• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.5
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• pp.733-747
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• 2017

In the shallow tunnel, the surrounding ground could be loosened and deformed, which could be the cause of stress change in the ground. Terzaghi has clarified the development of a ground arching induced by the deformation of a tunnel crown in the trap door tests. However, he considered only the case in which that the tunnel crown deformed uniformly. He did not consider the effect of deformation shapes. Therefore, the relation between the shape of the ground relaxation above the tunnel crown and the deformation shape of the tunnel crown is not clear yet. In this study, model tests were performed for the three types of the tunnel crown, such as uniform, concave and convex shapes. As results, it was found that the vertical load would be transferred in various types depending on the deformation shapes of the tunnel crown.

• 건설안전세미나
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• s.1
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• pp.75-114
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• 1990

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.2
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• pp.133-141
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• 2005

The behavior of the ground in crossed zone due to the excavation of new lower tunnel rectangularly crossed to that was studied by model tests and numerical analysis in shallow cover. Results of the model tests show that earth pressure of the ground in crossed zone were redistributed due to the longitudinal arching effect by the excavation of lower tunnel. By the numerical analysis, minimum principal stress in crown of single tunnel has more decrease than parallel tunnel or crossed tunnel. Vertical stress at rectangularly crossed tunnel decrease more than single tunnel by stress shadow.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.3
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• pp.115-124
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• 2003

In this study, the relationships between the displacement and stress of the tunnel using various analysis methods were compared with monitoring results carried out during construction and maintenance monitoring. The behavior of tunnel were measured in the subway tunnel passing comparative soft the weathering and analyzed both security and mechanical characteristics of the tunnel lining. With the results of simplified monitoring observed in top heading and bench excavation tunnel, it is confirmed that the crown settlement is larger than the surface settlement. it is interesting to note that the crown settlement and the crown shotcrete lining stress are widely used monitoring items for the back analysis. It is analyzed that the residual water pressure applied in the drainage type tunnel is reasonable.

• Journal of the Korean Geosynthetics Society
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• v.9 no.2
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• pp.41-50
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• 2010

The concrete lining of a tunnel constructed by NATM used to be regarded as facing material which does not support any load from the surrounding ground. But the recent appraisal of the decrepit tunnels revealed that rockbolts and shotcrete deteriorate with time resulting in loss of supporting capability. Consequently, concrete lining has to support part of the load which used to be supported by rockbolts and shotcrete, and thus should be regarded as the final supporting structure in a tunnel. One of the common, and perhaps the most serious problem in concrete lining is the longitudinal cracks taking place at the tunnel crown. The longitudinal cracks, mostly related to the construction procedures, can be developed by many reasons such as the lack of thickness, wrong materials, bad curing environment, and excessive external forces. Many efforts has been made to control and suppress these cracks but efficient and economic way is yet to be found. For efficient crack control in concrete lining, reinforcement by composite fibers, which is the mixture of steel fiber and nylon fiber, is suggested in this study.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.6
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• pp.887-903
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• 2017

Lots of shallow tunnels are constructed in the mountainous areas where the stress distribution in the ground around tunnel is not simple, also the impact of stress conditions on the longitudinal load transfer characteristics is unclear. The tunnel construction methods and the ground conditions would also affect the longitudinal load transfer characteristics which would be dependant on the displacement patterns of tunnel face. Therefore, in this study, the slope of the ground surface was varied in $0^{\circ}$, $10^{\circ}$, $20^{\circ}$, $30^{\circ}$, and the longitudinal load transfer depended on the deformation conditions of tunnelface (that were maximum deformation on the top, constant deformation, and maximum deformation on the bottom), and the stress distribution at tunnelface. As results, when the tunnelface deformed, the earth presure on the tunnelface decreased and the load at tunnel crown increased. The load transferred on the crown was influenced by the earth presure on tunnel face. Smaller load would be transfered to the wide areas when the slope of ground surface decreased. When the slope of ground surface became larger, the longitudinal load transfer would be smaller and would be concentrated on tunnelface, In addition, the shape of the transferred load distribution in the longitudinal direction was dependant on the deformation shape of tunnelface. The deformation shape of tunnelface and stress conditions in longitudinal sections would affect the shape and the magnitude of the load transfer in the longitudinal directions.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.5
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• pp.761-778
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• 2017

