[논문]Voronoi 입자기반 개별요소모델을 이용한 암석 균열의 열에 의한 미끄러짐 해석: 국제공동연구 DECOVALEX-2023 Task G(Benchmark simulation)

박정욱; 박찬희; 이창수

doi:10.7474/tus.2021.31.6.593

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

터널과 지하공간: 한국암반공학회지 = Tunnel and underground space, v.31 no.6, 2021년, pp.593 - 609

박정욱 (한국지질자원연구원) , 박찬희 (한국지질자원연구원) , 이창수 (한국원자력연구원)

초록
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본 연구에서는 입자기반 개별요소모델(grain-based distinct element model, GBDEM)을 이용하여 결정질 암석 내 포함된 균열의 열-역학적 거동을 평가할 수 있는 수치해석기법을 제시하고 열에 의한 균열의 미끄러짐 거동을 해석하였다. 이는 DECOVALEX-2023 프로젝트 Task G의 일환으로 수행된 벤치마크 모델링 연구로, Task G는 결정질 암반 내 균열의 열-수리-역학적 복합거동을 해석하기 위한 수치해석기법을 개발하는 데에 목표가 있다. 여기에서는 Voronoi diagram을 이용하여 다면체 개별입자의 집합체로서 해석모델을 생성하고, 입자 및 입자간 접촉에서 발생하는 열-역학적 거동을 개별요소프로그램인 3DEC을 통해 해석하였다. 암석 시험편의 탄성거동을 재현하기 위하여 등가연속체 개념을 적용하여 입자와 접촉의 미시물성을 산정하였으며, 균열에 상응하는 접촉에는 Coulomb slip model을 부여하여 인장강도와 전단강도를 갖는 불연속면을 모사하였다. 경계응력과 열응력에 의한 균열의 거동을 수치적으로 모델링하였으며, 경계조건에 따라 균열의 미끄러짐이 발생하는 열-역학적 메커니즘을 정량적으로 분석하였다. 해석 결과, 본 연구에서 제시한 해석모델이 암석 내 열팽창과 열응력의 증가, 균열 응력과 변위, 경계조건의 영향 등을 합리적으로 재현하고 있음을 확인하였다. 본 연구의 해석모델은 Task G에 참여하는 국외 연구팀들과의 의견 교류와 워크숍을 통해 지속적으로 개선하는 한편, 향후 실내실험에 적용하여 타당성을 검증할 예정이다.

Abstract ▼ AI-Helper

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.

주제어

표/그림 (17)

표 Table 1. Coupled thermo-mechanics benchmark model condition
$Fig. 1. Creation of a single fracture embedded in Voronoi diagram using Neper, Gmsh and 3DEC by (a) splitting domain into two halves and (b) merging partial blocks$ 그림 Fig. 1. Creation of a single fracture embedded in Voronoi diagram using Neper, Gmsh and 3DEC by (a) splitting domain into two halves and (b) merging partial blocks
그림 Fig. 2. Model generation for thermo-mechanics benchmark
그림 Fig. 3. Boundary condition of thermo-mechanics benchmark model
$Fig. 4. Numerical result at completion of mechanical loading (before heating): (a) rock displacement magnitude, (b) fracture normal stress and (c) fracture shear stress magnitude$ 그림 Fig. 4. Numerical result at completion of mechanical loading (before heating): (a) rock displacement magnitude, (b) fracture normal stress and (c) fracture shear stress magnitude
$Fig. 5. Theoretically and numerically calculated fracture stress states under the given boundary stress (before heating)$ 그림 Fig. 5. Theoretically and numerically calculated fracture stress states under the given boundary stress (before heating)
그림 Fig. 6. Contour plots of temperatures at T_c = 11°C, 20°C, 30°C, 40°C and 50°C
그림 Fig. 7. Fracture temperature change over time
그림 Fig. 8. Changes in boundary stress and rock stress at center over time
$Fig. 9. Changes in normal and shear stresses of fracture contacts with increasing temperature and Mohr's circle presentation of boundary stresses at T<sub>c</sub> = 11°C and 50°C$ 그림 Fig. 9. Changes in normal and shear stresses of fracture contacts with increasing temperature and Mohr's circle presentation of boundary stresses at T_c = 11°C and 50°C
$Fig. 10. Numerical result at completion of thermal loading (after heating): (a) rock displacement magnitude (unit: m), (b) fracture normal stress (unit: Pa) and (c) fracture shear stress magnitude (unit: Pa)$ 그림 Fig. 10. Numerical result at completion of thermal loading (after heating): (a) rock displacement magnitude (unit: m), (b) fracture normal stress (unit: Pa) and (c) fracture shear stress magnitude (unit: Pa)
그림 Fig. 11. Boundary condition of thermo-mechanics benchmark model – Case 2
그림 Fig. 12. Changes in boundary stress and rock stress at center over time – Case 2
$Fig. 13. Changes in normal and shear stresses of fracture contacts with increasing temperature and Mohr's circle presentation of boundary stresses at T<sub>c</sub> = 11°C and 50°C – Case 2$ 그림 Fig. 13. Changes in normal and shear stresses of fracture contacts with increasing temperature and Mohr's circle presentation of boundary stresses at T_c = 11°C and 50°C – Case 2
그림 Fig. 14. Contour plots of rock displacement magnitudes (unit: m) at T_c = 11°C, 20°C, 30°C, 40°C and 50°C
$Fig. 15. Change in fracture shear displacement with temperature$ 그림 Fig. 15. Change in fracture shear displacement with temperature
$Fig. 16. Fracture shear displacement vs. fracture position (r: position relative to fracture center)$ 그림 Fig. 16. Fracture shear displacement vs. fracture position (r: position relative to fracture center)

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