• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.4
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• pp.111-119
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• 2016

Rebound hammer test, SonReb method and concrete core test are most useful testing methods for estimate the concrete compressive strength of deteriorated concrete structures. But the accuracy of the NDE results on the existing structures could be reduced by the effects of the uncertainty of nondestructive test methods, material effects by aging and carbonation, and mechanical damage by drilling of core. In this study, empirical procedure for verifying the in-situ compressive strength of concrete is suggested through the probabilistic analysis on the 268 data of rebound and ultra-pulse velocity and core strengths obtained from 106 bridges. To enhance the accuracy of predicted concrete strength, the coefficients of core strength, and surface hardness caused by ageing or carbonation was adopted. From the results, the proposed equation by KISTEC and the estimation procedures proposed by authors is reliable than previously suggested equation and correction coefficient.

• Journal of the Korean Arthroscopy Society
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• v.13 no.2
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• pp.174-178
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• 2009

Purpose: We introduce arthroscopic assisted core decompression for humeral head osteonecrosis. Operative technique: After diagnostic shoulder arthroscopy is performed using posterior and anterior portal, we make a 2 cm lateral skin incision approximately 3 cm distal to 1/3 of lateral margin of the acromion and place short gray cannula to prevent adjacent soft tissue injury when insert guide pin. Under C-arm fluoroscopic and arthroscopic guidance, 3 to 4 guide pins are inserted toward the necrotic area. Then we perform drilling using 7.0 mm reamer. Conclusion: We believe this technique is a less invasive approach and avoids the complications comparing to deltopectoral approach. Arthroscopic assisted core decompression is an effective procedure in management of early stage of the humeral head osteonecoris.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.359-365
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• 2008

As housing supply ratio has become over 100%, the strategic vision of government's policies has been changed from new construction to maintenance and regeneration of old architectural-structures. This fact has brought a light on the reconstruction and remodeling industries and a need for retrofit and rehabilitation techniques of existing foundation. Various methods of foundation for architectural-structures do exist. Among them, micropiling technologies are increasingly applied in foundation rehabilitation and seismic retrofitting projects. Micropiling techniques provide environmental-friendly methods for minimizing disturbance to adjacent structures, ground, and the environment. The installation is possible in restrictive area and general ground conditions. The fact that the installation procedures cause minimal vibration and noise and require very low ceiling height makes the micropiling methods to be commonly used for underpin existing structures. Specialized drilling equipment is often required to install the micropiles for existing basement facilities. This paper presents a case study in which micropiles were constructed to support a superstructure for vertical extension of existing elevator core and provide accessibility to underground parking lot. It is intended to become useful reference for the similar remodeling project.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.2
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• pp.135-141
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• 2011

In this study, the variation of the cutting forces generated in the machining process were evaluated experimentally. A material of $Al_{2}O_{3}$ ceramic and a tool of the dynamometer were used for the measurements of the cutting forces. With the constant rates of the feed and the tool rotation, the cutting forces were measured along three axial directions(X, Y, Z axis) for the various values of the hollow ratio. It was found that the cutting force be increasing linearly along the direction of Z axis, but along X, Y axis be not varied. Also from the viewpoint of the precesses of the hole drilling, the cutting force was found to be increasing sharply at the beginning process, but from the eighth process be increasing smoothly. As conclusions, the cutting force generated by machining for the material of $Al_{2}O_{3}$ ceramic are influenced more significantly by the feed rate and the hollow ratio than by the tool rotational speed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.18-24
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• 2003

A three node triangular element with drilling rotations incorporating improved higher-order zig-zag theory(HZZT) is developed to analyze the vibration of pretwisted composite plates with embedded damping layer. Shear force matching conditions are enforced along the interfaces between the embedded damping patch and the border patch by matching the shear forces of the embedded damping patch to the shear forces of the adjacent border patch. The natural frequencies and modal loss factors are calculated for cantilevered pretwisted composite blade with damping core with the present triangular element, and compared to experiments and MSC/NASTRAN using a layered combination of plate and solid elements.

