• Journal of Soil and Groundwater Environment
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• v.25 no.3
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• pp.12-22
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• 2020

Managed aquifer recharge (MAR) is a promising water management strategy for securing stable water resources to overcome water shortage and water quality deterioration caused by global environmental changes. A MAR demonstration site was selected at Imgok-ri, Sangju-si, Korea, based on screening for the frequency of drought events and local water supply situations. The abundant groundwater discharging from a nearby abandoned coal mine is one of the potential recharge water sources for the MAR implementation. However, it has elevated levels of arsenic (~12 ㎍/L). In this study, the potential of the natural attenuation of arsenic by the field geological media was investigated using batch and column experiments. The adsorption and desorption parameters were obtained for two drill core samples (GM1; 21.8~22.8 m and GM2; 26.0~27.8 m depth) recovered from the potentially water-conducting fracture-zones in the injection well. The effluent arsenic concentrations were monitored during the continuous flow of the mine drainage water through the columns packed with the core samples. GM2 removed about 60% of arsenic in the influent (0.1 mg-As/L) while GM1 removed about 20%. The results suggest that natural attenuation is an acitive process occurring during the MAR operation, potentially lowering the arsenic level in the mine drainage water below the regulatory standard for drinking water. This study hence demonstrates that using the mine drainage water as the recharge water source is a viable option at the MAR demonstration site.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.05a
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• pp.29-34
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• 2002

[ $Nb/MoSi_2-ZrO_2$ ] laminate composites have been successfully fabricated by alternately stacking $MoSi_2-ZrO_2$ powder layer and Nb sheet, followed by hot pressing in a graphite mould. The fabricating parameters were selected as hot press temperatures. The instrumented Charpy impact test was carried out at the room temperature in order to investigate the relationship between impact properties and fabricating temperatures. The interfacial shear strength between $MoSi_2-ZrO_2$ and Nb, which is associated with the fabricating temperature and the growth of interfacial reaction layer, is also discussed. The plastic deformation of Nb sheet and the interfacial delamination were macroscopically observed. The $Nb/MoSi_2-ZrO_2$ laminate composites had the maximum impact value when fabricated at 1623K, accompanying the increase of fracture displacement and crack propagation energy. The interfacial shear strength of $Nb/MoSi_2-ZrO_2$ laminate composites increased with the growth of interfacial reaction layer, which resulted from the increase of fabricating temperature. there is an appropriate interfacial shear strength for the enhancement of impact value of $Nb/MoSi_2-ZrO_2$ laminate composites. A large increase of interfacial shear strength restrains the plastic deformation of Nb sheet.

• Tunnel and Underground Space
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• v.13 no.4
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• pp.304-315
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• 2003

In this paper, the DDA method with a new hydro-mechanical algorithm is used to study the effect of rock discontinuities on uplift and seepage in concrete gravity dam foundations. This paper presents an alternative method of predicting uplift and seepage at the base of concrete gravity dams. A sensitivity analysis was carried out to study the importance of several parameters on dam stability such as the orientation, spacing, and location of discontinuities. The study shows that joint water flow and adverse geological conditions could result in unusual uplift at the base of concrete gravity dams, well in excess of what is predicted with the classical linear or hi-linear pressure assumption. It is shown that, in general, the DDA program with the hydro-mechanical algorithm can be used as a practical tool in the design of gravity dams built on fractured rock masses.

• Tunnel and Underground Space
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• v.13 no.1
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• pp.44-51
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• 2003

Changes of the hydraulic conductivity resulting from the redistribution of stresses by underground excavation are examined using the strain-dependent hydraulic conductivity modification relation, where the modulus reduction ratio and induced strain are the major parameters. The modulus reduction ratio is defined in terms of RMR(Rock Mass Rating) to represent the full gamut of rock mass condition. Though shear dilation has the effect on the modification of hydraulic conductivity, the extent of it depends on RMR When the extensional strain is applied to a fracture, the hydraulic conductivity increases with the decrease of RMR Loading configuration has the effect on the modification of hydraulic conductivity, where the differential stress mode with a magnitude of the minimum principal stress $($\sigma$_x)$ fixed and a magnitude of the maximum principal stress $($\sigma$_y)$ varied is found to exert the greatest effect on the change of hydraulic conductivity.

• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.711-723
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• 2012

Structural tests were performed to investigate the structural performance of concrete-filled steel tube column using different strength steels in their flange and web with high-strength steel HSA800 and mild steel SM490, respectively. The test parameters included the strength of column flange and infill concrete, and effect of concrete infill. Connection between different grade steels were welded using the electrode appropriate for mild steel and verified its performance. To evaluate the behavior of test specimens, eccentric loading tests were performed and the results were compared with the prediction by current design codes. Axial load and moment carrying capacity of test specimens increased with the yield strength of compression flange and weld fracture occurred after the specimen shows full strength. The prediction result for axial load-bending moment relationship and effective flexural stiffness gave good agreement with the test result.

• Journal of Mechanical Science and Technology
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• v.18 no.11
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• pp.1932-1940
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• 2004

Although the previous researches evaluated the fatigue behavior of Al/GFRP laminates using the traditional fracture mechanism, their researches were not sufficient to do it : the damage zone of Al/GFRP laminates was occurred at the delamination zone instead of the crack-metallic damages. Thus, previous researches were not applicable to the fatigue behavior of Al/GFRP laminates. The major purpose of this study was to evaluate delamination behavior using the relationship between crack length (a) and delamination width (b) in Al/GFRP laminate. The details of investigation were as follows: 1) Relationship between the crack length (a) and the delamination width (b), 2) Relationship between the delamination aspect ratio (b/a) and the delamination area rate ((A$\_$D/)/subN// (A$\_$D/)$\_$All/), 3) The effect of delamination aspect ratio (b/a) on the delamination shape factor (f$\_$s/) and the delamination growth rate (dA$\_$D// da). As results, it was known that the delamination aspect ratio (b/a) was decreased and the delamination area rate ((A$\_$D/)$\_$N// (A$\_$D/)$\_$All/) was increased as the normalized crack size (a/W) was increased. And, the delamination shape factors (f$\_$s/) of the ellipse-II(f$\_$s3/) was greater than of the ellipse-I(f$\_$s2/) but that of the triangle (f$\_$s1/) was less than of the ellipse-I(f$\_$s2/).

• The Korean Journal of Pain
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• v.21 no.3
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• pp.197-201
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• 2008

Background: Kyphoplasty is a minimally invasive procedure that can stabilize osteoporotic and neoplastic vertebral fractures. We retrospectively evaluated the clinical outcomes of kyphoplasty for the treatment of vertebral compression fractures in cancer patients. Methods: We reviewed the clinical data of 27 cancer patients who were treated with kyphoplasty (55 vertebral bodies) between May 2003 and Feb 2008. The clinical parameters, using a visual analog 10 point scale (VAS) and the mobility scores, as well as consumption of analgesic, were evaluated preoperatively and at 1 week after kyphoplasty. Results: A total 55 cases of thoracic and lumbar kyphoplasties were performed without complications. The mean age of the patients was 66 years. All the patients experienced a significant improvement in their subjective pain and mobility immediately after the procedures. The pain scores (VAS), mobility scores and other functional evaluations using the Oswestry disability score and the SF-36 showed significant differences between the pre- and postoperational conditions. Conclusions: Kyphoplasty is an effective, minimally invasive procedure that can relieve the pain of patients with vertebral compression fractures and these fractures are the result of metastasis.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.16 no.1
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• pp.100-109
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• 2020

