• Proceedings of the Korean Geotechical Society Conference
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• 1998.03a
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• pp.381-386
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• 1998

• Journal of the Korean Geotechnical Society
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• v.24 no.7
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• pp.5-16
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• 2008

Most of roadway tunnels have been constructed in the form of parallel twin tunnel in Korea. If parallel twin tunnel does not have a sufficient separation distance between tunnels, the problem of tunnel stability can occur. Generally, it is reported that tunnels are not influenced by each other when a center distance between tunnels is two times longer than tunnel diameter under the complete elastic ground and five times under the soft ground. In this study, the scaled model tests of closely-spaced parallel twin tunnel using homogeneous material are performed and induced displacements are measured around the tunnel openings during excavation. The influence of separation distance between tunnels on the behavior of closely-spaced tunnel is investigated. The experimental results are expressed by the induced displacement vector and progress of crack during construction and at failure. The results show that based on the analysis of induced displacement at the crown during construction, the additional displacement of the preceding tunnel induced by the excavation of following tunnel decreases as the separation distance between twin tunnel increases until the center to center distance is two times of tunnel diameter. Beyond this point, however, the additional displacement has become stabilized.

• Journal of the Korean GEO-environmental Society
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• v.12 no.11
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• pp.39-49
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• 2011

In this paper it was focused on the characteristics of displacement and stress due to the construction of diagonal twin tunnel. In this research, the characteristics have been analyzed with the presumption that the tunnel's diameter (D) is 13m and the ground was formed by weathered rock. In analysis, the width of pillar is 2.0D, 2.5D, 3.0D, the height of soil cover is 3D, 4D, 5D, and the installation angle of diagonal twin tunnel has been changed into $15^{\circ}$, $30^{\circ}$, $45^{\circ}$. And the program used in this analysis is FLAC which is widely used in solution problems of ground engineering in order to gain and analyze occurring shotcrete and rockbolt stress and nearby ground displacement according to pillar width, the height of soil cover and installation angle of diagonal twin tunnel. As a result, in the weathered rock grounds, when the width of pillar is more than 2.0D, the height of soil cover is over 5.0D, and the installation angle of diagonal twin tunnel is lower, they lessen effects on the ground and favorable on the stability of tunnel.

• Tunnel and Underground Space
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• v.14 no.5
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• pp.381-390
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• 2004

In this study, scaled model tests were performed to investigate the deformation behaviors around twin tunnels. Eleven types of test models which had respectively different pillar widths, rock types and loading conditions were mode, where the modelling materials were the mixture of sand, plaster and water. The models with shallower pillar width were cracked under lower pressure than the models with thicker pillar width, and they showed the more tunnel convergences and the clear spatting failures. The models of hard rock were cracked under 50% higher pressure than the models of soft rock and they showed the less tunnel convergences. The failure and deformation behaviors of twin tunnels were also dependent on the loading conditions of models. Futhermore, the results of FLAC analysis were qualitatively coincident with the test results.

• Geomechanics and Engineering
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• v.28 no.3
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• pp.225-237
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• 2022

Settlement evaluation is important for shallow tunnels in big cities to estimate the settlement that occurs due to the excavation of twin tunnels. The majority of earlier research on analytical solutions, on the other hand, concentrated on calculating the settlement for a single tunnel. This research introduces a procedure to evaluate the settlement induced by the excavation of twin tunnels (two parallel tunnels). In this study, a series of numerical analysis were performed to validate the analytical solution results. Two geological conditions were considered to derive the settlement depending on each case. The analytical and numerical methods were compared, which involved considering many sections and conducting a parametric study; the results have good agreement. Moreover, a comparison of the 3D flat model and 2D (FEM) with the analytical solution shows that in the fill soil, the maximum settlement values were obtained by the analytical solution. In contrast, the values obtained by the analytical solution in the rock is more conservative than those in the fill. Finally, this method was shown to be appropriate for twin tunnels dug side by side by utilizing finite element analysis 3D and 2D (PLAXIS 3D and PLAXIS 2D) to verify the analytical equations. Eventually, it will be possible to use this approach to predict settlement troughs over twin tunnels.

