• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.1
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• pp.21-26
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• 2015

This study represents the effective fire and smoke control in the case of fire in deep underground tunnels, even if the exhaust system can be calculated, the optimal smoke capacity can be determined by establishing technical standards for the transverse ventilation system focusing on the design as a basis for deriving the parameters for utilization. Numerical analyses were performed using the FDS program as a function of the unsteady flow in a deep underground tunnel fire. The analysis results were calculated within 250 m smoke using an inside wind velocity of 0m/s when the capacity of smoke was exhausted, $80m^3/s$, whereas in case of an internal wind velocity of 3m/s, the capacity of smoke exhaust was $197.1m^3/s$, showing an approximately 2.5 fold increase.

• Journal of Korean Tunnelling and Underground Space Association
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• v.25 no.6
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• pp.469-478
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• 2023

The deep tunnel in urban area is a future-oriented construction plan that allows the above-ground space to be used as an eco-friendly park and transportation infrastructure to be constructed in the underground space. However, tunnel construction is often depicted as to cause ground collapse in some media and movies. In fact, while the construction of a deep tunnel in the urban area is underway, the project face with difficulties due to opposition complaints from residents near the route. In this study, we sought to identify perceptions on deep space development and citizen concerns through a public opinion survey regarding deep tunnels. By analyzing laws relevant with the promotion of deep tunnel construction, we reviewed the possibility of public engagement at each stage of the construction and investigated separated surface rights related to compensation for underground space. Through the results of the public opinion survey, it was identified that the concerns of citizens were problems that current technology could solve. Citizen's concerns were improved into a system that confirmed the stability of tunnel construction through public participation, and improvement measures were presented to encourage cooperation from those concerned regarding the establishment of divided superficies.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.6
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• pp.371-384
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• 2021

Underground space, especially very-deep tunnel development in urban area, is a good alternative to solve the problem of insufficient ground space, and the need for underground space development is steadily increasing. However, due to the complex and time-consuming nature of design and construction, public conflicts related to the deep tunnel project are getting aggravating and more complex. In addition, since the public budget is mainly invested, when civil complaints arise, they often respond passively, resulting in amplification of conflicts or prolonging the deadlock in many cases. In this study, by analyzing the progress of major conflicts related to the construction of very-deep tunnels in urban area, the causes of conflicts, factors prolonging conflicts, and solutions are reviewed. Through a survey targeting ordinary citizens and tunnel experts, thoughts about the deep tunnel construction and major conflict factors were analyzed, and suggestions for minimizing conflicts were presented. The results of this study can be used to prepare alternatives such as various public involvement measures and improvement of project procedures to form a civic consensus on the construction of very-deep tunnels, and to prepare measures to improve prejudice against very-deep tunnels.

• Tunnel and Underground Space
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• v.30 no.2
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• pp.109-135
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• 2020

Globally, the deepening depth in the underground is a situation of the high interest for a purpose of the development of various facilities. The development of deep underground space should be based on the structural stability of rocks. Spalling is known to have an impact on the structural stability degradation in deep underground space. As an attempt to predict spalling, many researchers have proposed predicted conditions in accordance with stress states which occur around the tunnel, rock conditions, and types of rock. In addition, the analysis on spalling method has been verified by using computer modeling such as FLAC, EXAMINE, Insight 2D, UDEC and FRACOD, along with in-situ measurement results. In Canada URL (Underground Research Tunnel), CWFS model (Cohesion Weakening Frictional Strengthening) was used to precisely predict for the state of spalling, comparing spalling modeling. CWFS model has been identified as a reliable method for predicting such phenomena. This study aims to analyze several cases of spalling, and then make a comparison between the conditions for spalling occurrence and the predicted results of model CWFS. With this, it investigates the applicability of prediction of spalling, targeting pillar under deep depth condition.

• Tunnel and Underground Space
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• v.31 no.4
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• pp.211-220
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• 2021

Tunnel collapse often occurs during deep underground tunneling (> 40 m depth) in South Korea. Natural cavities as well as water supply pipes, sewer pipes, electric power cables, artificial cavities created by subway construction are complexly distributed in the artificial ground in the shallow depths of the urban area. For deep tunnel excavation, it is necessary to understand the properties of the ground which is characterized by porous elements and various geological structures, and their influence on the stability of the ground. This study analyzed geological factors for risk assessment in deep excavation in South Korea based on domestic and overseas case study. As a result, a total of 7 categories and 38 factors were derived. Factors with high weights were fault and fault clay, differential stress, rock type, groundwater and mud inrush, uniaxial compressive strength, cross-sectional area of tunnel, overburden thickness, karst and valley terrain, fold, limestone alternation, fluctuation of groundwater table, tunnel depth, dyke, RQD, joint characteristics, anisotropy, rockburst and so forth.

