• Journal of Korean Tunnelling and Underground Space Association
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• v.4 no.2
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• pp.167-174
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• 2002

In this study, a numerical stability analysis was performed for a large tunnel considering excavation sequence. In most cases, stability of a tunnel is analyzed based on the stability of the final excavation stage only. In this study, stability analysis of a tunnel was performed at each excavation stage. In summary, it can be inferred that there is no problem in stability of the tunnel. However, thorough and careful measurements are recommended. Also, it is found that the stability of the tunnel at the 5th excavation stage when the right half of the main tunnel is excavated is rather lower than that of the tunnel at the final excavation stage.

• Geomechanics and Engineering
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• v.19 no.3
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• pp.283-293
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• 2019

Evaluating the stability of the excavation face of the cross-river shield tunnel with good accuracy is considered as a nonlinear and multivariable complex issue. Understanding the stability evaluation method of the shield tunnel excavation face is vital to operate and control the shield machine during shield tunneling. Considering the instability mechanism of the excavation face of the cross-river shield and the characteristics of this engineering, seven evaluation indexes of the stability of the excavation face were selected, i.e., the over-span ratio, buried depth of the tunnel, groundwater condition, soil permeability, internal friction angle, soil cohesion and advancing speed. The weight of each evaluation index was obtained by using the analytic hierarchy process and the entropy weight method. The evaluation model of the cross-river shield construction excavation face stability is established based on the idea point method. The feasibility of the evaluation model was verified by the engineering application in a cross-river shield tunnel project in China. Results obtained via the evaluation model are in good agreement with the actual construction situation. The proposed evaluation method is demonstrated as a promising and innovative method for the stability evaluation and safety construction of the cross-river shield tunnel engineerings.

• Journal of the Korean Society of Safety
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• v.31 no.2
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• pp.57-63
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• 2016

Recently, subways in the city are formed a vast underground network which is interfered with construction when large-scale infrastructure will be planned to nearby existing subway tunnels. Researches have been restricted to estimate stability of existing subway tunnel due to adjacent excavation causued by small construction such as buildings. In this paper, OO underpass is planned on the top of existing subway tunnel, which will be need large-scale excavation, is selected as a subject of study. And the purpose of this study is to analyze the effects on existing subway tunnel due to excavation by stages on construction of underpass. The 3D-numerical analysis was performed by using the MIDAS/GTS program. The stability on existing subway tunnel caused by sequential excavation is analysed using numerical results. Based on the analysis, the excavation orders and reinforcement methods was suggested for stability of exiting subway tunnel.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1442-1447
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• 2005

Based on the field measuring data obtained from excavation sections in Inchon International Airport project, the relationships between the horizontal displacement of sheet-pile walls and the deformations of soft ground around the excavation were investigated. The horizontal displacements of walls according to supporting method are largely occurred in order of anchors, anchors with struts, and struts. The depths of maximum horizontal displacement are varied with supporting systems. If the stability number shows lower than ${\pi}$, the maximum horizontal displacement and the velocity of maximum horizontal displacement are respectively developed less than 1% of excavation depth and 1mm/day. When the stability number shows lower than ${\pi}+2$, the maximum horizontal displacement and the velocity are respectively developed less than 2.5% of excavation depth and 2mm/day. Also, when the stability number shows more than ${\pi}+2$, the maximum horizontal displacement and the velocity are rapidly increased.

• Journal of the Korea Construction Safety Engineering Association
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• s.47
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• pp.56-62
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• 2008

In order to apply the Limit Equilibrium Method generally used for the slope stability analysis to the vertical excavation walls reinforced by soil-nailing, in this study, the Limit Equilibrium Method for the temporary shoring facilities reinforced by soil-nailing was proposed, which is based on the stability for the horizontal displacement. In this study, the relation of the internal friction angles of the ground and the vertical excavation depths was arranged, which is satisfying the stability on the horizontal displacement by using the verification of the Limit Equilibrium Method. And then, the rational reinforcing length of soil-nailing was proposed for the critical areas. In addition, the modified safety ratio satisfying the stability on the horizontal displacement was proposed, when the Limit Equilibrium Method was applied to the vertical excavation walls reinforced by soil-nailing.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.4
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• pp.435-450
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• 2020

