• Journal of the Korean Geosynthetics Society
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• v.17 no.1
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• pp.111-118
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• 2018

In case of excavation of the tunnel under weak ground conditions, such as fault zone, leg pile reinforcement with the purpose of suppressing tunnel crown settlement and side wall displacement is commonly applied. There are convergence, crown settlement, leg settlement, and the axial force of leg as a main factor for confirming the safety of support considering the installation angle and length of leg pile reinforcement according to the increase in rate of change of tunnel cross-section. In particular, the influence of right corner settlement, among variables for safety confirmation during excavation, has been analyzed as the dominant factor in the most important priority management showing larger displacement tendency than the increase in rate of the cross-section. And, it was analyzed that the occurrence tendency of axial force on leg pile reinforcement showed the influence of behavior according to the friction support concept mechanism of the pile reinforcement rather than the increase in rate of tunnel cross-section, as it showed a small increase compared to the increase rate of the tunnel cross-section which did not show a great correlation from the viewpoint of the change of the axial force by the length of each leg pile reinforcement with regards to the change in rate of increase in tunnel cross-section. If a certain length of the leg pile reinforcement is selected based on the above grounds, even if the cross-section of the tunnel in poor ground condition is somewhat larger, it has been proved to be a more reasonable method considering the workability and economical efficiency by not extending the length of the leg pile reinforcement by force.

• Proceedings of the KSR Conference
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• 2000.11a
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• pp.382-389
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• 2000

The purpose of present study is to investigate for reducing pressure fluctuations in tile case of installing tile air-shafts on the side wall of the tunnel with small cross-sectional area on conventional line. Experiments were performed with a 1/61-scale moving model rig for the tunnel of 0.764km length in the condition of tunnel cross-section area of 28 ㎡ According to the results, the maximum pressure fluctuation is reduced by 45% for 19 air-shafts. This results have the speed-up effects of about 33.4km/h for the train running in tunnel.

• Wind and Structures
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• v.31 no.3
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• pp.209-216
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• 2020

Aiming at the wind-resistant design of a sea-crossing arch bridge, the static aerodynamic coefficients of its girder (composed of stretches of π-shaped cross-section and box cross-section) were studied by using computational fluid dynamics (CFD) numerical simulation and wind tunnel test. Based on the comparison between numerical simulation, wind tunnel test and specification recommendation, a combined calculation method for the horizontal force coefficient of intermediate and small span bridges is proposed. The results show that the two-dimensional CFD numerical simulations of the individual cross sections are sufficient to meet the accuracy requirements of engineering practice.

• Explosives and Blasting
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• v.26 no.2
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• pp.29-37
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• 2008

In general, the size of tunnel cross section in construction site is $50{\sim}200m^2$. But, electric cable tunnel, telecommunication cable tunnel, mine tunnel. Waterproof tunnel have small cross section less than $20m^2$. There are so many problem at small sectional tunnel: restriction of equipment, dead pressure by precompression, loss of efficiency, increase of work time. Especially, explosives remainder by precompression of previous detonation is serious problem. To find its measures of dead pressure (explosives remainder), the following series of progress have been conducted: (1) survey of previous study (2) investigate causes of dead pressure (3) set up of its measures (4) application and appraisal at tunnel site. The measures, change of cut pattern, hole space over 40cm, adjustment of delay time, are proved by experimental results.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.313-336
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• 2007

Unlike a conventional railway system, a high-speed rail system experiences various aerodynamic problems in tunnel sections. Trains running at a high speed in a small tunnel, when compared with the open field, face significant air pressure, resulting in reduced operating stability and fast change in pressure inside the tunnel. These phenomena further cause some unexpected problems such as the passengers onboard feeling an aural discomfort and an impulsive noise at the tunnel exit. To solve these problems, this paper introduces analysis of aerodynamic characteristics for determination of tunnel cross section. The optimum cross-section that satisfies the criteria of aural discomfort was reviewed through lots of numerical simulation analysis. Also, the pressure inside the passenger car of a train operating on Kyungbu HSR line was measured, and the pressure inside the tunnel and the micro-pressure waves at tunnel exit were measured at Hwashin 5 Tunnel. At the same time, a test of train operation model was performed and then the measurement results and test results were compared to verify that various parameters used as input conditions for the numerical simulations were appropriate.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.341-348
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• 2001

