• Geomechanics and Engineering
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• v.35 no.4
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• pp.395-409
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• 2023

Long-span suspension bridges have tunnel anchor systems to maintain stable cables. More investigations are required to determine how closely tunnel excavation beneath the tunnel anchor impacts the stability of the tunnel anchor. In order to investigate the impact of the adjacent tunnel's excavation on the stability of the tunnel anchor, a large-span suspension bridge tunnel anchor is utilised as an example in a three-dimensional numerical simulation approach. In order to explore the deformation control mechanism, orthogonal tests are employed to pinpoint the major impacting elements. The construction of an advanced pipe shed, strengthening the primary support. Moreover, according to the findings the grouting reinforcement of the surrounding rock, have a significant control effect on the settlement of the tunnel vault and plug body. However, reducing the lag distance of the secondary lining does not have such big influence. The greatest way to control tunnel vault settling is to use the grout reinforcement, which increases the bearing capacity and strength of the surrounding rock. This greatly minimizes the size of the tunnel excavation disturbance area. Advanced pipe shed can not only increase the surrounding rock's bearing capacity at the pipe shed, but can also prevent the tunnel vault from connecting with the disturbance area at the bottom of the anchorage tunnel, reduce the range of shear failure area outside the anchorage tunnel, and have the best impact on the plug body's settlement control.

• Tunnel and Underground Space
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• v.21 no.4
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• pp.251-263
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• 2011

The geomechanical characteristics of rock and the structural geological feature of the fault should be studied and examined for the successful construction of large-span tunnel. In this case study, that is a important case for the tunnel collapse and reinforcement during the construction for the waterway tunnel at large thrust fault zone in schist, we carried out geological and geotechnical survey for make the cause and mechanism of tunnel collapse. Also, we have designed the reinforcement and re-excavation for the safe construction for collapse zone and have carried out successfully the re-excavation and finished the final concrete lining.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.2
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• pp.257-266
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• 2019

Ground water generated under tunnel excavation has a major impact on tunnel construction and stability. Thus, effective waterproof grouting is needed to reduce the inflow of groundwater. Most tunnel designs are applying the Pre Grouting. However there are no propriety analysis for grouting material and waterproof effect. In this study, numerical analysis was performed in order to investigate the effect of waterproof with decrease of coefficient of permeability of the grouting area based on the case of grouting construction.

• Geomechanics and Engineering
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• v.28 no.6
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• pp.573-584
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• 2022

Water inrush may occur during seaside urban tunnel excavation. Various factors affect the water inrush, and the water inrush mechanism is complex. In this study, nine evaluation indices having potential effects on water inrush were analysed. Specifically, the geographic and geomorphic conditions, unfavourable geology, distance from the tunnel to sea, strength of the surrounding rock, groundwater level, tidal action, cyclical footage, grouting pressure, and grouting reinforced region were analysed. Furthermore, a two-step interval risk assessment method for water inrush management during seaside urban tunnel excavation was developed by a multi-index system and interval risk assessment comprised of an interval analytic hierarchy process, fuzzy comprehensive evaluation, and relative superiority analysis. The novel assessment method was applied to the Haicang Tunnel successfully. A preliminary interval risk assessment method for water inrush was performed based on engineering geological conditions. As a result, the risk level fell into a risk level IV, which represents a section with high risk. Subsequently, a secondary interval risk assessment method was performed based on engineering geological conditions and construction conditions. The risk level of water inrush is reduced to a risk level II. The results agreed with the current tunnel situation, which verified the reliability of this approach.

• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.3
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• pp.185-193
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• 2002

In this paper, deformation behavior of shallow subway tunnel excavated in weathered soil and reinforcement effects of longitudinal support measures are investigated via three dimensional FDM analysis. Two excavation methods, half-face excavation and full-face excavation, are considered in simulation to study the influences of excavation methods on tunnel deformation behavior. In addition, the reinforcing effects of RPUM and fiberglass pipe are compared. Face extrusion, covergence, preconvergence, and sidewall displacement are investigated to analyze tunnel deformation behavior, and surface settlement is used to analyze the effects of excavation methods and longitudinal supports measures. The simulation results show that half-face excavation induces larger convergence, preconvergence, sidewall displacement, surface settlement than full-face excavation, while full-face excavation induces larger extrusion than half-face excavation. In addition, under same excavation method, all displacements are larger when RPUM is only used for longitudinal support than when RPUM is jointly used with fiberglass pipes.

