry) are employed to determine the flow patterns in a square tank. Results are obtained when there is no draining and with draining. The flow field is visualized both in horizontal and vertical planes.

• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.109-119
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• 2017

In this research, it was investigated that whether the upper sand deposited in Nakdong River Estuary Delta region has the role of horizontal drains like sand mat. The results from tests for particle size distribution and permeability of the upper sand deposit did not meet completely the criteria for the horizontal drain material. Thus, numerical analysis has been conducted additionally. Numerical analyses of consolidation of soft soils with upper layer of sand deposit are conducted in both the sand mat with a thickness of 1m and the upper sand deposit with 1, 2, 3, and 4 m of thickness and their results are compared. As the results of numerical analysis, the upper sand deposit with a thickness of 2m or more may play the role of horizontal drains similar to a sand mat. If a PVD is installed, the ability of upper sand deposit as horizontal drains is increased. Form this study, it was concluded that the upper sand deposited in Nakdong River Estuary Delta has the role of horizontal drain.

• Journal of the Korean GEO-environmental Society
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• v.8 no.5
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• pp.31-38
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• 2007

The practical design method on sandmat uses a drain length, rate of consolidation settlement and permeability of sand as a major design factors. And, on the basis of this design process, it has been installed beneath the embankment with same thickness. However, the possibility the underestimation on the thickness of sandmat and the delayed drain have been pointed out by several authors caused by a differential settlement at the center and the end of embankment. In this study, therefore, the effect of the differential settlement on the thickness of sandmat and delayed drain through the numerical analysis of embankment was analyzed. As a result, a substantial sandmat thickness becomes small and the possibility of the delayed drain can be certified because of the development of differential settlement at the center and ends of embankment. As a countermeasure to overcome this problem, the applicability of the mound type sandmat was also investigated by the numerical method. It can be concluded that it maintains the designated substantial sandmat thickness throughout consolidation process, and is useful method to maintain the drain capacity. Especially, the mound type sandmat is effective method for a construction site where can cause a differential settlement such as embankment. Furthermore, it has to be designed on the basis of the accurate prediction of consolidation settlement as well as rate of consolidation settlement, drain length and permeability of sand.

• Geotechnical Engineering
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• v.10 no.3
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• pp.33-40
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• 1994

The effects of smear and well resistance should be taken into account for the design of sand drains. Practically, simple design, which employs the method using 112 reduced diameter of drains or assuming the coefficient of consolidation in horizontal direction equals to that in vertical direction, based on the theory neglecting these effects, has been used. In this study, the reliability of existing simple design methods as well as the influences of smear and well resistance was investigated with the equations proposed by Hansbo and Onoue. It is shown that the consolidation time is chiefly governed by the effect of smear for drains with highly permeable sands. For general soil condition and placing type of sand drain, consolidation time is underestimated for simple design wi어. 1/2 reduced diameter of drains, and it is overestimated for that with the assumption that the coefficient of consolidation in horizontal direction equals to that in vertical direction. Through the investigations on different reduced diameter, it was shown that simple design with 1/4 reduced diameter of drains yielded the reliable results with errors less than 6%.

• Geotechnical Engineering
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• v.1 no.1
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• pp.73-84
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• 1985

This Paper aims at investigating the distribution of stresses and the displacement of soft foundation layer subject to embankment load by the finite elements method (FEM). The stresses include the volumetric stress, the Pore water Pressure, the vertical stress. The horizontal stress and the shear stress. The Christian-Boehmer's method was selected as technique for FEM and the general elasticity model and modified Cam-clay model as the governing equations under Plain-strain condition depending on drained and undrained conditions. The results obtained are as follows: 1. The volumetric stress is almost consistent with the pore water pressure. This means that the total stress is the same value with the pore water pressure under the undrined condition 2. The vertical stress appears in the same value regardless of the drained or undrained condition and the model of the constitutive equations. 3. The horizontal stress has almost same value with the drain condition model. 4. depending on the constitutive model. The shear stress is affected by both the drain condition and the constitute model. The resulted value by the modified Cam-clay model has the largest. 5. The direction of the displacement vector turns outward near the tip of load during the increasing load. 6. The magnitude of displacement due to the modified Cam.clay model is as twice large as that due to elastic model.