• Geomechanics and Engineering
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• v.23 no.5
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• pp.405-418
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• 2020

Deep excavation may have impact on the adjacent tunnels. It is obvious that the excavation will adversely affect and even damage the existing tunnels if the induced deformation exceeds the capacity of tunnel structures. It hence creates a high necessity to predict tunnel displacement induced by nearby excavation to ensure the safety of tunnel. In this paper, a simplified method to evaluate the heave of the underlying tunnel induced by adjacent excavation is presented and verified by field measurement results. In the proposed model, the tunnel is represented by a series of short beams connected by tensile springs, compressional springs and shear springs, so that the rotational effect and shearing effect of the joints between lining rings can be captured. The proposed method is compared with the previous modelling methods (e.g., Euler-Bernoulli beam, a series of short beams connected only by shear springs) based on a field measured longitudinal deformation of subway tunnels. Results of these case studies show a reasonable agreement between the predictions and observations.

• Proceedings of the KSR Conference
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• 2007.05a
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• pp.375-378
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• 2007

The selection of the support system is an important design parameter in design and construction of the tunnel using the new Australian tunnel method. It is a common practice to select the support based on the rock mass grade, in which the rock mass is classified into five rock groups. The method is applicable if the characteristics of the rock mass are uniform in the direction of tunnel excavation. However, such case is seldom encountered in practice and not applicable when the properties vary along the longitudinal direction. This study performs comprehensive three dimensional finite difference analyses to investigate the ground deformation pattern for cases in which the rock mass properties change in the direction of the tunnel axis. The numerically calculated displacements at the tunnel crown show that the displacement is highly dependent on the stiffness contrast of the rock masses. The results strongly indicate the need to select the support type $0.5\sim1.0D$ before the rock mass boundary. The paper proposes a new guideline for selecting the support type based the results of the analyses.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.9
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• pp.669-678
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• 2007

In this study, the ventilation characteristics is investigated numerically of the longitudinal ventilation method in the curved long road tunnel. Numerical work has been conducted for the jet fan location by utilizing the commercial finite-volume code, FLUENT. Configuration of the tunnel is three-lane, 1600 m long, $120m^2$ in area, 3000 m curvature radius. The velocity profile, distribution of mono-dioxide carbon and flow rate of air are examined in the tunnel. Through the analysis, it is found that the difference of ventilation flow rate Is a little by the jet fan location, but tunnel outlet setup (CASEIII) of jet fans is the most efficient concerned with CO concentration.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.2
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• pp.119-131
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• 2005

The two dimensional behaviors of the existing upper tunnel and the ground at crossed area due to the excavation of a lower tunnel were studied experimentally, The model tests were conducted by changing the relative location of the existing upper tunnel and the lower tunnel. The results of the study show that a vertical earth pressure outside the loosened area was increased due to longitudinal arching effect same as a single tunnel. In case vertical distance between the upper and lower tunnel is 0.7 H and 1.0 H respectively (H is a height of the lower tunnel), vertical earth pressure increased in the loosened area behind the tunnel face. But when a vertical distance is 1, 3 H, ground behaviors appeared similarly to a single tunnel.

• Geomechanics and Engineering
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• v.33 no.5
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• pp.477-486
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• 2023

In the studies on fault dislocation of tunnel, existing literatures are mainly focused on the problems caused by normal and reverse faults, but few on strike-slip faults. The paper aims to research the deformation and failure mechanism of a tunnel under strike-slip faulting based on a model test and test-calibrated numerical simulation. A potential faulting hazard condition is considered for a real water tunnel in central Yunnan, China. Based on the faulting hazard to tunnel, laboratory model tests were conducted with a test apparatus that specially designed for strike-slip faults. Then, to verify the results obtained from the model test, a finite element model was built. By comparison, the numerical results agree with tested ones well. The results indicated that most of the shear deformation and damage would appear within fault fracture zone. The tunnel exhibited a horizontal S-shaped deformation profile under strike-slip faulting. The side walls of the tunnel mainly experience tension and compression strain state, while the roof and floor of the tunnel would be in a shear state. Circular cracks on tunnel near fault fracture zone were more significant owing to shear effects of strike-slip faulting, while the longitudinal cracks occurred at the hanging wall.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.5
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• pp.855-867
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• 2018