The divergence section of a double-deck tunnel can be divided into a 'widening pre-divergence section', a large cross-section with a cap shape and a 'post-divergence section' where the separation between the main and the branch tunnel is made. Since the cross-section of the widening pre-divergence section is considerably larger than that of the post-divergence section, the influence of excavation due to the different sizes and shapes in the cross-section should be considered in the examination of the tunnel stability. In this study, the effect of the preceding excavation, that is the excavation of the widening pre-divergence section, on excavation stability of the post-divergence section was examined by varying the excavation methods and bench lengths through 3D finite element analysis. The results showed that although the effects of the excavation methods and the bench lengths are not significant on the variation of principal stresses, the preceding excavation causes a relatively large variation on the stresses which may have an impact on the stability of the post-divergence section from the comparison of Stress-Strength Ratio (SSR) between the cases with and without the consideration of the preceding excavation effect by 2D finite element analysis.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.1433-1437
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• 2010

The deep excavation work in Korean downtown is almost excuted near by existing structures and utility lines because of the diminution of available yard for construction. So, it was required more and more that the accurate control of displacement on the earth retaining system for minimizing the popular complaint and the damage from constructional accident. Automatic monitoring system is adopted in fracture zone for real time monitoring. In addition, Face mapping is carried out on the face of fracture zone according to excavation sequence. As the result of automatic monitoring system and face mapping, we was able to take the necessary reinforcement and changing excavation method within suitable time. This paper is informed about a stability case on the deep rock excavation site with fracture zone in urban area by automatic monitoring system.

• Proceedings of the Korean Geotechical Society Conference
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• 2001.10c
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• pp.103-122
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• 2001

For prediction of ground movement per the excavation step, observational results of ground movement during the construction was very different with prediction during the analysis of design. step because of the uncertainty of the numerical analysis modelling, the soil parameter, and the condition of a construction field, etc. however accuratly numerical analysis method was applied. Therefore, the management system through the construction field measurement should be achieved for grasping the situation during the excavation. Until present, the measurement system restricted by ‘Absolute Value Management system’only analyzing the stability of present step was executed. So, it was difficult situation to expect the prediction of ground movement for the next excavation step. In this situation, it was developed that ‘The Management system TOMAS-EXCAV’ consisted of ‘Absolute value management system’ analyzing the stability of present step and ‘Prediction management system’ expecting the ground movement of next excavation step and analyzing the stability of next excavation step by‘Back Analysis’. TOMAS-EXCAV could be applied to all uncertainty of earth retaining structures analysis by connecting ‘Forward analysis program’ and ‘Back analysis program’ and optimizing the main design variables using SQP-MMFD optimization method through measurement results. The application of TOMAS-EXCAV was confirmed that verifed the three earth retaing construction field by back analysis.

• Structural Engineering and Mechanics
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• v.84 no.6
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• pp.743-765
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• 2022

Near-surface excavations may cause the tilting and destruction of the adjacent superstructures in big cities. The stability of a huge excavation and its nearby superstructures was studied in this paper. Some test instruments monitored the deformation and loads at the designed location. Then the numerical models of the excavation were made in FLAC3D (a three-dimensional finite difference code) and Plaxis-3D (a three-dimensional finite element code). The effects of different supporting and reinforcement tools such as nails, piles, and shotcretes on the stability and bearing capacity of the foundation were analyzed through different numerical models. The numerically approximated results were compared with the corresponding in-field monitored results and reasonable compatibility was obtained. It was concluded that the displacement in excavation and the settlement of the nearby superstructure increases gradually as the depth of excavation rises. The effects of support and reinforcements were also observed and modeled in this study. The settlement of the structure gradually decreased as the supports were installed. These analyses showed that the pile significantly increased the bearing capacity and decreased the settlement of the superstructure. As a whole, the monitoring and numerical simulation results were in good consistency with one another in this practically important project.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.10a
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• pp.3-14
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• 2005

Reliable predictions of the movement of earth retaining structures and the ground adjacent to braced walls in urban excavation are often difficult due to many variable factors. The ground settlement and the damage of adjacent structures in urban excavation has been an important issue. Therefore, the stability of the adjacent structures must be secured with the excavation support and research on the protection of adjacent structure is necessary. This study showed an urban excavation case and introduce observation method for case of damage behavior in urban excavation.