• Title/Summary/Keyword: Underground excavation

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Determination of Mode I Fracture Toughness of Rocks Using Wedge Splitting Test (쐐기 분열 시험을 이용한 암석의 모드 I 파괴인성 측정)

  • Ko, Tae Young;Kim, Taek Kon;Lee, Dae Hyuk
    • Tunnel and Underground Space
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    • v.29 no.6
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    • pp.523-531
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    • 2019
  • In the applications of rock mechanics or rock engineering including drill and blast, drilling and mechanical excavation, the fracture toughness is an important factor. Several methods have been proposed to measure the fracture toughness of rocks. In this study, wedge splitting test specimen which is prepared with ease and tested under compression loading was used to obtain mode I fracture toughness of rocks. The equation of stress intensity factor through numerical analysis is proposed from the stress state of crack tip considering both vertical and horizontal loads due to the vertical load acting on the wedge. The validity of the wedge splitting test method was confirmed by comparing the mode I fracture toughness values obtained by the GD and SENB test specimens.

3D Finite Element Analysis of Rock Behavior with Bench Length and Gther Design Parameters of Tunnel (터널의 벤치길이를 중심으로 한 설계변수에 따른 암반거동의 3차원 수치해석)

  • 강준호;정직한;이정인
    • Tunnel and Underground Space
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    • v.11 no.1
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    • pp.30-35
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    • 2001
  • Focusing on the bench length, this paper presents the results of 3-dimensional elafto-plastic FE Analysis un tunnels of full face, mini-bench and short bench excavated in weathered rock. Influences of unsupported span, horizontal to vertical stress ratio, thickness of shotcrete on the behavior of rock and support were a1so studied. Results showed that displacements of mini-bench tunnels responded more sensitively to bench lengths than those of short bench. The effects of bench excavation on upper half displacement increased with longer unsupported span. Horizontal to vertical stress ratio showed a greater influence on displacement and preceding displacement ratio or sidewall rather than those of crown and invert.

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Design of the reinforced concrete lining in bakun diversion tunnels (말레이지아 바쿤 가배수로 터널의 철근콘크리트 라이닝 설계)

  • 지왕률;임태정
    • Tunnel and Underground Space
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    • v.9 no.1
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    • pp.20-26
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    • 1999
  • The completion of the Bakun Diversion Tunnel is subsequently to the Main Dam construction. Therefore, the completion date is very important for the Bakun Hydroelectric Project. Generally, the tunnel lining work as a finishing phase of the tunnelling project occupies a important portion as well as an excavation and a support work of the tunnels in respect to the construction cost and period. Internal section of Bakun Diversion Tunnel is designed circular shape to reduce the roughness of the water flow with 12 meters in diameter of total length 4314.6 meters of 3 tunnels. The lining thickness is varied between 500 mm and 700 mm depending on the structural condition. From the original Tender design of the Bakun tunnels, the required quantity of steel bars was 5,985 ton designed by Reinforced Concrete (RC) through the entire tunnel linings. During the detail design stage by the consideration of the rock conditions and various load conditions, we could suggest five kinds of RC lining type including plain concrete lining type. Through the detail design modification, we could reduce the required amount of steel bars to 2,178 ton, as a half of original Bill of Quantity. Finally, this design modification give us the time and cost saving effect to catch up the construction progress in time.

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A New Method for Elasto-Plastic Analysis of Concrete Lining Installed in a Deep Circular Tunnel (심부 원형터널에 시공된 콘크리트 라이닝의 새로운 탄소성해석법)

  • Lee, Youn-Kyou;Park, Kyung-Soon;Song, Won-Kyong;Park, Chul-Whan;Choi, Byung-Hee
    • Tunnel and Underground Space
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    • v.19 no.4
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    • pp.355-365
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    • 2009
  • This paper proposes an elasto-plastic finite difference method which is useful for the stability evaluation of concrete lining installed in a deep circular tunnel. Mohr-Coulomb criterion is assumed for the condition of yielding in both the rock mass and concrete lining. In order to take into account the installation delay of lining after the excavation, the outer boundary pressure acting on the lining was calculated with the consideration of the convergence occurred before the lining installation. The distributions of stress and displacement in the rock mass and lining were calculated based on the method proposed Lee & Pietruszczak (2008). The applicability of the proposed method was demonstrated by conducting the elasto-plastic analysis of concrete lining supporting an imaginary compressed air storage tunnel. The analysis result revealed that the exact determination of the boundary pressures acting on the concrete lining is of importance in the stability analysis of concrete lining.

A Case Study of Tunnel Stability due to the Shallow Shaft and Change Penetrating Location (터널 갱구부 저토피 및 관통부 변경에 따른 안정성 검토 사례 연구)

  • Lee, Saik;Choi, Youngchul;Jung, Wooyong;Kim, Kookhan;Kim, Dongin
    • Tunnel and Underground Space
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    • v.23 no.2
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    • pp.87-98
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    • 2013
  • Around 70% of Korea is mountainous, an increase in tunnel construction. It's due to the growing interest of the public for the environment and land required for the road construction is very scarce. During construction of 'Daedong 1 tunnel' in the expressway expansion project between Naengjeong and Busan, there are shallow shaft due to this tunnel located in the valley and the shafts are separated, and penetrating location change was inevitable for construction was delayed because of complaint. So, we change the position of the penetrating by applying multi-channel TSP, and conducted a stability analysis. The analysis results showed that there is no problem on the stability of the tunnel. To secure the construction of additional stability, We installed instrument, performed mechanical excavation, added reinforcement at shallow shaft and conducted bench cut.

