• Proceedings of the Korean Institute of Industrial Safety Conference
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• 2002.11a
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• pp.204-207
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• 2002

주로 터널 등에 사용되는 숏크리트는 콘크리트와 달리 높은 압력으로 뿜어붙이기 때문에 콘크리트와 다른 역학적 특성이 보이게 된다. 그러나 국내에서는 이러한 숏크리트의 중요한 역학적 특성인 내구성능에 관한 실험이 미미한 실정으로 본 연구에서는 숏크리트 장비를 이용하여 실험시편을 급결제의 종류, 혼화제의 종류, 혼화재(실리카흄, 고로슬래그, 플라이애쉬)의 종류 등에 따라 제작하여 강도실험(28일 및 56일 압축강도, 28일 휨강도, 56일 할렬인장강도), 동결융해실험, 내투수성실험, 중성화실험 등의 폭 넓은 실험을 통해 고성능 숏크리트의 전반적인 내구특성을 규명할 수 있었다.(중략)

• Journal of Korean Tunnelling and Underground Space Association
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• v.9 no.2
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• pp.99-107
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• 2007

A method was suggested by You et al. (2000) to calculate safety factor of a tunnel based on numerical analysis with the shear strength reduction technique. In the method, the shotcrete is assumed to fail when its stress exceeds the allowable stress. The proposed method had been steadily developed by You et al. (2005) and Han et al. (2006). In this study, the previous routine was corrected so that tunnel construction sequences could be considered in calculating the safety factor of a tunnel. In addition, a proper way to model shotcrete is to be suggested by comparing with the previous studies.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.3
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• pp.433-452
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• 2019

This study deals with shotcrete reinforcing performance according to the amount of synthetic fiber (PP fiber) and proper evaluation method. The shotcrete compressive strength, flexural strength and flexural toughness were tested by setting the mixing amounts of steel fiber ($37.0kg/m^3$) and synthetic fiber (PP fiber) as parameters ($5.0kg/m^3$, $7.0kg/m^3$ and $9.0kg/m^3$). Particularly, circular panel flexural toughness test (Road and Traffic Authority, RTA) was performed to evaluate the shotcrete energy absorption capacity. As a result, the compressive strength and the bending strength of the steel fiber reinforced shotcrete were large, but the flexural toughness of the synthetic fibe (PP fiber) reinforced shotcrete was large. Therefore, synthetic fiber (PP fiber) reinforced shotcrete is considered to have a reinforcing effect comparable to that of steel fiber reinforced shotcrete. Analysis of the relationship between the flexural toughness and the energy absorption capacity of synthetic fiber (PP fiber) reinforced shotcrete revealed that the energy absorbing ability is exhibited at a flexural toughness lower than the allowable standard (3.0 MPa). (Class A: 2.55 MPa = 202J, Class B: 2.72 MPa = 282J, Class C: 3.07 MPa = 403J). As a result of this study, it can be concluded that the actual shotcrete support performance can be evaluated by evaluating the support performance of the shotcrete measured at less than the allowable standard (3.0 MPa) at the actual tunnel site.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.77-91
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• 2006

Domestic practices in shotcrete use have developed in many respects even now, but it still has issues about material, construction, quality standard and so on. In overseas, the construction using high strength shotcrete with $39.2{\sim}58.8 MPa$ of compressive strength is becoming common based on the shotcrete technology of high strength and durability. However, domestic shotcrete design strength is low at around 20.6 MPa of compressive strength and a long term durability is also insufficient. In this paper, field tests using high-quality additives and accelerators were performed to obtain the improvement of shotcrete strength and EFNARC standard was used to evaluate the field test results. In addition, deterioration test combined with the freezing-thawing and carbonation was also performed in order to investigate a long-term durability of high-strength shotcrete. As a result of the field test, the promotion ratio of early strength was $90{\sim}97%$ in case of using alkali-free accelerators. And the compressive strength of the shotcrete using Micro-silica fume was $45.2{\sim}55.8MPa$ and flexible strength was $5.01{\sim}6.66MPa$, so the promotion ratio of strength was $37{\sim}79%$ and $17{\sim}61%$ respectively. The promotion effect of strength by silica fine additives ratio of $7.5{\sim}10%$ for cement mass was much superior to the other cases. It was especially examined that using Micro-silica fume reduced deterioration due to mixed steel fiber and improved a long-term durability of shotcrete.

• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.427-434
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• 2005

An experimental investigation was carried out in order to verify the compressive strength, flexural strength, equivalent bending strength, rebound rate of shotcrete according to silicate accelerator, aluminate accelerator, cement mineral accelerator respectively and to especially evaluate the performance of shotcrete using cement mineral accelerator for high quality. The test result of compressive strength was showed that all accelerators were satisfied the required test value for each age, for the requirement of having the $75\%$ or higher compressive strength ratio to plain concretes at 28 days, cement mineral accelerator with $87\%$ compressive strength ratio was only satisfied. In flexural strength test, cement mineral accelerator was satisfied the flexural strength requirement in steel fiber reinforced shotcrete for each age. Aluminate type was conformed to the requirement for 28 days, but not at 1 day, silicate type was failed to satisfy standard requirement. Rebound rate was measured between $11{\~}19\%$ and cement mineral accelerator was showed comparatively lower rebound rate. Based on the test results, cement mineral accelerator exhibited excellent strength improvement and lower rebound rate compared to the conventional accelerator, its result is showed the possibility of making high performance shotcrete.

• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.2
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• pp.143-152
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• 2005

Shotcrete for support of tunnel structures may contact with groundwater. The hazardous components in groundwater may cause corrosion of shotcrete. Also, the hazardous components may deteriorate the engineering properties of shotcrete, such as compressive strength, bond strength, flexural strength and so forth. The more the effect of the hazardous components on the shotcrete may increase, the more the stability of tunnel structure may decrease. The specimens were artificially immersed in various chemical solutions including hazardous components after the specimens were made at the tunnel construction site. It was performed to analyze the effect of the hazardous components in ground water on the engineering properties of shotcrete. The uniaxial compressive strength test, XRD, SEM were conducted to evaluate the durability and corrosion of shotcrete.

• Geotechnical Engineering
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• v.13 no.2
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• pp.155-168
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• 1997

Lattice girder is a new steel support developed in Europe for the replacement of an existing H-shaped steel set, which is installed after tunnel excavation. Lattice girder has the following several advantages : 1. Lattice girder minimizes the amount of shotcrete shadow which happens to occur behind a steel support. 2. A triangular shape of lattice girder makes shotcrete placed efficiently. 3. Lattice girder provides a good bond strength for shotcrete, which makes the composite structure of lattice girder and shotcrete behave monolithic, and therefore, the rock load can be supported effectively by the lattice girder system, This paper presents the results from a model wall test, a strength test for shotcrete shot on the model wall and a strength test for the bond between lattice girder and shotcrete. These tests proved that lattice-girder system is superior to H-shaped steel-set system concerning the shotcrete rebound rate, the developed shotcrete strength and the adhesion characteristics.

• Proceedings of the Korea Concrete Institute Conference
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• 1992.10a
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• pp.119-124
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• 1992

최근들어 고속도로, 고속철도,지하철 등의 건설이 급격히 증가함에 따라 터널의 건설이 늘어나고 있다. 이러한 터널등의 건설에서 필수적으로 따르는 것이 숏크리트의 시공이며 이러한 숏크리트의 시공은 앞으로 더욱 증가할 추세에 있다. 그러나 숏크리트의 광범위한 시공에도 불구하고 현재 여러 가지 문제점을 내포하고 있는 것이 사실이다. 따라서 본 연구에서는 우리나라 현행 숏크리트의 현황과 문제점을 도출하여 성능개선을 위한 최적 배합을 도출하고 고품질의 숏크리트 시공을 위하여 실리카퓸 숏크리트의 개발 및 적용과 인성(Toughness)과 연성(Ductility)을 대폭 증가시키고 시공속도를 빠르게 하여 안전성과 함께 경제성을 확보할 수 있는 강섬유보강 숏크리트의 개발 및 적용에 대한 연구를 집중적을 수행하였다. 본 연구로부터 숏크리트의 최적 배합을 도출하였고 강도와 내구성을 함께 증가시키고 리바운드율을 대폭 감소시킬 수 있는 실리카퓸 숏크리트를 개발하였다. 또한 wiremesh를 대체할 수 있는 강섬유보강 숏크리트를 개발하여 실내시험 및 현장 적용성 시험을 수행하였다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.3
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• pp.237-247
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• 2006

The use of high-performance shotcrete lining is indispensable to improve long-term durability of a tunnel and to apply the single-shell tunnelling method. Among a lot of shotcrete admixtures, pozzolan materials such as silica fume have positive effects on increasing the strength and the durability of shotcrete. It is also well known that a cement-based accelerator is much faster in setting time and more eco-friendly than conventional accelerators. This study aimed to improve the properties of wet-mix shotcrete by incorporating with Metakaolin and the calcium aluminate based accelerator. To compare Metakaolin with silica fume, mixing ratios of each material were varied as 4% and 8% of cement weight. Moreover, Metakaolin was blended with silica fume, and their binder was also set to 4% and 8% of cement weight. At each mixing condition, setting time, compressive strength, flexural strength, permeability and freezing-thawing resistance were measured. From the experiments, it was revealed Metakaolin could be a substituting material for silica fume.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.5
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• pp.55-64
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• 2008

Shotcrete have become a deterioration which was exposed to harmful environments. In this study, in order to evaluate the deterioration properties of shotcrete, visual examination, compressive strength, adhesive strength, microstructural analysis were investigated up to the 60th weeks of exposure. The attack solutions for test are sodium sulfate and hydrochloric acid solution with different concentrations, respectively. From the results, although the compressive strength of shotcrete specimens and the adhesive strength between specimens and rocks were high at the early immersion age, they rapidly dropped in the subsequent phases, especially in 5% sodium sulfate and pH1 hydrochloric acid solution. With continued exposure, various harmful ions penetrated into the shotcrete specimen, reacted with the cement hydrate, and generated expansion substances. It was verified that the shotcrete specimens suffered a serious deterioration by chemical attack.