• Tunnel and Underground Space
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• v.24 no.2
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• pp.120-130
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• 2014

Recently, a few mega projects of subsea tunneling are completed or ongoing or under planning stage all across the world. In Korea, subsea tunnels connecting to Japan and China have been considered in the past decades. At the same time, subsea tunnels connecting to domestic islands were planned with preliminary design concepts. Development and improvement of indigenous techniques regarding subsea tunneling are essential in light of current technical level in Korea and their future impact on tunneling industry. In this paper, distinct features of subsea tunnel and construction trend of subaqueous tunnels are analyzed via case studies. Also, case studies about incidents related to subsea tunneling and required techniques to secure safety are presented.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.251-265
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• 2018

This paper concerns the development of an optimized NATM secondary lining design system for a subsea tunnel. The subsea tunnel is normally laid down under the sea water and submarine ground which consists of soil or rock. The design system is the series of process which can predict lining member forces by ANN (artificial neural network system), analyze suitable section for the designated ground, construction and tunnel conditions. Finally, this lining design system aims to be connected for designing the subsea tunnel automatically. The lining member forces are predicted based on the ANN which was calculated by a FEM (finite element analysis) and it helps designers determine its lining dimension easily without any further FEM calculations.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.3
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• pp.319-329
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• 2016

Underground structures such as subsea tunnel having large section should be stable against seismic loads. In general, underground structures show more stable behavior due to the limited dynamic motion and force, and considerable energy dissipation; however, severe damage was reported from recent earthquakes. Therefore, more sophisticated and analytic approach is required to investigate the seismic response of underground structure like subsea tunnel. In this study, seismic analysis of virtual Honam-Jeju subsea tunnel are performed. Consequently, stresses and forces of tunnel lining increased at fractured and/or weak rock zones. Stresses and forces of tunnel lining also increased at large section under axially deformed condition; however, decrease under transversely deformed condition.

• Journal of the Korean Geotechnical Society
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• v.38 no.11
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• pp.69-86
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• 2022

The railway is widely used to transport passengers and freight due to its punctuality and large transport capacity. The recent remarkable development in construction technology enables various subsea railway tunnels for continent-continent or continent-island connectivity. In Korea, design and construction experience is primarily based on the successful completion of the Boryeong subsea tunnel (2021) and the Gadeok subsea tunnel (2010). However, frequent earthquakes with diverse magnitudes, globally induced and continuously increased the awareness of seismic risks and the frequency of domestic earthquakes. The effect of an earthquake on the subsea tunnel is very complicated. However, ground conditions and seismic waves are considered the main factors. This study simulated four ground types of 3-dimensional numerical models, such as soil, rock, composite, and fractured zone, to analyze the effect of ground type and seismic wave. A virtual subsea railway shield tunnel considering external water pressure was modeled. Further, three different seismic waves with long-term, short-term, and both periods were studied. The dynamic analyses by finite difference method were performed to investigate the displacement and stress characteristics. Consequently, the long-term period wave exhibited a predominant lateral displacement response in soil and the short-term period wave in rock. The artificial wave, which had both periodic characteristics, demonstrated predominant in the fractured zone. The effect of an earthquake is more noticeable in the stress of the tunnel segment than in displacement because of confining effect of ground and structural elements in the shield tunnel. 

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.2
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• pp.153-166
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• 2015

Long subsea tunnel to be built below the seabed, as compared to the general railway tunnel, is subject to many restrictions in terms of spatial limitation when vertical or inclined shafts are built for the purpose of ventilation and fire safety. So, the construction of some artificial island is required to provide ventilation. But, because of construction difficulty and cost increase, it is necessary to minimize the artificial island construction. The longer ventilation distance is, the more fresh air requirement is needed. When supply airflow becomes excessive, duct size is restricted by the limitations of structure clearance and fan pressure and power increase exponentially. Therefore, in order to build a long subsea tunnel, it is necessary to overcome these practical problems and to develop technical solution that can keep the comfortable condition of tunnel environment during construction. In this study, as on ventilation method development suitable for long subsea tunnel, through comparison of temporary ventilation capacity calculation methods during construction phase, domestic and abroad, the application of Swiss SIA 196 code is found suitable for long subsea tunnel. And, through experiment on leakage of the duct connector, we confirmed that the leakage ratio per 100 m of domestic duct connection type is between 1.5~3.0%. Based on S-class duct of SIA 196 code, ventilation distance is 10.2 km, So, ventilation distance can be longer if duct connection method is improved. So, we confirmed that the improvement of leakage ratio is key issue in the construction-phase ventilation of long subsea tunnel.

