| 1. |
- He, Chen, et al.
(författare)
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True-triaxial simulation of sandstone with full range of σ2 based on the Rigid-Body-Spring method
- 2024
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Ingår i: Computers and geotechnics. - : Elsevier BV. - 0266-352X .- 1873-7633. ; 165
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Tidskriftsartikel (refereegranskat)abstract
- Accurately simulating the mechanical properties of rock under true-triaxial stress conditions (σ1 > σ2 > σ3) is crucial for understanding deep underground rock masses. Although discrete approaches have advantages in describing rock fracturing behavior, further development seems necessary for quantitatively simulating the intermediate principal stress σ2 effects on rock strength. In this paper, we study the failure mechanisms of microscopic contacts of a discrete approach, the modified Rigid-Body-Spring Method (mRBSM), in response to σ2. Numerical results indicate that the model calibrated by axisymmetric-triaxial tests underestimates the strength of Yunnan sandstone when the stress state approaches σ2 = σ1. To address this discrepancy, we propose a new microscopic contact failure criterion that takes into consideration not only the normal and shear stresses on the contact but also the average Cauchy stress tensor around the contact. Results show that the mRBSM with the new failure criterion is able to reproduce the true-triaxial strength of Yunnan sandstone more accurately than the original model, especially under high σ2 and σ3 conditions. In addition, the corresponding stress–strain curves and failure modes under the influence of σ2 still show reasonable trends under true-triaxial stress conditions. This study indicates that when simulating rock failure under three-dimensional stress conditions using the rigid-body-spring system, the contact failure criterion might be influenced by the local stress state.
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| 2. |
- Jin, Yunzhe, et al.
(författare)
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Effects of in-situ stress on heat transfer in fracture networks
- 2024
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Ingår i: Geomechanics for Energy and the Environment. - : Elsevier BV. - 2352-3808. ; 37
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Tidskriftsartikel (refereegranskat)abstract
- Stress-induced fracture deformation is the principal cause for permeability change in geothermal systems. This study focuses on the influence of the nonlinear deformation and dilation effect of fractures on the geothermal system under the action of in-situ stress. By adopting a nonlinear constitutive model of rock fractures and embedding discrete fracture networks, numerical studies are first conducted to investigate the effects of different in-situ stress schemes on fracture aperture evolution using a rigid-body spring method. Based on the anisotropic aperture field of the fracture network caused by the in-situ stress, a finite element method is then used to study the flow and heat transfer process. The effects of different stress schemes on the heat flow transfer process are analyzed. Numerical simulation results show that when the ratio of horizontal to vertical stresses is not sufficient to cause shear dilation effects, the nonlinear normal deformation is the main factor affecting flow and heat transfer. In this case, the heat extraction efficiency is reduced. As the stress ratio increases, the shear dilation gradually becomes the dominant mechanism, and the heat extraction performance is improved. The obtained results provide a practical guide for geothermal site siting and optimizing heat extraction efficiency in geothermal reservoirs.
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| 3. |
- Jin, Yunzhe, et al.
(författare)
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Experimental and numerical simulation study on the evolution of mechanical properties of granite after thermal treatment
- 2024
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Ingår i: Computers and geotechnics. - : Elsevier BV. - 0266-352X .- 1873-7633. ; 172
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Tidskriftsartikel (refereegranskat)abstract
- High temperature significantly influences the mechanical properties of granite, which is relevant to various engineering applications, including geothermal energy extraction. The objective of this study is to investigate the meso-mechanics of granite, specifically focusing on the formation of thermal cracks and the temperature-dependent mechanical properties in heterogeneous rock. Firstly, we heat the granite to 25–1000 ℃ by muffle furnace. Following this, we conduct triaxial compression tests with 0–20 MPa confining pressures on the heated-specimens cooled by cold water. Subsequently, we combine the grain-based model (GBM) and the finite-discrete element method (FDEM) to simulate the heat treatment process and the triaxial experiments. We calibrate the micromechanical parameters of granite by experimental results. Results show that the mechanism behind the formation of thermal cracks in granite subjected to high-temperature is the differential thermal expansion coefficients of mineral particles in granites, leading to the degradation of mechanical properties in thermal-treated granite. The temperature threshold for the formation of thermal cracks is between 500 °C and 550 °C. Particularly, the stress-strain curve of granite exhibits ideal elastic-plastic characteristics under temperature is 1000 °C. These results can help to demonstrate the temperature-dependent evolution of mechanical properties of crystalline rocks, providing a theoretical basis for the utilization of engineering applications.
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