When a weak zone exists ahead of tunnel face, the stress in the adjacent area would increase due to the longitudinal arching effect and the stability of the tunnel is affected. Therefore, it is critical to prepare a countermeasure through the investigation of the frontal weakness zone of the excavated face. Although there are several researches to predict the existence of weak zone ahead of tunnel face, such as geophysical exploration, numerical analysis and tunnel support, lack of studies on the relaxation zone depending on the width or distance from the vulnerable area. In this study, the impact of the weak zone on the formation of the relaxation zone was investigated. For this purpose, a series of laboratory test were carried out varying the width of the weak zone and the separation distance between tunnel face and weak zone. In the model test, sand with a water content of 3.8% was used to form a model ground. The model weak zone was constructed with dry sand curtains. The tunnel face was adjusted to allow a sequential excavation of upper and lower half part. load cells were installed on the bottom of the foundation and the tunnel face and measuring instruments for displacement were installed on the surface of the model ground to measure the vertical stress and surface displacements due to tunnel excavation respectively. The test results show that the width of weak zone did not affect the ground settlement while the ground subsidence drastically increased within 0.25D. The vertical stress and horizontal stress increased from 0.5D or less. In addition, the longitudinal arching effect is likely within the 1.0D zone ahead of the tunnel face, which may reduce the vertical stress in the ground following tunneling direction.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.5
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• pp.733-747
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• 2017

In the shallow tunnel, the surrounding ground could be loosened and deformed, which could be the cause of stress change in the ground. Terzaghi has clarified the development of a ground arching induced by the deformation of a tunnel crown in the trap door tests. However, he considered only the case in which that the tunnel crown deformed uniformly. He did not consider the effect of deformation shapes. Therefore, the relation between the shape of the ground relaxation above the tunnel crown and the deformation shape of the tunnel crown is not clear yet. In this study, model tests were performed for the three types of the tunnel crown, such as uniform, concave and convex shapes. As results, it was found that the vertical load would be transferred in various types depending on the deformation shapes of the tunnel crown.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.2
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• pp.141-149
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• 2004

In this study, smoke movement in tunnel fire with natural and longitudinal ventilation systems has been investigated. Reduced-scale experiments were carried out under the Froude scaling using 14.55kW fire source with a wick and experimental data is obtained with 1/18 model tunnel test. Temperature profiles were measured under the ceiling and vertical direction along the center of the tunnel and poisonous gas was measured at emergency exit point. The results show that refuge time for 225m intervals of emergency exit in case of natural ventilation systems is 256 seconds and critical velocity for sufficient back-layer prevention is 2.8m/s for fire strength of 20MW.

• Tunnel and Underground Space
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• v.16 no.6 s.65
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• pp.526-535
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• 2006

An experimental study was carried out on a reduced scale tunnel model to grasp the behavioral feature of fire-induced smoke in the long tunnels. Based on Froude modeling, the 1/50 scaled tunnel model (20 m long) was constructed by acrylic tubes and paraffin gas was released inside the tunnel to simulate the 20 MW fire-induced smoke. me test results show, that after approximately 2 minutes of fire generation, was descended from the tunnel ceiling through the decrease of buoyancy, then it was symmetrically propagated about 90 meters for 4 minutes before jet fans were operated. The smoke was effectively controlled when the jet fans were operated and an air stream velocity was getting closed to reach a critical velocity (the minimum air velocity that requires to suppress the smoke spreading against the longitudinal ventilation flow during the tunnel fire situations). It was also found out that a range of smoke was spreaded about 3 meters from the origin of fire but the range was not propagated to the escape direction anymore. The early stage of the In operation, however, showed that the smoke was hardly controlled. It means that the operation of emergency ventilation system has many dangerous factors such as an intercepting breathing zone.

• Tunnel and Underground Space
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• v.8 no.1
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• pp.53-66
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• 1998

Considering the mechanical cracking in the concrete lining of tunnels occurring in relatively short period of time after the construction, there is a need for the study on the mechanical behavior and the cracking characteristics of double lining support system(shotcrete and concrete lining). For the proposed study, downscaled lining models of Kyung-Bu High Speed Railway tunnels were tested. Most longitudinal cracks at about 93 percentage developed within 30 arch degree from the vault. Cracking load was about 30 percentage of the failure load and the deflection under the cracking load was 10 percentage of the deflection under the failure load. The overbreak around the vault contributed to the reduction of the capacity for cracking and failure by the percentage greater than the reduced effective depth. Of several rock block types considered in this research, the triangular block was the most critical, and the right triangular block under eccentric load was secondly critical for the stability of the tunnel lining system. The dimensionless support reaction curves were derived from the experimental results for single and double lining. The general equation to compute the designed flexural moment was modified.