• Tunnel and Underground Space
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• v.15 no.1 s.54
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• pp.28-38
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• 2005

According to the recent development of measurement system utilizing one or a set of boreholes, visualization of the explored underground became to be a major issue. It induced even the introduction of monitoring apparatuses on the borehole wall with multi-function tool, but the usage of these was often limited by where is unfavorable rock condition and a few of engineers can approach. And so, a portable type of borehole camera with only the essential function has been investigated and a few of commercial models about this is recently being applied into the field condition. This paper was based on the monitoring results obtained using a commercial model by Dr. Nakagawa. Discontinuities in rock mass were the topic for the visualization, and it was studied how can visualize their three dimensional distribution and what a numerical formulation is needed and how to understand the visualization result. The numerical formulation was based on the geometric correlation between the dip direction / dip of discontinuous plane and the trend / plunge of borehole, a set of the equation of a plane was induced. As field application of this into two places, it is found that the above visualization methodology will be especially an useful geotechlical tool for analyzing the local distribution of discontinuities.

• Journal of the Mineralogical Society of Korea
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• v.19 no.4 s.50
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• pp.239-246
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• 2006

KAERI Underground Research Tunnel (KURT) was recently constructed through the site investigation from the yea. of 2003 at KAERI site, Dukjin-dong, Yuseong-gu, Daejeon city. The geo-logic setting of the site has been slightly metamorphosed. There are small fractures developed in the rock and several kinds of secondary filling minerals exist in the fractures. We examined mineralogical characteristics of fracture-filling calcite, which is not only largely distributed, but also can significantly affect the radionuclides migration. The calcite is found along fractures like other secondary minerals, forming thick veins in part. Most calcite-filled fractures contain quartz, iron oxides, and dolomite as minor minerals. The calcite crystals show an characteristic appearance with an uniformly oriented growth, coated with goethite on the edge and the etch-pit sites of their surface. Some calcite crystals have been newly formed by the precipitation of elements dissolved from the tunnel shotcrete wall, and their morphology changed according to the chemistry and flow of groundwater. The calcite can modify the groundwater chemistry and significantly affect the sorption behavior of radionuclides. The characteristic crystal structure and surface morphology of the calcite examined in the KURT site will be used as important basic data for the radionuclide migration experiment in the future.

• Tunnel and Underground Space
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• v.11 no.3
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• pp.257-269
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• 2001

Numerical simulation is performed to understand the structural behavior of an underground radwaste repository, assumed to be located at the depth of 500 m, in a granitic rock mats, in which a fault intersects the roof of the repository cavern. Two dimensional universal distinct element code, UDEC is used in the analysis. The numerical model includes a granitic rock mass, a canister with PWR spent fuels surrounded by the compacted bentonite inside the deposition hole, and the mixed bentonite backfilled in the rest of the space within the repository cavern. The structural behavior of three different cases, each case with a fault of an angle of $33^{\circ},\;45^{\circ},\;and\;58^{\circ}$ passing through the cavern roof-wall intersection, has been compared. And then fro the case with the $45^{\circ}$ fault, the hydro-mechanical, thermo-mechanical, and thermo-hydro-mechanical interaction behavior have been studied. The effect of the time-dependent decaying heat, from the radioactive materials in PWR spent fuels, on the repository and its surroundings has been studied. The groundwater table is assumed to be located 10m below the ground surface, and a steady state flow algorithm is used.

• Journal of the Korean Geosynthetics Society
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• v.19 no.1
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• pp.25-33
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• 2020

To improvement the swelling characteristics of the existing cutoff wall against the moisture, the permeability of the sand, calcium bentonite and solidifier mixture according to the contact with trichloroethylene (TCE) was evaluated. Characteristics analysis and the permeability test of the research materials were performed. The permeability was decreased as the mixing ratio of the calcium bentonite was increased and it was increased as the mixing ratio of the solidifier was increased. In conclusion, when mixing 15% of calcium bentonite and more than 30% of solidifier, the permeability coefficient in the underground water movement was analyzed as more than α × 10^-4 cm/sec showing that it does not block the underground water movement. In addition, as the permeability coefficient of mixtures after TCE reaction was analyzed as less than α ×10^-7 cm/sec, it satisfied the condition of blocking layer (less than 1.0 × 10^-6 cm/sec). Therefore, the calcium bentonite and solidifier can be utilized as barrier that showing the characteristic of percolation ability conversion in soil and underground water contaminated with TCE.

