• Title/Summary/Keyword: Rock stress

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Seismic Performance Assessment of Atmospheric Surge Tank (노출형 조압수조의 해석모델별 내진성능평가)

  • Kim, Yongon;Ok, Seung-Yong;Kim, Il Gyu;Ryu, Seonho;Bae, Jungjoo
    • Journal of the Korean Society of Safety
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    • v.31 no.5
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    • pp.67-73
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    • 2016
  • This study investigates the seismic performance of the surge tank which is of the atmospheric type and constructed above the ground. For that purpose, three different numerical models of the surge tank have been taken into account. Two models are constructed to describe the surge tank with different support conditions: one is to model all supports as fixed, and the other is to use spring element for the rock conditions. The third model is constructed to describe not only the surge tank with spring element of the rocks but also the vertical waterway tunnel. Through the time-history analysis of the surge tank subjected to three artificially excited ground motions, it is demonstrated that there can be much difference between the three models of our interest according to the support conditions and inclusion of the vertical waterway tunnel. However, their seismic performances still remain below the safety criteria, i.e., dynamic allowable stress. Also, the numerical results let us know where the critical sections occur. These results could be used to develop the efficient seismic enhancement method for the surge tank.

Prediction of Ground Condition Changes Ahead of Tunnel Face Using Three-Dimensional Absolute Displacement Analysis (터널 3차원 절대변위 해석기법을 이용한 막장전방지반 예측)

  • Bang, Joon-Ho;Han, Il-Young
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.8 no.2
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    • pp.101-113
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    • 2006
  • Arching effect occurs around the unsupported excavation surface near to tunnel face when a tunnel is excavated in a stable rock mass. If a weak fracture zone exists in front of tunnel face, a displacement occurs between tunnel face and weak fracture zone due to stress concentration. If three-dimensional absolute coordinates (longitudinal, transverse, vertical direction) is measured at tunnel face by geodetic method, the ground change in front of the tunnel face can be predicted by analysing three-dimensional absolute displacement. The purpose of this study is to verify the analysis method of three-dimensional absolute displacement by comparing the trend of displacement ratio at crown and sidewall of tunnel and the influence line/trend line of crown settlement compared with TSP results in the same section.

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A preliminary numerical analysis study on the seismic stability of a building and underground structure by using SSI (SSI를 이용한 건물과 인접지하구조물의 내진 안정성에 대한 기초 수치해석 연구)

  • You, Kwang-Ho;Kim, Young-Jin
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.20 no.1
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    • pp.23-38
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    • 2018
  • Up to now, most of studies on seismic analysis have been limited to analyze buildings and underground structures individually so that the interaction between them could not be analyzed effectively. Thus, in this study, a dynamic analysis was conducted for soil-structure interaction with a complex underground facility composed of a building and an adjacent underground structure constructed on a surface soil and the bed rock ground conditions. Seismic stability was analyzed based on interstory drift ratio and bending stress of structure members. As a result, an underground structure has more effect on a high-rise building than a low-rise building. However the above structures were proved to be favorable for seismic stability. On the other hand, tensile bending stresses exceeded the allowable value at the underground part of the building and the adjacent underground structure so that it turned out that the underground part could be weaker than the above part. Therefore, it is inferred that above and underground structures should be analyzed simultaneously for better prediction of their interaction behavior during seismic analyses because there exist various structures around buildings in big cities.

Failure Load Prediction of Tunnel Support using DOE and Optimization Algorithm (실험계획법과 최적화알고리듬을 이용한 터널지보의 파손하중 예측)

  • Lee, Dong-Woo;Cho, Seok-Swoo
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.13 no.4
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    • pp.1480-1487
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    • 2012
  • Recently, the safety of the coal-mining tunnels has been improved greatly, but accidents occur continually. Most tunnel support failures occur because the fish plate part that connects the I-beams is unable to withstand ground pressure. In the case of XX coal mine, the arch part of tunnel support bends to the upper direction. In such a case, excessive horizontal load as well as vertical load acts on the tunnel support. Horizontal load is caused by the sudden loosing of underground rock mass or the leakage of underground water, so it is fairly complex to predict horizontal loading on a tunnel support. To predict the horizontal load on this component is defined as the problem that determines the horizontal load conditions in wedges of tunnel support. This is an optimization problem in which maximum bending stress and horizontal load are considered by an objective function and design variables, respectively. Therefore, in this study, design of experiments and optimization algorithm were applied to identify the horizontal load in tunnel support.

Building of Large Triaxial Testing Apparatus and Static Triaxial Testing for Railway Ballast (대형삼축압축시험장비 구축과 도상자갈의 정적압축시험 평가)

  • Lee, Sung-Jin;Kim, Yun-Ki;Lee, Il-Wha;Lee, Jun-S.;Park, Jae-Jun
    • Journal of the Korean Society for Railway
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    • v.13 no.1
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    • pp.84-91
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    • 2010
  • We built multi-purpose large triaxial testing system that can test and evaluate various geotechnical design parameters such as shear strength, deformation modulus and stress-strain behaviour for large diameter granular materials, which are the most commonly used construction materials in the railway, road embankments. The details of the built testing system and the results obtained from static triaxial test carried out for gneiss ballast material are discussed within the scope of this paper. Ballast is hardly saturated and is confined at low overburden pressure, since the depth is shallow and the permeability is very high. Herein we ascertained that the confining pressure can effectively be controlled by vacuum. The rational trend could be checked up through triaxial test results such as shear strength, deformation, and particle breakage. And the shear strength envelope could be non-linearly represented with the parent rock strength, confining pressure of the triaxial test and proper parameters.

