• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.269-286
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• 2018

Backfill injection pressure in shield TBM affects not only ground settlement but also adjacent underground structures. Therefore, it is essential to estimate a suitable backfill injection pressure in advance in design stage. In this paper, seven suggested equations worldwide to calculate the backfill injection pressure were reviewed and compared. By assuming 6 cases of virtual ground condition, backfill injection pressures were calculated and analyzed. it was confirmed that the backfill injection pressure increases as the depth of overburden increases, but the increasing ratio decreases. The numerical analysis was carried out by applying the calculated backfill injection pressure to investigate the influence of backfill injection pressure on the settlement of surface and crown of tunnel. It was confirmed that the final settlement at the surface and crown of tunnel on the both unsaturated and saturated condition are more influenced by the applied face pressure than the applied backfill injection pressure. In addition, the effect of backfill injection pressure decreases as the depth of overburden increases, and the effect of backfill injection pressure increases as the applied face pressure decreases.

• Proceedings of the Korean Geotechical Society Conference
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• 1994.09a
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• pp.225-230
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• 1994

This paper concerns a case study on the design concept, analysis, construction methodology of a subway tunnel excavated in the soft ground beneath an existing building where the distance between the bottom of the building and the crown of the tunnel is separated by about 3 meters only. The silot tunnels are excavated in advance, and side reinforced-concrete walls are installed. Then, main tunnels are excavated with ring cut method. The steel ribs are installed and supported by the side walls made in advance. Between the steel ribs and the side walls, the screw jack is installed to apply prestressing so that settlement can be controlled at minimum. Various in-situ seasurements are made and compared with computed values obtained by numerical methods. By choosing this underpinning method with very caraful construction control, tunnelling projects could be finished successfully without having any damage to the building located very closely to the tunnel crown.

• The Journal of Engineering Geology
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• v.19 no.1
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• pp.43-50
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• 2009

A 3-D numerical analysis was carried out to observe potential effects of orientation of inherent weak zones to tunnel behaviors and stress distributions during tunnel excavation. Weak zones used for the analysis were placed at the upper 1D part from crown, on the crown and on the center of face, using orientations derived from the 6th RMR parameter for assessment of joint orientation effect on tunnel. Mechanical properties of rock mass were derived through a in-situ displacement measurement-based back analysis. Finally, a classification chart for crown settlement with five ranks based on orientation and location of weak zones is suggested.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1324-1334
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• 2005

This study investigated the applicability of the Artificial Neural Network (ANN) technique for prediction of tunnel behavior. For training data collection, a series of finite element analyses were conducted for actual tunnel project site. Using the data, optimimzed ANNs were developed through a sensitivity study on internal parameters. The developed ANNs can make tunneling related predictions such as tunnel crown settlement, shotcrete lining stress, ground surface settlement, and groundwater inflow rate. The results indicated that the developed ANNs can be used as an effective and efficient tool for tunnelling related prediction in practical tunneling situations.

• 한국터널공학회:학술대회논문집
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• 2005.04a
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• pp.105-116
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• 2005

This study investigated the applicability of the Artificial Neural Network(ANN) technique for prediction of tunnel behavior. For training data collection, a series of finite element analyses were conducted for actual tunnel project site. Using the data, optimimzed ANNs were developed through a sensitivity study on internal parameters. The developed ANNs can make tunneling related predictions such as tunnel crown settlement, shotcrete lining stress, ground surface settlement, and groundwater inflow rate. The results indicated that the developed ANNs can be used as an effective and efficient tool for tunnelling related prediction in practical tunneling situations.

• 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.

• Journal of the Korean Society of Safety
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• v.7 no.4
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• pp.55-61
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• 1992

An engineer designing a tunnel in an urban area should be to predict the magnitude and distribution of ground movements which are important to Investigate the potential damage to the existing structures around tunnel. The present study examines available theories and emprical equations, and tries to investigate quantativily ground movements around tunnel with tunnel progressing. Approcaches to the problem of ground movements associated with twin tunnel was and elasto - plastic finite element method. Typical section in Seoul Subway were selected in numerical study. The analysis and study was done with respect. to surface, subsurface and crown settlements with varying ground conditions, tunnel geommetry and construction conditions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.5
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• pp.1957-1968
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• 2013

Design criteria for rock load on tunnel concrete lining has not been established yet. Generally rock load on tunnel concrete lining is empirically estimated, which leads to a conservative design. Ordinary estimation method of rock load includes various problems. Estimating by numerical analysis is very complicated and has not been verified with field measurements. Therefore, it is necessary to conduct a study on practical method of estimating rock load which is more accurate to the real rock load on tunnel concrete lining. This study, presents estimation method of rock load on tunnel concrete lining. Crown settlement of the tunnel construction site has been measured and it was been back analyzed to estimate the rock load. The rock load was estimated to be smaller compare to the ordinary estimation method.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.140-153
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• 2005

During the tunnel construction the major failure mode can be categorized as: tunnel failure just after the tunnel excavation without support, failure after application of shotcrete and finally failure after setting the concrete lining. The failure mode just after the tunnel excavation without support, can be further classified as : bench failure, crown failure, face failure, full face failure, failure due to weak strata and failure due to overburden. Moreover the failure after application of shotcrete is classified as heading face failure, settlement of shotcrete support, local failure of shotcrete lining and invert shotcrete. To find out the major causes of tunnel collapse, the investigation was done in case of the second phase of Seoul subway construction. The investigation results depicted that the major causes of tunnel collapse were due to the weak layer of rock/fault and sudden influx of ground water from the tunnel crown. While the investigation results of the mountain road tunnels construction have shown that the major causes of tunnel failure were inadequate analysis of tunnel face mapping results, intersection of faults and limestone cavities. In this paper some recent measurement in order to mitigate such tunnel collapse are presented

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3C
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• pp.167-174
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• 2010

In this study, numerical analysis has been performed to compare the ground movements in a single ground layer and multiple ground layers due to nearby tunnel excavation. The numerical analysis has been conducted in the different ground layer conditions considering different construction conditions (volume loss at excavation face), and the results of the maximum surface settlement and horizontal displacement have been compared considering the ground layer and construction conditions. In addition, the maximum surface settlement from the numerical analysis has been compared with the maximum settlement at tunnel crown considering the ground layer and construction conditions, and the maximum surface settlement has been also compared with the maximum horizontal displacement with the ground layer conditions. Besides, the volume loss($V_L$) at tunnel excavation face has been compared with the total surface settlement volume($V_s$) with the variation of ground layer condition. The results from the numerical analysis have been compared with field measurements and by this comparison it is believed that the numerical results in this study can be utilized practically in analyzing the nearby ground behavior in different ground layer and construction conditions due to tunnel excavation.