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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。
Stress relaxation under high stress conditions is an important aspect in the study of long-term mechanical properties of rock. Triaxial relaxation tests of muddy siltstone with confining pressure of 15-35 MPa were carried out. Analysis of the stress relaxation curve under high confining pressure shows that the stress relaxation of rocks can be divided into two stages: attenuation relaxation and stability relaxation. When the initial relaxation stress is low, the specimens are dominated by the attenuation relaxation and tend to be stable quickly. When the initial stress level is close to the peak stress of the rock, the stress relaxation obviously increases and the stable relaxation stage appears. Comparisons of relaxation curves show that the rock is in the viscoelastic stage when the initial relaxation stress is low and the confining pressure has a relatively small effect on the rock relaxation characteristics. With the increase of the initial stress of relaxation, As the stress level approaches the peak stress, the stress relaxation of the rock decreases with increasing confining pressure. Based on the analysis of the results of triaxial relaxation tests, a model of Nishihara was established to reflect the triaxial relaxation of muddy siltstone and the rationality of the model was verified.