• Proceedings of the KSR Conference
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• 2003.10b
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• pp.460-465
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• 2003

In this paper, we have studied the expected problems when tunnel is excavated under the wetland, and described the measure to maintain the wetland's ecosystem environment. Firstly, we investigated the wetland's ecosystem such as plants and animals, and executed ground investigation including in-situ tests and geophysical survey. And we analyzed the foreign similar cases for tunnel excavation near the wetland. We also evaluated the runoff and infiltration quantity of groundwater and hydraulic behaviour of rock mass and wetland by numerical analysis. Finally, we established the effective measure to minimize the ecosystem's influence by tunnel excavation.

• Explosives and Blasting
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• v.23 no.1
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• pp.41-46
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• 2005

Overbreak is an inevitable during tunnel excavation. It significantly affects tunnel construction cost and safety The overbreak occurs due to incorrect expectations to the geologic structures, excessive charge or strength of explosives, etc. This paper introduces multi-hole drilling method to minimize the overbreak in tunnel excavation. Although the drilling cost of the method is more expensive than those of the existing other drilling method, it is expected at that cost will be reduced.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.448-453
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• 2005

Tunnel excavation is an inevitable process for railroad construction in Korea and it being a one of the major issues of its environmental impact assessment. Ground water flow by tunnel excavation is an important parameter to determine environmental effects. The current method to determine the ground water flow is used a unit number induced a highway construction site. But it does not consider any site characteristics; ground water level, soil properties and others. The purpose of this study is to suggest the determination way of ground water flow considering site characteristics in tunnel construction.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.06b
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• pp.165-193
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• 2003

The Han River tunnel connecting Yoido and Mapo was constructed as a part of the Seoul subway line No.5, which is 52 km long, to improve the traffic conditions of Seoul. It is constructed 15.6∼30m below the river floor. It Is the first under-river tunnel in Korea with the length of 1,288m. Geological conditions of the ground under the Han River were more complex and irregular than expected at the design stage, because there were several faults, fracture zones and slickensided joints coated with graphite. It was thus indispensable to estimate the ground condition of the tunnel face to apply proper excavation and reinforcement methods. Advance borings and face mappings were performed before excavation to improve constructional efficiency and excavation stability.

• Geomechanics and Engineering
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• v.35 no.1
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• pp.29-39
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• 2023

As the intensity of urban underground space development increases, more and more tunnels are planned and constructed, and sometimes it is inevitable to encounter situations where tunnels have to underpass the river embankments. Most previous studies involved tunnels passing river embankments perpendicularly or with large intersection angle. In this study, a project case where two EPB shield tunnels with 8.82 m diameter run parallelly underneath a river embankment was reported. The parallel length is 380 m and tunnel were mainly buried in the moderate / slightly weathered clastic rock layer. The field monitoring result was presented and discussed. Three-dimensional back-analysis were then carried out to gain a better understanding the interaction mechanisms between shield tunnel and embankment and further to predict the ultimate settlement of embankment due to twin-tunnel excavation. Parametrical studies considering effect of tunnel face pressure, tail grouting pressure and volume loss were also conducted. The measured embankment settlement after the single tunnel excavation was 4.53 mm ~ 7.43 mm. Neither new crack on the pavement or cavity under the roadbed was observed. It is found that the more degree of weathering of the rock around the tunnel, the greater the embankment settlement and wider the settlement trough. Besides, the latter tunnel excavation might cause larger deformation than the former tunnel excavation if the mobilized plastic zone overlapped. With given geometry and stratigraphic condition in this study, the safety or serviceability of the river embankment would hardly be affected since the ultimate settlement of the embankment after the twin-tunnel excavation is within the allowable limit. Reasonable tunnel face pressure and tail grouting pressure can to some extent suppress the settlement of the embankment. The recommended tunnel face pressure and tail grouting pressure are 300 kPa and 550 kPa in this study, respectively. However, the volume loss plays the crucial role in the tunnel-embankment interaction. Controlling and compensating the tunneling induced volume loss is the most effective measure for river embankment protection. Additionally, reinforcing the embankment with cement mixing pile in advance is an alternative option in case the predicted settlement exceeds allowable limit.