• Journal of the Korean Society of Safety
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• v.17 no.2
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• pp.52-57
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• 2002

In this study. stress-strain relationships were investigated by performing the confined extension tests for seven types of geosynthetics such as geotextiles, composite geosynthetics and geogrids. A comparison was made between unconfined and confined moduli for each geosynthetic material to quantify the soil confinement effect on stress-strain properties. A comparison was also made between the increase of moduli at the same strain level with the types of the geosynthetics to demonstrate the different stress-strain responses. Based on the result of the extension tests, the higher the confining stress, the larger the secant modulus of geosynthetics. The secant modulus at 5% strain is twice as much as that of 10% strain, especially there is a noticeable increasing of secant modulus for the two nonwoven geotextiles.

• Laser Solutions
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• v.11 no.2
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• pp.15-19
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• 2008

Electron beam (EB) weldability of pure grade Nb sheet was studied. One of Nb sheets was as-annealed and the other was cold rolled. Microstructures, Vickers hardness, and transverse weld tensile test were carried out for the base metal, the heat affected zone (HAZ) and weld metal. In the case of the EB welds made using the annealed Nb sheeet, fine equiaxed grains and coarse grains were dominant at the base metal and the HAZ, respectively, and columnar grains were observed at the weld metal. For the EB welds made using the cold rolled Nb sheet, elongated grains in the rolling direction at the base metal, and the microstructures of the weld metal and the HAZ are similar to those of the EB welds made using the annealed Nb sheet, respectively. For both annealed and cold rolled Nb sheet, the width of the HAZs are unusually wide in spite of using high density heat source, i.e. electron beam, and the grain sizes of both HAZs are similar. When tensile test was carried out using the transverse weld specimens, the failure occurred at the HAZ for both EB welds made using Nb sheets annealed and cold rolled, respectively and the tensile strengths of both specimens were 161MPa. Vickers hardness of EB welds made using annealed Nb was 56-57 Hv at both base metal and weld metal, 52-53 Hv at the HAZ. On the other hand, Vickers hardness of EB welds made using cold rolled Nb was 97-99 Hv at the base metal, but the hardness values of weld metal were similar to those obtained at the weld metal of annealed Nb.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.750-758
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• 2009

This study, as basic research which was intended to develope the surface reinforcement method using reinforcement material which is applicable to very soft ground in Korea, was aimed at proposing the design parameter for the surface ground improvement method. To that end, a wide width tensile test using geotextile, geogrid and steel bar (substitute for bamboo) and 25 kinds of the laboratory model tests with the end restraint conditions of the reinforcement that comprises the constrained and partially constrained (3 types) conditions were conducted. And the result indicated that the modulus of subgrade reaction or $N_c$ value (5.3) apparently overestimated the bearing capacity of very soft ground such as dredged ground. Moreover, as a result of model test by partially constraining the preload of 23.0kgf using geotextile, the effect of bearing capacity($q_1$) appeared to be the largest till the loading stress was $0.4tf/m^2$ due to cohesion, while it reached 75% of the maximum bearing force after $0.4tf/m^2$ due to increase in the effect of bearing capacity($q_2$) caused by the tensile force of the reinforcement. Such results tended to have appeared constantly or very similarly with each other, irrespective of the type of reinforcement (geogrid, steel bar) and constraint conditions.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.303-314
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• 2010

This study, as basic research which was intended to develope the surface reinforcement method using reinforcement material which is applicable to very soft ground in Korea, was aimed at proposing the design parameter for the surface ground improvement method. To that end, a wide width tensile test using geotextile, geogrid and steel bar (substitute for bamboo) and 49 kinds of the laboratory model tests were conducted. And the result the study suggested $\beta_s$, the stiffness coefficient to evaluate the stiffness effect of reinforcement materials. Then, it was also found that the stiffness coefficient, $\beta_s$ as the testing constant would be appropriate as high as 1.0, 1.1 and 1.5 for geotextile, geogrid and steel bar, respectively. And It was evaluated that the stiffness effect affecting reinforcement improvement effect would be reduced as the thickness of embeded depth increases and that RFe, the stiffness effect reduction coefficient would have positive correlation with H/B. Finally, it was confirmed that the bearing capacity gained from the method to calculate bearing capacity, which was suggested in the study, would almost correctly estimate the capacity, demonstrating the appropriateness of the proposed bearing capacity calculation method.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.339-344
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• 1999

For the Tailor Welded Blank sheet used for automobile body panel, the characteristics of fatigue strength and crack propagation behavior were studied. The thickness of specimen was machined to be same (0.9mm+0.9mm) and different (0.9mm+2.0mm). As a base test, mechanical properties around welding zone were examined. The results indicated that there were no significant decreases in mechanical properties, but hardness around welding bead is 2.3 times greater than base material. The fatigue strength was the highest when the loading direction was parallel to the welding direction, which was about 85% of tensile strength of base material. It was decreased by 8.5% when the thickness of specimen and base material was different, and it is increased by 25% when pre-strain was applied. The crack propagation rate was noticeable decreased around welding line and rapidly increased as it passed by welding line. Reviewing the shape of the crack propagation, crack width around welding line was wide around the welding zone due to retardation of crack growth, but it became narrow passing welding line due to decreased toughness.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.96-102
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• 2006

