• 한국터널공학회:학술대회논문집
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• 2005.04a
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• pp.251-258
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• 2005

In this study, a new concept for simulating a long-term mechanical degradation mechanism of shotcrete in tunnels has been proposed. In fact, it is known that the degradation takes place mainly by internal cracks and reduced stiffness, which results mainly from volume expansion of shotcrete and corrosion of cement materials, respectively. This degradation mechanism of shotcrete in tunnels appears similar to those of the most kinds of chemical reactions in tunnels. Therefore, the mechanical degradation induced by a kinds of chemical reaction was generalized and mathematically formulated in the framework of thermodynamics. The numerical model was implemented to a 3D finite element code, which can be used to simulate behaviour of shotcrete structures undergoing external forces as well as chemical degradation in time. A number of illustrative examples were given to show the feasibility of the model in tunnel designs with consideration of long-term degradation effect of shotcrete quantitatively for increase of long-term safety of tunnels.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.3
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• pp.319-332
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• 2015

The pressure wave formed by the piston effects of the train proceeds within the tunnel when a train enters the tunnel with a high speed. Depending on the condition of tunnel exit, the compression waves reflect at a open end, change to the expansion waves, transfer to tunnel entrance back. Due to interference in the pressure waves and running train, passengers experience severe pressure fluctuations. And these pressure waves result in energy loss, noise, vibration, as well as in the passengers' ears. In this study, we performed comparison between numerical analysis and field experiments about the characteristics of the pressure waves transport in tunnel that appears when the train enter a tunnel and the variation of pressure penetrating into the train staterooms according to blockage ratio of train. In addition, a comparative study was carried out with the ThermoTun program to examine the applicability of the compressible 1-D model(based on the Method of Characteristics). Furthermore examination for the adequacy of the governing equations analysis based on compressible 1-D numerical model by Baron was examined.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.2
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• pp.249-260
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• 2014

When a train enters the tunnel at high speed, the pressure wave occurs. When this pressure wave reaches at the exit of tunnel, some are either emitted to the outside or reflected in tunnel by the form of expansion wave. The wave emitted to the outside forms the impulsive pressure wave. This wave is called 'Micro Pressure Wave'. The micro pressure wave generates noise and vibration around a exit portal of tunnel. When it becomes worse, it causes anxiety for residents and damage to windows. Thus, it requires a counterplan and prediction about the micro pressure wave for high speed railway construction. In this paper, the effects of train head nose and tunnel portal shape were investigated by model test, measurement for the micro pressure wave at the operating tunnel as well as numerical analysis for the gradient of pressure wave in the tunnel. As results, a method for predicting the intensity of the micro pressure wave is suggested and then the intensity of the micro pressure wave is analyzed by the tunnel length and the cross-sectional area.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.39-53
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• 2018

Generally, the total ventilation resistance coefficient in a tunnel consists of inlet/outlet loss coefficient, wall friction coefficient, and other loss coefficient caused by sudden expansion and contraction of cross-section, etc. For the tunnel before opening, when the running ventilation fan is stopped, the wind speed in the tunnel is reduced by the total ventilation resistance drag. The velocity decay method is comparatively stable and easy to estimate the wall friction coefficient in the pre-opening tunnel. However, the existing study reported that when the converging wind speed is a negative value after the ventilation fan stops, it is difficult to estimate the wall friction coefficient according to the velocity decay method. On the other hand, for the operating tunnel in which the piston effect acts, a more complex process is performed; however, a reasonable wall friction coefficient can be estimated. This paper aims at suggesting a method to minimize the measurement variables of the piston effect and reviewing a method that can be applied to the operating tunnel. Also, in this study, a new method has been developed, which enables to calculate an variation of the piston effect if the piston effect is constant with a sudden change of external natural wind occurring while the wind speed in the tunnel decreases after the ventilation fan stops, and a programming logic has been also developed, which enables dynamic simulation analysis in order to estimate the wall friction coefficient in a tunnel.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.3
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• pp.259-271
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• 2006

This paper aims to predict the corrosion of a fully cement-grouted rockbolt induced by chloride diffusion in a cement mortar grout. From the viewpoint of the long-term durability, a rockbolt may be deteriorated by chemical components, such as sulphate and chloride, in groundwater. Especially, the steel rod of a rockbolt is corroded mainly by chloride. The rockbolt corrosion results in the volume expansion of a rod and then the cracking of a cement grout. In this study, the chloride diffusion coefficient of a cement mortar grout was used to evaluate the possibility of rockbolt corrosion by chloride, and to predict the long-term durability of a rockbolt. The electric acceleration test method was adopted to measure the chloride diffusion coefficient. In addition, a simple pullout testing system was newly proposed to measure the pullout capacity of a rockbolt more easily in a laboratory condition. From the experiments, it was showed that the chloride could diffuse in the cement grout more easily than in ordinary concrete materials. As a result, it was considered that a rockbolt might be easily corroded in a short term by the diffusion of chemical components with high concentration, although it was fully grouted.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.5
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• pp.705-715
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• 2017