The purpose of present study is to investigate for reducing pressure fluctuations in the case of installing the air-shafts on the side wall of the tunnel with small cross-sectional area on conventional line. Experiments were performed with a 1/61-scale moving model rig for the tunnel of 0.764 km length in the condition of tunnel cross-section area of $28 m^2$. According to the results, the maximum pressure fluctuation is reduced by 45 % for 19 air-shafts. This results have the speed-up effects of about 33.4 km/h for the train running in tunnel.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.3
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• pp.375-388
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• 2017

In order to solve the traffic congest and environmental issues, small-cross section tunnel for small car only is increasing, but there is not standard for installation of disaster prevention facility. In this study, in order to investigate the behavioral characteristics of thermal environment and smoke in a small cross section tunnels with a large port exhaust ventilation system, the A86, the U-Smartway and the Seobu moterawy tunnel, Temperature and CO concentration in case of fire according to cross sectional area, heat release rate and exhaust air flow rate were analyzed by numerical analysis and the results were as follows. As the cross-sectional area of the tunnel decreases, the temperature of the fire zone increases and the rate of temperature rise is not significantly affected by heat release rate. However, there is a difference depending on the change of the exhaust air flow rate. In the case of applying the exhaust air flow rate $Q_3+2.5Ar$ of the large port exhaust ventilation system, the temperature of the fire zone was 7.1 times for A86 ($Ar=25.3m^2$) and 5.4 time for U-smartway ($Ar=37.32m^2$) by Seobu moterway tunnel ($Ar=46.67m^2$). The CO concentration of fire zone also showed the same tendency. The A86 tunnels were 10.7 times and the U-Smartways were 9.5 times more than the Seobu moterway. Therefore, in the case of a small section tunnel, the thermal environment and noxious gas concentration due to the reduction of the cross-sectional area are expected to increase significantly more than the cross-sectional reduction rate.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.3
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• pp.261-275
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• 2020

When excavating a small cross-section tunnel in a fault fracture zone using the shield TBM method, there is a high possibility of excessive convergence and collapse. Appropriate ground reinforcement is required to minimize construction cost loss and trouble due to a fault fracture zone. In this study, the optimal reinforcement area was suggested and the surrounding ground behavior was investigated through numerical analysis using MIDAS GTS NX (Ver. 280). For the parameters, the width of the fault fracture zone, the existence of fault gouge, and the groundwater level and depth of cover were applied. As a result, when there is not fault gouge, the convergence and ground settlement are satisfied the standard when applying ground reinforcement by up to 0.5D. And, due to the high permeability coefficient, it is judged that it is necessary to apply 0.5D reinforcement. There is a fault gouge, it was possible to secure stability when applying ground reinforcement between the entire fault fracture zone from the top of the tunnel to 0.5D. And, because the groundwater discharge occurred within the standard value due to the fault gouge, reinforcement was unnecessary.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.3
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• pp.215-226
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• 2015

In this study, with variables the cross section area ($97m^2$, $58m^2$, $38m^2$) and the wind velocity(0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 m/s), the time of getting off train dependent on the way of itself and the width of the evacuation route was analyzed, and also fire and evacuation characteristics is reviewed by cross section area of each wind velocity. As the result, if cross section become smaller, the density of harmful gases in the tunnel increased more than the ratio of decreasing cross section area. In the case of small cross sectional area, the surrounding environment from initial fire is indicated to exceed the limit criteria suggested in performance based design. In the analysis of effective evacuation time for evacuation characteristics, the effective evacuation time was the shortest in the case of evaluating effective evacuation time by the visibility. Also, there was significant difference between the effective evacuation time on the basis of performance based evaluation and the effective evacuation time obtained by analyzing FED (Fractional effective dose), one of the analysis method obtaining the point that deaths occur, against harmful gases.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.152-165
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• 1991

Elasto-plastic and Visco-elastic sytress analyses were conducted for standard cross-section of subway tunnel in Seoul . Considering the procedure of excavation and reinforcement, excavated region was divided to multiple elements. And the progress of tunnel is simulated to be the removal of a series of layerd elements by means of diminishing the stiffness of the portion progressively. Another method is to be free of stress due to excavation instead of stiffness. In the analysis multiple element method was conducted with ADINA program, the stiffness removal method was adopted . For the same model, stress release method was carried out with Visco-Elastic Analysis program developed in Rock mechanics laboratory, Seoul National University(SNU-VBA) . When upper tunnel excavated, displacements in roof were same for two results, but when bottom tunnel removed completely , displacement changes of rock in the stress release method exhibited very small amount compared with stiffness removal method.