The Study on the Correlation between Unconfined Compressive Strength and Point Load Strength within the Gneiss Complex in Gyunggi Province (경기 동부 지역 편마암복합체내의 일축압축강도와 점하중강도의 상관관계에 관한 연구)

  • Cha, Areum;Song, Joonho;Choi, Hyunseok;Chun, Byungsik
    • Journal of the Korean GEO-environmental Society
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    • v.8 no.1
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    • pp.21-26
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    • 2007
  • The strength evaluation of rocks is a very important factor in designing and constructing tunnels or underground excavation. However, it takes a lot of time and endeavor to perform the unconfined compressive strength test for practice and a number of tests are limited. In order to make up for this method, the point load strength test is suggested. Generally, the strength of a rock differs depending on its type and region. However, as people unite the Point Load Strength Indexes of various regions and types to use in practice in many cases, they find difficulty in analogizing the exact strength. The purpose of this study is suggestion of the value in construction site by analizing the relation of both unconfined compressive and point load strength in the Gyeonggi gneiss complex.

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Characteristics of Tunnel Convergence Behaviour based on Variation of Rock Mass Rating (암반 등급 변화에 따른 터널 내공 변위 거동 특설)

  • Kim, Kwang-Yeom
    • The Journal of Engineering Geology
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    • v.18 no.4
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    • pp.545-553
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    • 2008
  • Face mapping and displacement monitoring during tunnel construction are the most influential information for the stability assessment of ground and around structures. Especially, the result of face mapping and displacement analysis is essential to the excavation and support design in NATM which is based on the drilling and blasting. However, there have not been so many studies to put those useful information into practice for decision-making process during construction. The study reviewed the tunnel behaviour based on the RMR rating and displacement monitoring when the geological condition of rock mass varies inevitably. The study analysed the crown settlement using convergence equation in order to compensate the disparity induced by the location and time of measurement and found a distinct relation between the geological condition and the line of influence. As a result of analysing the various parameters related to the tunnel convergence according to the geological condition, the study suggested the basic knowledge about the relation between face mapping and displacement behaviour of tunnel.

Application of Fracture Toughness for Scaled Model Test (파괴인성의 축소모형실험 적용 연구)

  • Kim, Jong-Gwan
    • Tunnel and Underground Space
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    • v.30 no.1
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    • pp.87-97
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    • 2020
  • Fracture toughness of rock is a constant that can indicate the initiation and propagation of cracks due to blasting, excavation, etc. Scaled model tests have been applied to the behavior of tunnels and the stability of limestone mines. Through the scaled model, damaged zone evaluation due to blasting is also carried out, and the scale factor is not applied to the failure-related factors. In this study, DCT (diametral compression test) and finite element method ATENA2D numerical analysis results were compared to determine whether the scale factor could be applied to the fracture toughness of rock. The theoretical values of the scale factor applied to the fracture toughness of the rock and the DCT test results and the numerical results are 0.21~0.46, 0.40, and 0.99MPa ${\sqrt{m}}$ respectively, so these three values should be considered when determining scale factor. It is necessary to derive a suitable scale factor in consideration of the length, time, and mass to which the scale factor is applied, as well as the values of the scale factor of major design factors such as uniaxial compressive strength and density.

Analysis of Subsidence Mechanism and Development of Evaluation Program (지반침하 메커니즘 분석 및 평가 프로그램 개발)

  • Choi Sung O.;Jeon Yang-Soo;Park Eu-Sup;Jung Yong-Bok;Chun Dae-Sung
    • Tunnel and Underground Space
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    • v.15 no.3 s.56
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    • pp.195-212
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    • 2005
  • Surface subsidence which occurs with several reasons, such as collapse of gangway, discharge of groundwater, compaction of weak rock mass, and tunnel excavation in shallow depth, gives rise to a serious problem in national infra-structures. In this study, therefore, the mechanism of subsidence has been examined numerically to overcome the passive approach on subsidence occurrence area. With many kinds of numerical studies, the major geotechnical parameters have been selected and the weighted values have been defined for each parameters. Also the authors developed the numerical program which can estimate the possibility of subsidence occurrence, and proposed the decision method for objective and quantitative guideline. It is anticipated that this research will be helpful to establish the hazard map on subsidence region.

A study on the Rock-support response behavior in tunnelling (터널링에 의한 암반-지보 반응거동에 관한 연구)

  • 백승한;문현구
    • Tunnel and Underground Space
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    • v.8 no.4
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    • pp.321-331
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    • 1998
  • A reliable analysis of tunnelling is needed to accomplish technically sound design and safe and economical construction. For the reliable analysis, a series of procedures of construction which include excavation and support stages must be considered. In this study, rock-support response behavior is studied and simulated in 2-D and 3-D finite element methods. Through the analysis of rock-support response behavior, the effects of the properties of shotcrete on the load distribution ratio can be quantified. The load distribution ratios for different rock types, different unsupported spans and various lateral earth pressure coefficients can be determined from the results of the 3-D finite element analysis. This load distribution ratios can be applied to a practical tunnel design through understanding of the trend of those various factors affecting the rock-support interaction.

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