Pipelines subjected to ground movement would be easily exposed to large-scale deformation. Since such deformations may cause the pipeline failure, it is important to ensure the safety of pipelines in various operation conditions. However, crack in weld metal have been considered as one of the main causes that can deteriorate the structural integrity of the pipeline. For this reason, the structural integrity of the pipe containing the crack in the weld should be obtained. In order to assess cracked pipe, J-integral and crack-tip opening displacement(CTOD) have been applied widely as the elastic-plastic fracture mechanics parameters representing crack driving force. In this study, engineering solutions to calculate the J-integral and CTOD of pipes with a circumferential outer surface crack in the weld are proposed. For this purpose, 3-dimensional elastic-plastic finite element(FE) analyses have been performed considering the effect of overmatch and width of weld. The shape of the weld was simplified to I-groove, and axial displacement was employed as for loading condition. Based on FE results, the effects of crack size, material properties and width of weldment on J-integral and CTOD were investigated. Additionally, the J-integral and CTOD for I-groove were compared with those for V-groove to examine the effects of the weld shape, and a proportionality coefficient of J-integral and CTOD was calculated from the results of this paper.

• Ocean and Polar Research
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• v.36 no.4
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• pp.423-435
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• 2014

Verifying the similarity of environmental characteristics between an artificial impact site and a preserved or reference site is necessary to quantitatively and qualitatively evaluate the environmental impact of mining activity. Although an impact site (BIS station) and a preserved site (called KOMO station) that have been selected in the Korea manganese nodule contract area may share similar environmental characteristics, similarities in terms of the water column environment between both sites has not been investigated. In this study, we compared the chemical properties of the water columns and sinking particle fluxes between BIS and KOMO stations through two observations (August 2011 and September 2012). Additionally, we observed particle fluxes at the KOMO station for five years (July 2003~July 2008) to understand long-term natural variability. Vertical distributions of water column properties such as dissolved oxygen, inorganic nutrients (N, P, Si), total organic carbon below surface layer (within the depth range of 200 m) were not considerably different between the two sites. Especially, values of water column parameters in the abyssopelagic zone from 4000 m to bottom layer (~5000 m) were very similar between the BIS and KOMO sites. Sinking particle fluxes from the two sites also showed similar seasonality. However, natural variation of particle flux at the KOMO site varied from 3.5 to $129.9mg\;m^{-2}day^{-1}$, with a distinct temporal variation originating from ENSO events (almost forty times higher than a minimum value). These results could provide valuable information to more exactly evaluate the environmental impact of mining activity on water columns.

• Journal of Korean Neurosurgical Society
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• v.42 no.3
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• pp.195-199
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• 2007

Objective : Bilateral laminotomy and unilateral laminotomy for bilateral decompression are becoming the minimally invasive procedures for lumbar spinal stenosis (LSS). With the aim of less invasiveness and better preservation of spinal stability. these techniques have been developed. But there are no large randomized studies to show the surgical results between these two techniques. The objective of this study was to examine the safety and efficacy of these two minimally invasive techniques. Methods : A total of 80 patients were included in this study (Group I : bilateral laminotomy, Group II : Unilateral laminotomy for bilateral decompression). Perioperative parameters and complications were analyzed. Symptoms and scores such as visual analog scale (VAS) scores, Oswestry Disability Index (ODI) scores, and SF-36 scores of prospectively accrued patients were assessed preoperatively and at 1 month and 12 months after surgery. Paired-t test, two-sample student-t tests, and non parametric tests were used to determine cross-sectional differences between two groups. Results : No major complications such as spinal instability or deaths occurred during follow-up periods. VAS, ODI scores and SF-36 body pain and physical function scores showed statistically significant improvements in both groups (p<0.001). The significant widening of the spinal canal diameter was also noted in both groups. But, in Group II. there were minor postoperative complications such as dural tear (2 cases 5.0%), fracture of ipsilateral inferior facet (1 case 2.5%), and 5 cases of transient leg symptoms of contralateral side. Conclusion : Both bilateral laminotomy and unilateral laminotomy for bilateral decompression allow achievement of adequate and long-lasting operative results in patients with LSS. But postoperative complications are more frequent in Group II (unilateral laminotomy and bilateral decompression). These results indicate that bilateral laminotomy is the preferred minimally invasive technique to treat symptomatic LSS.