• Geomechanics and Engineering
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• v.35 no.5
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• pp.525-538
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• 2023

The development of a city is closely linked to the construction and operation of its subway system. However, constructing a new subway tunnel under an existing station is an extremely complex task, and the deformation characteristics and mechanical behavior of the new subway tunnel during the excavation process can greatly impact the normal operation of the existing station. Although the previous studies about the case of underpass engineering have been carried out, there is limited research on the condition of a newly-built subway tunnel that closely undercrossing an existing station with zero distance between them. Therefore, this study analyzes the deformation law and mechanical behavior characteristics of the preliminary lining of the underpass tunnel during the excavation process based on the real engineering case of Chengdu Metro Line 8. This study also makes an in-depth comparison of the influence of different excavation methods on this issue. Finally, the accuracy of numerical simulation is verified by comparing it with on-site result. The results indicate that the maximum bending moment mainly occurs at the floor slab of the preliminary lining, while that of the ceiling is small. The stress state at the ceiling position is less affected by the construction process of the pilot tunnel. Compared to the all-in-one excavation method, although the process of partial excavation method is more complicated, the deformation of preliminary lining caused by it is basically less than the upper limit value of the standard, while that of the all-in-one excavation method is beyond standard requirements.

• Tunnel and Underground Space
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• v.33 no.4
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• pp.255-264
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• 2023

As the demand for urban underground space increases recently, urban tunnel planning is actively progressing. In the urban area, a underground station is planned in consideration of the living environment of residents, and 2-arch tunnel is applied for the stability of existing structures and reduction of environmental damage. However, since the depth of weak rock mass is deeply distributed in the urban area due to severe weathering, careful planning is required to secure tunnel stability. In addition, if TBM mechanical excavation is applied as the main tunnel excavation method considering the composite ground in urban area, the construction connectivity with the 2-arch tunnel of the NATM concept may be deteriorated. In this study, the design case of applying TBM pre-excavation type 2-arch tunnel for the first time in Korea was mainly described. The main considerations for the segment design of TBM pre-excavation type 2-arch tunnel were explained for side tunnels. Also, a stability analysis was conducted to verify the effectiveness and adequacy of the TBM pre-excavation type 2-arch tunnel.

• Proceedings of the KSR Conference
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• 2004.06a
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• pp.1007-1013
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• 2004

A three-arch NATM tunnel with a total length of 53.5m has been constructed for a metropolitan subway station in Daejon, Korea. The tunnel, whose crown is located 22m below the ground, crosses the old Daejon station underneath. Since the tunnel comprises a very large section (10${\times}$28 m; largest in Korea), it shows complicated mechanical behaviors, especially near portal, due to its short length relative to width. As far as its construction step is concerned, the center tunnel is excavated with pre-excavated pilot tunnel, which is a unique feature of this tunnel (first in Korea) to secure safety during construction and prevent excessive settlements. The both side tunnels are then excavated along with the center tunnel. Since significant amount of settlement was predictable from the design stage, extensive monitoring was performed during construction. During excavation of the side tunnels, unexpected large settlements up to ${\~}$140mm (estimated 41.8 mm at design stage) was measured at the center tunnel. In this paper, we study the causes of this unusually large ground settlement. We believe that the extra-wide tunnel excavation increases the stress influence zone of portal in longitudinal direction and consequently add more settlements to the existing due to excavation and consolidation.

• Tunnel and Underground Space
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• v.16 no.1 s.60
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• pp.73-84
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• 2006

Effects of railway tunnel excavation on water level at a national groundwater monitoring station in Mokpo were evaluated by field investigation and numerical groundwater modeling. The water level at the station has experienced a decline of about 5 m within 1 year since July 2002. From the field investigation, it was concluded that decrease of precipitation oo increase of grundwater use was not reason for the decline. The Mokpo tunnel of new Honam railway, 70 m apart from the national station, appeared most plausible cause and a period of the tunnel excavation generally well matches up that of the drawdown. To quantify the effects of the tunneling on the water level, a groundwater flow modeling was performed. Especially, a most probable conceptual model was optimized through multiple preliminary simulations of various scenarios because there were few hydrogeological data available for the study area. The optimized model was finally used for the quantification. Based on the field investigation and the numerical simulations, it was concluded that the tunnel excavation was one of the most probable reasons for the substantial water level decline but further hydrogeologic investigation and continuous monitoring are essentially required for the surrounding area.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.285-292
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• 1999

