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| Unloading strength and failure pattern of marble under true triaxial test |
| SHA Peng1,WU Faquan1,CHANG Jinyuan2 |
| (1. Centre of Rock Mechanics and Geological Disaster,College of Civil Engineering,Shaoxing University,Shaoxing,Zhejiang 312000,China;2. Zhejiang Engineering Investigation Institute,Ningbo,Zhejiang 315012,China) |
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Abstract Brittle rocks have high strain energy under high in-situ stress. The quick release of strain energy during excavation often leads to fast unloading deformation and failure in the rock,which may induce the intense engineering hazards like rock burst. Based on the real conditions of Jinping Hydropower Station,a series of true tri-axial unloading tests were carried out under different stress paths together with acoustic emission monitoring and scanning electron microscopy(SEM) analysis. We investigate the strength characteristics of and the fracture evolution in the high strain energy rock induced by fast unloading process. The results indicate that the strength under true tri-axial condition is remarkable smaller than compressive rock strength,characterized by – ,due to the unloading rate effect and the complexity of stress path. Acoustic emission(AE) system is used to monitor the failure process of rock tests. The characteristics of AE parameters were used to figure out the typical micro-fracture development of Jinping marble during the tests. The damage of rock initiates during the unloading cycle,with a number of tensile cracks generated in the specimen. The shear cracks are generated by the interconnection of tensile cracks to form the fracture,a large amount of elastic strain energy releases at the same time. The mechanism of the tensile-shear process is remarkably influenced by different stress paths and loading rates. This fracture pattern can be interpreted through a combination of modified Griffith′s strength theory,spalling limit and non-linear Mohr-Coulomb theory. All results can simulate well the different types of unloading failure process,such as rock burst in the large underground works.
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