三轴压缩下粉砂质泥岩蠕变力学特性试验研究

为揭示三峡地区巴东组二段粉砂质泥岩的蠕变力学特性,采用RLJW-2000岩石流变伺服仪对饱和粉砂质泥岩进行了三轴压缩蠕变试验。试验在分级加载条件下进行,试验围压为1 MPa。基于试验结果,定量研究了粉砂质泥岩蠕变过程中轴向蠕应变与径向蠕应变的差异、轴向蠕变速率与径向蠕变速率的差异,得出了岩石的长期强度。研究结果表明:1)在各级应力水平下,试样径向蠕应变占径向总应变的比例始终比轴向蠕应变占轴向总应变的比例大,岩石的径向蠕变效应更明显。2)在破裂应力水平下,岩石径向蠕变比轴向蠕变先进入加速蠕变阶段,径向的初始蠕变速率、稳态蠕变速率以及加速蠕变速率均高于轴向相应的蠕变速率,以径向蠕变特征来判别粉砂质泥岩是否发生蠕变破坏更合理。工程实践中,应加强对岩石径向蠕变特性的监测工作,这对于工程失稳的预测预报更有意义。3)粉砂质泥岩的长期强度仅为其瞬时强度的74.4%,长期强度折减较大。4)试验中获得的长期强度实际上应为粉砂质泥岩的径向长期强度,径向先发生蠕变破坏从而导致试样破坏。

Experimental study of creep properties of silty mudstone under triaxial compression

In order to reveal the creep properties of silty mudstone in Badong Formation strata in the Three Gorges area, the creep test of saturated silty mudstone under triaxial compression was carried out on the RLJW-2000 rock microcomputer-controlled rheology servo test system by step loading method. The confining pressure was 1MPa in the test. Based on the test results, the differences of the creep strain and the creep rate between the axial and radial direction of the specimen under different stress levels were quantitatively studied. The long-term strength of silty mudstone was determined by the test results. The results showed that: (1)The ratio of radial creep strain to radial total strain was always higher than that of axial creep strain to axial total strain under each stress level, so the radial creep characteristics were more significant than the axial creep characteristics for the specimen. (2)The accelerating stage in the radial creep course appeared earlier than that in the axial creep course, and the primary creep rate, steady-state creep rate and accelerating creep rate in the radial creep course was larger than that in the axial creep course respectively for the specimen under the fracture stress level. Therefore, it was more reasonable to determine whether the silty mudstone occurred creep rupture based on the radial creep characteristics of the specimen. The monitoring of radial creep characteristics of the rock should be strengthened in engineering practice, which would be more valuable for the prediction of the failure of rock engineering. (3)The long-term strength of silty mudstone was 74.4 percent of the triaxial compressive strength, so the long-term strength of the rock decreased remarkably. (4)The creep rupture first appeared in the radial direction of silty mudstone, so the long-term strength of silty mudstone obtained in the test was actually the radial long-term strength of the rock.