• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.947-956
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• 2018

Subsea tunnel built in abyssal zone is exposed to environment under high water pressure caused by seawater and etc., and this high pressure from underground water may facilitate leaching. In particular, since underground water can be easily flown in during construction, this might cause many problems related to cutoff water. Therefore, in order to secure safety, it is necessary to apply grouting equipment and materials which are appropriate to construction environment. Accordingly, in this research, evaluation was made on the physical characteristics of grouting materials (strength, leaching and etc. depending on curing methods for each of used materials and condition) which can be applied during subsea tunnel construction. As a result of this research, stable strength increase was found in CA and CSA type, and it is determined that no decrease in their durability was found, so these can be used as stable materials for structures under influenced by seawater.

• Geomechanics and Engineering
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• v.12 no.1
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• pp.35-52
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• 2017

In order to evaluate the grouting effects of water-rich fault in tunnels systematically, a feasible and scientific method is introduced based on the extension theory. First, eight main influencing factors are chosen as evaluation indexes by analyzing the changes of permeability, mechanical properties and deformation of surrounding rocks. The model of evaluating grouting effects based on the extension theory is established following this. According to four quality grades of grouting effects, normalization of evaluation indexes is carried out, aiming to meet the requirement of extension theory on data format. The index weight is allocated by adopting the entropy method. Finally, the model is applied to the grouting effects evaluation in water-rich fault F4-4 of Qingdao Jiaozhou Bay Subsea Tunnel, China. The evaluation results are in good agreement with the test results on the site, which shows that the evaluation model is feasible in this field, providing a powerful tool for systematically evaluating the grouting effects of water-rich fault in tunnels.

• 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.20 no.6
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• pp.1061-1071
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• 2018

A subsea tunnel, being a super-sized underground structure must ensure safety at the time of earthquake, as well as at ordinary times. At the time of earthquake, in particular, of a subsea tunnel, a variety of response behaviors are induced owing to relative rigidity to the surrounding ground, or difference of displacement, so that the behavior characteristics can be hardly anticipated. The investigation aims to understand the behavior characteristics switched by earthquake of an imaginary subsea tunnel which passes through a fault zone having different physical properties from those of the surrounding ground. In order to achieve the aim, dynamic response behaviors of a subsea tunnel which passes through a fault zone were observed by means of indoor experiments. For the sake of improved earthquake resistance, a shape of subsea tunnel to which flexible segments have been applied was considered. Afterward, it is believed that a D/B can be established through 3-dimensional earthquake resistance interpretation of various grounds, on the basis of verified results from the experiments and interpretations under various conditions. The present investigation performed 1 g shaking table test in order to verify the result of 3-dimensional earthquake resistance interpretation. A model considering the similitude (1:100) of a scale-down model test was manufactured, and tests for three (3) Cases were carried out. Incident seismic wave was introduced by artificial seismic wave having both long-period and short-period earthquake properties in the horizontal direction which is rectangular to the processing direction of the tunnel, so that a fault zone was modeled. For numerical analysis, elastic modulus of the fault zone was assumed 1/5 value of the modulus of individual grounds surround the tunnel, in order to simulate a fault zone. Resultantly, reduced acceleration was confirmed with increase of physical properties of the fault zone, and the result from the shaking table test showed the same tendency as the result from 3-dimensional interpretation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.3
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• pp.295-303
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• 2015

This paper presents the study of leakage effect due to multi-cell inflater of rapid protection system to protect the possibilities of tunnel damages by flooding threats and unusual leakage to be occurred during and after subsea tunnel construction. Particularly, this protect system should be necessary in subsea tunnel. This research concentrates the physical model tests due to several multi-cell inflater to study protection capacity of leakage between the inflater and tunnel liner. A 27:1 small scale model are used in the model tests. The leakage rate, water pressure and axial displacement of inflater are measured during the model tests. According to the results, the minium leakage rate clearly shows in the case of two-cell inflater compared with in other cases. It is concluded that the results of this research will be very useful to understand the fundamental information of inflater structure design and development the technology of tunnel protection structures in the future.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.5
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• pp.431-443
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• 2014

In this paper case studies of artificial ground freezing, which have not been applied in Korea, have been investigated for the water cut-off in a subsea tunnel under high water pressure and the most commonly used cooling mediums of brine and liquid nitrogen are examined. Since sea water with pressure has the lower freezing point than pure water, the lower temperature cooling medium is required in the application of subsea tunnel. Also, the cooling medium must have refrigeration safety and is able to reduce executing time. Brine freezing system can reuse cooling medium and is safer than liquid nitrogen freezing. But it takes more time to freeze ground and needs complex circulation plants. On the other hand, liquid nitrogen freezing system can't recycle cooling medium and may cause breathing problems or asphyxiation through oxygen deficiency. But, freezing with liquid nitrogen is fast and requires simple refrigeration equipment. Principal elements of design for ground freezing in subsea tunnel have been extracted and these elements are needed further research.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.1
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• pp.13-30
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• 2016

This paper concerns the development of an optimized TBM segmental 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 segmental 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 with a BIM system 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 segmental lining dimension easily without any further FE calculations.

• Journal of the Korean GEO-environmental Society
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• v.18 no.6
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• pp.5-19
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• 2017

In this study, the effect of rock mass curtain grouting was investigated by analyzing the correlation between the parameters of the RMR & grout injection volume, Lugeon value & RQD, Lugeon value & cement injection volume. In order to investigate the effect of rock mass curtain grouting, we analyzed the grout injection volume of 315 curtain grouting holes at 9 tunnel face of NATM Subsea tunnels in gneiss area. The total grout injection volume in the Subsea tunnels study was slightly changed in some tunnels face but decreased with increasing the rating of parameters in spacing of discontinuity (R3, Js) and groundwater condition (R5). The geological anomalies of seismic survey (3D, TSP) and the inflow of probe hole were found to be more correlated of relative than the parameters of RMR. The unit injection volume was found to decrease with higher ratings in the parameters of the RMR except the weathering degree of the discontinuity (Jc, R4). The correlation between RQD and Lugeon values is not significant, but it can be confirmed that the Lugeon value tends to decrease as the RQD value increases.

• Magazine of korean Tunnelling and Underground Space Association
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• v.21 no.1
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• pp.32-48
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• 2019

• Journal of Korean Tunnelling and Underground Space Association
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• v.17 no.3
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• pp.383-392
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• 2015

In subsea tunnelling, prediction of the fractured zone (or water bearing zone) ahead of tunnel face saturated by seawater with high water pressure has been a key factor for safe construction. This study verified the feasibility of utilizing induced polarization (IP) survey at tunnel face for predicting the ground condition ahead of the subsea tunnel face. A pore model was proposed to compute chargeability in granular material, and the relationship correlating chargeability with the variables affecting the chargeability was derived from the model. Parametric study has been performed on the variables to figure out the most influential factors affecting the chargeability. The results of the parametric study show that the size of narrow pores ($r_1$) and the salinity of pore water are the most influential factors on chargeability. Laboratory tests were conducted on various types of ground condition by changing the salinity of pore water, the thickness of the fracture zone and the existence of gouge (weathered granite) within the joints of the fractured zone to figure out the effect of the ground characteristics on the IP phenomenon. Test results show that the chargeability of the fractured zone saturated by seawater increases if the joints in the fractured zone are filled with gouge since the infilled gouge will decrease the size of narrow pores ($r_1$).