• Journal of the Korea Institute of Building Construction
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• v.9 no.4
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• pp.111-117
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• 2009

Considering the entire critical path, underground works in construction projects occupy a large part of the total construction period, as well as a large part of the construction costs. Particularly in the downtown area, the scale of underground work has been increasing every year. Currently, underground retaining walls, which are built at construction sites, require many skilled workers, and the works are being undertaken by means of the Euroform+Soldier system, which is quite disadvantageous in terms of the construction period. In order to complement this, forms made of new materials and new construction methods have been developed. Now more than eyer, the shortening of construction periods and the reduction of construction costs is required. Considering this, in this study, the researcher has tried to compare the Euroform+Soldier system, which has been the system most frequently used on construction sites, to the non-supporting form system, which has been used on the sites of civil engineering work. The results of the research revealed that although the Euroform+Soldier system was advantageous from the perspective of material costs, it was disadvantageous in terms of labor costs. It is thought that an additional study on a method for reducing the material costs is required, so as to revitalize the application of non-supporting forms to the construction site.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.3
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• pp.189-199
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• 2010

In a high-level waste (HLW) repository, heat is generated by the radioactive decay of the waste. This can affect the safety of the repository because the surrounding environment can be changed by the heat transfer through the rock. Thus, it is important to determine the heat transfer coefficient of the atmosphere in the underground repository. In this study, the heat transfer coefficient was estimated by measuring the indoor environmental factors in the Korea Atomic Energy Research Institute Underground Research Tunnel (KURT) under forced convection. For the experiment, a heater of 5 kw capacity, 2 meters long, was inserted through the tunnel wall in the heating section of KURT in order to heat up the inside of the rock to $90^{\circ}C$, and fresh air was provided by an air supply fan connected to the outside of the tunnel. The results showed that the average air velocity in the heating section after the provision of the air from outside of the tunnel was 0.81 m/s with the Reynolds number of 310,000~340,000. The seasonal heat transfer coefficient in the heating section under forced convection was $7.68\;W/m^2{\cdot}K$ in the summer and $7.24\;W/m^2{\cdot}K$ in the winter.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.6
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• pp.495-512
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• 2022

Due to the concentration of population in the city center, the aboveground structures are saturated, and the development of underground structures becomes important. In addition, it is necessary to apply the reinforcement construction method for the pillar part of the adjacent tunnel that can secure stability, economy, and workability to the site. In this study, the tunnel pillar reinforcement method using prestress and grouting was reviewed. There are various reinforcement methods that can compensate for the problems of the side tunnel, but as the tunnel pillar construction method using prestress and grouting is judged to be excellent in field applicability, stability, and economic feasibility, it is necessary to review the theoretical and numerical analysis of the actual behavior mechanism. Therefore, a scaled-down model experiment was conducted. The reduced model experiment was divided into PC stranded wire + steel pipe reinforcement grouting + prestress (Case 1), PC strand + steel pipe reinforcement grouting (Case 2), and no reinforcement (Case 3), and the displacement of the pillar and the earth pressure applied to the wall were measured. Through experiments, it was confirmed that the PC stranded wire + steel pipe reinforcement grouting + prestress method is the most excellent reinforcement method among various construction methods. It was judged that it could be derived.

• Journal of the Korean Wood Science and Technology
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• v.2 no.2
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• pp.32-34
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• 1974

