大理岩真三轴卸载强度特征与破坏力学模式

Unloading strength and failure pattern of marble under true triaxial test

深部高储能岩体开挖导致应变能释放,并引起快速的卸载破坏,形成岩爆等严重的工程灾害。根据锦屏水电站地下厂房工程环境以及开挖扰动特征,采用真三轴卸载实验、声发射监测、SEM电镜扫描等手段,对高储能岩体在不同应力路径与荷载速率下的卸载强度和破裂演化特征进行研究。实验结果表明:真三轴卸载条件下,大理岩宏观破坏与常规压缩实验过程有显著差别,高储能岩体受卸载路径及卸载速率控制,表现出原位强度为c0.45σ~c0.6σ。结合SEM扫描电镜图像以及声发射参数特征揭示,大理岩卸载破坏呈现张性萌生–剪切交汇–贯通破坏的渐进过程,并受不同的应力路径、卸载速率影响显著。基于上述卸载渐进破坏力学模式,采用劈裂界线、修正的Griffith强度曲线和非线性Mohr-Coulomb强度曲线的组合来解释原位岩体破坏的"S"型曲线规律。研究结果为认识不同条件下地下工程建设中岩爆等快速卸载破坏的形成机制提供理论依据。

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 0.45σ_c–0.6σ_c,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.