• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.683-688
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• 2000

Nowadays, shotcrete plays an essential part in the construction of underground structures, and fiber reinforcement is so useful for increasing the toughness of the concrete that is spotlighted at tunnel or pavement construction. Therefore, many type of fibers have been introduced on the site and variety of tests have been developed to measure and quantify the improvements achievable in fiber reinforced concrete and shotcrete. Therefore, this study focuses on the flexural toughness according to the fiber types and appraisal methods. The major interests are fiber types, volume fractions and evaluation methods.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.3
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• pp.187-195
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• 2005

When a tunnel is excavated below groundwater table, the groundwater flow occurs towards the tunnel resulting in the seepage pressure. In this paper, the effect of groundwater flows on the behavior of shotcrete lining installed between ground-liner interfaces was studied considering permeability ratio between the ground and the shotcrete into account. Three-dimensional coupled finite element analysis was performed for this assessment. Seepage forces will seriously affect the shotcrete behavior since arching phenomena do not occur in seepage forces. A parametric study was conducted on the various tunnelling situations including interfacial properties between ground and shotcrete lining, the shape of tunnel cross-section and the thickness of liner, etc. Moreover, the convergence-confinement method (CCM) of a NATM tunnel considering seepage forces was proposed. The result showed that the more water tight is the shotcrete, the smaller is the convergence and the larger is the internal pressure. Therefore, the watertight fiber-reinforced shotcrete is found to be even more advantageous when used in under water tunnel.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5C
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• pp.221-229
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• 2012

Steel ribs such as H-beam or lattice girder are often reinforced to secure the stability of NATM tunnel when the ground is in the bad condition. When designing, however, steel ribs are not often taken into consideration on the numerical analysis when they are regarded as temporary tunnel supports until shotcrete shows its best performance or if they are, there are various modeling methods. This study shows behavior and loading capacity of steel ribs and shotcrete through the strength test on the bending, pressure and full-scaled. Also, we conducted and analyzed the experiment of composite member consisting of shotcrete and steel ribs under the same condition. Through the result, we can find the fact that shotcrete and steel ribs do not work as one unit because of slipping on the boundary. Also, when numerical analyzing, it was concluded that steel ribs cover all bending moment and shotcrete and steel ribs share with axial force according to the compressive strength.

• Tunnel and Underground Space
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• v.20 no.3
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• pp.169-182
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• 2010

H-beam and lattice-girder are the two most commonly used steel supports in domestic tunnels. Reinforced Ribs of Shotcrete(R.R.S.), which is frequently used in Scandinavian countries, is yet to be employed in Korea despite its advantages over H-beam or lattice girder in terms of economy and constructional efficiency. In this study, laboratory tests were conducted to determine the most suitable design of R.R.S in domestic tunnels. Various configuration of steel reinforcements including double layer of steel rebars were tested and compared. Reinforcement with H-beam and lattice girder were also analyzed. Results of this study can be of great use in selecting and designing of tunnel supports when the tunnel is excavated by NATM or Norwegian Method of Tunnelling(NMT).

• Journal of the Society of Disaster Information
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• v.7 no.1
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• pp.43-50
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• 2011

The Application of Steel Fiber Shotcrete in tunneling construction has become part of tunneling practice at least since the 1970s because of its high bending and tensile properties. Over the past 3 decades, researcher from all over the world have been significantly developing the associated technologies for improved performance of SFRS. But still it has some major drawbacks in terms of durability, damage of pumping hose, wastage due to rebound concrete, corrosion and it costs high. To overcome this situation researcher has to look for some alternative material. Therefore, this part study deals with the three types of fiber in order to find good alternative for steel fiber. Polyamide and Polypropylene fiber were used in this study with 0.6, 0.5% mixing ratio. To evaluate its fresh and harden properties air content, slump, compressive, split tensile and bending strength were measured. After comparing the results of all three types of fiber reinforced concrete with its different mixing proportion this study propose that polyamide fiber with addition ratio of 0.6 % for field use.