A Study on the Concrete Lining Behavior due to Tunnel Deterioration (터널 열화로 인한 콘크리트 라이닝의 거동에 관한 연구)

  • Han, Young-Chul;Jeong, Sang-Seom
    • Journal of the Korean Geotechnical Society
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    • v.30 no.4
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    • pp.21-34
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    • 2014
  • This paper studies the time-dependent behaviors of tunnel and surrounding ground due to tunnel deterioration. In the first part, the literature on deterioration characteristics of tunnels was reviewed. In the second part, a numerical analysis was performed to investigate the behavior of concrete lining on the typical section of Korean high-speed rail tunnel (weathered rock) after determination of input variables related to deterioration impact. The result shows that the settlement at the crown of tunnel and surface ground increased up to 7.0% and 30.2% of the total settlements during construction stage, respectively, and the internal convergence reduction of 9.0 mm for concrete linings was generated within 30 years after completion of tunnel construction. Also the loosening height increased up to 2.55 times of tunnel height within 50 years, which is higher than that of Terzaghi's recommendation on ultimate state. Due to this process of extending zones, it is found that additional loads were applied to concrete lining with the axial stress about 3.20~3.66 MPa, which accelerates tunnel deterioration. Finally the quantitative design approach to evaluate time-dependent behavior of lining and surrounding ground due to tunnel deterioration was proposed.

Experimental Study of Thermal-mechanical Influence on the Hydraulic Properties of Rock (암반의 수리인자에 미치는 열적.역학적 영향에 대한 실험적 검증)

  • 전석원;홍창우;이주현;강주명;배대석
    • Journal of the Korean Geotechnical Society
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    • v.19 no.5
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    • pp.59-67
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    • 2003
  • In this study, the change in hydraulic conductivity according to the changes in the contact area, aperture, confining pressure and temperature was observed to improve the reliability of the analysis of underground water flow. Also, the mechanical and thermal properties of domestic crystalline rocks in a great depth were obtained. It was found that the averaged intial aperture ranged from 544.33${\mu}{\textrm}{m}$ to 898.62${\mu}{\textrm}{m}$ and it followed a log-normal distribution. The hydraulic conductivity decreased with the increase of normal stress on the fracture surface and the hydraulic conductivity decreased as temperature increased. The change in hydraulic conductivity was strongly correlated with the change in contact area. It was verified by experiments that hydraulic conductivity was inversely proportional to the contact area. The measured mechanical and thermal properties were very close to the existing typical properties of domestic granites.

A Study on the Behaviour of an Earth and Rockfill Dam Due to Reservoir Water (저수변화에 따른 사력댐의 거동 연구)

  • Shin, Jong-Ho
    • Journal of the Korean Geotechnical Society
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    • v.19 no.6
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    • pp.61-70
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    • 2003
  • The behaviour of an earth and rock-fill dam is complicated due to reservoir water and various materials in zoned dams. Different materials with a wide range of permeability and seasonal variation of reservoir water result in the time dependent post-constructional behaviour. In aged dams it is often required to control water level to keep the dams safe. In this case information on the post-constructional dam behaviour is important. However, present geotechnical knowledge does not fully support the occasion. In this study the post-constructional behaviour of a dam is investigated using coupled finite element models for series of idealized water reservoir cases: impoundment, draw down, seasonal fluctuation with different rising and falling speeds. Numerical results were analysed in respect of geotechnical parameters such as load transfer, hydraulic fracturing potential and stress paths. It is shown that the control of water level is an important factor while operating dams.

Seismic behaviors of twin tunnel with flexible segment (Flexible Segment가 설치된 병렬터널의 지진시 동적거동)

  • Kwak, Chang-Won;Park, Inn-Joon
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.17 no.6
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    • pp.695-702
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    • 2015
  • Recently, the improvement of mechanical and theoretical issues in geo-centrifuge test enhances the applicability and accuracy of the test. Geo-centrifuge test is appropriate to simulate the behaviors of underground structures like tunnel, since tunnel interacts with the soil and/or rock around it and the test can embody the in-situ stress conditions effectively. In this study, the seismic behaviors of twin tunnel were analyzed based on geo-centrifuge test. Flexible segment to mitigate seismic acceleration were implemented in the model with thin and thick thickness. Based on the test results, it was found that flexible segment can decrease the peak acceleration generally, however, thin flexible segment was not able to reduce peak acceleration in short-period seismic wave. Thick flexible segment was more effective in case of high bedrock acceleration condition. Additionally, 3-dimensional numerical analysis was performed to verify the characteristics of seismic behavior and the effect of flexible segment. Consequently, the numerical analysis result showed good agreement with the test result.

Consideration on design procedure of room-and-pillar underground structure part II: selection of shape to design supports (주방식 지하구조물의 설계 방법 고찰 Part II: 지보 설계 필요 단면 검토)

  • Lee, Chulho;Hur, Jinsuk;Hyun, Younghwan;Chang, Soo-Ho
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.16 no.5
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    • pp.497-506
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    • 2014
  • In this study, analysis results described in the companion paper was used to determine shapes of room-and-pillar underground structure. To select optimized shapes, structural stability, space applicability and vehicle applicability were considered. In the structural stability step, ratio between strength and stress of the pillar and the critical strain at the roof span were adopted. The space applicability was used to retain the sufficient space of underground structure as its purpose is for human activity. The vehicle applicability was used to consider a radius for rotation of construction equipments in the room-and-pillar underground structure. From the given procedure in this study, proper shapes of rock pillar and room can be selected to design supports at the pillar and roof.