• Geomechanics and Engineering
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• v.21 no.2
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• pp.133-142
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• 2020

Submerged floating tunnel (SFT) is a type of tunnel which causes the tunnel segments to float in the water. When the SFTs are connected to the ground, the connection between the SFT and the subsea bored tunnel is fragile due to the difference in behavioral characteristics between the two types of tunnels. Therefore, special design and construction methods are needed to ensure the stability of the area around the connection. However, since previous research on the stability of the connection site has not been undertaken enough, the basic step necessitates the evaluation of ground behavior at the shore connection. In this study, the numerical analysis targeting the shore connection between the subsea bored tunnel and the SFT was simulated. The strain concentration at the shore connection was analyzed by numerical simulation and the effects of several factors were examined. The results showed the instability in the ground close to the shore connection due to the imbalance in the behavior of the two types of tunnels; the location of the strain concentration varies with different environmental and structural conditions. It is expected that the results from this study can be utilized in future studies to determine weak points in the shore connection between the submerged floating tunnel and the subsea bored tunnel, and devise methods to mitigate the risks.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.5
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• pp.563-573
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• 2015

For hard rock subsea tunnels the most challenging rock mass conditions are in most cases represented by major faults/weakness zones. Poor stability weakness zones with large water inflow can be particularly problematic. At the pre-construction investigation stage, geological and engineering geological mapping, refraction seismic investigation and core drilling are the most important methods for identifying potentially adverse rock mass conditions. During excavation, continuous engineering geological mapping and probe drilling ahead of the face are carried out, and for the most recent Norwegian subsea tunnel projects, MWD (Measurement While Drilling) has also been used. During excavation, grouting ahead of the tunnel face is carried out whenever required according to the results from probe drilling. Sealing of water inflow by pre-grouting is particularly important before tunnelling into a section of poor rock mass quality. When excavating through weakness zones, a special methodology is normally applied, including spiling bolts, short blast round lengths and installation of reinforced sprayed concrete arches close to the face. The basic aspects of investigation, support and tunnelling for major weakness zones are discussed in this paper and illustrated by cases representing two very challenging projects which were recently completed (Atlantic Ocean tunnel and T-connection), one which is under construction (Ryfast) and one which is planned to be built in the near future (Rogfast).

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.58-69
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• 2010

Turkey Eurasia Tunnel Project is large scale road construction project of which the total length is 14.6km. The subsea shield TBM tunnel will be constructed under Bosphorus strait and the project site is in poor condition as composite ground, high water pressure and earthquake. The design procedure of subsea tunnel was introduced with tender design materials. That procedure contains tunnel type, TBM type and the principal design items considering geological condition such as high water pressure, composite ground and seismic area. This paper states the progress for geotechnical investigation, seismic analysis and TBM tunnel design. Analysis for geotechnical investigation is in progress, aseismatic design is going on stability study for liquefaction and structure. In addition, the performance of shield TBM to be considered such as advance rate and improvement of TBM was reviewed. The plan of fire safety was also reviewed with respect to fire protection.

• 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.17 no.6
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• pp.587-596
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• 2015

Recent years have shown great advances in the feasibility of long subsea tunnels. Projects such as the Channel Tunnel, the Stoerebelt Tunnel or the Bosporus Crossing have pushed the boundaries of TBM tunneling technology and fueled the work on feasibility studies for even more challenging projects such as crossing the Qiongzhou or Gibraltar Straits. There are numerous geotechnical challenges such as wide variations of ground conditions, high operation pressures or long tunnel distances and finally geological uncertainties which must be solved in order to attempt such projects. Several operational challenges such as large muck quantities interventions under difficult conditions and long transport distances also have to be tackled. TBM manufacturer and construction industry have developed a number of approaches to these challenges which point into the right technical direction and have been proven successfully in recent experiences. Their further development will allow attempting several megaprojects which are currently under discussion.