• Tunnel and Underground Space
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• v.20 no.3
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• pp.131-144
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• 2010

The design and construction of tunnels has been followed an large parallel tunnels with a small clearance because of the various conditions. Rock pillar between each single tunnel is supposed to be under heavy load by rock mass. The stability of pillar is very important for the ensure the stability of the large parallel tunnels. In this study, the analysis of stress state of pillar at various construction cases is reviewed to investigate the mechanical behaviour of tunnels and stability of the pillar.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.4
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• pp.421-430
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• 2008

In discontinuous rock masses, hydraulic-mechanical coupled analyses are required since groundwater flow in joints have a great influence on the stability of a subsea tunnel. In this study, a sensitivity analysis was performed based on coupled analysis to verify the routine which can estimate the safety factor of a tunnel in discontinuous rock mass. To this end, 324 cases of numerical calculations were performed with a commercial program, UDEC-2D. As a result, it was confirmed that the proposed routine for coupled analysis in discontinuous rock mass could give a reasonable result for the estimation of safety factor of a tunnel. Therefore, it is expected that the safety factor estimation method used in this study can be effectively applied for the stability estimation of a subsea tunnel in discontinuous rock masses.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.6
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• pp.545-556
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• 2016

If a back analysis is used in various measurement information for the estimation of an operating subsea tunnel safety, it is possible to obtain the results within efficient error rate. With such a commercial geotechnical analysis program as FLAC3D, back analysis is performed with a DEA which was validated in previous studies. However, there is a problem that is relatively a time-consuming analysis. For this reason, beam-spring model-based FEM solver which takes shorter relative analysis time, was developed by Python language, and then combined with the built-DEA. In order to consider the assessment of safety of an operation tunnel near real-time, a program for longitudinal direction tunnel was developed due to its relative easy development for analysis solver engine.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.2
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• pp.195-212
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• 2017

When back analysis is used for the assessment of an operating subsea tunnel safety in various measurement information such as stress, water pressure and tunnel lining and ground stiffness degradation, the reliable results within tolerable error rate can be obtained. By utilizing a commercial geotechnical analysis program FLAC3D, back analysis can be performed with a DEA which has already been successfully validated in previous studies. However, relative more time-consumption is the drawback of this approach. For this reason, this study introduced beam-spring model-based on FEM solver which uses less analysis time relatively. Beam-spring program capable of structural analysis of a circular tunnel section was developed by using Python language and combined with the built-DEA. From the measurement datum, expected to estimate the stability of an operation tunnel close to real-time.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.389-399
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• 2016

Efficiency for estimation of subsea tunnel safety can be increased through reflecting back analysis algorithm to displacement measurements besides other measurement information such as stress, water pressure and ground stiffness degradation. In this study, the finite difference code FLAC3D built-in FISH language is used. In addition, the stability of the tunnel lining will be evaluated from the development of displacement-based algorithm and its expanded algorithm with conformity of several parameters such as stress measurements, water pressure measurements, tunnel lining degradation measurements and ground stiffness degradation measurements. By using additional measurement information to assess the stability of subsea tunnel, it was confirmed that the error rate is reduced to the tunnel back analysis.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.2
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• pp.301-317
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• 2017

In this study, as an initial study for development of stability analysis program of a double-deck tunnel during life cycle, a structural analysis solver based beam-spring model for the double-deck tunnel is constructed. Effect of parameters(slab supporting type, depth of the tunnel and ground elastic modulus) is analyzed with the beam-spring model. The model is also compared and verified by commercial structural analysis program. It is considered that the slab supporting type affects the integrated behavior with segment lining and influence of intermediate slab on the stability of the tunnel decreases as the tunnel depth increases. The relationship between the ground elastic modulus and the effect of the intermediate slab on the segment lining needs further investigation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.361-374
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• 2018

The country has built and is operating IT-based integrated management system for efficient management of national highway tunnels used publicly these days. Since this system doesn't include the management function on earthquakes, it is impossible to promptly respond to earthquakes and to select the sections requiring seismic reinforcement. Tunnels designed and constructed after 1999 have been subjected to seismic design for an earthquake with a return period 1000 years. Therefore, it is necessary to evaluate the stability of structures in case of earthquakes more than this. Since it takes a lot of time to perform the stability evaluation on various earthquake magnitudes, a method that can easily evaluate earthquakes is needed. In this paper, the empirical simplification method that can easily evaluate the earthquake was proposed. For this, the study calculated ground displacement by conducting one-dimensional ground response analysis, and examined the safety of tunnels in the event of occurrence of an earthquake using two means of response displacement method (analytics and numerical analysis).

• Tunnel and Underground Space
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• v.9 no.2
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• pp.102-113
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• 1999

Two-dimensional and three-dimensional DEM programs, UDEC and 3DEC, were used to investigate the mechanical stability of the conceptual design of deposition drift and deposition holes constructed in a crystalline rock mass. From the simulations, the influence of discontinuities, the number of deposition holes, and deposition hole interval on the stability of deposition drift and deposition holes could be determined. From the two-dimensional and three-dimensional analysis. it was concluded that three-dimensional analysis should be carried 7ut fur deriving reliable conclusions. Even though the deposition hole interval changed from 8 m to 3 m, which did not damage the mechanical stability of the deposition drift.

• Tunnel and Underground Space
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• v.13 no.2
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• pp.77-86
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• 2003

The finite element method and statistics of the convergence measurement are useful method of the stability analysis of the tunnel adjacent to the pier. It is the purpose of the this case study to certificate of validity of the application of those methods. The safety of the pilot tunnel method and LW pre-grouting has been evaluated from the FEM analysis. The three-dimensional finite element method is carried out for the decision of the level of stress redistribution at the two-dimensional numerical analysis. An analysis of the convergence is carried out by the estimation of preceding convergence at tunnel excavation. F-examination is applied for this estimation. As results of that analysis, The F-value is from 10.81 to 158.74 and the coefficient of determination is from 0.82 to 0.99. An analysis of convergence is carried out by using regression analysis. Consequently, it is shown that the convergence can be modeled as following function C(t)=a[1-exp(-bt)].

• Tunnel and Underground Space
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• v.23 no.2
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• pp.130-140
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• 2013

In this study, scaled model tests were performed to investigate the stability of twin tunnels with small clearance, where the pillar widths were 0.5D and 0.25D, respectively. The tunnels were supposed to be constructed in anisotropic weathered rocks with $30^{\circ}$ inclined bedding planes, and the model tests were conducted under the condition of lateral pressure ratio, 1. Six types of test models which had respectively different pillar widths and support conditions were experimented, where crack initiating pressures, maximum pressures, failure modes of pillar and deformation behaviors around tunnels were investigated. The models with wider pillar were cracked under higher pressure than the models with shallower pillar. The models with lining support were cracked under higher pressure and showed less tunnel convergence than the unsupported models. The models with both lining and pillar reinforcement were proved to be most stable among the tested models. In particular, as the model of 0.25D pillar width with only lining support showed shear failure of pillar according to the existing bedding planes, so both lining and pillar reinforcement were thought to be indispensable in that case of tunnel.