• Geomechanics and Engineering
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• v.9 no.4
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• pp.427-445
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• 2015

By means of finite element numerical simulation and pseudo-static method, the shallow-buried bilateral bias twin-tube tunnel subject to horizontal and vertical seismic forces are researched. The research includes rupture angles, the failure mode of the tunnel and the distribution of surrounding rock relaxation pressure. And the analytical solution for surrounding rock relaxation pressure is derived. For such tunnels, their surrounding rock has sliding rupture planes that generally follow a "W" shape. The failure area is determined by the rupture angles. Research shows that for shallow-buried bilateral bias twin-tube tunnel under the action of seismic force, the load effect on the tunnel structure shall be studied based on the relaxation pressure induced by surrounding rock failure. The rupture angles between the left tube and the right tube are independent of the surface slope. For tunnels with surrounding rock of Grade IV, V and VI, which is of poor quality, the recommended reinforcement range for the rupture angles is provided when the seismic fortification intensity is VI, VII, VIII and IX respectively. This study is expected to provide theoretical support regarding the ground reinforcement range for the shallow-buried bilateral bias twin-tube tunnel under seismic force.

• Wind and Structures
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• v.10 no.4
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• pp.383-398
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• 2007

The paper describes a study of the effects of structural coupling on the wind-induced response of twin tall buildings connected by a skybridge. Development of a dual high-frequency force balance used in wind tunnel investigation and background information on the methodology employed in analysis are presented. Comparisons of the wind-induced building response (rooftop acceleration) of structurally coupled and uncoupled twin buildings are provided and the influence of structural coupling is assessed. It is found that the adverse aerodynamic interference effects caused by close proximity of the buildings can be significantly reduced by the coupling. Neglecting of such interactions may lead to excessively conservative estimates of the wind-induced response of the buildings. The presented findings suggest that structural coupling should be included in wind-resistant design of twin tall buildings.

• Tunnel and Underground Space
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• v.15 no.3 s.56
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• pp.177-184
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• 2005

The Sapaesan tunnel, the longest twin tube tunnel (4km) in Korea with 4 lanes each, is under construction with two years of delayed schedule because of the strong opposition from environmental bodies. Therefore, maximizing the construction efficiency was needed in tunnel project to compensate for time delay. This study includes improvements in the construction of the Sapaesan tunnel such as increasing excavation length and changing excavation sequence. In this paper the system for predicting tunnel face ahead is also introduced. Bulk-Emulsion explosive and Cylinder-Cut method were adopted in tunnel blasting to increase the excavation length. Optimum tunnel excavation step was designed to make up delayed time. Tunnel foe mapping, TSP survey and geological prediction system using computerized jumbo-drill were performed fnr safe construction of long and large twin tube tunnel.

• Geomechanics and Engineering
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• v.16 no.3
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• pp.295-308
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• 2018

The excavation of twin tunnels is a process that destabilizes the ground. The stability of the tunnel lining, the control of ground displacements around the tunnel resulting from each excavation and the interaction between them must be controlled. This paper provides a new approach for replacing the costly 3D analyses with the equivalent 2D analyses that closely reflects the in-situ measurements when excavating twin tunnels. The modeling was performed in two dimensions using the FLAC2D finite difference code. The three-dimensional effect of excavation is taken into account through the deconfinement rate ${\lambda}$ of the soil surrounding the excavation by applying the convergence-confinement method. A comparison between settlements derived by the proposed 2D analysis and the settlements measured in a real project in Algeria shows an acceptable agreement. Also, this paper reports the investigation into the changes in deformations on tunnel linings and surface settlements which may be expected if the twin tunnels of T4 El-Harouche Skikda were constructed with a tunneling machine. Special attention was paid to the influence of the excavation phase shift distance between the two mechanized tunnel faces. It is revealed that the ground movements and the lining deformations during tunnel excavation depend on the distance between the tunnels' axis and the excavation phase shift.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.938-945
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• 2004

In order to cope with ever growing traffic flow and complexity in the urban area, construction demands for expanding and realigning of existing urban roads and massive development of underground space within the urban area are in its increasing trend, it is fact that, mainly due to lack of statistical data accumulation through real construction, technology and construction practice to support such demands can hardly be said to have been established enough and leave many things still to be developed. These circumstances therefore came to motivate me to get into a study for a particular subject of "Design Basics for Closely Neighbored Twin Tunnel" among others, and also to put forward subjects required to be further studied in this connection in the future as follows: 1) To make a new economical design model for closely neighbored twin tunnel not only to make a drain for center perfect but also a tunnel construction safe. 2) Further efforts should be exerted for establishment of general standards for design and construction of various types of large cross-section tunnels including Twin structure.