• Proceedings of the KSR Conference
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• 2004.10a
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• pp.1156-1161
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• 2004

The factors affecting the long-term design strength of geogrid for railroad reinforcement can be classified into factors on creep deformation, installation damage, temperature, chemical degradation, biological degradation. Especially, creep deformation and installation damage are considered as main factors to determine the long-term design strength of geogrid. This paper describes the results of a series of experimental study, which are carried out to assess the combined effect of installation damage and creep deformation for the long-term design strength of geogrid reinforcement. In this study, a series of field tests are carried out to assess installation damage of a various geogrids according to different fill materials, and then creep tests are conducted to assess the creep properties of both undamaged and damaged geogrids.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.561-568
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• 2005

The factors affecting the long-term design strength of geogrid can be classified into factors on creep deformation, installation damage, temperature, chemical degradation and biological degradation. Especially, creep deformation and installation damage are considered as main factors to determine the long-term design strength of geogrid. Current practice in the design of reinforced soil is to calculate the long-term design strength of a reinforcement damaged during installation by multiplying the two partial safety factors, $RF_{ID} and RF_{CR}$. This method assumes that there is no synergy effect between installation damage and creep deformation of geogrids. Therefore, this paper describes the results of a series of experimental study, which are carried out to assess the combined effect of installation damage and creep deformation for the long-term design strength of geogrid reinforcement. The results of this study show that the tensile strength reduction factors, RF, considering combined effect between installation damage and creep deformation is less than that calculated by the current design method.

• Geomechanics and Engineering
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• v.21 no.2
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• pp.171-178
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• 2020

Mountainous areas cover more than 70% of Korea. With the rapid increase in tunnel construction, tunnel-collapse incidents and excessive deformation are occurring more frequently. In addition, longer tunnel structures are being constructed, and geologically weaker ground conditions are increasingly being encountered during the construction process. Tunnels constructed under weak ground conditions exhibit long-term deformation behavior that leads to tunnel instability. This study analyzes the behavior of the bottom region of tunnels under geological conditions of long-term deformation. Long-term deformation causes various types of damage, such as cracks and ridges in the packing part of tunnels, as well as cracks and upheavals in the pavement of tunnels. We observed rapid tunnel over-displacement due to the squeezing of a fault rupture zone after the inflow of a large amount of groundwater. Excessive increments in the support member strength resulted in damage to the support and tunnel bottom. In addition, upward infiltration pressure on the tunnel road was found to cause severe pavement damage. Furthermore, smectite (a highly expandable mineral), chlorite, illite, and hematite, were also observed. Soil samples and rock samples containing clay minerals were found to have greater expansibility than general soil samples. Considering these findings, countermeasures against the deformation of tunnel bottoms are required.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.4
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• pp.1033-1040
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• 1995

To simulate strength reliability and durability of ceramic parts under gas turbine application environments, particle impact damage behaviors in silicon carbide oxidized at 1673 K and 1523 K for 200 hours in atmosphere were investigated. The long-term oxidation produced a slight increase in the static fracture strength. Particle impact caused a spalling of oxide layer. The patterns of spalling and damage induced were dependent upon the property and impact velocity of the particle. Especially, the difference in spalling behaviors induced could be explained by introducing the formation mechanism of lateral crack and elastic-plastic deformation behavior at impact sit. At the low impact velocity regions, the oxidized SiC showed a little increase in the residual strength due to the cushion effect of oxide layer, as compared with the as-received SiC without oxide layer.

• Korean Circulation Journal
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• v.48 no.11
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• pp.1014-1024
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• 2018

Background and Objectives: Intense exercise (IE) induced myocardial fibrosis (MF) showed contradictory findings in human studies, making the relationship between IE and the development of MF unclear. This study aims to demonstrate exercise induced MF is associated with cardiac damage, and inflammation is essential to the development of exercise induced MF. Methods: Sprague-Dawley rats were submitted to daily 60-minutes treadmill exercise sessions at vigorous or moderate intensity, with 8-, 12-, and 16-week durations; time-matched sedentary rats served as controls. Enzyme-linked immunosorbent assay (ELISA) was used to measure serum cardiac troponin I (cTnI) concentration. After completion of the exercise protocol rats were euthanized. Biventricular morphology, ultrastructure, and collagen deposition were then examined. Protein expression of interleukin $(IL)-1{\beta}$ and monocyte chemotactic protein (MCP)-1 was evaluated in both ventricles. Results: After IE, right but not left ventricle (LV) MF occurred. Serum cTnI levels increased and right ventricular damage was observed at the ultrastructure level in rats that were subjected to long-term IE. Leukocyte infiltration into the right ventricle (RV) rather than LV was observed after long-term IE. Long-term IE also increased protein expression of proinflammation factors including $IL-1{\beta}$ and MCP-1 in the RV. Conclusions: Right ventricular damage induced by long-term IE is pathological and the following inflammatory response is essential to the development of exercise induced MF.