The important results which have been obtained in the investigation can be recapitulated as follows. 1. As demonstrated by the experimental results and analyses concerning their effects in the on-ground type mushroom house, the constructions in relation to the side wall and ceiling of the experimental house showed a sufficient heat insulation on effect to protect insides of the house from outside climatic conditions. 2. As the effect on the solar type experimental mushroom house which was constructed in a half basement has been shown by the experimental results and analyses, it has been proved to be effective for making use of solar heat. However there were found two problems to be improved for putting solar house to practical use in the farm mushroom growing: (1) the construction of the roof and ceiling should be the same as for the on ground type house, and (2) the solar heat generating system should be reconstructed properly. 3. Among several ventilation systems which have been studied in the experiments, the underground earthen pipe and ceiling ventilation, and vertical side wall and ceiling ventilation systems have been proved to be most effective for natural ventilation. 4. The experimental results have shown that ventilation systems such as the vertical side wall and underground ventilation systems are suitable to put to practical use as natural ventilation systems for farm mushroom house. These ventilation systems can remarkably improve the temperature of fresh air which is introduced into the house by heat transfers within the ventilation passages, so as to approach to the desired temperature of the house without any cooling or heating operation. For example, if it is assuming that X is the outside temperature and Y is the amount of temperature adjustment made by the influence of the ventilation system, the relationships that exist between X and Y can be expressed by the following regression lines. Underground iron pipe ventilation system. Y=0.9X-12.8 Underground earthen pipe ventilation system. Y=0.96X-15.11 Vertical side wall ventilation system. Y=0.94X-17.57 5. The experimental results have 8hown that the relationships existing between the admitted and expelled air and the $CO_2$ concentration can be described with experimental regression lines or an exponent equation as follows: 5.1 If it is assumed that X is an air speed cm/sec. and Y is an expelled air speed in cm/sec. in a natural ventilation system, since the Y is a function of the X, the relationships that exist between X and Y can be expressed by the regression lines shown below: 5.2 If it IS assumed that X is an admitted volume of air in $m^3$/hr. and Y is an expelled volume of air in $m^3$/hr. in a natural ventilation system, since the Y is a function of the X, the relationships that exist between X and Y can be expressed by the regression lines shown below. 5.3 If it is assumed that expelled air speed in emisec. and replacement air speed in cm/sec. at the bed surface in a natural ventilation system are shown as X and Y. respectively, since the Y is a function of the X. the relationships that exist between X and Y can be expressed by the following regression line: GE(100%)-CV (50%) ventilation system. Y=-0.54X+0.84 5.4 If it is assumed that the replacement air speed in cm/sec. at the bed surface is shown as X, and $CO_2$ concentration which is expressed by multiplying 1000 times the actual value of $CO_2$ % is shown as Y, in a natural ventilation system, since the Y is a function of the X, the relationships that exist between X and Y can be expressed by the following regression line: GE(100%)-CV(50%) ventilation system. Y=114.53-6.42X 5.5 If it is assumed that the expelled volume of air is shown as X and the $CO_2$ concencration which is expressed by multiplying 1000 times the actual of $CO_2$% is shown as Y in a natural ventilation system, since the Y is a function of the X, the relationships that exist between X and Y can be expressed by the following exponent equation: GE(100%)-CV(50%) ventilation system. Y=$127.18{\times}1.0093^{-x}$ 5.6 The experimental results have shown that the ratios of the cross sectional area of the GE and CV vent to the total cubic capacity of the house, required for providing an adequate amount of air in a natural ventilation system, can be estimated as follows: GE(admitting vent of the underground ventilation) 0.3-0.5% (controllable) CV(expelling vent of the ceiling ventilation) 0.8-1.0% (controllable) 6. Among several heating devices which were studied in the experiments, the hot-water boilor which wasmodified to be fitted both as hot-water boiler and as a pressureless steam-water was found most suitable for farm mushroom growing.

• Tunnel and Underground Space
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• v.20 no.3
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• pp.183-193
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• 2010

The present paper highlights some important fragmentation issues experienced in the limestone quarry blast rounds. In light of these major issues, the paper outlines influence of a few important design parameters, which bear merit to alter the blast performance in order to duly resolve the issues in field scale blast rounds. A comprehensive field based program for evaluation of such blast rounds has also been suggested. The knowledge disseminated in the paper, backed up by sufficient images, is largely based on the experience of the authors, while designing, implementing and evaluating numerous field scale blast rounds in cement grade limestone quarries.

• Computers and Concrete
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• v.26 no.3
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• pp.227-237
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• 2020

Strain rate investigations are needed to calibrate strain-rate-dependent material models and numerical codes. An appropriate material model, which considers the rate effects, need to be used for proper numerical modeling. The plastic concrete cut-off wall is a special underground structure that acts as a barrier to stop or reduce the groundwater flow. These structures might be subjected to different dynamic loads, especially earthquake. Deformability of a structure subjected to dynamic loads is a principal issue which need to be undertaken during the design phase of these structures. The characterization of plastic concrete behavior under different strain rates is essential for proper designing of cut-off walls subjected to dynamic loads. The Cowper-Symonds model, as one of the most commonly applied material models, complies well with the behavior of a plastic concretes in low to moderate strain rates and will be useful in explicit dynamics simulations. This paper aims to present the results of an experimental study on mechanical responses of one of the most useful types of plastic concrete and Cowper-Symonds constant determination procedures in a wide range of strain rate from 0.0005 to 107 (1/s). For this purpose, SHPB, uniaxial, and triaxial compression tests were done on plastic concrete samples. Based on the results of quasi-static and dynamic tests, the dynamic increase factors (DIF) of this material in different strain rates and stress state conditions were determined for calibration of the Cowper - Symonds material models.