• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.4
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• pp.335-341
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• 2005

In construction of a large cross section NATM tunnel, to keep the tunnel face stability by the ground itself bench cut method is commonly used. In order to necessity of partial face excavation method, we have to look for more enhanced method that can maintain better stress intensity. This paper presents a stress distribution of the Center Diaphragm Method from the partial face excavation methods, with the numerical analysis, and induced the optimal face distance, which is minimizing stress concentration and the optimal excavation step. Commerical 3 dimensional continuum analyzing FLAC-3D Ver. 2.1 program is used for the analysis. Analyses were performed to investigate ground behavior for tunnels with variable bench-length varying from 2m to 40m.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.1
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• pp.83-89
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• 2007

As tunnel excavation generats stress release, a stability security of tunnel face is mainly important in case of tunnel excavation in the weak grounds. Using the steel bar or glass fiber pipe which had regular hardness, a face bolt method to reinforce previously is applied to an excavation object tunnel face aspect among measures methods regarding this. Therefore, used $FLAC^{3D}$ Ver. 2.1 on 5 Case of 0.5D (2EA), 1.0D, 1.5D, 2.0D with the length and 6 Case of 0, 20, 40, 60, 80, 100EA with the number of the bolt that a face bolt method was installed at these papers in the necessary weak grounds in order to review applicability of the tunnel face reinforcement method that used these face bolts, and executed three dimension continuous analysis.

• Journal of the Korean Magnetics Society
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• v.15 no.6
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• pp.311-314
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• 2005

We investigated the composition dependence of the tunneling magnetoresistance (TMR) behavior and the stability of the magnetic tunnel junctions (MTJs) with TiAlOx barrier and the microstructural evolution of TiAl alloy films. The TMR ratio increased up to $49\%$ at $5.33\;at\%$ Ti. In addition, a significant tunneling magnetoresistance (TMR) value of $20\%$ was maintained after annealing at $450^{\circ}C$, and the breakdown voltage ($V_B$) of and 1.35 V were obtained in the MTJ with $5.33\;at\%$ Ti-alloyed AlOx barrier. These results were closely related to the enhanced quality of the barrier material microstructure in the pre-oxidation state. Ti alloying enhanced the barrier/electrode interface uniformity and reduced microstructural defects. These structural improvements enhanced not only the TMR effect but also the thermal and electrical stability of the MTJs.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.947-956
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• 2018

Subsea tunnel built in abyssal zone is exposed to environment under high water pressure caused by seawater and etc., and this high pressure from underground water may facilitate leaching. In particular, since underground water can be easily flown in during construction, this might cause many problems related to cutoff water. Therefore, in order to secure safety, it is necessary to apply grouting equipment and materials which are appropriate to construction environment. Accordingly, in this research, evaluation was made on the physical characteristics of grouting materials (strength, leaching and etc. depending on curing methods for each of used materials and condition) which can be applied during subsea tunnel construction. As a result of this research, stable strength increase was found in CA and CSA type, and it is determined that no decrease in their durability was found, so these can be used as stable materials for structures under influenced by seawater.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.6
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• pp.485-502
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• 2021

In order to evaluate the impact of ground subsidence and superstructures that are inevitably caused by tunnel excavation, a total of seven major influencing factors of surface subsidence and structural soundness reduction were set, and a Parameter Study using numerical analysis was conducted. Stability analysis was performed using scheme of Boscardin and Cording method and the maximum subsidence amount and the angular displacement, and correlation analysis was performed for each major influencing factor. In addition, it was applied that used the mutual behavior of the ground and the structure by parameter analysis in the site of the 𐩒𐩒𐩒 tunnel located in Hwaseong-si, Gyeonggi-do, and the applicability of the site was analyzed. As a result, the error was found to be 1.0%, and it could be used as a basic material for determining the appropriate tunnel route under various conditions when evaluating the stability of the structure according to tunnel excavating at the design stage.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.6
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• pp.829-843
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• 2017

Subsea tunnel needs to be built over 50 km long to connect between nations and continents. However there are only 19 tunnels longer than 5 km until recently. And there is no history of constructing and operating tunnel longer than 50 km. In Korea, subsea tunnels with a length of more than 50 km are being planned, such as Korea~Japan, Korea~China, Honam~Jeju subsea tunnels. Because of the geographical conditions of Korea, most of these tunnels are inter-contry tunnels. So technology preemption for the subsea tunnel construction is getting more and more important. Most of these subsea tunnels are ultra-long tunnels under high water pressure conditions. So new technologies are required such as ventilation and disaster prevention of high-speed tunnels, securing of structural stability under high pressure conditions, and pressure reduction in high-speed conditions. These technologies are different from those of ground tunnels. Therefore, this paper describes the ultra-long subsea tunnel design under high water pressure of maximum 16 bars through the Honam (land) - Jeju (island) virtual subsea project. We proposed a reasonable solution to various problems such as securing structural stability in high pressure condition and ventilation disaster prevention system of ultra long-tunnel.

