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对于锦屏二级引水隧洞,脆性岩体破裂损伤发展的时间效应已从现场围岩破坏情况及多种监测仪器长期监测数据中得到反映,成为影响引水隧洞长期稳定性的控制因素。为系统研究这一问题,针对锦屏二级引水隧洞沿线所占比例最大的岩层之一——白山组大理岩,在论述岩体破裂扩展时间效应的现场体现的基础上,进行破裂时效室内试验,得到破裂时效拟合式和临界驱动应力比;继而采用CPM模型建立可以考虑脆–延–塑转换特征的白山组大理岩数值试样,标定其微观参数,并进行室内破裂扩展试验的PFC模拟;最后,首次对工程尺度的引水隧洞进行破裂扩展时效的PFC模拟,研究不同岩性、不同埋深下,在100 a运行期内引水隧洞围岩的破裂情况。结果表明,室内试验中破坏时间的增加和荷载的降低呈现出较明显的指数非线性关系,且亚临界裂纹开始扩展,具有一个门槛值(定义为临界驱动应力比),对于白山组大理岩此应力比为0.492。采用CPM模型标定的PFC短期细观参数可较好反映锦屏白山组大理岩试样的三轴压缩应力–应变曲线及屈服破坏特征表现出的明显围压相关性,低围压下裂纹数目随围压增加明显,高围压下增加速度减缓,且拉裂纹在高围压下数目不再随围压增高而增加。数值试验中发现轴向应变和裂纹数目发展均表现出明显的蠕变三阶段特征。随着驱动应力比减少,由蠕变产生的应变量值是增加的。侵蚀裂纹的发展也符合蠕变三阶段特征,驱动应力比越小,侵蚀裂纹数目基本线性增加,但侵蚀裂纹发展速率呈指数减少。在开挖完成100 a后,II类大理岩岩体中引水隧洞的破裂区最大范围为2.1~3.1 m,III类大理岩为3.3~4.5 m,引水隧洞的长期稳定性可以得到较好保障。
The time effect of the development of the fracture damage of brittle rock mass in the Jinping second-stage diversion tunnel has been reflected by the on-site surrounding rock failure and long-term monitoring data of various monitoring instruments, becoming the control factor that affects the long-term stability of the diversion tunnel. In order to systematically study this problem, aiming at the marble of Baishan Formation, one of the rock formations with the largest proportion along Jinping II diversion tunnel, on the basis of the on-site reflection of the time effect of rock mass rupture expansion, , Then the fracture age and critical stress ratio were obtained. Then, the CPM model was used to establish the marble specimen of the Baishan Formation, which can consider the brittle - ductile - plastic transformation characteristics. The microscopic parameters were calibrated and the PFC simulation Finally, for the first time, the PFC simulation of the engineering scale of the diversion tunnel is carried out under the condition of rupture and extension aging. The rupture of the surrounding rock of the diversion tunnel is investigated under different lithologies and depths for 100 years. The results show that the increase of failure time and the decrease of load show obvious exponential nonlinearity, and the subcritical crack begins to expand with a threshold value (defined as the critical driving stress ratio). For the Baishan Formation marble The stress ratio is 0.492. The short-term fine parameters of PFC calibrated by CPM model can well reflect the obvious confining pressure correlations of triaxial compression stress-strain curves and yield failure characteristics of marble samples of Jinpingbaishan Formation. The number of cracks under low confining pressure The confining pressure increased obviously, the increasing speed slowed down under the high confining pressure, and the number of the crazing cracks at the high confining pressure no longer increased with the confining pressure increasing. Numerical tests show that both the axial strain and the number of cracks show obvious three-phase creep characteristics. As the drive stress ratio decreases, the magnitude of the strain due to creep increases. The development of erosion cracks also accords with the creep three-stage characteristics. The smaller the ratio of driving stress is, the more the number of erosion cracks increases linearly, but the growth rate of erosion cracks decreases exponentially. After 100 years of excavation, the maximum range of the fractured zone of the diversion tunnel in the type II marble rock mass is 2.1-3.1 m and that of the type III marble is 3.3-4.5 m. The long-term stability of the diversion tunnel can be well protected.