• Title/Summary/Keyword: Micro-mechanics

Search Result 374, Processing Time 0.018 seconds

Voronoi Grain-Based Distinct Element Modeling of Thermally Induced Fracture Slip: DECOVALEX-2023 Task G (Benchmark Simulation) (Voronoi 입자기반 개별요소모델을 이용한 암석 균열의 열에 의한 미끄러짐 해석: 국제공동연구 DECOVALEX-2023 Task G(Benchmark simulation))

  • park, Jung-Wook;Park, Chan-Hee;Lee, Changsoo
    • Tunnel and Underground Space
    • /
    • v.31 no.6
    • /
    • pp.593-609
    • /
    • 2021
  • We proposed a numerical method for the thermo-mechanical behavior of rock fracture using a grain-based distinct element model (GBDEM) and simulated thermally induced fracture slip. The present study is the benchmark simulation performed as part of DECOVALEX-2023 Task G, which aims to develop a numerical method to estimate the coupled thermo-hydro-mechanical processes within the crystalline rock fracture network. We represented the rock sample as an assembly of Voronoi grains and calculated the interaction of the grains (blocks) and their interfaces (contacts) using a distinct element code, 3DEC. Based on an equivalent continuum approach, the micro-parameters of grains and contacts were determined to reproduce rock as an elastic material. Then, the behavior of the fracture embedded in the rock was characterized by the contacts with Coulomb shear strength and tensile strength. In the benchmark simulation, we quantitatively examined the effects of the boundary stress and thermal stress due to heat conduction on fracture behavior, focusing on the mechanism of thermally induced fracture slip. The simulation results showed that the developed numerical model reasonably reproduced the thermal expansion and thermal stress increment, the fracture stress and displacement and the effect of boundary condition. We expect the numerical model to be enhanced by continuing collaboration and interaction with other research teams of DECOVALEX-2023 Task G and validated in further study experiments.

Comparison on Accuracy of Static and Dynamic Contact Angle Methods for Evaluating Interfacial Properties of Composites (복합재료의 계면특성 평가를 위한 접촉각 방법의 정확도 비교)

  • Kwon, Dong-Jun;Kim, Jong-Hyun;Park, Joung-Man
    • Journal of Adhesion and Interface
    • /
    • v.23 no.3
    • /
    • pp.87-93
    • /
    • 2022
  • To analyze the interfacial property between the fiber and the matrix, work of adhesion was used generally that was calculated by surface energies. In this paper, it was determined what types of contact angle measurement methods were more accurate between static and dynamic contact angle measurements. 4 types of glass fiber and epoxy resin were used each other to measure the contact angle. The contact angle was measured using two types, static and dynamic contact angle methods, and work of adhesion, Wa was calculated to compare interfacial properties. The interfacial property was evaluated using microdroplet pull-out test. Generally, the interfacial property was proportional to work of adhesion. In the case of static contact angle, however, work of adhesion was not consistent with interfacial property. It is because that dynamic contact angle measurement comparing to static contact angle could delete the error due to microdroplet size to minimize the surface area as well as the meniscus measuring error.

Numerical Modelling for the Dilation Flow of Gas in a Bentonite Buffer Material: DECOVALEX-2019 Task A (벤토나이트 완충재에서의 기체 팽창 흐름 수치 모델링: DECOVALEX-2019 Task A)

  • Lee, Jaewon;Lee, Changsoo;Kim, Geon Young
    • Tunnel and Underground Space
    • /
    • v.30 no.4
    • /
    • pp.382-393
    • /
    • 2020
  • The engineered barrier system of high-level radioactive waste disposal must maintain its performance in the long term, because it must play a role in slowing the rate of leakage to the surrounding rock mass even if a radionuclide leak occurs from the canister. In particular, it is very important to clarify gas dilation flow phenomenon clearly, that occurs only in a medium containing a large amount of clay material such as a bentonite buffer, which can affect the long-term performance of the bentonite buffer. Accordingly, DECOVALEX-2019 Task A was conducted to identify the hydraulic-mechanical mechanism for the dilation flow, and to develop and verify a new numerical analysis technique for quantitative evaluation of gas migration phenomena. In this study, based on the conventional two-phase flow and mechanical behavior with effective stresses in the porous medium, the hydraulic-mechanical model was developed considering the concept of damage to simulate the formation of micro-cracks and expansion of the medium and the corresponding change in the hydraulic properties. Model verification and validation were conducted through comparison with the results of 1D and 3D gas injection tests. As a result of the numerical analysis, it was possible to model the sudden increase in pore water pressure, stress, gas inflow and outflow rate due to the dilation flow induced by gas pressure, however, the influence of the hydraulic-mechanical interaction was underestimated. Nevertheless, this study can provide a preliminary model for the dilation flow and a basis for developing an advanced model. It is believed that it can be used not only for analyzing data from laboratory and field tests, but also for long-term performance evaluation of the high-level radioactive waste disposal system.

Report on Extended Leak-Off Test Conducted During Drilling Large Diameter Borehole (국내 대구경 시추공 굴진 중 Extended Leak-Off Test 수행 사례 보고)

  • Jo, Yeonguk;Song, Yoonho;Park, Sehyeok;Kim, Myung Sun;Park, In-Hwa;Lee, Changhyun
    • Tunnel and Underground Space
    • /
    • v.32 no.5
    • /
    • pp.285-297
    • /
    • 2022
  • We report results of Extended Leak-Off Test (XLOT) conducted in a large diameter borehole, which is drilled for installation of deep borehole geophysical monitoring system to monitor micro-earthquakes and fault behavior of major fault zones in the southeastern Korean Peninsula. The borehole was planned to secure a final diameter of 200 mm (or more) at a depth of ~1 km, with 12" diameter wellbore to intermediate depths, and 7-7/8" (~200 mm) to the bottom hole depth. We drilled first the 12" borehole to approximately 504 m deep and installed American Petroleum Institute standard 8-5/8" casing, then annulus between the casing and bedrock was fully cemented. XLOT was carried out for several purposes such as confirming casing and cementing integrity, measuring rock stress states. To that end, we drilled additional 4 m long open hole interval to directly inject water and pressurize into the rock mass using the upper API casings. During the XLOT, flow rates and interval pressures were recorded in real time. Based on the logs we tried to analyze hydraulic conductivity of the test interval.