• Title/Summary/Keyword: rock tunnel

Search Result 2,167, Processing Time 0.026 seconds

Characteristics of Creep Deformation Behavior of Granite under Uniaxial Compression (단축압축하중을 받는 대전 화강암의 크립 변형거동 특성에 관한 연구)

  • 홍지수;전석원
    • Tunnel and Underground Space
    • /
    • v.14 no.1
    • /
    • pp.69-77
    • /
    • 2004
  • Investigation of the time-dependent behavior of rock and the associated mechanisms are of key interest in long-term stability analysis of many engineering applications. In this study, creep tests were performed on Daejeon granite samples of 25.4mm diameter under uniaxial compression at varying stress levels. The effect of moisture was investigated by testing both air-dried and fully water-saturated samples. The creep behavior of Daejeon granite exhibited three distinctive stages of primary, secondary and tertiary creep. The ultimate strength of granite under a constant stress decreased considerably with time. Saturation and immersion of the test specimen in water markedly increased the total creep strain as well as the secondary creep rate. The experimental creep curves are fitted to Burger's model as well as two other empirical models suggested by previous researchers. A number of the parameters determined for each model are dependent on stress and influenced by the presence of water. Based on the experimental results, an empirical relation between the applied stress and the time-dependent strain is established separately for each air-dried and fully water-saturated Daejeon granite.

Estimation of the Characteristics of Delayed Failure and Long-term Strength of Granite by Brazilian Disc Test (압열인장시험을 이용한 화강암의 지연파괴특성 및 장기안정성 평가)

  • Jung, Yong-Bok;Cheon, Dae-Sung;Park, Eui-Seob;Park, Chan;Lee, Yun-Su;Park, Chul-Whan;Choi, Byung-Hee
    • Tunnel and Underground Space
    • /
    • v.24 no.1
    • /
    • pp.67-80
    • /
    • 2014
  • Long-term stability and delayed failure of granite were evaluated through the laboratory test based on Wilkins method and Brazilian disc test (BDT) which yields tensile strength, mode I fracture toughness and subcritical crack growth parameters. Then, the long-term strength of granite was estimated by using analytical models and long-term stability of compressed air-energy storage (CAES) pilot cavern pressurized up to 5 ~ 6 MPa was evaluated using numerical code, FRACOD with the determined subcritical crack growth parameters. The results of test and analyses showed that the subcritical crack growth index, n was determined as 29.39 and the inner pressure of 5 ~ 6 MPa had an insignificant effect on the long-term stability of pilot cavern. It was also found that the measurement and analysis of acoustic emission events can describe the accumulation of damage due to subcritical crack growth quantitatively. That is, AE monitoring can provide the current status of rock under loading if we make an identical installation condition in the field with that of the laboratory test.

Mine Haulage System Design for Reopening of Yangyang Iron Mine using 3D Modelling (3차원 모델링을 이용한 재개광 양양철광의 운반시스템 설계)

  • Son, Youngjin;Kim, Jaedong
    • Tunnel and Underground Space
    • /
    • v.22 no.6
    • /
    • pp.412-428
    • /
    • 2012
  • To achieve mine development, a large amount of data concerned with the geological structure and the ore body had to be investigated and collected through geological survey, drilling and geophysical explorations. In most previous cases, however, the data were usually analyzed two dimensionally and those results showed some limits because of their 2D presentation. Those 2D maps such as geological plane sections or longitudinal sections cause lots of difficulties in understanding the complex geological structure or the feature of ore body in a spatial way. In this study, research area was set on the abandoned Yangyang iron mine in Korea and the Sugaeng ore body within the mine was selected as the research target to design a mine haulage system for reopening. A 3D mine model of this area was tried to be constructed using a 3D modelling software, GEMS. An accurate 3D model including the ore body, the geological structure, the old underground mine drifts and the new mine drifts was constructed under the purpose of reopening of the abandoned iron mine. Especially, mine design for trackless haulage system was conducted. New inclines and drifts were planned and modelled 3 dimensionally considering the utilization of old drifts and shaft. In addition to the 3D modelling, geostatistical technique was adopted to generate a spatial distribution of the ore grade and the rock physical properties. 3D model would be able to contribute in solving problems such as evaluating ore reserves, planning the mine development and additional explorations and changing the development plans, etc.

