• Geomechanics and Engineering
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• v.21 no.2
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• pp.165-170
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• 2020

The groundwater during tunnel excavation not only affects the stability of the tunnel and constructability but also causes the subsidence of the upper ground due to the lowering of groundwater. Generally, the cutoff grouting is applied as a countermeasure to reduce the groundwater inflow during tunnel excavation, and the cutoff grouting is often applied in the range of plastic zone around the tunnel. However, grouting in the plastic zone is only appropriate for ground reinforcement purposes, and guidelines for the application range of cutoff grouting and the targeted permeability coefficient of the grouting zone are required. In this study, the relationship between groundwater inflow into tunnel and application range of cutoff grouting and permeability coefficient is proposed and compared with numerical analysis results. It was found that grouting with tunnel radius thickness is appropriate to reduce the groundwater inflows effectively. More than 90% reduction in groundwater inflow can be achieved when the annular area of the tunnel radius thickness is grouted with a permeability reduction ratio of 1/50~1/200.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.1
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• pp.79-89
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• 2024

Excessive inflow of groundwater during tunnel excavation not only affects the stability and constructability of the tunnel, but is also one of the main causes of ground settlement due to groundwater level drawdown. The most commonly applied measure against excessive groundwater inflow during tunnel excavation in soil or fractured zone is to reduce the ground permeability coefficient by injecting grout material. Generally, the grouting area is assumed to be same as the plastic zone that occurs during tunnel excavation, but injecting grout material in the area of plastic zone is appropriate only for reinforcement grouting. In order to determine the thickness of cutoff grouting, the amount of reduction in the water permeability coefficient due to the application of cutoff grouting must be considered. In this study, a method for estimating the range of cutoff grouting considering the reduction in permeability coefficient was mathematically derived and evaluated through computer numerical analysis.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.947-956
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• 2018

Subsea tunnel built in abyssal zone is exposed to environment under high water pressure caused by seawater and etc., and this high pressure from underground water may facilitate leaching. In particular, since underground water can be easily flown in during construction, this might cause many problems related to cutoff water. Therefore, in order to secure safety, it is necessary to apply grouting equipment and materials which are appropriate to construction environment. Accordingly, in this research, evaluation was made on the physical characteristics of grouting materials (strength, leaching and etc. depending on curing methods for each of used materials and condition) which can be applied during subsea tunnel construction. As a result of this research, stable strength increase was found in CA and CSA type, and it is determined that no decrease in their durability was found, so these can be used as stable materials for structures under influenced by seawater.