Recent development cases of transportation utilities using tunnelling method in metropolitan sites have been increased due to the heavily complex environments and restrictions of construction works. The progress of tunnel design and construction to be supported by the tunnel analysis and measurement techniques using computers have increased adoptions of large section tunnels. In this paper, many factors to be considered in designing large section tunnels are discussed and the case of the construction of the subway station tunnel which is recently completed is introduced. This tunnel has a width of 24 m, a height of 16 m, and a excavation section area of 366 ㎡.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.6
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• pp.535-544
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• 2016

Special tunnel design and construction methods have been suggested due to developments of subway and tunnel. Collapse accidents of tunnel bring enormous damage. So, observation and analysis for the safety of tunnelling and behaviour of surrounding ground are important. But, it is not economical to implement the field test in every time. Therefore, this study has measured ground behaviour due to excavation of 2-arch tunnel station according to offset between grouped pile and tunnel by laboratory model test. For the model test, trapdoor device was adopted. Tunnelling is simulated by volume loss of 2-arch tunnel. Ground displacements are observed by close range photogrammetric method and image processing. In addition, these data are compared with numerical analysis.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.242-247
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• 2017

Over- and under-excavation are factors that increase construction cost of tunnels, which makes management essential. Total stations have been used for tunnel surveying because GNSS is difficult to use in tunnels. However, it takes much time to acquire data using total stations. In this study, a total station was integrated with a 3D laser scanner and used for tunnel surveying in Namyangju-si, Gyeonggi-do. The scanning total station reduced the work time compared to the conventional method. Furthermore, reports were effectively generated for overbreak and underbreak for each section and compared with the design. In addition, we could analyze both the cross section and scanned area effectively by using the scanning data. This method can improve the efficiency of tunnel surveying work by combining the advantages of a conventional total station and a 3D laser scanner.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.83-97
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• 2018

Tunnels are widely used for special purposes including roads, railways and culvert for power transmission, etc. Its cross-section shape is determined by uses, ground condition, environmental or economic factor. Many papers with respect to behaviours of adjacent ground and existing structure tunnelling-induced have been published by many researchers, but tunnel cross-section have rarely been considered. A collapse of tunnel causes vaster human and property damage than structures on the ground. Thus, it is very important to understand and analyse the relationship between behavoiurs of ground and cross-section type of tunnel. In this study, the behaviour of ground due to tunnel excavation for underground station below the grouped pile supported existing structure was analysed through laboratory model test using a trap-door device. Not only two cross-section types, 2-arch and box, as station for tunnel, but also, offset between tunnel and grouped pile centre (0.1B, 0.25B, 0.4B) are considered as variable of this study. In order to measure underground deformation tunnelling-induced, Close Range Photogrammetry technique was applied with laboratory model test, and results are compared to numerical analysis.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.1062-1068
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• 2009

Urban construction has numerous difficulties due to ground weakness and various complaints from third party, so it is not economically efficient and constructability is not favorable. Therefore, underground, which has good ground conditions, was used for construction field and facilities such as stations, and they are scaled up to enhance accommodation of facility limitation and function of stations. Large section tunnel station construction has numerous risk factors such as work boundary of excavation equipment, a relaxation of stress concentration, a safety plan of tunnel stability, and so on. Therefore, by using large section tunnel station stability analysis considering construction step, we expect to analyze the latent problem during construction, and to stabilize a future project plan of a large section structure design by using an auxiliary method and a support design.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.1087-1094
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• 2010

With recent growth of population and industry, urban development grows into grand scheme of excavation and construction in urban area. As the development progress advanced, the developments get large and deepen. With a progress of technology development in geotechnical engineering in Korea, most our grand scheme of projects follows great progress. On the other hand, some excavation in construction site caused direct or indirect event that affects the adjacent or surrounding structures by excavation from time to time. This event usually happens around residential and commercial area where underground tunnel, subway station, commercial building, and high-rises excavation site is, could lead great damage on economy as well as personal injury or human casualties. In order to prevent this event, the study has to be done with analysis on various events of excavation and its cause. In this paper, the research has collected the various excavation events and their causes to analyze on each site and event to define emphasis on surrounding environment.