布孔参数对导向缝槽-静态膨胀协同致裂效果的影响规律研究

    Study on the influence laws of hole distribution parameters on guided groove -static expansion synergistic fracturing effect

    • 摘要: 为进一步提升静态膨胀致裂技术顶板弱化能力,探究施工参量对钻孔周围应力分布的影响规律,基于弹性力学、断裂力学揭示了导向缝槽-静态膨胀协同致裂力学机制;采用PFC2D离散元法建立了相应静态膨胀致裂数值模型,通过设置不同施工参量来进行双向围压与静态膨胀耦合作用下的数值模拟研究。结果表明:相较于常规单孔无围压静态膨胀致裂,导向缝槽可有效提升静态膨胀致裂效果,距离孔心越远的位置提升作用越明显;离散元法可有效模拟静态膨胀致裂过程中应力分布情况,静态膨胀力、孔径以及导向缝槽长度与环向应力呈现正相关关系,导向缝槽角度、应力系数以及埋深与环向应力呈现负相关关系;布孔参量敏感参数排序为:孔径>缝槽角度>缝槽长度,实际应用时应尽量增大孔径与缝槽长度,减小缝槽角度;导向缝槽改变了环向应力分布特征,但缝槽的引导作用存在局限性,缝槽尖端与钻孔周边存在竞争起裂、扩展行为。

       

      Abstract: To further enhance the weakening capability of the roof by static expansion fracturing technology, the study explores the influence of construction parameters on the stress distribution around boreholes. Based on the principles of elasticity and fracture mechanics, the synergistic fracturing mechanism between guided groove and static expansion was revealed. Adopting the PFC2D discrete element method, a corresponding numerical model for static expansion fracturing was established and biaxial confinement and static expansion interaction simulations were conducted by setting different construction parameters. The results indicate that: compared to the conventional single-hole unconfined static expansion fracturing, the guided groove can effectively enhance the effect of static expansion fracturing, and the further the distance from the hole center, the more obvious the lifting effect; the discrete element method can effectively simulate the stress distribution during the static expansion-induced cracking process. There is a positive correlation between the static expansion force, borehole diameter, and the length of the guided groove, and the circumferential stress. Conversely, the angle of the guided groove, the stress coefficient, and the burial depth are negatively correlated with the circumferential stress; the sensitivity ranking of hole parameters is as follows: borehole diameter > groove angle > groove length. In practical applications, the aperture and slot length should be increased as much as possible and the groove angle should be reduced; the groove alters the characteristics of circumferential stress distribution; however, the guiding effect of the groove has its limitations. There exists competitive crack initiation and propagation behavior between the tip of the groove and the surrounding area of the borehole.

       

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