• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.2
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• pp.177-186
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• 2002

This paper describes the magnetic flux leakage(MFL) type non-destructive testing(NDT) system to detect the 3D defects in underground gas pipe. Magnetic systems with permanent magnets and yokes are analyzed by 3D non-lineal finite element method(FEM) with optimum design. In case of under-saturation of gas pipe, sensing signals are too weak to detect. In case of over-saturation, the changes of the sensing signals are too low to detect the defects sensitively. So, the operating points of the magnetic system are optimized to increase the changes of the MFL signals. The effects of the depth and size of the defects on the sensing signals are analyzed to define the range and resolution of the MFL sensors. To increase the sensor's sensitivity, the back-yoke sensors are introduced and tested.

• Journal of the Korean Institute of Gas
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• v.5 no.3 s.15
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• pp.63-72
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• 2001

An alternating current (AC) corrosion using coupon and electric resistance (ER) probe has been studied. Coupon coupled with ER probe were applied in terms of AC voltage from high value to low value through the survey of AC voltages on buried gas transmission pipeline over the country. Parameters such as AC current density of coupon, AC voltage, cathodic protection potential, soil resistivity and frequency were monitored continually. Corrosion induced by AC was observed even under cathodically protected condition that met cathodic protection criterion (below -850mv vs. CSE). Corrosion rate was affected mainly not by AC voltage but by both of frequency and AC current density. An experimental corrosion rate relationship could be obtained statistically, In which AC corrosion rate increased linearly with effective AC current density and its slope was 0.619 in case of coupon and 0.885 in case of ER probe.

• Composites Research
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• v.15 no.1
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• pp.21-31
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• 2002

To overcome the disadvantages of conventional excavation technology various trenchless (or excavation free, or no-dig) repair-reinforcement technologies have been developed and tried. But trenchless technologies so far developed have some drawbacks such as high cost and inconvenience of operation. In this study, a repairing-reinforcing process for underground pipes with glass fiber fabric polymer composites using VARTM (Vacuum Assisted Resin Transfer Molding) has been developed. The developed process requires shorter operation time and lower cost with smaller and simpler operating equipments than those of the conventional trenchless technologies. For the reliable operation of the developed method, a simple method to apply pressure and vacuum to the reinforcement was devised and flexible mold technology was tried. Also, resin filling and cure status during RTM process were monitored with a commercial dielectrometry cure monitoring system, LACOMCURE. From the investigation, it has been found that the developed repairing-reinforcing technology with appropriate process variables and on-line cure monitoring has many advantages over conventional methods.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.11
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• pp.1555-1565
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• 2010

This paper presents a new method for indentifying the location of impact source in a buried duct. In a gas pipeline, the problem of leakage occurs due to the mechanical load exerted by construction equipment. Such leakage can cause catastrophic disasters in gas supply industries. Generally, the cross-correlation method has been used for indentifying the location of impact source in a pipeline. Since this method involves the use of the dispersive acoustic wave, it derives an amount of error in process of estimating the time delay between acoustic sensors. The object of this paper is to estimate the time delay in the arrival of the direct wave by using the wavelet transform instead of the dispersive wave. The wavelet transform based method gives more accurate estimates of the impact location than the cross-correlation method does. This method is successfully used to identify the location of impact force in an actual buried gas duct.

• Journal of the Korean Geotechnical Society
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• v.20 no.1
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• pp.91-99
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• 2004

Researches on the induced trench method using compressible materials such as clay, mud, straw have been performed to reduce the load acting on buried conduits under a high fill in USA and Canada. And in-situ tests on load reductionmethod using EPS block as a compressible inclusion have been performed in Japan and Norway. Using a EPS block as a compressible materials can have various benefits such as cost-effective design, enlargement of safety and easy construction of structure under high fills. This paper analyzes the arching material function of EPS which can result in reduction of earth pressure by arching effect in Corrugated Steel Pipe. A series of tests were conducted to evaluate the reduction of earth pressure on conduits using EPS. Based on field test it is found that the magnitude of vertical earth pressure on conduits was reduced to about 35∼40% compared with conventional flexible conduit systems.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.05a
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• pp.11-20
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• 2002

This paper describes the magnetic flux leakage(MFL) type non-destructive testing(NDT) system to detect the 3D defects on underground gas pipe. Magnetic systems with permanent magnets and yokes are analyzed by 3D non-lineal finite element method(FEM) with optimum design. In case of under-saturation of gas pipe, sensing signals are too weak to detect. In case of over-saturation, the changes of the sensing signals are too low to detect the defects sensitively. So, the operating points of the magnetic system are optimized to increase the changes of the MFL signals. The effects of the depth and size of the defects on the sensing signals are analyzed to define the range and resolution of the MFL sensors. To increase the sensor's sensitivity, the back-yoke sensors are introduced and tested.

• Korean Journal of Construction Engineering and Management
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• v.21 no.4
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• pp.12-20
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• 2020

The demand for maintenance of underground facilities buried beneath the road continues to increase significantly, due to environmental problems caused by excessive noise and dust and complaints from urban residents, the demand for eco-friendly and low-noise road cutters is increasing. Therefore, we analyzed the cutting performance of low noise cutter and eco-friendly cutter and reviewed the improvement. Based on the field construction cases, problems and improvements were obtained according to the cutting machine working procedure. The productivity for cutting operations of eco-friendly cutters (36.0 seconds/m) was somewhat improved compared to the low noise cutters (37.6 seconds/m). However defects occurred in some sections and improvement was required.

• Journal of the Korean Geosynthetics Society
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• v.14 no.4
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• pp.35-43
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• 2015

In this study, it was performed in characteristics of settlement of roadbed materials with variation of water content using cylinder model device. The ratio of settlement ($R_e$) of subgrade soils in the initial water content were about 2.08, whereas it was increased about 4.06 which resulted in increase two times in the initial water content. Also, it was monitoring long-term to measure variation of the field water contents at concrete track using rainfall measuring sensors. The water content at directly underneath of concrete track rarely seems to affect the variation of water content, but it was increased by about 4% than intial water content with 20 mm/hr rainfall index at slope section. As for the result from the field date, it was determined that the water content of the inner subgrade layer was rarely affect caused by more than 20 mm/h rainfall index during if good drainage system at concrete track properly maintained.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2009.10a
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• pp.347-350
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• 2009

The latticed mesh grounding is compared with the diagonal mesh grounding. In the result, The latticed mesh grounding better than the diagonal mesh grounding at the maximum touch voltage, the grounding resistance and the total length of conductors.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2045_2046
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• 2009

광역상수도관에 대하여 외면부식직접평가(ECDA)를 실시하였다. ECDA평가는 과거 방식이력 등에 대한 사전검사, CIPS-DCVG-비저항 측정의 3단계 간접검사를 통해서 배관의 부식가능성이 큰 지점을 검출하여 위험성 우선순위를 판정하고 최종적으로 굴착을 통한 직접 검사 우선순위를 선정하였다. 직접 검사후 사후단계로 수집한 모든 데이터를 종합적으로 분석하여 검사구간의 건전성을 종합 평가를 하였다. 이러한 검사기법을 도입함으로써 배관의 부식위험지역을 파악하고 적절한 조치를 취할 수 있는 체계적인 근거를 마련한 것으로 판단하였다.