瓦斯抽采钻孔孔周裂纹扩展规律

Crack propagation around gas drilling borehole

为研究瓦斯抽采钻孔孔周裂纹扩展规律,制作不同抗压强度的含钻孔试样并进行全应力—应变单轴压缩试验,采用数字散斑相关测量方法获取试样表面破坏图像序列及其表面破坏过程中的全场应变.研究不同强度试样破坏过程中的裂纹分布,孔周位移及裂纹张开位移.结果表明:低抗压强度试样较高抗压强度试样的破坏形式更加多样,裂纹分布形式也更加繁杂;两种试样的孔顶和孔底始终保持相对收缩的趋势,孔洞断面形状在试样破坏的过程中逐渐由圆形变为椭圆形;试样强度对裂纹扩展的影响较大,低强度试样孔周位移约为高强度试样的2~4倍,其裂纹扩展开始时间早于高强度试样,且裂纹张开位移高1~2个数量级;轴向应力σ在0.2σmax^0.5σmax时T类裂纹首先扩展,σ>0.8σmax时I类和N类裂纹扩展并逐渐连通.

For studying the law of crack propagation around the gas drilling borehole,an experimental study of samples with different strength and borehole under uniaxial compression was carried out with digital speckle correlation method capturing the images of coal failed.The sequential images and full-field strain of sample failing process were obtained.The crack distribution,displacement around the borehole and crack opening displacement in the failing process were researched.The results show that the lower strength samples have more diverse of failure process and more complex distribution of crack as compared to the higher.The top and the bottom of borehole keep tending to relative contraction in both condition and sectional form of borehole gradually turns from round to ellipse in the failing process.The strength of samples has great influence on the crack propagation.The displacement around borehole of the lower strength sample is 2~4 times of the higher.The crack propagation initial time of the lower strength simple is earlier than the higher and its crack opening displacement is 1~2 orders of magnitude more massive than the higher.First,the T crack propagates when axial stress σ is between 0.2σmax and 0.5σmax,then the I crack and the N crack propagate and gradually connected when σ>0.8σmax.