• Tunnel and Underground Space
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• v.17 no.5
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• pp.411-427
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• 2007

Reliability in tunnel analysis is necessary to accomplish technically sound design and economical construction. For this, a thorough understanding of the construction procedure including the ground-support interaction has to be obtained. This paper describes a proper modelling technique to simulate the behavior of the steel fiber reinforced shotcrete (SFRS) which maintain the supporting capability in post-failure regime. The additional supporting effect of the steel support was also verified by 3-D analyses and a new load distribution factor were proposed. The use of the plastic moment limit (PML) alone can eliminate the occurrence of the awkwardly high tensile stress in the shotcrete and can successfully model the post-peak ductile behavior of the SFRS. But with this method, moment is limited whenever the stress caused by moment reaches tensile strength of the shotcrete irrespective of the stress by axial force. Therefore, it was necessary to find a more comprehensive method which can reflect the influence of the moment and axial force. This can be accomplished by the proper use of "liner element" which is the built-in model in FLAC. In this model, the peak and residual strength as well as the uniaxial compressive strength of the SFRS can be specified. Analyses were conducted with these two models on the 2-lane road tunnels excavated in class IV and V rock mass and results were compared with the conventional elastic beam model. Results showed that both models can reflect the fracture toughness of the SFRS which could not be accomplished by the elastic beam model.

• Structural Engineering and Mechanics
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• v.23 no.1
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• pp.43-61
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• 2006

An investigation of the effectiveness of the interface treatment when column concrete jacketing is performed is presented. Alternative methods of interface connection were used in order to investigate the performance of strengthened concrete columns. These connecting techniques involved roughening the surface of the original column, embedding steel dowels into the original column and a combination of these two techniques. The experimental program included three strengthened specimens, one original specimen (unstrengthened) and one as-built specimen (monolithic). The specimens represented half height full-scale old Greek Code (1950's) designed ground floor columns of a typical concrete frame building. The jackets of the strengthened specimens were constructed with shotcrete. All specimens were subjected to displacement controlled earthquake simulation loading. The seismic performance of the strengthened specimens is compared to both the original and the monolithic specimens. The comparison was performed in terms of strength, stiffness and hysteretic response. The results demonstrate the effectiveness of the strengthening methods and indicate that the proper construction of a jacket can improve the behaviour of the specimens up to a level comparable to monolithic behaviour. It was found that different methods of interface treatment could influence the failure mechanism and the crack patterns of the specimens. It was also found that the specimen that combined roughening with dowel placement performed the best and all strengthened columns were better at dissipating energy than the monolithic specimen.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.2
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• pp.357-367
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• 2017

Bending and axial forces simultaneously occur at the cross-section of a shotcrete lining reinforced with steel supports due to the tunnel geometry. The shotcrete has changing flexural stiffness depending on the axial forces and, as a result, severely nonlinear behavior. The mechanical properties of a shotcrete-steel composite also depend on the type of steel support. This study presents a fiber section element model considering the effect of axial force to evaluate the nonlinear behavior of a shotcrete-steel composite. Additionally, the model was used to analyze the effects of different types of steel supports on the load capacity. Furthermore, a modified hyperbolic model for ground reaction, including strain-softening, is proposed to account for the ground-lining interaction. The model was validated by comparing the numerical results with results from previous load test performed on arched shotcrete specimens. The changes in mechanical responses of the lining were also investigated. Results show a lining with doubly reinforcement rebar has similar load capacity as a lining with H-shaped supports. The use of more materials for the steel support enhances the residual resistance. For all types of steel reinforcement, the contribution of steel supports during peak load decreases as the ground becomes stiffer.

• Journal of the Society of Disaster Information
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• v.10 no.1
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• pp.61-70
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• 2014

Synthetic fiber reinforced concrete is applicable to many applications for construction material. In general, synthetic fibers have low tensile strength and elastic modulus, but they have many advantages such as high crack resistance, impact resistance, chemical resistance, flexural behavior and corrosion free in fiber reinforced concrete. Recently, fiber reinforced concrete with macro synthetic fibers has been used to improve performance of structures in tunnel shotcrete, precast segmental lining and bridge slab and precast concrete structures. This study investigated the influence of bundled type polyamide fiber reinforced concrete on the flexural behavior in accordance with ASTM C 1609 and KS F 2566 standards.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.629-634
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• 2003

The cement-based composites have relatively low tensile strength and toughness. The fiber addition is one of the most important ways of increasing the toughness of concrete. The steel fibers have been used conventionally in the shotcrete of tunnel lining. Recently, the structural synthetic fibers were developed and used frequently in some actual tunnel shotcreting in foreign countries. There are so many method to evaluate a toughness; ASTM, JCI, EFNARC, etc. But these methods contain a few defects. So most researchers are studying to develope a new toughness evaluation method. A RTA is one of these methods. The purpose of this study is to explore the strength and toughness characteristic of the fiber reinforced concrete panel according to the geometry; diameter, thickness. The result were compared with those of steel fiber reinforced concrete.