泥质粉砂岩高围压三轴压缩松弛试验研究

Triaxial stress relaxation properties of argillaceous siltstone under high confining pressure

高应力条件下应力松弛特性是岩石长期力学特性研究的重要方面,开展了泥质粉砂岩围压为15~35 MPa的三轴松弛试验研究。高围压下应力松弛曲线的分析表明,岩石的应力松弛可以分为衰减松弛和稳定松弛两个阶段。当松弛初始应力水平较低时,试样主要以衰减松弛为主,很快趋于稳定,当松弛初始应力水平接近岩石峰值应力时,应力松弛明显增大,并出现明显的稳定松弛阶段。不同围压条件下,试样松弛曲线对比分析表明,松弛初始应力水平较低时,岩石处于黏弹性阶段,围压对岩石松弛特性的影响相对较小,随着松弛初始应力水平的增大,当应力水平接近峰值应力时,岩石的应力松弛将随围压的增大而减小。基于三轴松弛试验结果的分析,建立了能够反映泥质粉砂岩三轴松弛特性的西原模型,并验证了模型的合理性。

The stress relaxation properties of soft rock are an important aspect of its long-term mechanical properties, which are very important to keep soft rock tunnel long-term stability. The triaxial stress relaxation tests on argillaceous siltstone are carried out under confining pressures from 15 to 35 MPa. The relaxation curves can be divided into two stages： the transient relaxation and steady relaxation. When the stress relaxation starts with the initial deviatoric stress, which is much lower than the peak stress of the specimen, the relaxation is mainly composed of transient relaxation. However, when the initial deviatoric stress approaches to the peak stress of the specimen, obvious steady relaxation is observed. The comparisons of relaxation curves obtained from specimens under different confining pressures show that when the initial deviatoric stress is much lower than the peak stress of the specimen, the confining pressure has little effect on the relaxation behaviour of the specimen; and when the initial deviatoric stress approaches to the peak stress of the specimen, the relaxation stress decreases with the increase of the confining pressure. Based on the analysis on the results of triaxial relaxation tests, the Nishihara model is employed to describe the relaxation behaviour of argillaceous siltstone, and the comparisons between numerical and measured relaxation stress indicate the rationality of the Nishihara model.