• Tunnel and Underground Space
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• v.10 no.1
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• pp.59-69
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• 2000

Acoustic emission is n burst of microseismic waves generated by microscopic failure due to deformation in materials. The study on the detection of initiation and propagation of microcracks from acoustic emission measurement is very important for the evaluation of the stability of underground rock structures by the nondestructive letting method. In this study, acoustic emission was measured under uniaxial stiffness loading test used to obtain the complete stress-strain curves of marble and concrete used as reinforced materials of rock structures. The analysis of acoustic emission parameters and source location were performed to discuss the characteristics of the deformation and failure behavior of rock and concrete. And acoustic emission was measured under cyclic loading test to verify the Kaiser effect associated with the damage of materials, in situ stress of rock, and stress history of concrete structure.

• Journal of the Society of Disaster Information
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• v.7 no.1
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• pp.43-50
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• 2011

The Application of Steel Fiber Shotcrete in tunneling construction has become part of tunneling practice at least since the 1970s because of its high bending and tensile properties. Over the past 3 decades, researcher from all over the world have been significantly developing the associated technologies for improved performance of SFRS. But still it has some major drawbacks in terms of durability, damage of pumping hose, wastage due to rebound concrete, corrosion and it costs high. To overcome this situation researcher has to look for some alternative material. Therefore, this part study deals with the three types of fiber in order to find good alternative for steel fiber. Polyamide and Polypropylene fiber were used in this study with 0.6, 0.5% mixing ratio. To evaluate its fresh and harden properties air content, slump, compressive, split tensile and bending strength were measured. After comparing the results of all three types of fiber reinforced concrete with its different mixing proportion this study propose that polyamide fiber with addition ratio of 0.6 % for field use.

• Journal of Korean Association for Spatial Structures
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• v.18 no.2
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• pp.59-67
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• 2018

Various pilotis are installed in the lower part of high rise buildings. Strong winds can generate sudden airflow around the pilotis, which can cause unexpected internal airflow changes and may cause damage to the exterior of the piloti ceiling. The present study investigates the characteristics of peak wind pressure coefficient for the design of piloti ceiling exteriors by conducting wind pressure tests on high rise buildings equipped with penetration-type and end-type pilotis in urban and suburban areas. The minimum peak wind pressure coefficient for penetration-type piloti ceilings ranges from -2.0 to -3.3. Minimum peak wind pressure coefficient in urban areas was 30% larger than in suburban areas. In end-type piloti ceilings, maximum peak wind-pressure coefficient ranges from 0.5 to 1.9, and minimum peak wind-pressure coefficient ranges from -1.3 to -3.6. With changes in building height, peak wind pressure coefficient decreases as the aspect ratio increases. Peak wind-pressure coefficient increases with taller pilotis. On the other hand, when piloti height decreases, the absolute value of the minimum peak wind pressure coefficient increases.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.285-294
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• 2002

Embankment Piles, which is subjected to damage due to lateral movement of soft ground, can be classified into pile slab, cap beam pile, and isolated cap pile according to the installation pattern of pile cap. In the cap beam pile and the isolated cap pile method, the soil arch is developed by the different stiffness between pile and soil, and most embankment loads are transferred into embankment piles through soil arch. In these two methods, the difference of soil arch is that the soil arch of the cap beam pile method develops like the arch from of tunnel between cap beams and the soil arch of the isolated cap pile method develops like dome between isolated caps. Therefore, theoretical analysis methods on soil arching effect of the cap beam pile and the isolated cap pile method were respectively proposed according to their own arch form considering the limiting equilibrium of stresses in a crown of soil arch. And a series of model tests were performed both to investigate the load transfer by soil arching in fills above embankment piles and to verify the reliability of the theoretical analysis.

• Tunnel and Underground Space
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• v.27 no.6
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• pp.387-392
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• 2017

Recently, road cave-ins, also referred to as ground sinking, have become a problem in urban environments. Public utility facilities such as sewage pipelines, communications pipes, gas pipes, power cables, and other types of underground structures are installed below the roads. It was reported that cave-ins are caused by the aging and lack of proper maintenance of underground facilities, as well as by construction problems. A road cave-in is first initiated by the formation of cavities typically induced by the breakage of underground pipelines. The cavities then grow and reach the base of the pavement. The traffic load applied at the surface of the roads causes an abrupt plastic deformation. This type of accident can be considered as a type of disaster. A road cave-in can threaten both human safety and the economy. It may even result in the loss of human life. In the city of Seoul, efforts to prevent damage before cave-ins occur have been prioritized, through a method of discovering and repairing joints through the 3D GPR survey.

