脆性岩体破裂扩展时间效应对引水隧洞长期稳定性影响研究

 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。

INFLUENCE OF TIME-DEPENDENT OF CRACK PROPAGATION OF BRITTLE ROCK ON LONG-TERM STABILITY OF JINPING WATER DIVERSION TUNNEL

The time-dependent propagation of cracks was observed from the failure of field surrounding rock and the monitored data of the water diversion tunnels in Jinping and became the dominating factor of the long-term stability of the tunnel. A long-term loading test was conducted on the marble from Jinping leading to the establishment of a fitted formula for the time-dependent behavior and a threshold ratio of driving stresses. A numerical specimen based on CPM model was set up considering the transitional characteristics from brittle-ductile-plastic and a numerical test of long-term loading was performed. A full scale PFC-based model was constructed for the water diversion tunnel and the long-term stability of the tunnel with various depths and rock types was assessed. It was found that in the test the failure time varied with the loading level exponentially. The subcritical crack began to expand if only a threshold of stress level, termed as the critical ratio of driving stresses, was reached. The ratio is 0.492 for Jinping marbles. The CPM-based numerical specimen reproduced nicely the triaxial behavior and the effect of confining pressure. The growth trend of the crack numbers was notable under the lower confining stress，but less noticeable under the higher confining stress. The number of the tensile cracks remained unchanged under the higher confining stress. During the numerical test of long-term loading，the axial strain and the growth of the number of cracks were in accordance with the three stage curve of creep. As the ratios of the driving stresses decreased，the strains due to creep increased. The development of the cracks due to the stress corrosion was also in accordance with the three stage curve of creep. A smaller ratio of driving stress led to a linear growth of the number of cracks of stress-corrosion but an exponentially decreased rate of growth of it. The results of the full scale PFC simulation suggested that after 100 years，the fracture zone of the tunnel would be with the range of 2.1–3.1 m for the class II marble and 3.3–4.5 m for the class III marble. It was thus confirmed that the long-term stability of the water diversion tunnel could be guaranteed.