• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.2
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• pp.143-154
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• 2016

This study investigated the occurrences, causes, and mitigation of the recent ground subsidence and underground cavity generation events in Korea. Two main causes of ground subsidence are (1) the soil erosion by seepage during tunneling and earth excavation and (2) the damage of underground pipes. The main cause of the soil erosion during tunneling was the uncontrolled groundwater flow. Especially, when excavating soft grounds using a tunnel boring machine (TBM), the ground near TBM operation halt points were found to be the most vulnerable to failure. The damage of underground pipes was mainly caused by poor construction, material deterioration, and differential settlement in soft soils. The ground subsidence during tunneling and earth excavation can be managed by monitoring the outflow of groundwater and eroded soils in construction sites. It is expected that the ground subsidence by the underground pipe damage can be managed or mitigated by life cycle analysis and maintenance of the buried pipes, and by controlling the earth pressure distribution or increasing the bearing capacity at the upper ground of the buried pipes.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.3
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• pp.275-281
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• 2004

Socket weldment used to change the flow direction of fluid nay have flaws such as lack of fusion and cracks. Liquid penetrant testing or Radiography testing have been applied as NDT methods for flaw detection of the socket weldment. But it is difficult to detect the flaw inside of the socket weldment with these methods. In order to inspect the flaws inside the socket weldment, a ultrasonic testing method is established and a ultrasonic transducer and automated ultrasonic testing system are developed for the inspection. The automated ultrasonic testing system is based on the portable personal computer and operated by the program based Windows 98 or 2000. The system has a pulser/receiver, 100MHz high speed A/D board, and basic functions of ultrasonic flaw detector using the program. For the automated testing, motion controller board of ISA interface type is developed to control the 4-axis scanner and a real time iC-scan image of the automated testing is displayed on the monitor. A flaws with the size of less than 1mm in depth are evaluated smaller than its actual site in the testing, but the flaws larger than 1mm appear larger than its actual size on the contrary. This tendency is shown to be increasing as the flaw size increases. h reliable and objective testing results are obtained with the developed system, so that it is expected that it can contribute to safety management and detection of repair position of pipe lines of nuclear power plants and chemical plants.

• Journal of the Korea Concrete Institute
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• v.24 no.5
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• pp.509-516
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• 2012

The aims of this research is to develop a fire resistant admixture to enhance high-pressured pumping of high-strength concrete (HSC) with a compressive strength of 60~80 MPa. Generally, the efficiency of HSC high-pressured pumping is dramatically reduced due to entanglement of short fibers added to prevent fire spalling. Therefore, the fire resistant admixture that can facilitate pumping of fire resistant HSC is urgently needed presently. The fire resistant HSC mix is comprised of Polypropylene fiber, Nylon fiber and Polymer powder. The test results showed that the slump-flow was improved by approximately 70% of the HSC without fire resistant admixture. However, the air void content was increased slightly due to the addition. The standard design compressive strength at 28-days was satisfied, while its flexural strength was similar to the concrete without the admixture. Since the flexural strength was 12~15% of its compressive strength, the general trend of flexural to compressive strength ratio in normal concrete was maintained. Even though its elastic modulus was decreased by adding the admixture, the study results showed that the concrete can be used for construction since all of the test results exceeded the code requirements.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.2
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• pp.141-151
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• 2015

A new rock excavation method using an abrasive injection waterjet system has been developed to enhance the efficiency and reduce the vibration of tunnel excavation. The abrasive feed rate is an important factor for the cutting performance and the economical efficiency of waterjet-based excavation. In this study, various experiments were performed to explore the effects of major process parameters for both the abrasive feed rate and the suction pressure occurring inside the mixing chamber when the abrasives are inhaled. Experimental results reveal that the abrasive feed rate is affected by geometry parameters (abrasive pipe height, length, and tortuosity), abrasive parameters (abrasive particle size), and jet energy parameters (water pressure and water flow rate). In addition, the relation between the cutting performance and the abrasive feed rate was discussed on the basis of the results of an experimental study. The cutting performance can be maximized when the abrasive feed rate is controlled appropriately via careful management of major process parameters.

• The Journal of Pediatrics of Korean Medicine
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• v.20 no.3
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• pp.143-160
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• 2006

Objectives : As the side effect brought up by internet game addiction, many reports come out, but most of past articles are for middle or high school students. There is seldom a poisoning game treatise to a primary school student, if there is treatise, it is real condition that treatise for lead pipe with psychological reasons is seldom discussion about physical symptoms. This research searches high grade elementary students' game use actual conditions and when divide to general user group, latent danger use group, high dangerous use group, according to serious illness degree of game poisoning, three groups and game poisoning happens, recognized about body symptoms that happen much. Methods : Target population of these questionnaire are fifth and sixth grade elementary student of Seoul city 2 school. Chose 263 elementary students, 144 men, 119 women who understand purpose of research and admit participation is 25 October, 2006 since 1 September, 2006 Results : As poisoning serious illness degree is high, there are many number of game times, much more boys are addicted to internet game than girs, insomnia is apt to happen frequently in game poisoning danger group, and correlation is high by megrim, shoulder ache, digestive trouble. Insomnia, symptoms that show next even if some symptoms show first because there is high correlation between megrim, shoulder ache, digestive trouble is high possibility to happen among four symptoms. Insomnia, megrim, shoulder ache, digestive trouble that happen by internet game poisoning, is apt to increase by increasing addiction. Symptoms treatment can divide by internal treatment that treat insomnia, megrim, digestive trouble, external treatment that is typical symptoms of VDT syndrome shoulder ache, headache, fatigue persimmon. Root treatment is mind symptoms treatment. Game addiction treatment is relationship method 'seven emotions injury treatment' in oriental medicine. 'promote the normal flow of qi' and 'adjustment of suitable emotion' can talk as pivotal point of treatment.

