高应力区峰后红砂岩蠕变特性及模型分析

在实验室通过RLW-2000型岩石三轴流变仪,对2组9个红砂岩样进行高应力区峰后单轴压缩蠕变试验,研究了红砂岩峰后瞬时应变、蠕变应变与应力水平的关系,分析了红砂岩峰后/峰前蠕变关联特性,探讨了红砂岩蠕变破坏机制,确定了峰后红砂岩高应力区蠕变本构模型。结果表明:随着蠕变应力水平提高,峰后岩样瞬时应变呈减小趋势,蠕变应变与蠕变应变速率呈增加趋势,峰后岩样同样具有瞬时加载四阶段与蠕变水平三阶段特征;相同应力水平下,岩样峰后/峰前状态对瞬时应变比影响大于蠕变应变比;应力水平越高,岩样瞬时应变比与蠕变应变比越大,但应力水平对岩样蠕变应变比影响大于瞬时应变比;峰后破坏岩样主控破裂面形态复杂,高径比越小,岩样内部破坏越充分,高径比越大,越易产生压剪破坏;Burgers-Kelvin模型能够表征峰后红砂岩高应力区蠕变特性。

Creep characteristics and model analysis of red sandstone in post-peak high stress zone

In this paper, uniaxial compression creep experiment is performed for two groups of nine red sandstone specimens in post-peak high stress area by using RLW-2000 rock triaxial rheometer. The relations among stress level, post-peak instantaneous strain and creep strain of red sandstone specimens were studied. Its post-peak/pre-peak creep correlation characteristics were analyzed. Its creep failure mechanism was discussed, and creep constitutive model in high stress area wa determined. Experimental results show that with the increase of creep stress level, the instantaneous sstrain of post-peak rock sample decreases, and creep strain and creep strain rate increase. The post-peak rock sample is also characterized by four-stage instantaneous loading and three-stage creep level. At the same stress level, the effect of post-peak/pre-peak state on instantaneous strain ratio is greater than creep strain ratio. The higher the stress level is, the greater the instantaneous strain ratio and creep strain ratio are, while the effect of stress level on creep strain ratio of rock sample is greater than that of instantaneous strain ratio. The main controlled fracture surface morphology is complex in post-peak failure rock specimens. The smaller the high-diameter ratio is, the more fully the internal damage of rock sample, and the larger the high-diameter ratio is, the easier the compression-shear failure happens. Burgers-Kelvin model can characterize creep features of post-peak red sandstone specimens in high-stress area.