• The Journal of Engineering Geology
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• v.26 no.2
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• pp.207-221
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• 2016

As greater numbers of fill dams and reservoirs become old, the risks of damage or embankment collapse increases. However, few studies have considered the deterioration and hazard classification of the internal core layers of fill dams. This study reports the results of geotechnical investigations of 13 earth-cored fill dams in Korea, based on no-water borehole drilling, Standard Penetration Test, and 2D and 3D electrical resistivity surveys along with in situ and laboratory testing. High-capacity no-water boring minimized core layer disturbance while providing continuous core sample recovery. The results allow the classification of potential hazards related to the existing core layers based on both visual inspection of the recovered samples and the results of engineering surveys and tests. Four types of potential hazard are classified: locally fluidized core with a high water content, rapid water inflow to a borehole, cores with granular materials, and relatively low stiffness of core. Among these, the locally fluidized core is the most critical hazard that requires remedial action because it is related to the potential internal flow path and internal erosion. The other three hazard types are of medium importance and require careful monitoring and regular inspection. Of note, there was no correlation between age and core deterioration. The results are expected to aid the safe management and potential upgrading of aging cored fill dams.

• Tunnel and Underground Space
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• v.5 no.4
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• pp.347-362
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• 1995

The purpose of this study was that manage effectively the excavation process of the transport tunnel in DONGHAE mine area by investigating the variationof the surface and groundwater flow system around the tunnel and neighbouring villages. Thus, the effect of excavation and water-prrofing process on the water system has been studied through the naked eye survey of the tunnel and the surface outcrop, joint survey, core drilling, the measurement of the surface water quantity, evapotranspiration and precipitation analysis, rock hydraulics approach, the pressure test of boreholes, the variation of the water level, and finally the numerical analysis. From above approachs, we derived the conclusion that the exhaustion of the surface water was not caused by the tunnel excavation on the groundwater system was minimized by effective water proofing process.

• Economic and Environmental Geology
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• v.27 no.3
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• pp.289-294
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• 1994

This paper describes an effective utilization method of well logging data and boring cores for understanding the geology of Keoje-do area. Six holes were drilled in 1988-1989, and all rock cores were recovered. Nevertheless, seven kinds of logs were carried out in each borehole. The geologic situations of the drilling sites are accurately evaluated from a comparison between core descriptions and well logging data. Porosities and clay contents of sedimentary rocks can be calculated using the data of density and gamma-ray logs. Fractured zones are easily detected from the change in inside diameter of borehole by caliper log. Sonic, density and gamma-ray logging data clearly indicate alternated and dyke zones; the former can be detceted from an acoustic wave attenuation and a decline of compaction by sonic and density logs, the latter can be detected from the amount of potassium contents of bed rock and dyke by gamma-ray log.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2004.02a
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• pp.51-59
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• 2004

The geological research as a part of HLW disposal program in Korea is carried out to provide necessary data for the establishment of the reference repository system in term of design and safety assessment in the crystalline rock terrains. Six deep boreholes were drilled to obtain hydrogeological and hydrochemical data from Jurassic granites in the Yuseong area, Korea. The core observation, televiewer logging and hydraulic testing were carried out during and after drilling and multi-packer system were installed in the boreholes of 500m depth for hydraulic and hydrochemical monitoring including environmental isotopes. The integration of hydrogeochemical and hydrodynamic data would be built greater confidence for the understanding of groundwater system in fractured rock mass. This geoscientific program could be possible to suggest a general guideline to develop the reference disposal concept of high-level radioactive waste in Korea.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.04a
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• pp.435-440
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• 2000

In this study, we aims to develop the machining technology for the ultra precision surface and profile accuracy. For this purpose, we construct the electrolytic in process grinding system (ELID grinding) and apply to the cylindrical and internal grinding. Through the various machining experiments such as SCM steel., ceramics, tungsten carbide etc., we have obtained nanometer surface roughness. And we have applied this mirror grinding technique to hydraulic manual valve and mold core of mini disk optical pick-up base. For the development of fine mechanical part machining technology, e have made multi fiber optical connector using fine grinding technology. And constructed micro drilling system with process monitoring system which is possible to drill 50${\mu}{\textrm}{m}$ diameter hole.