• Journal of Korean Society of Disaster and Security
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• v.10 no.1
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• pp.1-10
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• 2017

Recently, increasing cases of ground subsidence in the urban area has become social issue, and related bill has been passed. Ground subsidence occurs through complex combination of various factors, and numerical analysis of this problem is limited thereby. This is why verification of ground subsidence mechanism has been conducted through physical modelling. Previous researches has been focused on modelling ground subsidence caused by utility pipe defects, and there has been insufficient physical modelling study on ground subsidence caused by various reasons such as groundwater flow and excavation activity. Also, most previous physical modelling studies were performed in 1g condition, which cannot take the in-situ stress condition into the evaluation of the ground subsidence mechanism. Therefore, in this study, physical modelling techniques to simulate various conditions is discussed by studying the previous researches on the ground subsidence mechanism through physical modelling. Also, centrifuge modelling test is suggested in this study as the technique to perform more reliable evaluation of ground subsidence mechanism. Lastly, this study suggests to apply the techniques used in the evaluation of ground subsidence mechanism into Ground Stability Assessment.

• Journal of Bio-Environment Control
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• v.9 no.3
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• pp.156-160
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• 2000

The Plasma film treated with a high electric voltage was developed to enhance flow down of condensation drops on inside plastic film. Arch type greenhouse framed with iron pipe of 25mm diameter defand 1.5mm thickness were covered with either the developed plasma film or surfactant film(control). Green pepper seedlings raised for 40 days in plug trays were transplanted at a density of 110cm by 30cm in each greenhouse. The mount of condensational water on film surface, generated by 7$0^{\circ}C$ water bath chimney systems and flew down, was collected and measured. The amount of collected water after 150 minutes was 2.56 mL.100c $m^{-2}$ and 0.94mL.100c $m^{-2}$ , respectively, in the plasma film and surfactant film-covered greenhouses. The amount of condensational water drops attached on the cover at 08:20 a.m. at 60 days filter covering was 0.34mL.100c $m^{02}$ and 0.32mL.100c $m^{-2}$ , respectively, in the plasma film- and surfactant film-covered greenhouses. Solar irradiance transmitted into greenhouse was 2.0% higher in the greenhouse covered with the plasma film tan that in the greenhouse covered with the surfactant film. Air temperature in the plasma film-covered greenhouse was higher than the surfactant film-covered greenhouse by 0.5$^{\circ}C$. However, there was no difference in relative humidity between the two greenhouse. Plant height, leaf area, dry weight and early yield showed no significant differences.s.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.201-207
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• 2013

When hot weather concrete is utilized, the cooling methods of cooling pipe, liquid nitrogen, ice, etc., are used to prevent the poor consistency and cold joint due to high temperature. These methods, however, spike the production cost and energy consumption, and make quality control difficult. Among these methods is one that involves the use of a retarder. Although economical, retarder is caused difficulty of retarded hardening and setting time control due to inaccurate weighing and poor working condition. Therefore, how to make a tablet for hot weather concrete, as with the existing pharmacy and foods, is discussed in this study, including the following items: mortar setting time, flow test by elapsed time, physical and mechanical properties of concrete. As a result, gluconic acid is superior to lignosulfonic acid and the possibility of using them for such purpose without quality degradation was confirmed in this study, when retarder is tabletting.

• Clean Technology
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• v.14 no.1
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• pp.53-60
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• 2008

The condensation heat transfer coefficients and pressure drops of hydrocarbon refrigerants (R-290 and R-600a) and hydrochlorofluorocarbon (HCFC) refrigerants were measured in the two horizontal double pipe heat exchangers with inner diameters of 10.07 mm and 5.80 mm at a mass flux of $35.5{\sim}210.4\;kg/m^2s$ and the condensation temperature of $40^{\circ}C$. The average condensation heat transfer coefficients of hydrocarbon refrigerants were higher than that of HCFC refrigerant(R-22). The pressure drop had a magnitude in the order of R-600a > R-290 > R-22. The pressure drops in the tubes with inner diameter of 10.07 mm were approximately $6{\sim}15%$, $9.8{\sim}12.5%$ and $2.1{\sim}4.6%$ higher for R-600a, R-290 and R-22, respectively, than those with inner diameter of 5.80 mm. The condensation heat transfer coefficients were compared with the published experimental data, and showed the best agreement with Haraguchi et al.'s correlation.

• Economic and Environmental Geology
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• v.49 no.1
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• pp.31-41
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• 2016

A program code was developed to calculate block hydraulic conductivity of the 2-D DFN(discrete fracture network) system based on equivalent pipe network, and implemented to examine the effect of joint orientation distribution on the hydraulic characteristics of fractured rock masses through numerical experiments. A rock block of size $32m{\times}32m$ was used to generate the DFN systems using two joint sets with fixed input parameters of joint frequency and gamma distributed joint size, and various normal distributed joint trend. DFN blocks of size $20m{\times}20m$ were selected from center of the $32m{\times}32m$ blocks to avoid boundary effect. Twelve fluid flow directions were chosen every $30^{\circ}$ starting at $0^{\circ}$. The directional block conductivity including the theoretical block conductivity, principal conductivity tensor and average block conductivity were estimated for generated 180 2-D DFN blocks. The effect of joint orientation distribution on block hydraulic conductivity and chance for the equivalent continuum behavior of the 2-D DFN system were found to increase with the decrease of mean intersection angle of the two joint sets. The effect of variability of joint orientation on block hydraulic conductivity could not be ignored for the DFN having low intersection angle between two joint sets.