• Journal of Electrical Engineering and Technology
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• v.7 no.2
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• pp.200-206
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• 2012

In order to develop a deep-underground great train express (GTX) in South Korea, the specifications decision and development of a traction control system (including an inverter and a traction motor), which considers a variety of route conditions, must be advanced. In this study, we examined the running resistance properties of a high-speed traction system based on a variety of tunnel types and vehicle organization methods. Then, we studied the power requirements necessary for the traction motor to maintain balanced speed in the high-speed traction system. From this, we determined the design criteria for the development of a high-speed traction system for use in the deep-underground GTX. Finally, we designed a linear induction motor (LIM) for a propulsion system, and we used the finite element method (FEM) to analyze its performance as it travelled through deep-underground tunnels.

• Nuclear Engineering and Technology
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• v.33 no.6
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• pp.605-618
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• 2001

For the mechanical stability assessment of a deep underground high-level waste repository. computer simulations using FLAC3D were carried out and important parameters including stress ratio, depth, tunnel size, joint spacing, and joint properties were chosen from sensitivity analysis. The main effect as well as the interaction effect between the important parameters could be investigated effectively using fractional factorial design . In order to analyze the stability of the disposal tunnel and deposition hole in a discontinuous rock mass, different modelings were performed under different conditions using 3DEC and the influence of joint distribution and properties, rock properties and stress ratio could be determined. From the three dimensional modelings, it was concluded that the conceptual repository design was mechanically stable even in a discontinuous rock mass.

• Geomechanics and Engineering
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• v.16 no.1
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• pp.35-47
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• 2018

This paper investigates the mechanisms of tunnel spalling and massive tunnel failures using fracture mechanics principles. The study starts with examining the fracture propagation due to tensile and shear failure mechanisms. It was found that, fundamentally, in rock masses with high compressive stresses, tensile fracture propagation is often a stable process which leads to a gradual failure. Shear fracture propagation tends to be an unstable process. Several real case observations of spalling failures and massive shear failures in boreholes, tunnels and underground roadways are shown in the paper. A number of numerical models were used to investigate the fracture mechanisms and extents in the roof/wall of a deep tunnel and in an underground coal mine roadway. The modelling was done using a unique fracture mechanics code FRACOD which simulates explicitly the fracture initiation and propagation process. The study has demonstrated that both tensile and shear fracturing may occur in the vicinity of an underground opening. Shallow spalling in the tunnel wall is believed to be caused by tensile fracturing from extensional strain although no tensile stress exists there. Massive large scale failure however is most likely to be caused by shear fracturing under high compressive stresses. The observation that tunnel spalling often starts when the hoop stress reaches $0.4^*UCS$ has been explained in this paper by using the extension strain criterion. At this uniaxial compressive stress level, the lateral extensional strain is equivalent to the critical strain under uniaxial tension. Scale effect on UCS commonly believed by many is unlikely the dominant factor in this phenomenon.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.469-485
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• 2016

The failure of rock mass around deep tunnel, different from shallow tunnel largely affected by discontinuities, is dominated by magnitudes and directions of stresses, and the failures dominated by stresses can be divided into ductile and brittle features according to the conditions of stresses and the characteristics of rock mass. It is important to know the range and the depth of the V-shaped notch type failure resulted from the brittle failure, such as spalling, slabbing and rock burst, because they are the main factors for the design of excavation and support of deep tunnels. The main features of brittle failure are that it consists of cohesion loss and friction mobilization according to the stress condition, and is progressive. In this paper, a three-dimensional numerical model has been developed in order to simulate the brittle behavior of rock mass around deep tunnel by introducing the bi-linear failure envelope cut off, elastic-elastoplastic coupling and gradual spread of elastoplastic regions. By performing a series of numerical analyses, it is shown that the depths of failure estimated by this model coincide with an empirical relation from a case study.

• Geotechnical Engineering
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• v.39 no.6
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• pp.66-87
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• 2023