• Proceedings of the Korean Geotechical Society Conference
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• 1999.10a
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• pp.139-146
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• 1999

Geological and geotechnical surveys, in general, should precede the excavation to ensure the stability of the tunnel md should be followed up according to the various geological condition during the excavation. However actually the standard support patterns which were decided during the design phases used be insisted for the whole excavation phases in spite of the various geological conditions. When $\bigcirc$$\bigcirc$ tunnel was excavated up to 25m long, the severe displacement was generated in the Portal area of $\bigcirc$$\bigcirc$ tunnel and the tunnel face was pally collapsed. Therefore, this paper present the case study on construction associated with the Umbrella Arch Method used in silty ground by the NATM.

• Proceedings of the Korean Geotechical Society Conference
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• 1997.10a
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• pp.133-140
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• 1997

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.5
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• pp.773-786
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• 2018

In this paper, viscosity features of sealant (bentonite-cement slurry), which is used for umbrella arch method in tunnel, were studied. The sealant must secure optimal strength and capacity for the waterproof and stabilization of borehole as well as to satisfy groutability. In this study, the variation of viscosity was measured with different mixing processes. With an increase of initial mixing period with water and bentonite mixture, the required time for the rapid increase of viscosity of the sealant is shorten. With increase of mixing period, the possibility of swelling of bentonite will increases and this can lead increase of the viscosity of the mixture. In addition, the behaviors of sealant vary with a drastic increase of the viscosity: thixotropy and rheopexy. Furthermore, the bentonite/water mixing period influences on the bleeding features of the sealant. Further study is required to introduce the guideline, which can be applicable in the field in the aspect of required capacity of the sealants and mixing processes of the ingredients.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.6
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• pp.407-416
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• 2010

A new tunnel auxiliary method is proposed in this paper which utilizes the concept of cavity expansion for tuunel reinforcement by forming an umbrella arch on the roof of tunnel. When an inflatable pipe is inserted and expanded by pressure in the bore hole of umbrella arch, the ground around the bore hole can be compacted so that the stress condition above the tunnel perimeter is favorably changed. In order to verify the reinforcement effect of new concept, pilot-scale chamber test, trapdoor test and numerical analysis were performed and compared. In pilot-scale chamber test, three types of inflatable pipes are tested to verify the capability of expansion, and the results arc compared with analytical results obtained by applying cavity expansion theory and with results obtained from finite clement analysis, and the experimental results showed agreeable matches with analytical and numerical ones. Numerical analysis of a tunnel and trapdoor test applied with the inflatable pipes are also performed to figure out the reinforcement effect of the proposed techniques, and the results implied that the new method with 3 directional inflatable pipe (no pressure to downward direction) can contribute to reduce tunnel convergence and face settlement.

• Journal of Korean Tunnelling and Underground Space Association
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• v.3 no.1
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• pp.11-19
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• 2001

The purpose of this study is to improve the problems in Umbrella Arch Method, such as the oxidation, the difficulties in installation and cutting of the steel pipe. The applicability of the high strength FRP (Fiber-Reinforced-Plastic) materials composed of glass fiber as a substitute of steel pipe was investigated in this study. The results of this study show that FRP material is better than steel pipe in work performance and the durability of material except for its price. From the numerical analysis with various types of FRP, it was evaluated that the equiangular curve type is more efficient than the flat type developed abroad, and the supporting effect of FRP-grout mixture is similar to that of steel-grout mixture in results of bending strength test.

• Journal of the Korean Geotechnical Society
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• v.19 no.6
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• pp.245-259
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• 2003

This paper deals with an Umbrealla Arch Reinforcement Method (UARM) in tunnelling. It is known that the mechanism of the reinforcement system is too complex to be simulated in existent finite element (FE) frameworks when considering its complex geometry of pipe arrangements and contribution of each component of the reinforcement to reinforcing effect. In this study a 3-D elastoplastic FE procedure is, therefore, proposed by introducing homogenisation technique, which is used to define mathematically elastic as well as elastoplastic characteristics of a reinforced ground material as a composite. A number of practical suggestions are addressed considering staged constructions of tunnels. For illustrative purposes, a series of parametric studies are undertaken and anisotropic characteristics of the reinforced ground as well as effects of the reinforcement on tunnel convergences are investigated. It is found that the reinforced ground material defined in homogenisation framework has its mechanical characteristics reasonably representing inherent geometrical and quantitative characteristics of each of constituents.

• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.57-70
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• 2009

Considerable advance has been made on research on effect of steel pipe Umbrella Arch Method (UAM) and mechanical reinforcement mechanism through numerical analyses and experiments. Due to long analysis time of three-dimensional analysis and its complexity, un-quantitative two-dimensional analysis is dominantly used in the design and application, where equivalent material properties of UAM reinforced area and ground are used, For this reason, development of reasonable, theoretical, quantitative and easy to use design and analysis method is required. In this study, both field UAM tests and laboratory tests were performed in the residual soil to highly weathered rock; field tests to observe the range of reinforcement, and laboratory tests to investigate the change of material properties between prior to and after UAM reinforcement. It has been observed that the increase in material property of neighboring ground is negligible, and that only stiffness of steel pipe and cement column formed inside the steel pipe and the gap between steel pipe and borehole contributes to ground reinforcement. Based on these results and concept of Convergence Confinement Method (CCM), two dimensional axisymmetric analyses have been performed to obtain the longitudinal displacement profile (LDP) corresponding to arching effect of tunnel face, UAM effect and effect of supports. In addition, modified load distribution method in two dimensional plane-strain analysis has been suggested, in which effect of UAM is transformed to internal pressure and modified load distribution ratios are suggested. Comparison between the modified method and conventional method shows that larger displacement occur in the conventional method than that in the modified method although it may be different depending on ground condition, depth and size of tunnel, types of steel pipe and initial stress state. Consequently, it can be concluded that the effect of UAM as a beam in a longitudinal direction is not considered properly in the conventional method.

• Geomechanics and Engineering
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• v.21 no.2
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• pp.207-213
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• 2020

Umbrella Arch Method (UAM) often employed in the tunnel construction under poor rock mass conditions in Korea. Insertion of steel pipes at the periphery of the tunnel and infiltration of grouts along the pipes into the rock masses increases tunnel stability. There are two major effects of grouts expected at the tunnel face: 1) increase of face stability by enhancing the frictional resistance of discontinuities and 2) decrease of permeability along the rock masses. Increase of resistance and decrease of permeability requires a certain curing time for the grout. In Korea, we require 24 hours for curing of grout, which means no progress of excavation for 24 hours after infiltration of grouts. This step delays the tunnel construction sequences. To eliminate such inefficiency, we propose MTG (Method for Tunnel construction using Grouting technology), which uses extended length of steel pipes (14 m) compared to conventional pipe roof method (12 m). The merit of MTG is the reduction of curing time. Because of the approximately 2 m extension of the length of steel pipe, blasting can be done after infiltration of grouting. For this paper, we conducted experiments on the shear strength behaviors of grout infilled rock joint with elapsing of curing time and blasting induced vibration. The results show that blasting induced vibration under MTG does not influence the mechanical features of grout material, which indicates no influence on the mechanical behaviors of grout, contributing to the stability of tunnels during excavation. This result indicates that MTG is a cost effective and fast construction method for tunneling in Korea.

• Journal of the Korean Geotechnical Society
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• v.20 no.3
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• pp.97-106
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• 2004

In case of tunnel construction with a shallow soil cover in cohesionless soils or highly weathered rocks, reinforcement measures are required for a tunnel stability during the tunnel construction. Recent developments show that the use of Umbrella Arch Method(UAM) as tunnel reinforcement and water cut-off in domestic projects has increased. Unfortunately, guidelines for the design and construction of UAM have not been established, only empirical designs and applications in tunnel construction have been performed so far. In this study, behaviour of the steel pipes installed on the tunnel roof was analyzed through the monitoring of bending and axial stresses of the pipes with the advance of the tunnel face. The monitoring results were used in the establishment of the loading mechanism around the pipe. This paper suggests, the guidelines used in the determination of the total length, overlapping length and lateral spacing of the reinforcing pipes obtained from the established loading mechanism.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.129-141
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• 2003

The precise prediction of ground displacement plays an important role in planning and constructing tunnels. In this study, an equation for predicting the surface and crown settlement is suggested by examining the theories of ground movement caused by tunnel excavation. From the 3D numerical modeling, the reinforcement effect of UAM (Umbrella Arch Method) is quantitatively analyzed with respect to deformation modulus and overburden. By using a regression technique for the numerical results, an equation for predicting the settlement is suggested.