• Journal of the Korean Institute of Gas
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• v.4 no.3 s.11
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• pp.26-32
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• 2000

Because of the continuous growth of energy consumption, and also the tendency to site power lines and pipelines along the same routes, the close proximity of high voltage structures and metallic pipelines has become more and more frequent. Moreover, normal steady state and fault currents become higher as electric networks increase in size and power Therefore, there has been and still is a growing concern(safety of people marking contact with pipeline, risk of damage to the pipeline coating, the metal and equipment connected to pipeline, especially cathodic protection system) about possible hazards resulting from the influence of high voltage power system on metallic structures(gas pipeline, oil pipeline and water pipeline etc.). Therefore, we analyze the interference problems when the gas pipeline is buried with power cable in the same submarine tunnel. This paper present the results of the study about interference mechanism, AC corrosion limitation of safety voltage and analysis of induction voltage.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.132-140
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• 2010

The very erosive cavitation is simulated by an inclined propeller dynamometer in the medium-size cavitation tunnel of MOERI. The inclined shaft for propeller makes strong cavitaion, which occurs around the root of a propeller blade. The cavitation begins at the leading edge of the propeller and contracted toward the trailing edge through the reentrant jet action. The cavity focused on the region near the trailing edge collapsed over the blade surface. As the impact pressure by the cavitation collapsing is too strong, it can damage the blade surface in the form of pit. This cavitation impacts created by the collapsing process are similar to the full-scale ones and are different from those by other erosion test methods. The newly developed cavitation erosion test method can be applied to evaluate the materials such as metals, ceramics and coatings in terms of cavitation resistance.

• Journal of the Korean GEO-environmental Society
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• v.21 no.12
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• pp.11-16
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• 2020

It is necessary to assess the proper performance of the existing rockfall prevention net in order to minimize the damage to human lives and property in the event of rockfall. However, there is no standard for performance evaluation of rockfall prevention net in Korea, and only the design of rockfall prevention net exists by calculating energy that can be absorbed energy. Therefore, laboratory pullout test was conducted for the performance evaluation of the rockfall prevention net, cuts and load-displacement characteristics of the PVC coating net used in the laboratory pullout test are determined to identify the performance of the rockfall prevention net.

• Tunnel and Underground Space
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• v.20 no.1
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• pp.15-27
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• 2010

Geo-hazard shows a rapid increasing tendency with establishment of frequent great slopes in various construction sites, especially in the unfavorable topographic condition in which about 70% of the surface is covered by the mountainous area. An repeatedly taking place on the heavy rain season is accompanied by a large scale of rockfall, and causes great damage to an individual as well as a property. Even though lots of field studies and fundamental studies have been performed to reduce this hazard, however, an essential study on the mechanism of the rockfall should be limited to the conventional studies on the slope reinforcement and/or the rockfall risk analysis. In this study, the mechanism of rockfall depending on the morphologic characteristics of slope has been simulated numerically with the PFC2D, one of the discrete element programs. For analyzing its mechanism, the input parameters relating to the slope such as surface condition, gradient, number of benches, bench gradient, and the ratio of bench width to rockfall size were taken into consideration.

• Tunnel and Underground Space
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• v.18 no.1
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• pp.1-9
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• 2008

Acoustic emission (AE) and Microseimsic (MS) activities are law-energy seismic events associated with a sudden inelastic deformation such as the sudden movement of existing fractures, the generation of new fractures or the propagation of fractures. These events rapidly increase before major failure and happen within a given rock volume and radiate detectable seismic waves. The main difference between AE and MS signals is that the seismic motion frequencies of AE signals are higher than those of MS signals. As the failure of geotechnical structures usually happens as a high velocity and small displacement, it is nat easy ta determine the precursor and initiation stress level of failure in displacement detection method. To overcame this problem, AE/MS techniques far detection of structure failure and damage have recently adapt in civil engineering. This study deal with the basic theory of AE/MS and state of arts in monitoring technique using AE/MS.