• Tunnel and Underground Space
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• v.19 no.2
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• pp.132-145
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• 2009

Faults in rock mass have strong influences on the behaviors of rock structure such as rock slope, tunnel and underground space. Thus, it is very important to analyse for the characteristics of fault rocks in design for tunnel. But, due to the limitation of geotechnical investigation in design stages, tunnel engineers have to carry out the face mapping and additional geological survey during tunnel excavation to find the distribution of faults and the engineering properties of faults for support and reinforcement design of tunnel. In this study, various geological survey and field tests were carried out to analyse the characteristics of the large thrust fault zone through the large sectional tunnel is constructed in mica-schist region. Also, the distribution of structural geology, the shape of thrust faults and the mechanical properties of fault rock were studied for the reasonable design of the reinforcement and support method for the highly fractured fault zone in the large-span tunnel.

• Journal of the Korean GEO-environmental Society
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• v.24 no.8
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• pp.13-20
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• 2023

Tunnelling through the geological anomalies has widely known to have many difficulties such as bottom heave, crack of lining, squeezing and so on. To stabilize the tunnel during the construction or after construction, various reinforcing methods have been introduced and applied such as micropiling at the bottom of tunnel to prevent the bottom heave. In this study, long-term behavior of tunnel in the presence of geological anomalies was predicted using numerical analyses. To this end, material properties for swelling rock model capable of representing the rock swelling behavior was obtained using matching process with measured data to validate the adopted model. After the model validation, simulations were performed to predict the long-term behavior of tunnel in the geological anomalies.

• Journal of the Korean Geosynthetics Society
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• v.15 no.2
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• pp.55-64
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• 2016

The construction of the road NATM tunnel, which undergoes the weathered zone of the mountain, was in process with the reinforcement methods such as the rock bolt, shotcrete depositing, and the multi step grout with large diameter steel pipe. The collapse from the ceiling, and on the ground surface area(sink hole), of which were measured to be 25m from the ground surface($V=12m(W){\times}14m(L){\times}5m(H)=840m^3$), as well as excessive displacements in the tunnel, had occurred. In order to execute the necessary reconstruction work, the causes of the surface collapses were inspected through the field investigation, in-situ tests, and numerical analysis. As a result, several proper solutions were suggested for both internal and external reinforcements for the tunnel. As a result of numerical analysis, the collapsed zone of the tunnel was reinforced up to 0.5D~1.0D laterally by the cement grouting on the ground surface, 0.5D longitudinally by the multi step grout with large diameter steel pipe in tunnel. With further reinforcement implemented by rebars in lining, the forward horizontal boring was executed to the rest of the tunnel to evaluate the overall status of the tunnel face. Appropriate reinforcement methods were provided if needed.

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.109-120
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• 2007

Auxiliary support systems such as the reinforced protective umbrella method have been applied before tunnel excavation to increase ground stiffness and to prevent the large deformation. However, determination procedure of geotechnical parameters along the construction sequence contains various errors. This study suggests a method to characterize the time-dependent behavior of pre-reinforced zones around the tunnel using elastic waves. Experimental results show that shear strength as well as elastic wave velocities increase with the curing time. Shear strength and strength parameters can be uniquely correlated to elastic wave velocities. Obtained results from the laboratory tests are applied to numerical simulation of tunnel considering its construction sequences. Based on numerical analysis, initial installation part of pre-reinforcement and portal of tunnel are critical for tunnel stability. Result of the time-dependent condition is similar to the results of for $1{\sim}2$ days of the constant time conditions. Finally, suggested simple analysis method combining experimental and numerical procedure which considering time-dependent behavior of pre-reinforced zone on tunnel would provide reliable and reasonable design and analysis for tunnel.

• Journal of Korean Tunnelling and Underground Space Association
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• v.26 no.4
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• pp.345-363
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• 2024

Steel pipe reinforced grouting method has been widely used to strengthen the crown of tunnel face and prevent groundwater leakage during tunnel excavation. Various injection procedures without sealing have recently been suggested to enhance efficiency. There are two representative injection methods. One is simultaneous injection in segmented batches, and the other is multiple injection using the external packer. The pros and cons of each method were discussed in terms of construction duration and equipment. However, it has yet to be discussed how the injection procedure affects the grout diffusion range in the ground. This study aims to evaluate the grout diffusion range quantitatively by considering the practical grouting sequences. The grout viscosity was measured by laboratory testing. Then, the numerical modeling was structured using the commercial computational fluid dynamics software. Finally, the grout diffusion range affected by the injection procedure and ground conditions was evaluated by performing the numerical parametric study. The results showed that the injection method highly affected the grout diffusion range, especially for inhomogeneous soil. Consequently, it is anticipated that the proper method of steel pipe reinforced grouting will be suggested.

