• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.323-330
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• 1999

Daylight collapse have been occurred by about 5.0m deep at ground surface and collapse of the crown head part of the tunnel have connected to the ground surface during first step of shotcrete work after blasting of upper half section of the tunnel driving at two-way double track tunnel face section on highway construction. This study is for a successful illustration case for the earth improvement method through applying such strengthening methods as cement milk grouting, S.G.R grouting,, steel pipe reinforced multi-step grouting etc. for the purpose of earth strengthening of loosened earth block occurred by tunnel collapse.

• Journal of the Korean Geosynthetics Society
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• v.9 no.4
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• pp.47-55
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• 2010

In general, ground surface strengthening such as using geotextile is needed to secure trafficability of construction equipment. There are many researches for mechanical beha-vior of very soft ground covered with geotextile, however, most of them are under the condition to fix geotextile completely. In this study, numerical analyses were carried out to figure out the effects of restricting conditions of geotextile on bearing mechanism of very soft ground covered with geotextile. In numerical analyses, joint elements were used to figure out the friction properties between ground and geotextile. The results of numerical analyses were compared with the results of model test. In conclusion, the effects of restricting conditions of geotextile on bearing mechanism of very soft ground covered with geotextile became clear.

• Geomechanics and Engineering
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• v.24 no.5
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• pp.491-503
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• 2021

Shallow tunnels are vulnerable to earthquakes, and shallow ground is usually inhomogeneous. Based on the limit equilibrium method and variational principle, a solution for the seismic collapse mechanism of shallow tunnel in inhomogeneous ground is presented. And the finite difference method is employed to compare with the analytical solution. It shows that the analytical results are conservative when the horizontal and vertical stresses equal the static earth pressure and zero at vault section, respectively. The safety factor of shallow tunnel changes greatly during an earthquake. Hence, the cyclic loading characteristics should be considered to evaluate tunnel stability. And the curve sliding surface agrees with the numerical simulation and previous studies. To save time and ensure accuracy, the curve sliding surface with 2 undetermined constants is a good choice to analyze shallow tunnel stability. Parameter analysis demonstrates that the horizontal semiaxis, acceleration, ground cohesion and homogeneity affect tunnel stability greatly, and the horizontal semiaxis, vertical semiaxis, tunnel depth and ground homogeneity have obvious influence on tunnel sliding surface. It concludes that the most applicable approaches to enhance tunnel stability are reducing the horizontal semiaxis, strengthening cohesion and setting the tunnel into good ground.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.02a
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• pp.14-22
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• 1999

Daylight collapse have been occurred by about 6.$^{0}$ m deep at ground surface which connected to the ground surface and excessive overbreak have been occurred by the space and height of 3.$^1$~6.$^2$m at crown head part of the tunnel during tunnelling of lower-half part after completing upper-half part on tunnelling of a phyllite mountain by NATM method at the construction work of two way-double track national road. This study is a successful illustration case of earth improvement by confirming structural safety of the tunnel in a whole through solving the cause of the tunnel collapse and the work have completed successfully through applying such earth strengthening method as cement mortarㆍcement milk injection, S.G.R, steel pipe reinforced multi-step grouting etc.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1256-1263
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• 2010

Suction Drain Method is soft ground improvement technique, in which a vacuum pressure can be directly applied to the Vertical Drain Board to promote consolidation and strengthening the soft ground. This method does not require a surcharge load, different to embankment or Preloading Method. In this study, ground improvement efficiency of suction drain method was estimated when duplex loading pressure with vacuum and pressure. During suction drain method process, surface settlement and pore pressure were monitored, and cone resistance test as well as water content were also measured after the completion of Suction Drain Method treatment.

• Structural Engineering and Mechanics
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• v.23 no.1
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• pp.43-61
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• 2006

An investigation of the effectiveness of the interface treatment when column concrete jacketing is performed is presented. Alternative methods of interface connection were used in order to investigate the performance of strengthened concrete columns. These connecting techniques involved roughening the surface of the original column, embedding steel dowels into the original column and a combination of these two techniques. The experimental program included three strengthened specimens, one original specimen (unstrengthened) and one as-built specimen (monolithic). The specimens represented half height full-scale old Greek Code (1950's) designed ground floor columns of a typical concrete frame building. The jackets of the strengthened specimens were constructed with shotcrete. All specimens were subjected to displacement controlled earthquake simulation loading. The seismic performance of the strengthened specimens is compared to both the original and the monolithic specimens. The comparison was performed in terms of strength, stiffness and hysteretic response. The results demonstrate the effectiveness of the strengthening methods and indicate that the proper construction of a jacket can improve the behaviour of the specimens up to a level comparable to monolithic behaviour. It was found that different methods of interface treatment could influence the failure mechanism and the crack patterns of the specimens. It was also found that the specimen that combined roughening with dowel placement performed the best and all strengthened columns were better at dissipating energy than the monolithic specimen.

• Journal of the Korean Geosynthetics Society
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• v.8 no.3
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• pp.9-16
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• 2009

In generally, ground surface strengthening such as using geotextile is needed to secure trafficability of construction equipment. Several calculation methods for bearing capacity for very soft ground improved by geotextile have been proposed already but they are not established yet. In this paper, elastoplastic finite element analysis is carried out to estimate bearing capacity improvement for very soft ground reinforced by geotextile. In conclusion, by reinforcing with geotextile the bearing capacity improvement of very soft ground is increased with the increase of the settlement after yielding. And it is enough that the length of geotextile is about 3~4 times of the loaded width for the effect to the bearing capacity improvement. Finally, the biggest tensile force of geotextile occurs at an edge of the uniform load.

• The Journal of Korean Physical Therapy
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• v.27 no.4
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• pp.228-233
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• 2015

Purpose: Gait is the most basic element when evaluating the quality of life with activities of daily living under ordinary life circumstances. Symmetrical use of the lower extremities requires complicated coordination of all limbs. Thus, this study examined asymmetry of muscle activity quadriceps femoris and tibialis anterior as a baseline for training during over-ground walking and stair walking of stroke patients. Methods: Subjects were 14 stroke patients included as one experimental group. Gait speed used in this study was determined by the subject. Low extremity paretic and non-paretic EMG was compared using the surface EMG system. Results: The low extremity EMG difference was statistically significant during over-ground walking and stair walking (p<0.05). The result of low extremity EMG substituted symmetry ratio formula was compared to EMG symmetry ratio in both legs during over-ground walking and stair walking. The average symmetry ratio of quadriceps femoris during over-ground walking was 0.65, and average symmetry ratio of quadriceps femoris during stair walking was 0.47, with significant difference (p<0.05). Conclusion: EMG data was higher in stair walking than over-ground walking. However, in the comparison of symmetry ratio, asymmetric EMG of quadriceps femoris was significantly increased during stair walking. These findings suggested that application of stair walking for strengthening of both legs can be positive, but the key factor is maintaining asymmetrical posture of both legs. Therefore, physical therapists should make an effort to reduce asymmetry of quadriceps femoris power during stair walking by stroke patients.