• Title/Summary/Keyword: 지보패턴

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Evaluation of Support Performance of Fiber-Net Integrated Shotcrete in Tunnel Support System (숏크리트용 섬유 그물망 일체형 터널 지보시스템의 지보 성능 평가)

  • Kim, Jiyoung;Choi, Seongcheol
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.8 no.4
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    • pp.545-552
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    • 2020
  • This study evaluated the support performance of fiber-net integrated shotcrete in tunnel support system developed for the purpose of improving constructability and stability while fully performing its mechanical performance as a tunnel support materials by four-point bending test, two-dimensional numerical analysis, and cross-sectional analysis. As a result of evaluating the flexural performance through a four-point bending test, in the case of fiber-net reinforced shotcrete, the tensile performance of fiber-net resulted in a continuous increase in load after crack occurrence, unlike steel fiber reinforced shotcrete. Also, the results of the tunnel cross-sectional structure analysis for ground conditions and the cross-sectional analysis of fiber-net and steel fiber reinforced shotcrete showed that sufficient support performance can be exhibited even if the thickness of fiber-net reinforced shotcrete was reduced compared to the previous one. Additionally, through these results, the support pattern of fiber-net integrated shotcrete in tunnel support system, which can be applied efficiently to the construction sections requiring higher stability among the rock mass class III, was proposed.

A study on the optimization of tunnel support patterns using ANN and SVR algorithms (ANN 및 SVR 알고리즘을 활용한 최적 터널지보패턴 선정에 관한 연구)

  • Lee, Je-Kyum;Kim, YangKyun;Lee, Sean Seungwon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.24 no.6
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    • pp.617-628
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    • 2022
  • A ground support pattern should be designed by properly integrating various support materials in accordance with the rock mass grade when constructing a tunnel, and a technical decision must be made in this process by professionals with vast construction experiences. However, designing supports at the early stage of tunnel design, such as feasibility study or basic design, may be very challenging due to the short timeline, insufficient budget, and deficiency of field data. Meanwhile, the design of the support pattern can be performed more quickly and reliably by utilizing the machine learning technique and the accumulated design data with the rapid increase in tunnel construction in South Korea. Therefore, in this study, the design data and ground exploration data of 48 road tunnels in South Korea were inspected, and data about 19 items, including eight input items (rock type, resistivity, depth, tunnel length, safety index by tunnel length, safety index by rick index, tunnel type, tunnel area) and 11 output items (rock mass grade, two items for shotcrete, three items for rock bolt, three items for steel support, two items for concrete lining), were collected to automatically determine the rock mass class and the support pattern. Three machine learning models (S1, A1, A2) were developed using two machine learning algorithms (SVR, ANN) and organized data. As a result, the A2 model, which applied different loss functions according to the output data format, showed the best performance. This study confirms the potential of support pattern design using machine learning, and it is expected that it will be able to improve the design model by continuously using the model in the actual design, compensating for its shortcomings, and improving its usability.

A study on the Correlation Between the Result of Electrical Resistivity Survey and the Rock Mass Classification Values Determined by the Tunnel Face Mapping (전기비저항탐사결과와 터널막장 암반분류의 상관성 검토)

  • Choi, Jai-Hoa;Jo, Churl-Hyun;Ryu, Dong-Woo;Kim, Hoon;Oh, Byung-Sam;Kang, Moon-Gu;Suh, Baek-Soo
    • Tunnel and Underground Space
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    • v.13 no.4
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    • pp.279-286
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    • 2003
  • Many trials to set up the correlation between the rock mass classification and the earth resistivity have been carried out to design tunnel support type based on the interpreted electrical resistivity acquired by surface electrical survey. But it is hard to find reports on the comparison of the real rock support type determined during the excavation with the electrical resistivity by the inversion of the survey data acquired before the tunneling. In this study, the rock mass classification based on the face mapping data and the resistivity inversion data are investigated to see if it is possible to design reliably the rock support type based on the surface electrical survey. To get the quantitative correlation, rock engineering indices such as RCR(rock condition rating), N(Rock mass number), Q-system and RMR(rock mass rating) are calculated. Since resistivity data has low resolution, Kriging method as a post processing technique which minimizes the estimated variance is used to improve resolution. The result of correlation analysis shows that the 2D electrical resistivity survey is appropriate to see the general trend of the geology in the sense of rock type, though there might be some local area where these two factors do not coincide. But the correlation between the result of 3D survey and the rock mass classification turns out to be very high, and then 3D electrical resistivity survey can make it possible to set up more reliable rock support type.

Study on the optimal construction of a concrete lining in a weathered rock (풍화암지반에 시공되는 콘크리트라이닝의 적정시공에 관한 연구)

  • Kim, Hyeongkeon;Lee, Chul;Lee, Sun-Woo;Park, Jun-Woo
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.17 no.1
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    • pp.33-47
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    • 2015
  • Concrete lining in tunnel construction is used as secondary support for downward loads when primary support decays. The use of concrete lining varies greatly depending on the intentions of engineer and/or client. An engineer uses much smaller deformation modulus which determines the concrete lining thickness than of a pattern 3, when supporting patterns 4 and 5 are used in a weathered rock and soil. Considering these conditions, this study intends to suggest optimal construction procedures through a back analysis using a computer program(MIDAS-civil). Cases of Seoul Subway System line${\bigcirc}{\bigcirc}$ zone${\bigcirc}{\bigcirc}$ were selected to be examined for this study. The results show that it is possible to reduce the thickness of concrete lining. When results from this study were applied to Seoul Metropolitan subway construction projects, it is expected to bring economic benefits.

A Study on Quantity of Shotcrete Sprayed in a NATM Tunnel Based on Field Measurements (현장 실측자료 분석을 통한 NATM 터널의 숏크리트 투입량에 관한 연구)

  • Lee, Cheol Ju
    • Journal of the Korean GEO-environmental Society
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    • v.12 no.9
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    • pp.47-54
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    • 2011
  • This study has analysed overbreaks, shotcrete rebound and the ratio between the actual quantity of shotcrete sprayed compared to designed quantity measured during a NATM tunnel construction. Based on the measurements of size of the excavated tunnel faces, an average overbreak was about 28.5 cm, which is about 260% of allowable overbreak. The measured shotcrete rebound was about 7.2% in average which is about half the allowable rebound(15%). In addition, due to overbreaks and rebound the actual quantity of shotcrete used in the tunnelling work was about 116.5 % of the designed value. It has been found from the field measurements that the quantity of shotcrete showed some relation with rock mass rating(RMR) and the standard guideline of tunnel supports, but the size of overbreak showed less correlation with RMR and the standard guideline of tunnel supports. Hence, the current tunnel design specifications stating the size of overbreak based entirely on the standard guideline for tunnel supports should perhaps be reestablished. The insight into the design guideline regarding overbreak and actual quantity of shotcrete will be reported and discussed.