软岩三轴蠕变特性的试验研究

采用重力加载式三轴流变仪,在低围压条件下对龙口矿区含油泥岩的蠕变特性进行三轴蠕变压缩试验研究,重点观察和分析蠕变条件下围压对岩石蠕变参数的影响,同时对其他时效变形特点进行分析.试验结果表明,含油泥岩存在一个起始蠕变应力阈值,该阈值随围压的加大呈线性增加;其蠕变破坏应力也大致与围压成比例关系,但两者随围压的增长率差异很大.含油泥岩的蠕变只有2个阶段：当轴向应力小于蠕变破坏应力时,蠕变呈衰减状态;当轴向应力大于蠕变破坏应力时蠕变转化为加速状态,但试验中没有观测到等速蠕变阶段.含油泥岩黏滞系数较小,显示出其流动变形大的特点.虽然黏滞系数近似为围压的线性函数,但增长率远小于前两者,表明低围压对软岩的流动变形影响较弱,该结果可为蠕变型软岩巷道的稳定性控制提供一定的试验依据.

EXPERIMENTAL STUDY ON CREEP PROPERTIES OF SOFT ROCK UNDER TRIAXIAL COMPRESSION

With the author-developed gravitation loading style rock creep test machine,under the conditions of constant temperature and constant humidity,triaxial compression creep experiments are conducted under different stress states.Oiliness mudstone samples are taken from Longkou Coalfields.The effects of confining pressure and creep parameters of soft rock were focused on;and other time-dependent behaviors were analyzed.The experimental results show that the stress threshold for the oil mudstone increases linearly with the confining pressure.The ultimate strength of creep is in direct proportion to confining pressure.The creep process of oil mudstone only goes through two phasest,hat is,one is in the damped creep phase when axial stress is less than the creep ultimate stress;and the other phase is accelerated when axial stress is larger than the creep ultimate stress.The even creep phase of oil mudstone is not observed in the test.The creep viscosity coefficient is become much smaller,which reveals the characteristics of large creep deformation.It is seen approximately as a linear function relation with the latter,but the viscosity coefficient increases slowly with the confining pressure.At the same time,the restriction of lower confining pressure to creep deformation is weaker.