• The Journal of Engineering Geology
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• v.23 no.1
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• pp.67-77
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• 2013

We conducted a Tunnel Seismic Prediction (TSP) survey in a spillway tunnel at Juam Dam to predict the locations of major discontinuities ahead of the tunnel face. We compared the results of the TSP survey with those from pre-construction inspections (including a surface resistivity survey and borehole investigations) as well as with direct tunnel-face mapping during excavation. The TSP method predicted the locations of major fracture zones that were unnoticed in the pre-construction inspections. The reinforcement patterns planned on the basis of pre-construction inspections were changed on the basis of the TSP results. The results demonstrate that TSP surveys are a cost-effective and reliably accurate method of predicting the locations of fracture zones. Although the TSP method has some limitations, these results suggest that the method is generally useful for predicting geological conditions prior to tunnel face construction.

• Journal of the Korean GEO-environmental Society
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• v.10 no.1
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• pp.55-61
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• 2009

Recently, highway tunnel construction has rapidly been increased due to the limited ground usage and geographical characteristic in Korea, i.e. Korea consists of 70% mountains. In this paper, it was analyzed tunnel collapse patterns in the weathered rockmass. Recent tunnel collapse pattern is quite different from that of past ten years. Tunnels in past years have been collapsed at shallow valley area because of shear strength decrease after heavy rain. Tunnels, which have been constructed recently, were collapsed at even the deeper ground position after primary support. Also in the case that proper reinforcement was not applied, it caused excessive crack at shotcrete and local collapse near tunnel face. In this paper, it was analysed the cause of the recent tunnel collapses and proper reinforcement for the collapsed tunnels.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.2
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• pp.655-666
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• 2013

A number of highway projects are in progress in Korea to accommodate increasing transportation demands. As the highway route becomes more complex, some projects include tunneling through unconsolidated sedimentary rock. Since an unconsolidated sedimentary rock mainly consists of rock and ground mass, the behavior and characteristics in unconsolidated sedimentary rock tunnel are quite different from typical rock tunnel. However, construction case histories and rock classifications method on unconsolidated sedimentary rock tunnel had not been developed or studied domestically. Consequently the case studies and rock classification system for unconsolidated sedimentary rock are required to better understand its behavior for tunneling. In this study, rock mass classification method is proposed to identify unconsolidated sedimentary rock based on point load and slake durability tests. Based on this, the proposed method of unconsolidated sedimentary rock can be applied well through comparisons with the results of convergence measurement.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.273-280
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• 2003

Tunneling in difficult geological conditions is often inevitable especially in urban areas. Ground improvement and reinforcement techniques are often required to guarantee safe tunnel excavations and/or to prevent damage to adjacent structures. The steel pipe-reinforced multi-step grouting method has been recently applied to tunnel sites in Korea as an auxiliary technique. In this study, the face stability with steel pipe-reinforced multi-step grouting was evaluated by simultaneously considering two factors: one is the effective stress acting on the tunnel face calculated by limit theorem and limit equilibrium method; the other is the seepage force obtained by means of numerical analysis. The study revealed that the influence of the steel pipe-reinforced multi-step grouting on the support pressure in dry condition is not significant while there is relatively a large amount of reduction in seepage forces by adopting the technique in saturated condition. The effect of the anisotropy of permeability on the seepage force acting on the tunnel face was also estimated by conducting the coupled analysis. It was found that a higher horizontal permeability compared with the vertical one causes reduction in the seepage force acting on the tunnel face.

• Journal of Korean Tunnelling and Underground Space Association
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• v.6 no.3
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• pp.259-267
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• 2004

The practice of introducing and grouting reinforced fiber glass pipes or bar into the core to be excavated to maintain stable the tunnel face during excavation has been applied to many tunnels, where difficult geotechnical conditions are present, with good results in terms of safety and speed of works. This reinforcing technique, initially developed to be used jointly with the mechanical precut in clay, has been widely used with other geotechnical conditions as the only type of reinforcement or joined with other ground consolidation and/or reinforcement techniques (i.e. steel pipes or jet-grouting umbrella). At present same numerical researches have been carried out to find which are the real working conditions of the reinforcing elements but no final results have been obtained for the definition of the best design approaches. In this work the results of a three dimensional parametric numerical model is presented.