Equivalent Friction Angle and Cohesion of the Generalized Hoek-Brown Failure Criterion in terms of Stress Invariants (응력불변량으로 표현한 일반화된 Hoek-Brown 파괴조건식의 등가 마찰각 및 점착력)

  • Lee, Youn-Kyou;Choi, Byung-Hee
    • Tunnel and Underground Space
    • /
    • v.22 no.6
    • /
    • pp.462-470
    • /
    • 2012
  • Implementing the generalized Hoek-Brown failure criterion in the framework of the Mohr-Coulomb criterion requires the calculation of the equivalent friction angle and cohesion. In the conventional method based on the Balmer (1952)'s theory, the tangential instantaneous friction angle and cohesion are expressed in terms of the minimum principal stress ${\sigma}_3$, which does not provide the information about the dependency of the equivalent parameters on the hydrostatic pressure and the stress path. In this study, this defect of the conventional method has been overcome by representing the equivalent parameters in terms of stress invariants. Through the example implementation of the new method, the influence of the magnitude of the hydrostatic pressure and the Lode angle on the tangential instantaneous friction angle and cohesion is investigated. It turns out that the tangential instantaneous friction angle is maximum when the stress condition is triaxial extension, while the tangential cohesion is maximum when the stress condition is triaxial compression. The dependency of the equivalent Mohr-Coulomb strength parameters on the hydrostatic pressure and the Lode angle tends to be more substantial for the favorable rockmass of larger GSI value.

A Study on the Prediction of HLW Temperature from Natural Ventilation Quantity using CFD (전산유체학을 이용한 고준위 방사성 폐기물 처분장의 자연환기량에 의한 온도예측)

  • Roh, Jang-Hoon;Yu, Yeong-Seok;Jang, Seung-Hyun;Park, Seon-Oh;Kim, Jin
    • Tunnel and Underground Space
    • /
    • v.22 no.6
    • /
    • pp.429-437
    • /
    • 2012
  • This study predicted temperature in the disposal tunnels using computational fluid dynamics based on natural ventilation quantity that comes from high altitude and temperature differences that are the characteristics of high level waste repository. The result of the previous study that evaluated quantitatively natural ventilation quantity using a hydrostatic method and CFD shows that significant natural ventilation quantity is generated. From the result, this study performed the prediction of temperature in disposal tunnels by natural ventilation quantity by the caloric values of the wastes, at both deep geological repository and surface repository. The result of analysis shows that deep geological repository is effective for thermal control in the disposal tunnels due to heat transfer to rock and the generation of sufficient natural ventilation quantity, while surface repository was detrimental to thermal control, because surface repository was strongly affected by external temperature, and could not generate sufficient natural ventilation quantity. Moreover, this study found that in the case of deep geological repository with a depth of 200 m, the heatof about $10^{\circ}C$ was transferred to the depth of 500 m. Thus, it is considered that if the high level waste repository scheduled to be built in the country is designed placing an emphasis on thermal control, deep geological repository rather than surface repository is more appropriate.

Variations of Physico-Mechanical Properties of the Cretaceous Mudstone in Haman, Gyeongnam due to Freeze-Thaw Weathering (경남 함안군 백악기 이암의 동결-융해에 따른 물성변화 및 미세균열 발현특성)

  • Um, Jeong-Gi;Shin, Mi-Kyoung
    • Tunnel and Underground Space
    • /
    • v.19 no.2
    • /
    • pp.146-157
    • /
    • 2009
  • An experimental study of accelerated weathering on mudstone sample specimens from Haman, Gyeongnam was performed to investigate the variations of physico-mechanical properties of deteriorated rocks due to freeze-thaw weathering. Each complete cycle of freeze and thaw lasted 24 hours, comprising 2 hours of saturating in vacuum chamber, 8 hours of freezing at $-16{\pm}1^{\circ}C$ and 14 hours of thawing at room temperature. Total of 55 cycles of freeze-thaw were completed with measuring the index properties as well as geometries of microfractures. The measured specific gravity and P-wave velocity found to decrease with increasing freeze-thaw cycles. On the other hand, absorption ratio and effective porosity were continuously increased with increasing freeze-thaw cycles. It was found that the index properties of deteriorated sample specimen depend on its initial properties and flaws in rock. The size and density of the traces of the microfracture on slab specimen exhibited abrupt changes after 30 cycles of freeze-thaw weathering. The results obtained in this study show that the box fractal dimension($D_B$) given in this paper has the strong capability of quantifying the size and density of the microfracture.

Development and Verification of OGSFLAC Simulator for Hydromechanical Coupled Analysis: Single-phase Fluid Flow Analysis (수리-역학적 복합거동 해석을 위한 OGSFLAC 시뮬레이터 개발 및 검증: 단상 유체 거동 해석)

  • Park, Chan-Hee;Kim, Taehyun;Park, Eui-Seob;Jung, Yong-Bok;Bang, Eun-Seok
    • Tunnel and Underground Space
    • /
    • v.29 no.6
    • /
    • pp.468-479
    • /
    • 2019
  • It is essential to comprehend coupled hydro-mechanical behavior to utilize subsurface for the recent demand for underground space usage. In this study, we developed a new simulator for numerical simulation as a tool for researching to consider the various domestic field and subsurface conditions. To develop the new module, we combined OpenGeoSys, one of the scientific software package that handles fluid mechanics (H), thermodynamics (T), and rock and soil mechanics (M) in the subsurface with FLAC3D, one of the commercial software for geotechnical engineering problems reinforced. In this simulator development, we design OpenGeoSys as a master and FLAC3D as a slave via a file-based sequential coupling. We have chosen Terzaghi's consolidation problem related to single-phase fluid flow at a saturated condition as a benchmark model to verify the proposed module. The comparative results between the analytical solution and numerical analysis showed a good agreement.

