• Tunnel and Underground Space
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• v.18 no.1
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• pp.20-32
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• 2008

The study shows a method called a square-inventory method, which is a better and faster method than scanline survey and window method for an analysis of slope stability. The study area is located in the Changri area, Boeun-Gun, Chungbuk, and consists of many formations of the Okcheon Supergroup. Various types of failure are observed from the phyllite including the rocks in the study area. The physical properties of meta-sedimentary rocks are that minerals of the rocks are composed of microcrystalline quartz and sericite, which are arranged parallel to bedding (or schistosity) and crenulation cleavage. Therefore, such properties affect geotechnical ones of the rock. The slope stability are analyzed by selecting 3 areas, each of which are divided into 2 or 3 slopes of $1m{\times}1m$ area that represent each of 3 investigation sites. The possibility of wedge and toppling failure is very high in all 3 areas by using square-inventory method. Although possibility of plane failure is weak in the investigation site 2, the plane failures are frequently found from the slope of site 2. The bedding (or schistosity) plane and cleavage, another types of discontinuity coexist in meta-sedimentary rocks uulike igneous rocks, and therefore are important factors to be considered together with joint structures in th ε analysis of slope stability.

• Tunnel and Underground Space
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• v.26 no.5
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• pp.396-408
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• 2016

Rock fracture mechanics has been widely applied to various fields of rock and civil engineering. But most researches covered mode I behavior, though mode II behavior is dominant in rock engineering. Until now, there is only one ISRM suggested method for mode II toughness of rock. A new SCC (Short Core in Compression) mode II toughness test method was developed considering 1) application of confining pressure, 2) easiness of notch creation, 3) utilization of existing equipment, 4) simple test procedure. The stress intensity factors were determined by 3D finite element method considering line and distributed loading conditions. The tests with granite specimens were carried out using MTS 815 rock test system with a loading rate of 0.002 mm/s. The mean value of mode II fracture toughness of granite showed $2.33MPa{\sqrt{m}}$. Mode I toughness of the same granite was $1.12MPa{\sqrt{m}}$, determined by Brazilian disk test and $K_{IIC}/K_{IC}=2.08$. The smooth fracture surface with rock powder formation also supported mode II behavior of SCC method. The SCC method can be used for the determination of mode II fracture toughness of rocks based on the current results.

• Tunnel and Underground Space
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• v.26 no.5
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• pp.348-362
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• 2016

This study describes the results of blasting overbreak analysis using the stereo photogrammetry method in an underground mine. For comparing its quantitative measurements, LIDAR system was applied to the test site and blasting overbreak was analyzed for 4 test blasting operations. The difference in values obtained from the two methods showed only 0.81% in volume and 1.05% in area, respectively, therefore authors verify the field applicability of stereo photogrammetry method on underground mine. The volumes of overbreak measured from 4 test blastings were $29.84m^3$, $22.45m^3$, $14.54m^3$ and $5.46m^3$, respectively, in photogrammetry analysis on excavation surface, and it was shown that the volume of overbreak decreases with blasting sequence. From these measurements, it is concluded that the stereo photogrammetry method can describe the underground excavation surface effectively and the its quantitative data can be used for analysis of volume, area and overbreak of excavation zone.

• Tunnel and Underground Space
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• v.26 no.5
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• pp.363-374
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• 2016

All five independent elastic constants of a transversely isotropic rock sometimes need to be determined from a single specimen. Saint-Venant approximation has been widely used for a long time in the analysis of single specimen test. This paper has proven how this empirical equation can be mathematically transformed into a form of the apparent Young's modulus based on theory of elasticity. The transformed equation is a monotonous function on anisotropic angle and can be useful in the analysis of the in-situ stress measurement in an anisotropic rock mass. The estimations of data in literatures have shown that the measured values of $G^2$ are uniform on anisotropic angles and smaller than that of Saint-Venant's case. This decrement may be caused by sliding of the interface of strata and the decrement rate is inferred to relate well with the combination of bonding condition of strata and strength of rock material. Accumulation of these kinds of studies in the future enables to define the decrement and to determine elastic constants of a transversely isotropic rock from a single specimen from modifying Saint-Venant approximation.

• Tunnel and Underground Space
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• v.28 no.3
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• pp.209-231
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• 2018

Severe mine disasters have continued to occur around the world. To ensure worker's health and safety and enhance the productivity, a number of studies have been conducted for the development of wireless sensor network (WSN), environmental monitoring, and communication system in underground mines. An increase in development and application of these systems has just begun with the introduction of information and communication technology into the mining industry in Korea, and yet there have been only a few studies that considered the underground mine ventilation system. This study presented the literature review on the development of WSN and environmental monitoring in underground mines, and especially, on 7 subjects in terms of underground mine ventilation. Moreover, studies that especially conducted real-time environmental monitoring were reviewed and categorized by each commercial software commonly utilized for the ventilation network analysis. For the application in domestic underground mines, further issues were discussed regarding research subjects that may be needed in the future and domestic environmental standards that has been used in the underground mine operation. This paper is expected to be useful for the development of WSN-based environmental monitoring and communication system, as well as for related studies in the future.

