• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.1278-1289
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• 2008

Currently in increasing number of urban tunnels with small overburden are excavated according to the principle of the New Austrian Tunneling Method (NATM). Successful design, construction and maintenance of NATM tunnel in urban area demands prediction, control and monitoring of surface settlement, gradient and ground displacement with high accuracy. Use of measured displacement for parameter determination has been researched over the years, and one geotechnical engineering principle has been formed as back analysis. In this paper, back analysis of a ground deformational behavior involving nonlinear behavior is discussed. It is of primary importance to make reliable prediction of deformational behavior for shallow tunnels in soft ground. However, predictions made often prove to be incorrect due to complexity of constitutive law and other relevant factors. Back analysis therefore becomes more important, for it may be used to interpret measured displacement to derive nonlinear material characteristics. The paper shows some example in which a deformational mechanism is studied in the light of inhomogeneous distrubution of Young's module, from which a logic is derived to identify two different types of nonlinear constitutive relationships.

• Explosives and Blasting
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• v.26 no.2
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• pp.38-44
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• 2008

Recently, planning road construction in South Korea is focused on upgrading of the existing road by rerouting or restructuring. For this, roads under current construction in Korea go for more straight in its alignments and routing. Straight routing makes it all the more required to construct many mountain tunnels and bridges in Korea where mountains are so widely spread. Some portal of mountain tunnel is not rarely planed at high steep slope of mountain valley where it is not easy to secure working space for tunnel excavation. Reverse excavation is an alternative measure for excavation of tunnel portal at high steep slope. Construction in reverse excavation method has three important points requiring careful consideration: 1)planning of pilot tunnel in proper width, height, and length etc., 2)measure against the effect of one-side earth pressure to the direction of tunnel portal, 3)securing tunnel safety against shallow ground condition at portal zone. This paper intends to suggest applicable range of pilot tunnel for reverse excavation at the portal zone located at high steep slope, and shows result of study on the appropriateness of a reverse excavation by means of 3D numerical analysis. Result of 3D numerical analysis for reverse excavation at high steep slope shows that pilot tunneling will be applicable to start from the point $20{\sim}25m$ before the portal from inside the tunnel.

• Tunnel and Underground Space
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• v.28 no.6
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• pp.528-546
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• 2018

Cases of TBM tunnelling have been consistently increasing worldwide. In many recent subsea and urban tunnelling projects, TBM excavation has been preferably considered due to its advantages over drill and blast tunnelling. Difficult ground conditions are highly probable to appear in subsea and urban tunnels because of the shallow working depth and alluvial characteristics. Under the difficult ground conditions, ground reinforcement measures should be considered including grouting, while it is of great importance to select the optimal grout material and injection method to cope with the ground condition. The benefits from TBM excavation, such as fast excavation, increased safety, and reduced environmental impact, can be achieved by applying appropriate ground reinforcement with the minimum overrun of cost and time. In this report, various grouting methods were reviewed so that they can be applied in difficult ground conditions. In addition, domestic and international cases of successful ground reinforcement for difficult grounds were introduced for future reference.