A Novel Method for In Situ Stress Measurement by Cryogenic Thermal Cracking - Concept Theory and Numerical Simulation (저온 열균열 현상을 이용한 초기 응력 측정법 - 개념, 이론 및 수치해석)

  • Ryu, Chang-Ha;Ryu, Dong-Woo;Choi, Byung-Hee;Synn, Dong-Ho;Loui, John P.
    • Tunnel and Underground Space
    • /
    • v.18 no.5
    • /
    • pp.343-354
    • /
    • 2008
  • A new method is suggested herein to measure the virgin earth stresses by means of a borehole. This novel concept is basically a combination of borehole stress relieving and borehole fracturing techniques. The destressing of the borehole is achieved by means of inducing thermal tensile stresses at the borehole periphery by using a cryogenic fluid such as Liquid Nitrogen($LN_2$). The borehole wall eventually develops fractures when the induced thermal stresses exceed the existing compressive stresses at the borehole periphery in addition to the tensile strength of the rock. The above concept is theoretically analyzed for its potential applicability to interpret in situ stress levels from the tensile fracture stresses and the corresponding borehole wall temperatures. Coupled thermo-mechanical numerical simulations are also conducted using FLAC3D, with thermal option, to check the validity of the proposed techniques. From the preliminary theoretical and numerical analysis, the method suggested for the measurement of in situ stresses appears to be capable of accurate estimation of the virgin stresses by monitoring tensile crack formation at a borehole wall and recording the wall temperatures at the time of crack initiation.

Introduction of International Cooperation Project, DECOVALEX from 2008 to 2019 (2008년부터 2019년까지 수행된 국제공동연구 DECOVALEX 소개)

  • Lee, Changsoo;Kim, Taehyeon;Lee, Jaewon;Park, Jung-Wook;Kwon, Seha;Kim, Jin-Seop
    • Tunnel and Underground Space
    • /
    • v.30 no.4
    • /
    • pp.271-305
    • /
    • 2020
  • An effect of coupled thermo-hydro-mechanical and chemical (THMC) behavior is an essential part of the performance and safety assessment of geological disposal systems for high-level radioactive waste and spent nuclear fuel. Furthermore, numerical models and modeling techniques are necessary to analyze and predict the coupled THMC behavior in the disposal systems. However, phenomena associated with the coupled THMC behavior are nonlinear, and the constitutive relationships between them are not well known. Therefore, it is challenging to develop numerical models and modeling techniques to analyze and predict the coupled THMC behavior in the geological disposal systems. It is also difficult to verify and validate the development of the models and techniques because it requires expensive laboratory tests and in-situ experiments that need to be performed for a long time. DECOVALEX was initiated in 1992 to efficiently develop numerical models and modeling techniques and validate the developed models and techniques against the lab and in-situ experiments. In Korea, Korea Atomic Energy Research Institute has participated in DECOVALEX-2011, DECOVALEX-2015, and DECOVALEX-2019 since 2008. In this study, all tasks in the three DECOVALEX projects were introduced to the researcher in the field of rock mechanics and geotechnical engineering in Korea.

Properties of Disconitinuity for the Seoul Granite in the Northeastern Part of Seoul City (서울시 북동부의 서울화강암에 대한 불연속면의 특성)

  • 정상원;정상용
    • The Journal of Engineering Geology
    • /
    • v.12 no.2
    • /
    • pp.167-178
    • /
    • 2002
  • Properties of discontinuity for Seoul Granite in northeastern part of Seoul City were analyzed by dividing structural domains into Surak and Bulam Mtn. areas. Important parameters measured among several engineering properties of a rock during tunnel excavation and road construction are as follows: 1) Orientation of joint, 2) joint spacing, 3) joint density, and 4) uniaxial compressive strength. Orientation, spacing, and density of joints can be directly measured during field investigation using scanline survey, circle-inventory method, and window survey. Uniaxial compressive strength of the rock was calculated by a simple correlation equation although it is originally necessary to prepare core samples in measuring it. Major orientations of joints measured from both areas are 3 sets of joints with different orientations. In other words, they are 2 sets of orthogonal joint and 1 set of sheet joint that is dipping at low angle, and have very similar orientations in both areas. Joint densities in both areas range from 0.039 and 0.066/cm, and average joint length are between 1.30 and 4.52m. Average joint spacing also has values from 10.3cm up to 59.6cm, and shows significant difference along specific orientation of scanlines measured. Values of uniaxial compressive strength calculated on the basis of Schmidt hammer rebound values range from 217 to 335 MPa, which indicates very strong rock type by classification of wall strength.