法向边界条件对锚固节理岩体剪切力学及声发射特征的影响研究

Effect of normal boundary conditions on the shear mechanics and acoustic emission characteristics of anchored rock joints

  • 摘要: 认识锚固节理岩体剪切力学行为对岩体工程稳定性控制至关重要。通过开展恒定法向应力和恒定法向刚度边界条件下锚固和非锚固节理岩体直剪试验,并结合声发射技术,系统分析了初始法向应力、法向刚度影响下的节理岩体剪切力学特征、声发射特性及损伤破坏机制。结果表明:在CNL边界下,剪切应力-剪切位移曲线应力软化特征明显,在CNS边界下,曲线表现出由应力软化向应力硬化转变的趋势;τ1τ2均随法向应力的增大而增加,法向刚度对τ2的大小有显著提升;在CNS边界下,试样法向位移表现出由剪缩向剪胀转变的趋势,且非锚固节理试样剪缩和剪胀现象更为明显;锚固节理试样的AE能量和累计AE能量显著高于非锚固节理试样;AE定位点主要分布在节理面相交处及锚杆附近,CNS边界条件下AE定位点分布更集中;随着法向应力和法向刚度的增大,节理面破坏区域由孔壁附近向四周扩展,锚杆孔壁的破坏范围减小,锚杆呈现出“Z”型破坏特征。

     

    Abstract: Understanding the shear mechanical behavior of anchored rock joints is crucial for controlling of the stability of rock engineering structures. This study conducted direct shear tests on anchored and unanchored rock joints under constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions. We also adopted the acoustic emission (AE) technology to analyze the shear mechanical characteristics, AE characteristics, damage and failure mechanisms of jointed rock mass under initial normal stress and normal stiffness. Results show that 1) under the CNL boundary, the shear stress-shear displacement curve exhibited explicit stress softening, while under the CNS boundary, the curve showed transition from stress softening to stress hardening. 2) both τ1 and τ2 increased with increasing normal stress, and the normal stiffness significantly enhanced the magnitude of τ2.3) Under the CNS boundary, the normal displacement of the sample showed transition from shear contraction to shear expansion, and the shear contraction and expansion were more pronounced in unanchored joint samples.4) The AE energy and cumulative AE energy of the anchored joint samples were significantly higher than those of the unanchored joint samples.5) AE localization points were mainly distributed at the intersections of the joint surfaces and near the anchor bars, and the distribution of AE points was more concentrated under the CNS boundary conditions.6) As the normal stress and normal stiffness increased, the damage area of the joint surface expanded from the vicinity of the hole wall to the surrounding area, the damage range of the anchor hole wall decreased, and the anchor bars exhibited "Z" type failure.

     

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