Because of the increasing need to use clayey soil as the backfill in reinforced soil structures and embankment material, nonwoven geotextiles with the drain capability have been receiving much attention. However, there are few studies of the deformation behavior of nonwoven geotextiles at geosynthetics reinforced soil structures in the field because the nonwoven geotextile, which has low tensile stiffness and higher deformability than geogrids and woven geotextiles, is difficult to measure its deformation by strain gauges and to prevent the water from infiltrating. This study proposes a new, more convenient method to measure the deformation behaviour of nonwoven geotextile by using a strain gauge; and examines the availability of the method by conducting laboratory tests and by applying it on two geosynthetics reinforced soil (GRS) walls in the field. A wide-width tensile test conducted under confining pressure of 7kPa showed that the local deformation of nonwoven geotextile measured with strain gauges has a similar pattern to the total deformation measured with LVDT. In the field GRS walls, nonwoven geotextile showed a larger deformation range than the woven geotextile and geogrid; however, the deformation patterns of these three reinforcement materials were similar. The function of strain gauges attached to nonwoven geotextile in the walls works normally for 16 months. Therefore, the method proposed in this study for measuring nonwoven geotextile deformation by using a strain gauge proved useful.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.153-161
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• 2005

A series of installation damage tests and creep tests are performed to assess the combined effect of installation damage and creep deformation far the long-term design strength of geogrid reinforcement. Three types of geogrids are used to investigate the influence of the geogrid types. From the experimental results, it is shown that installation damage and creep deformation of geogrids significantly depends on the polymer types of the geogrids and the larger the installation damage, the more the combined effect of installation damage and creep deformation. In addition, The results of this study show that the tensile strength reduction factor, RF, considering the combined effect between installation damage and creep deformation is less than that calculated by the current design practice which calculates the long-term design strength of geogrids damaged during installation by multiplying two partial safety factors, $RF_{ID}$ and $RF_{CR}$.

• Journal of the Korean Geosynthetics Society
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• v.8 no.2
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• pp.11-20
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• 2009

This study, as basic research which was intended to develope the surface reinforcement method using reinforcement material which is applicable to very soft ground in Korea, was aimed at proposing the design parameter for the surface ground improvement method. To that end, a wide width tensile test using geotextile, geogrid and steel bar (substitute for bamboo) and 21 kinds of the laboratory model tests with the end restraint conditions of the reinforcement that comprises the constrained and partially constrained (3 types) conditions were conducted. Moreover, a new procedure was proposed to take into account the effect of the stiffness of Reinforce materials on bearing capacity theory of Surface Reinforcement Method for Soft Ground.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1118-1125
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• 2009

This study, as basic research which was intended to develope the surface reinforcement method using reinforcement material which is applicable to very soft ground in Korea, was aimed at proposing Bearing Capacity Evaluation method for the surface ground improvement method. To that end, a wide width tensile test using geotextile, geogrid and steel bar (substitute for bamboo) and 21 kinds of the laboratory model tests with the end restraint conditions of the reinforcement that comprises the constrained and partially constrained (3 types) conditions were conducted. According to result of tests, Terzaghi's bearing capacity method is adequate to calculate bearing capacity in non-stiff material(geotextile, geogrid). But, It can't adequate to stiff material(bamboo net). So, New bearing capacity method suggest surface reinforcement method of very soft ground which Terzaghi's bearing capacity method modify for effect of stiffness.

• Journal of the Korean Geotechnical Society
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• v.23 no.4
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• pp.25-32
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• 2007

Because of the increasing use of clayey soil as the backfill in reinfurced soil structures and embankments, nonwoven geotextiles of drain capability have been receiving much attention. However, there are few studies on the deformation behavior analysis of nonwoven geotextiles in reinforced soil structures in the site because nonwoven geotextiles which have low tensile stiffness and higher deformability than geogrids and woven geotextiles, are difficult to measure their deformation by using strain gauges. In this study, it was suggested that a new and more convenient method could measure the deformation behaviour of nonwoven geotextile using a strain gauge and examine the availability of the method by conducting laboratory tests and applying to two geosynthetics reinforced soil (GRS) walls in the site. The result of wide-width tensile test conducted under confining pressure of 70 kPa shows that the local deformation of nonwoven geotextile to be measured with strain gauges has a similar pattern to the total deformation measured with LVDT. In the GRS walls, nonwoven geotextile shows a larger deformation range than the woven geotextile and geogrid. However, the deformation patterns of these three reinforcement materials are similar. The function of strain gauges attached to nonwoven geotextile in the walls works normally for 16 months. Therefore, the method proposed in this study for measuring nonwoven geotextile deformation using a strain gauge has proved useful.