• Journal of the Korean Geosynthetics Society
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• v.4 no.4
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• pp.23-37
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• 2005

The factors affecting the long-term design strength of geogrid can be classified into factors on creep deformation, installation damage, temperature, chemical degradation and biological degradation. Especially, creep deformation and installation damage are considered as main factors to determine the long-term design strength of geogrid. Current practice in the design of a reinforced soil structures is to calculate the long-term design strength of a geosynthetic reinforcement damaged during installation by multiplying the two partial safety factors, $RF_{ID}$ and $RF_{CR}$. This method assumes that there is no evaluation of synergy effect between installation damage and creep deformation of geogrids. This paper describes the results of a series of experimental study, which are carried out to assess the combined effect of the installation damage and the creep deformation for the long-term design strength of geogrid reinforcements. A series of field tests was carried out to assess installation damage of various geogrids with respect to different fill materials, and then creep tests are conducted to evaluate the creep deformation of both undamaged and damaged geogrids. The results indicated that the tensile strength reduction factors, RF, considering the combined effect between the installation damage and the creep deformation is less than that calculated by the current design method.

• Journal of the Korean Geosynthetics Society
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• v.3 no.4
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• pp.29-40
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• 2004

The factors affecting the long-term design strength of geogrids can be classified into factors on creep deformation, installation damage, temperature, chemical degradation, biological degradation. Especially, creep deformation and installation damage are considered as main factors to determine the long-term design strength of geogrids. This paper describes the results of a series of experimental investigation, which were conducted to assess the installation damage according to different fill materials and creep characteristic of various geogrids. The results of this study show that the installation damage and creep deformation of geogrids significantly depends on a row material and a manufacturing process of geogrids.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2009.10a
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• pp.441-445
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• 2009

The most of the goals of pump designers and users are efficient operation and productivity. But the safety-grade pumps in nuclear power plants are needed to operate continuously for an essential condition of system operation. Also, most of the rules and regulatory standards that have been prepared for nuclear pumps are dedicated to achieve public safety. The study examined pump vibration in a pump outlet flow and distinguished the regions of pump vibration frequency cause by cavitation and recirculation. The study made a counterproposal in determination of pump outlet flow so that the discharge flow will be able to minimize the long-term damage of the pump.

• Journal of the Korean Geosynthetics Society
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• v.9 no.4
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• pp.75-84
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• 2010

In this study, the long-term performance tests, which have extensibility, creep deformation, installation resistance and durability characteristic, is conducted to apply geosynthetic strip in field. The strength reduction factors using the test results are evaluated in order to calculate long-term design tensile strength. First, the creep deformation was evaluated by both the stepped isothermal method(SIM) and the time-temperature superposition(TTS) method. The creep reduction factor is reasonable to apply 1.6. Second, the result of installation damage test had little damage of yarn, which affected strength of reinforcement. Therefore, it can be analyzed that the installation damage of geosynthetic strip has little effect of long-term design tensile strength. Finally, the durability reduction factor considering chemical, biological and outdoor exposure resistance is reasonable to apply 1.1, which is considered the stability and economic efficiency of reinforced earth wall using geosynthetic strip.

• Advances in Traditional Medicine
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• v.9 no.1
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• pp.39-48
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• 2009

We have evaluated the effect of long term treatment of Enicostemma littorale (E. littorale) in type 2 diabetic patients taking pills of aqueous extract of E. littorale regularly as a complimentary medicine for at least 9 months. The effects of E. littorale on glycemic control, lipid profile, cardiac function and DNA damage in these patients were compared with those who had not been regular in taking E. littorale but regular in taking other conventional anti-diabetics. Our data suggest that, E. littorale can maintain normal blood glucose, serum insulin, serum triglycerides levels of type 2 diabetic patients if taken regularly. E. littorale also improves insulin sensitivity, and normalize disturbed lipogram and elevated creatinine levels, thereby produces beneficial effect in preventing cardiovascular complications and may preserve the kidney function. The finding that E. littorale also prevents DNA damage suggest a long term effect in diabetic patients. E. littorale thus can be considered as safe supplementary therapy for a long term and effective management of type 2 diabetic patients.