川藏铁路孜拉山区片麻岩蠕变特性及本构模型研究

川藏铁路孜拉山区片麻岩分布广泛,岩石各向异性特征显著,深埋隧洞修建时围岩变形直接影响隧洞稳定及加固措施。为揭示川西—藏东孜拉山区片麻岩的蠕变特征,开展了三轴压缩蠕变试验,发现了一种裂纹异常扩展现象,在叠加原理的基础上通过绘制等时应力-应变曲线确定长期强度。基于Burgers模型建立一种更符合工程实际的蠕变本构模型,采用麦夸特算法和全局优化算法进行参数辨识。结果表明:同一围压条件下,试样瞬时应变增量随应力等级增大而变小,发生硬化现象;片麻岩试样在蠕变特性中表现出因微观结构各向异性而引起裂纹异常扩展的现象,在衰减蠕变阶段其蠕变速率因裂纹异常扩展而骤增;长期强度随围压增大而增大,与常规三轴试验条件相比,长期强度分别下降59.8%和21.3%。本研究构建的改进的Burgers模型更加符合实际情况,所得到的试验力学参数可为工程建设及灾害防治提供科学依据。

Creep Characteristics and Constitutive Model of Gneiss in Zilashan Area Along Sichuan-Tibet Railway Line

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.