In this study, applicability of compressed air form (CAF) fire water was verified in a bid to use the undersea effluent as fire water. Foam collector was fabricated in accordance with KS B ISO 7203-1 (Specification for low expansion foam concentrates for top application to water-immiscible liquids) and the test was conducted using fresh water as fire water for 19 times and using seawater as fire water 15 times that totaled 34 times. Foam reduction time was 237.73 seconds on average with fresh water and 215.60 seconds with seawater, which proved the applicability of CAF fire water using seawater. Besides, window breaker was fabricated to directly extinguish the fire in train and a full-scale fire test was conducted three times. At the final 3rd test, window glass was broken in 2 seconds to make the hole for fire extinguishing and suppressed the fire in 3 seconds using CAF fire extinguisher.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.1
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• pp.201-210
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• 2019

Recently, due to the efforts to mitigate traffic congestion and expansion of space efficiency, the construction of underground roads has been increased in big-scale cities. Since tunnels in the city have a higher chance for a fire leading to a great tragedy during a severe traffic jam than mountain tunnels, it is highly likely that it will be constructed as a tunnel, having a small cross section, for small vehicles. However, if they are constructed as such small-vehicle tunnels, it would be possible to reduce the design fire intensity while the concentration of harmful gases would increase due to a reduction in the small cross sectional area, led by a decrease in the tunnel height. In this study, behaviors of fire smoke by the installation interval and format of large-scale exhaust-gas ports were examined and compared in the analysis of temperatures and CO concentrations of a tunnel and its results were as the following. Although there were no significant differences in the smoke spreading distance between installation intervals, but in this study, 100 m was found to be the most effective installation interval. The smoke exhaustion performance was found to be excellent in the order of $4m{\times}3m$, $6m{\times}2m$, and $3m{\times}2m$ (2 lane) of the smoke spreading distance. Although there was no significant difference in the smoke spreading distance between formats of large-scale exhaust-gas ports, it was found that the smoke spreading distance was larger than other cases when it was $3m{\times}2m$ in the fire growing process. The analysis of smoke spreading distances by the aspect ratio showed that a smoke spreading distance was shorted when its the smoke spreading distance was found to be shorter when its traverse distance was relatively longer than its longitudinal distance.

• Tunnel and Underground Space
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• v.25 no.5
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• pp.435-449
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• 2015

Physical and microstructural properties of Pungchon and Maggol limestone were investigated quantitatively during 50 cycles of artificial freezing and thawing test. There were decrease in dry weight and P,S-wave velocity, and increase in absorption rate in both rock types. Porosity, pore volume, equivalent diameter, throat thickness and pore orientation were analyzed using X-ray computed tomography images. Porosity increased, and initiation and expansion of pores were investigated as weathering progresses. Physical and microstructural variation in Maggol limestone was larger than that of Pungchon limestone because Maggol limestone has more pores and microcracks at initial state. As this study analyzes physical and microstructural properties of rock specimens comprehensively, it can be applied to further rock weathering study and can be used as fundamental data of construction and resource development in cold regions.

• Journal of the Korean GEO-environmental Society
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• v.17 no.11
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• pp.55-64
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• 2016

Recently, it has been made many adjacent construction of inter-facility by the expansion of urban infrastructure facilities using the underground space. The complaints relating to the stability of the facility by adjacent construction is common. In this study, it was conducted for the subway line 5 Gimpo airport station structure in the upper Gimpo urban railway to determine the behavior characteristics of station structure according to adjacent construction. It was performed evaluation of the safety zone and excavation method for station structure. And after a review of damage evaluation, track irregularities and structural calculation by using a numerical analysis, stability of the station structure according to adjacent construction was evaluated to be secured. This study is expected to be used as basic data in advance if you need to review the effects of nearby structure according to adjacent construction.

• Tunnel and Underground Space
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• v.26 no.4
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• pp.327-337
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• 2016

In this study, laboratory hydraulic fracturing tests are carried out to evaluate the effects of the cleavage anisotropy of Pocheon granite. Breakdown pressure is smaller when cracks are generated to the direction of rift plane in constant pressurization rate condition because of higher microcracks density. Besides not only injection rate changes but also the amount of injection pressure for fracture initiation and crack expansion is detected while testing due to internal deformation. Pressurization rate is higher while hydraulic fracture testing with constant injection rate condition in case of the specimen which has rift plane perpendicular to borehole because there are much flow paths to penetrate compared to the specimen which has hardway plane perpendicular to borehole. Observation by X-ray CT scanning shows that almost all of cracks due to hydraulic fracturing are generated to the direction of plane which has higher microcrack density that is rift plane or grain plane.