• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.1060-1067
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• 2009

Previous research on the slope failure has mainly reported that most of the slope failures occur due to surface rainfall infiltration in the rainy season. A slope of which surface is protected by shotcrete or plants, can also fail due to increase in pore water pressure from the ground water flow beneath the surface, rather than from the surface. In this study such case of slope behavior is investigated using the model test and numerical method including strength reduction method. Hydraulic boundary conditions of the slopes is considered using coupled numerical scheme. The failure mechanism of the slope is investigated and the effect of pore water pressure on slope safety is identified. Increase in pore water pressure due to lateral infiltration has significantly reduced the stability of slope.

• Proceedings of the KSR Conference
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• 2005.11a
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• pp.860-865
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• 2005

In Korea, NATM (New Austrian Tunneling Method) has widely been used in order for constructing tunnels. The major support materials of the method are the shotcrete and rock bolt together with the arch-shaped tunnel section, which ensure the inherent strength of the rock masses. One of the most important features of the method is the feedback system between tunnel analyses and measurements, such as tunnel displacement and support stresses. This study, therefore, attempts to examine the difference in displacement and stresses between numerical results. and measurements in order for more practical design and construction of tunnels.

• Journal of the Korean Ceramic Society
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• v.47 no.3
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• pp.223-231
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• 2010

The serious issue of tall building is to ensure the fire-resistance of high strength concrete. The fire resistant finishing method is necessarily essential in order to satisfy the fire resistance time of 3 h required by the law. The fire resistant finishing method is installed by applying a fire resistant material as a method of shotcrete or a fire resistant board to high strength concrete surface. This method can reduce the temperature increase of the reinforcement embedded in high strength concrete at high temperature due to the installation thickness control. This study is interested in identifying the effectiveness of inorganic alumino-silicate compounds including the inorganic admixture such as fly ash and meta-kaolin as the fire resistant finishing materials through the analysis of fire resistance and components properties at high temperature. The study results show that the fire resistant finishing material composed of fly ash and meta-kaolin has the thermal stability of the slight decrease of compressive strength at high temperature. These thermal stability is caused by the ceramic binding capacity induced by alkali activation reaction by the reason of the thermal analysis result not showing the decomposition of calcium hydrate. Inorganic compounds composed of fly ash and meta-kaolin is evaluated to be very effective as the fire resistance material for finishing to protect the concrete substrate by the reason of those simplicity in both application and manufacture. The additional study about the adhesion in the interface with concrete substrate is necessary for the purpose of the practical application.

• Journal of Korean Tunnelling and Underground Space Association
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• v.5 no.2
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• pp.189-198
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• 2003

For the huge section of tunnel, it is highly required to observe the role of each rock support and their effect of rock reinforcement in order to investigate more reasonable rock support structure. Especially for unstable tunnel situation with no shotcrete strength right after an excavation, sufficient investigation is needed for rock support structure. In this paper, we clarify the relations of compressive strength and material age, cohesion strength and material age, and cohesion stiffness and material age of grout with time-dependence through tests and numerical analysis simulation with trial rock mass considering hardening of bolt grouting material. By means of this process, effect of rock reinforcement for rockbolt is investigated right after an excavation and modelling and physical constants of young aged rockbolts are obtained. Additionally, the effect of rock reinforcement with hydraulic tensile friction bolt is examined right after an excavation, which grout effect is no need to be waited.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3C
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• pp.159-165
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• 2010

The problems such as natural resource exhaustion, pollutant emission and waste generation are increasing worldwide with the industrial development. The quantity of the industrial by-product in Korea is 6 million tons a year, and even its basic treatment processes including landfill, incineration and storage have reached their limits. In this study, fly ash and silica fume were applied to shotcrete to develop a method for the reuse of resources and to increase the use of fly ash, which is an industrial waste. An environmental hazard evaluation is a must to actively address the worldwide environmental problems, though. Therefore, an environmental impact assessment was conducted using the chemical content analysis test and heavy metal exudation test, for ten mixtures that were obtained through the pre-mixing and compressive strength tests. The results of the compressive strength test showed that all mixtures satisfied national and international standards. Cr, Cd and Hg were not detected, and Pb was detected only in some cases with fly ash. Cu and As were detected in all mixtures, but all of them satisfied national and international standards.