• Journal of the Korean GEO-environmental Society
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• v.15 no.1
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• pp.53-62
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• 2014

In Korea, in general, separation distance between existing parallel tunnels was set at two to five times as distant as the diameter of the tunnels according to ground conditions. Recently, however, actual applicability of closely spaced parallel tunnels whose distance between tunnel centers was shorter than the diameter has increased due to environmental damages resulting from massive cutting, restriction in purchase of required land, and maintenance of linear continuity. In particular, when the pillar width of tunnel decreases, the safety of pillars affects behaviors of the tunnel and therefore the need for diverse relevant studies has emerged. However, research so far has been largely confined to analysis of behavior characteristics of pillars, or parameters affecting design, and actually applicable and quantitative data have not been presented. Accordingly, in order to present a stability evaluation method which may maximally reflect construction conditions of spots, this study reflected topographical and stratigraphic characteristics of the portal part with the highest closeness between the tunnels, simulated multi-layer conditions with rock mass and complete weathering, and assessed the degree of effect the stability of pillars had on the entire tunnels through numerical analysis according to changes in pillar width by ground strength. This study also presented composite analysis result on ground surface settlement rates, interference volume rates, and average strength to stress and a formula, which may be applicable to actual work, to evaluate safety rates of closely spaced parallel tunnel pillars and minimum pillar width by ground strength based on failure criteria by Hoek-Brown (1980).

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.6
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• pp.699-714
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• 2022

The objective of this study is to suggest a safe and economical pillar reinforcement method when very near-twin tunnels with a minimum interval of 1 m passes through a soft zone such as weathered soil or weathered rock. A standard cross-sectional view of a two-lane road tunnel was applied to suggest a pillar reinforcement method for the very near-twin tunnels. The thickness of the pillar was 1 m. The ground condition around the tunnel was weathered soil or weathered rock. There were four reinforcement methods for pillar stability evaluation. These were rock bolt reinforcement, pre-stressed steel strand reinforcement, horizontal steel pipe grouting reinforcement, horizontal steel pipe grouting + prestressed steel strand reinforcement. When the ground condition was weathered soil, only the pillar reinforced the horizontal steel pipe grouting + prestressed steel strand did not failed. When the ground condition was weathered rock, there were no failure of the pillar reinforced the horizontal steel pipe grouting or the horizontal steel pipe grouting + prestressed steel strand. It is considered that the horizontal steel pipe grouting reinforcement played a role in increasing the stability of the upper part of the pillar by supporting the upper load applied to the upper part of the pillar.

• Journal of the Korean Geotechnical Society
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• v.23 no.5
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• pp.29-41
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• 2007

An assesment technique for the quantitative evaluation of tunnel safety during tunnel excavation was newly proposed in this study using displacement measurements. First of all, field measurement guidelines used at tunnel construction sites in Korea and other countries were investigated. It was found out that the criteria of the guidelines were not clear and varied depending on the construction sites. The practical use of field measurement data for the evaluation of tunnel safety was very limited due to uncertainties of the guidelines related to the interpretation of measured data during the excavation. Critical strain concept is introduced in this study for the assesment of tunnel safety during the tunnel excavation. Moreover, the characteristics of tunnel displacements caused by the tunnel excavation were investigated in detail in order to investigate the practical application of the critical strain concept. The total tunnel displacements can be subdivided into three parts: displacements occurring ahead of tunnel face, displacements occurring prior to measurements, and displacements occurring after the installation of instruments. The characteristic of each portion of displacements is analysed in this study. Finally, a general method on the use of the displacement measurement data for the critical strain concept was suggested in the concrete manner, considering the field measurement practice in Korea.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.12
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• pp.8608-8615
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• 2015

We developed a system that can collect and transmit real-time environmental data such as temperature, humidity, wind direction, and wind speed, and equipment performing aging tests on fire detectors. This system was installed in three representative sites of railway tunnels in South Korea such as Gumjung, Solan, Seoul Subway Line 4 tunnels. The systems showed a stable performance and collected environmental data for over a year. We analyzed environmental data collected by two of our developed systems installed in the running tunnels of Gwacheon Line of Seoul Subway Line 4. The developed system was capable of safely analyzing tunnel environments for 24 h straight using a wireless communication network, and has potential for use in a variety of fields other than tunnels.