The need of the underground space for the infrastructures in urban area is increasing, and especially the demand for shallow tunnels increased drastically. It is very important that the shallow tunnel in the urban area should fulfill not only its own safety conditions but also the safety condition for the adjacent structures and the surrounding sub-structure. Most of the studies on the behavior of shallow tunnels concentrated only on their behaviors due to the local deformation of the tunnel, such as tunnel crown or tunnel sidewall. However, few studies have been performed for the behavior of the shallow tunnel due to the deformation of the entire tunnel. Therefore, in this study the behavior of the surrounding ground and the stability caused by deformation of the whole tunnel were studied. For that purpose, model tests were performed for the various ground surface slopes and the cover depth of the tunnel. The model tunnel (width 300 mm, height 200 mm) could be simulationally deformed in the vertical and horizontal direction. The model ground was built by using carbon rods of three types (4 mm, 6 mm, 8 mm), in various surface slopes and cover depth of the tunnel. The subsidence of ground surface, the load on the tunnel crown and the sidewall, and the transferred load near tunnel were measured. As results, the ground surface subsided above the tunnel, and its amount decreased as the distance from the tunnel increased. The influence of a tunnel ceased in a certain distance from the tunnel. At the inclined ground surface, the wider subsidence has been occurred. The loads on the crown and the sidewall were clearly visible, but there was no effect of the surface slope at a certain depth. The load transfer on the adjacent ground was larger when the cover depth (on the horizontal surface) was lager. The higher the level (on the inclined surface), the wider and smaller it appeared. On the shallow tunnel under inclined surface, the transfer of the ambient load on the tunnel sidewall (low side) was clearly visible.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.3
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• pp.640-655
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• 2018

Recently, the construction of the urban area has been rapidly increasing, and the excavation work of the ground has been frequently performed at the upper part of the existing underground structures. Especially, when the structure is constructed after the excavation of the ground, the loading and unloading process in the ground under the excavation basement can affect the existing underground structures. Therefore, in order to maintain the stability of the existing underground structure due to the excavation of the ground, it is necessary to accurately grasp the influence of the excavation and the structure load in the adjoining part. In this study, the effect of the excavation of the ground and the new structure load on the existing tunnel was experimentally implemented and the influence of the adjacent construction on the existing tunnel was investigated. For this purpose a large testing model with 1/5 scale of the actual size was manufactured. The influence of ground excavation, width of the load due to new structure, and distance between centers of tunnel and of excavation on the existing tunnel was investigated. In this study, it was confirmed that the influence on the existing tunnel gets larger, as the excavation depth get deeper. At the same distance, it was confirmed that the tunnel displacement increased up to three times according to the increase of the building load width. That is, the load width influences the existing tunnel larger than the excavation depth. As the impact of the distance between centers of tunnel and of excavation, it was confirmed that tunnel crown displacement decreased by 48%. The result showed that a tunnel is located in the range of 1D (D: tunnel diameter) from the center of excavation, the effect of excavation is the largest.

• 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.

• The Journal of Engineering Geology
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• v.27 no.1
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• pp.81-90
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• 2017

Preceding displacements in tunnel are difficult to predict since the measurements of displacements after excavation can not be performed immediately. In the present study, The longitudinal displacements which can be measured immediately after excavation are used to predict the crown settlements occurring before excavation only if fault is located at the tunnel crown. Three-dimensional finite element analysis was conducted using 28 numerical models with various fault attitudes to analyze the correlation between the longitudinal displacements on tunnel face and preceding crown settlements. The results, $L_{face}/C$ ratio show 2~12% in the drives with dip models and 2~13% in the drives against dip models individually. In addition, each model has a certain $L_{face}/C$ ratio. The result of the regression analysis show that the coefficient of determination is over 0.8 in most models. Therefore, crown settlements occurring before excavation can be predicted by analyzing the longitudinal displacements occurring on tunnel faces.