关键词: 川藏铁路, 片麻岩, 三轴压缩蠕变试验, 裂纹异常扩展, 本构模型

Abstract:

Gneiss is widely distributed in the Zilashan area along Sichuan-Tibet railway line, and the anisotropic characteristics of the rocks are remarkable. During the construction of deep-buried tunnels, wallrock deformation directly affects the stability and reinforcement measures. To reveal the creep characteristics of gneiss from the Zilashan area in western Sichuan to eastern Tibet, triaxial compression creeping tests were carried out. Therefore, an abnormal crack propagation phenomenon was discovered. Based on the superposition principle, the long-term strength was determined by drawing an isochronous stress-strain curve. Using the Burgers model, a creep constitutive model that is more suitable for engineering practice was established. The parameters were then identified through L-M algorithm and global optimization. The results clearly show that under the same confining pressure condition, instantaneous strain increment of the samples decreases with increasing stress level, and consequently hardening occurred. From the sample creep characteristics, the phenomenon of abnormal crack propagation caused by microstructure anisotropy occurs, and the sample creep rate increases sharply due to abnormal crack propagation in the attenuation creep stage. The long-term strength increases with peristaltic pressure. Compared with the conventional triaxial test, the long-term strength decreases by 59.8% and 21.3%, respectively, and the improved Burgers model is more practical. The mechanical testing parameters can form a scientific basis for engineering construction and disaster prevention and control.

Key words: Sichuan-Tibet railway, gneiss, triaxial compression creep test, abnormal crack propagation, constitutive model