• Tunnel and Underground Space
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• v.24 no.3
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• pp.201-211
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• 2014

In the present study, the thermal performance of multiple rock caverns for large-scale thermal energy storage (TES) was numerically investigated for different separation distances between the caverns through heat transfer analysis using a computational fluid dynamics code, FLUENT. The thermal performance of multiple caverns was assessed in terms of the thermal stratification within the caverns and the heat loss to the surroundings, and the heating characteristics of the rock around the caverns were investigated. The results of numerical simulation showed that there was little difference in thermal performance between multiple TES caverns with different separation distances when the surrounding rock was less heated and it reached thermal steady-state, which represent the thermal states of the surrounding rock at the early and long-term operational stages of the TES caverns, respectively. However, as the separation distance decreased, the rock between the caverns reached thermal steady-state more quickly, and thus the heat loss from the caverns tended to converge rapidly to the value of heat loss occurred under thermal steady-state conditions in the surrounding rock. This result implies that the operating cost of heating the surrounding rock (i.e., rock heating) can be reduced with a reduction in the separation distance between multiple caverns, and suggests that the separation distance should be determined by considering the operating cost of rock heating as well as the construction cost of the caverns.

• Tunnel and Underground Space
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• v.22 no.5
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• pp.346-353
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• 2012

Multi-specimen uniaxial compression test has been carried out in order to find the method to determine the five independent elastic constants from a single standard specimen of a transversely isotropic rock. Total 35 specimens of 7 different angles from a large block of rhyolite presenting the flow structure obviously are used in tests. This second report is to focus on the statistical evaluation of measured strains and analyzed elastic constants. And the determination of their true or near-true values is discussed. As the result of RSD analysis, it turns out that the reliability of measured strains is sufficiently obtained and Saint-Venant approximation is well applicable except 15 degree angled specimen in tests. RSD is decreasing on the increase of the angle of anisotropy. This tendency may be caused not only by the decreasing of the deviation of measured strains, but also by the better applicability of Saint-Venant approximation on the increase of angle. It can be concluded that the analyzed values are considered the near-true ones of five independent constants on the high reliability. But the variation of the apparent Young's modulus expected by these values is not proved to match the measured tendency. It is inferred that the factor to decrease the apparent Young's modulus and/or to increase the shear strain, is present in the test or in the nature of the anisotropy in consideration of this inconsistency.

• Tunnel and Underground Space
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• v.27 no.1
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• pp.39-49
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• 2017

The factor of safety (FOS) is commonly used as an index to quantitatively state the degree of safety of various rock structures. Therefore it is important to understand the definition and characteristics of the adopted FOS because the calculated FOS may be different according to the definition of FOS even if it is estimated under the same stress condition. In this study, four local factors of safety based on maximum shear stress, maximum shear strength, stress invariants, and maximum principal stress were defined using the Mohr-Coulomb and Hoek-Brown failure criteria. Then, the variation characteristics of each FOS along five stress paths were investigated. It is shown that the local FOS based on the shear strength, which is widely used in the stability analysis of rock structures, results in a higher FOS value than those based on the maximum principal stress and the stress invariants. This result implies that the local FOS based on the maximum shear stress or the stress invariants is more necessary than the local FOS based on the shear strength when the conservative rock mechanics design is required. In addition, it is shown that the maximum principal stresses at failure may reveal a large difference depending on the stress path.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.9 s.339
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• pp.9-18
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• 2005

To make high-performance, low-power transistors beyond the technology node of 60 nm complementary metal-oxide-semiconductor field-effect transistors(C-MOSFETs) possible, the effect of electron mobility of the thickness of strained Si grown on a relaxed SiGe/SiO2/Si was investigated from the viewpoint of mobility enhancement via two approaches. First the parameters for the inter-valley phonon scattering model were optimized. Second, theoretical calculation of the electronic states of the two-fold and four-fold valleys in the strained Si inversion layer were performed, including such characteristics as the energy band diagrams, electron populations, electron concentrations, phonon scattering rate, and phonon-limited electron mobility. The electron mobility in an silicon germanium on insulator(SGOI) n-MOSFET was observed to be about 1.5 to 1.7 times higher than that of a conventional silicon on insulator(SOI) n-MOSFET over the whole range of Si thickness in the SOI structure. This trend was good consistent with our experimental results. In Particular, it was observed that when the strained Si thickness was decreased below 10 nm, the phonon-limited electron mobility in an SGOI n-MOSFT with a Si channel thickness of less than 6 nm differed significantly from that of the conventional SOI n-MOSFET. It can be attributed this difference that some electrons in the strained SGOI n-MOSFET inversion layer tunnelled into the SiGe layer, whereas carrier confinement occurred in the conventional SOI n-MOSFET. In addition, we confirmed that in the Si thickness range of from 10 nm to 3 nm the Phonon-limited electron mobility in an SGOI n-MOSFET was governed by the inter-valley Phonon scattering rate. This result indicates that a fully depleted C-MOSFET with a channel length of less than 15 m should be fabricated on an strained Si SGOI structure in order to obtain a higher drain current.

• Journal of the Korean Geotechnical Society
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• v.30 no.12
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• pp.27-40
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• 2014

This paper is to provide the allowable limit blasting-induced vibration for road structures and facilities. For this purpose, first of all, this study examined various allowable limits of different structures from domestic and foreign countries, investigated related problems of the limits used in the country, and suggested the measures to minimize the related problems. Furthermore, this study proposed the blasting-induced vibration limit of road structures and facilities that could be used in the country from comparing and analyzing the various limits from foreign countries. To verify the proposed limit for a practical use in the field, field cases that had both a vibration magnitude and a damage level were collected and they were compared with the proposed limit. In addition, the proposed limit was also compared with the results of analytical and numerical analyses. The comparison and analysis indicated that the proposed limit of different road structures and facilities is valid for the practical use in the field. From this study, the proposed limit is expected to be used as the limit to estimate the damage levels of road structures and facilities due to blasting-induced vibrations in the field.