不同含水状态砂岩分级加载蠕变变形特性研究

针对矿山开采过程中矿柱在长期地应力作用下发生的蠕变破坏受其含水状态影响的问题，利用岩石蠕变-冲击试验机，开展了干燥、饱水和浸水状态下的砂岩分级加载蠕变试验。超声波特性能够反映岩石 内部结构和力学特性，因此基于超声波测试分析含水岩石蠕变过程中的声学特性，探索水对岩石力学特性弱化作用机理；研究含水状态对岩石蠕变破坏特性的影响，揭示含水矿柱蠕变破坏前兆和时间规律。基于干燥 和饱水砂岩分级加载蠕变过程超声波测试，讨论了加载过程中超声波波速、主频和幅值的变化规律。结果表明：随着应力水平增加，干燥和饱水砂岩的主频及幅值都在降低，出现“频率漂移”现象，砂岩饱水后表现 出低通滤波特性；与干燥状态下的砂岩相比，饱水状态使其损伤量增大。初始含水状态影响蠕变变形量和变形速率，浸水砂岩和饱水砂岩破坏的时间和应力水平低于干燥试样；试样破坏前都有蠕变应变从缓慢增大到 急剧增大的一个拐点，蠕变应变过了拐点后0.5 h之内试样破坏。干燥、浸水和饱水岩石蠕变破坏模式分别为X型破坏、整体破碎为多块和沿轴向张拉破坏。

Sandstone Creep in Different Water-bearing States under Graded Loading

In view of the problem that the creep damage of pillar under the effect of long-term in-situ stress is affected by its water content in the process of mining， creep tests of sandstone under step-loading under dry， immersed and saturated conditions were carried out. Based on ultrasonic tests， the ultrasonic characteristics of water-bearing rock during creep process are analyzed to explore the time effect of water on rock mechanical property degradation. The influence of water-bearing state on creep failure characteristics of sandstone is studied， and the precursor and time rule of creep failure of water-bearing pillar was revealed. The variations of ultrasonic wave velocity， dominant frequency and amplitude in the loading process were discussed， based on the ultrasonic test during creep processes of dry and saturated sandstones under multi-stage loads. The results showed that with the increase of stress level， the dominant frequency and amplitude of dry and saturated samples are reduced， resulting in a phenomenon termed with "frequency drift"， and the water-bearing sandstone shows a low-pass filtering characteristic. The damage of saturated sandstone is greater than that of dry rock. Influences of initial water-bearing state on creep deformation and its rate were obtained. The failure time arrives earlier and stress levels are lower， for the immersed and saturated groups. Before the specimens are destroyed， there is an inflection point where the creep strain increases slowly and then dramatically， and the specimens are destroyed within 0.5 hour after the creep strain beyond the inflection point. The creep failure modes of dry， immersed， and saturated sandstones are X-shape failure， entire fragmented blocks， and tensile failure along axis， respectively.