• Proceedings of the Korean Geotechical Society Conference
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• 1990.10a
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• pp.25-34
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• 1990

For the construction of twin single track subway tunnels by NATM within close proximity of existing vehicle underpass in the highly congested area of downtown Seoul, finite element analyses were performed to evaluate the ground responses during tunnelling and also the stability and safety of the underpass structure and subway tunnels. Results of the analyses indicated the need to improve the soil beneath the underpass, and pre-grouting was carried out prior to the tunnel excavation. During tunnel construction field measurement program was implemented to confirm the results of anslyses and to control the tunnel construction procedures, thus ensuring stability of the existing structres.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.6
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• pp.699-714
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• 2022

The objective of this study is to suggest a safe and economical pillar reinforcement method when very near-twin tunnels with a minimum interval of 1 m passes through a soft zone such as weathered soil or weathered rock. A standard cross-sectional view of a two-lane road tunnel was applied to suggest a pillar reinforcement method for the very near-twin tunnels. The thickness of the pillar was 1 m. The ground condition around the tunnel was weathered soil or weathered rock. There were four reinforcement methods for pillar stability evaluation. These were rock bolt reinforcement, pre-stressed steel strand reinforcement, horizontal steel pipe grouting reinforcement, horizontal steel pipe grouting + prestressed steel strand reinforcement. When the ground condition was weathered soil, only the pillar reinforced the horizontal steel pipe grouting + prestressed steel strand did not failed. When the ground condition was weathered rock, there were no failure of the pillar reinforced the horizontal steel pipe grouting or the horizontal steel pipe grouting + prestressed steel strand. It is considered that the horizontal steel pipe grouting reinforcement played a role in increasing the stability of the upper part of the pillar by supporting the upper load applied to the upper part of the pillar.

• Tunnel and Underground Space
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• v.34 no.5
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• pp.543-553
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• 2024

There has been increased interest, media coverage, and debate over constructing new underground structures to replace existing at-grade rail tracks. This new scheme aims to free up space to provide cities with room for more housing with green amenities. Due to urbanisation, tunnel engineers have encountered greenfield ground conditions in cities on only a few occasions. However, the new scheme provides opportunities to investigate a unique scenario where new tunnels are driven parallel to the existing rail tracks on the surface with little ground cover in soft ground. This paper presents findings obtained from a semi-empirical approach that aims to investigate the likely track irregularity associated with tunnelling-induced ground movements. This paper presents contour maps that show track rotation according to the relative position of the new tunnel and existing rail tracks. Tunnel engineers would consult these maps for their tunnel route design for the scheme.

• Structural Engineering and Mechanics
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• v.84 no.5
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• pp.699-706
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• 2022

Settlement control techniques are critical for the safety of shield tunnel constructions, especially for facing complex situations. In this study, the shield tunnel structure from Huaita east road station to Heping Road station in Xuzhou metro No.3 line (China) is taken as engineering background, which has various complex problems of the upper-soft and lower-hard composite stratum conditions, twin curve shield tunnels, and underpass the foundation of the piled raft. The deformation characteristics of shield tunnelling passing through buildings are explored. Subsequently, comprehensive research methods of numerical simulation and field measurement are adopted to analyzing the effectiveness of settlement control by using the top grouting technique. The results show that the settlement of the buildings has obvious spatial characteristics, and the hysteresis effect can be obviously observed in soil deformation caused by shield construction. Meanwhile, the two shield constructions can cause repeated disturbances, reducing the soil deformation's hysteresis effect. Moreover, the shield tunnel's differential settlement is too large when a single line passes through, and the shield construction of the outer curve can cause more significant disturbance in the tunnel than the inside curve. Notably, the proposed process control parameters and secondary topgrouting method can effectively control the deformation of the shield tunnel, especially for the long-term deformation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.5
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• pp.325-337
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• 2021

On the road and rail tunnels, the evacuation pathway and facilities such as smoke-control and fire suppression system are essential in tunnel fire. In the long twin tunnels, the cross-connection tunnel is usually designed to evacuate from the tunnel where the fire broke out to the other tunnel. In twin shield tunnels, the segment lining has to be demolished to construct the cross-connection tunnel. Considering the modern shield TBM is mostly the closed chamber type, the exposure of underground soil induced by removal of steel segment lining is the most danger construction step in the shield tunnel construction. This case study introduces the excavation method using the thrust of large steel pipe and reviews the measured data after the construction. The large steel pipe thrust method for the cross-connection tunnel can stabilize the excavated face with the two mechanisms. Firstly, the soil in front of excavated face is cylindrically pre-supported by the large steel pipe. Secondly, the excavated face is supported by the plugging effect caused by the soil pressed into the steel pipe. It was reviewed that the large steel pipe thrust method in the cross-connection tunnel is enough to secure the construct ability and stability in soil from the measurement results about the deformation and stress of steel pipe.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.5
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• pp.379-387
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• 2010

In this study, a case study was introduced for the design of a twin tunnel along high speed national highway Route 12 from Damyang to Sungsan. It was related to determine the optimal tunnel support pattern and excavation method based on a risk analysis in order to incorporate the uncertainty of ground properties. To this end, three alternatives with different amounts of support and excavation method were selected and risk analysis was performed by applying Monte Carlo simulation technique, respectively. Stability of the tunnel was quantified by the factor of safety. To improve the result, the 729 cases of the combination of ground properties (deformation modulus, cohesion, and internal friction angle) satisfying a Gaussian distribution were generated and applied. Also, stability of the tunnel was confirmed by analyzing the distribution of both displacement and shotcrete bending stress.

• Journal of the Korean Geotechnical Society
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• v.25 no.10
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• pp.77-85
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• 2009

This paper describes the findings obtained from a research project aimed at investigating, via 1 g laboratory model tests, the ground movements caused by multiple side-by-side (sbs) tunnel construction in clay. The ground movements above a second tunnel showed different trends from those observed above a first tunnel. These trends include an increase in the overall volume loss, and a widening of the settlement troughs on the near limb of the trough accompanied by a shift of the maximum settlement towards existing tunnel. This would suggest that the use of simple predictive methods of adopting a Gaussian curve for analysing the ground settlements associated with twin (sbs) tunnel construction is not appropriate. Therefore the current paper adopts a method that modifies the Gaussian curve approach in order to improve the predictions. This paper comments on the parameter selection involved with adopting this new method to apply it to full-scale field situations, and also discusses its limitations.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.1
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• pp.63-72
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• 2005

The influence of internal water pressure under the Probable Maximum Flood (PMF) on tunnel spillway is analysed using 3D FDM analysis. HEC-RAS program including 1-D hydrologic numerical model was also implemented to estimate the maximum pressure on the lining under the PMF, thereafter determined rational internal water pressure. Tunnel spillway was designed as twin tunnel and excavation and supporting stage are fully considered. Analysis was classified into the 3 cases; pressure is applied only to the left tunnel, only to right tunnel, and to both tunnels. The maximum tensile stress and axial force in supporting materials induced by water flow were compared with the critical values to assess the stablilty of the tunnel and the locations of stress concentration parts were also examined.