单轴压缩条件下砂岩蠕变变形时效性与声发射特性研究

发布时间：2018-03-01 00:08

  本文关键词： 岩石蠕变 一级加载 蠕变变形 时间效应 声发射监测　出处：《江西理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：针对地下结构处于一种常荷载状态下经过长期蠕变最终导致失稳破坏的现象,基于单轴压缩条件对砂岩进行一级加载状态下的蠕变声发射试验,研究了砂岩在蠕变过程中的轴向、横向与体积变形规律,进一步研究了蠕变应力、扩容点应力之间的比值(β值)与蠕变破坏时间的关系;最后,利用声发射技术对砂岩在不同蠕变阶段的声发射参数进行了分析研究。主要得到以下结论:(1)砂岩在蠕变过程中的横向蠕变进入减速与加速蠕变阶段的时间及变形量都要比轴向蠕变高,且体积扩容效应显著;岩石粒径越小、越均值,则砂岩越不容易发生蠕变变形;砂岩在蠕变过程中的损伤主要发生在减速与加速蠕变阶段;单轴压缩试验得到的平均扩容点应力可作为初步拟定蠕变应力水平的依据。(2)砂岩蠕变应力、扩容点应力之间的比值(β值)与蠕变破坏时间的关系表现为:随着β值的增加,蠕变破坏时间则逐渐减小。(3)声发射信号与蠕变速率呈现出正比的关系,表现为在减速蠕变阶段时,声发射信号随着时间的增加而逐渐减小;在等速蠕变阶段时,声发射信号大致处于较为平稳的状态,其频度与幅度较小;在等速与加速蠕变交界处,声发射信号出现大幅度的“突升”现象,但进入加速蠕变阶段后又很快下降并缓慢增长,但其频度与幅度均要高于前两个阶段;在蠕变破坏时,声发射信号大幅度、集群式的增长。声发射∑N/∑E(简称声发射r值)在减速蠕变阶段的值普遍要高于等速蠕变阶段,且在等速蠕变阶段时,声发射r值较为平稳;在加速蠕变阶段时,声发射r值明显下降,且在蠕变破坏时,降至最低水平。结合声发射参数与声发射r值在不同蠕变阶段的变化特征,在一定程度上可以对砂岩蠕变破坏进行预测与预判。(4)轴向应变曲线在减速与等速蠕变阶段时出现了“突变”的现象,这些“突变”经过短暂的调整后,仍能恢复稳定状态,此时的声发射信号出现了“突升”的现象,这表明岩石内部材料强度较低的地方发生了破裂,但对试样整体并未构成明显的损伤,声发射r值出现较小幅度的降低也正好说明了这一点。因此,声发射信号及r值能较好地描述岩石变形和损伤演化规律。
[Abstract]:Aiming at the phenomenon that the underground structure is under a constant load state, the creep acoustic emission test of sandstone under the first loading condition is carried out based on uniaxial compression condition. The law of axial, transverse and volume deformation of sandstone during creep is studied, and the relationship between creep stress, the ratio of stress at expansion point (尾 value) and creep failure time is further studied. The acoustic emission parameters of sandstone in different creep stages are analyzed by acoustic emission technique. The following conclusions are obtained: 1) the time and deformation of sandstone lateral creep entering deceleration and accelerating creep stage during creep process. The amount is higher than the axial creep, The smaller the grain size of rock, the less the mean value, the less the sandstone is liable to creep deformation, and the more the damage of sandstone is in the stage of deceleration and accelerated creep. The average expansion point stress obtained by uniaxial compression test can be used as the basis for preliminary determination of creep stress level. The relationship between the ratio of expansion point stress (尾 value) and creep failure time is as follows: with the increase of 尾 value, On the other hand, the creep failure time decreases gradually) the acoustic emission signal is proportional to the creep rate, which decreases gradually with the increase of time during the deceleration creep stage, and at the constant velocity creep stage. The acoustic emission signal is in a relatively stable state, and its frequency and amplitude are relatively small. At the junction of constant velocity and accelerated creep, the acoustic emission signal appears a large "sudden rise" phenomenon, but after entering the accelerated creep stage, the acoustic emission signal decreases quickly and increases slowly. However, its frequency and amplitude are both higher than those of the first two stages, and the acoustic emission signal increases by a large margin during creep failure, and the acoustic emission 鈭，

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