以非线性断裂力学理论为基础，通过应力叠加原理，推导出了ⅠⅡ型复合水力裂缝起裂角的解析模型。利用该模型计算了裂缝与最大水平主应力方向夹角为0°、30°、60°和90°时的裂缝端部塑性区域范围，并将利用该模型计算出的起裂角与利用最大周向应力准则计算出的起裂角进行了对比。结果表明：裂缝与最大水平主应力方向夹角为0°、30°、60°和90°时的裂缝端部塑性区域的范围分别是0～0.18，0～0.45，0～0.45和0～0.18倍半缝长；裂缝与最大水平主应力方向夹角为0°时，裂缝的起裂角为180°；当裂缝与最大水平主应力方向夹角增大至90°时，起裂角降为0°；在裂缝与最大水平主应力方向夹角及缝内流体压力相同的情况下，利用该模型计算出的起裂角比利用最大周向应力准则计算出的大0°～20°；在裂缝与最大水平主应力方向夹角相同的情况下，缝内流体压力为55 M Pa时的起裂角比缝内流体压力为45 M Pa时的大0°～40°。研究表明，利用非线性断裂力学研究泥页岩地层起裂是可行的，研究结果可以为水平井分段压裂优化提供一定的理论指导。
In the non-uniform stress field, the surrounding rock plastic zone of the circular roadway shows different shapes under the different confining pressure conditions. Based on the boundary shape characteristics of the plastic zone, the characteristic radii of the plastic zone were proposed, namely the horizontal,longitudinal and medial axis radii, which could reflect the plastic zone shapes characteristics and classify the sizes of the key parts. On the theoretical basis of elastic-plastic mechanics, analytical solutions for the characteristic radii were obtained by theoretical deduction, and the relationships between the characteristic radii and key influencing factors were analyzed. Finally, the evaluation criterion of the circular roadway surrounding rock plastic zone shapes, evaluation criterion of the location of potential hazards caused by the roadway surrounding rock and evaluation critical points of roadway dynamic disasters based on characteristic radii were proposed. This work could provide a theoretical basis for stability analysis of the surrounding rock, support design, and guide the prevention and control of dynamic roadway disasters.
Xiaofei GuoZhiqiang ZhaoXu GaoXiangye WuNianjie Ma