• Journal of Korean Tunnelling and Underground Space Association
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• v.14 no.3
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• pp.247-260
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• 2012

In order to reduce the amount of steel reinforcements in TBM tunnel segments, the use of Steel Fiber Reinforced Concrete(SFRC) is being tried. The steel fibers with higher aspect ratio than that used in tunnel shotcrete are preferred to compensate the deficiency in tensile strength of the segments. In this study, the tensile properties of SFRC with aspect ratio of steel fibers equal to 80 were evaluated through flexural test and Double Punch Test. In the results of flexural test, flexural strengths of the SFRC were increased about 30%~150% thanks to bond of steel fibers used to concrete and could be properly predicted by the equation proposed by Oh(2008). There was a great difference in the estimated direct tensile strengths of the SFRC by the equations presented in ACI and RILEM. It was found that the Double Punch Test could be suitable methodology to estimate the direct tensile strength presented in RILEM of the SFRC.

• Journal of the Korean Geosynthetics Society
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• v.21 no.4
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• pp.79-91
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• 2022

Recently, the frequency of damage to slopes for highways, railways, and complexes has been increasing according to abnormal climates such as heavy rainfall or snowfall. Rapid Hardening Composite Mat (RHCM) could be a satisfactory alternative because it has the advantages that large-scale earthwork is not essential and the period for restoration is minimized. Also, this method does not require heavy machines and a phase of maintenance for slopes against the shotcrete method or planted slope protection, which are representative slope protection methods. Furthermore, the curing time is shorter than Geosynthetic Concrete Composite Mat (GCCM). Therefore, RHCM could be useful for emergency restoration work. Thus, in this study, the strength and duration of RHCM are estimated, compared, and analyzed with GCCM. As a result of the laboratory test, the strength of RHCM is greater 51%, and the duration is larger 69% than GCCM.

• The Journal of Engineering Geology
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• v.30 no.3
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• pp.237-251
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• 2020

This study examined structural analysis of supports in tunnel and displacement and underground stress of tunnel by measurement, in order to evaluate the performance of high-strength lattice girders developed as a substitute for H-profiles. According to the three-dimensional nonlinear structural analysis results of the tunnel support, the load and displacement relationship between the H-profiles and the high-strength lattice girders showed almost the same behavior, and the maximum load of the high-strength lattice girders were 1.0 to 1.2 times greater than the H-profiles. By the results of the three-dimensional tunnel cross-section analysis of the supports, the axial force was occurred largely in the lower left and right sides of the tunnel, and showed a similar trend to the field test values. In the results of the measurement of the roof settlement and rod extension, the final displacement of the steel arch rib (H-profile) and high-strength lattice girder section in tunnel was converged to a constant value without significant difference within the first management standard of 23.5 mm. According to the results of underground displacement measurement, the final change amount of the two support sections showed a slight displacement change, but converged to a constant value within the first management standard of 10 mm. By the results of measurement of shotcrete stress and steel arch rib stress, the final change amount of the two support sections showed a slight stress change, but converged to a constant value within the first management standard of 81.1 kg/㎠ and 54.2 tonf.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.113-120
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• 2005

Soil nailing system can be mentioned to a method of supporting as the shear strength of in-situ soils is increased by passive inclusions. In the general soil nailing system, facing walls are used in two kind of a lattice concrete block or a cast in placed concrete wall. A case of lattice concrete blocks is used in slow slopes greater than 1:0.7. Also, a case of a cast in placed concrete wall is used in steep slopes less than 1:0.5. The cast in placed concrete walls are constructed to 30cm thick together with a shotcrete facing. In this study, the assembling soil nailing method as a new soil nailing system is proposed. This method is constructed assembly using precast concrete panels. Therefore ability of the construction and quality of the facings can be modified than a usual soil nailing system. Also, this method can be obtained the effects that a global slope stability increase, as precast concrete panels is put on cutting face after excavating a slope.

• 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.