非均匀应力场瓦斯抽采钻孔扰动煤体变形破坏特征

Deformation and failure characteristics of gas drainage drilling-reaming coal mass in non-uniform stress field

深部松软低透煤层瓦斯抽采钻孔周围煤体变形破坏特征影响着煤层瓦斯预抽效果。基于非均匀应力场条件,构建了钻孔扰动煤体的力学模型,推导了钻孔扰动煤体破碎区、塑性区、弹性区的应力、应变及位移的解析解,分析了侧压系数、载荷条件、黏聚力及扩孔行为等因素对扰动煤体“三区”分布的影响规律,并通过工程实例验证了理论模型的可靠性。研究结果表明:在非均匀应力场条件下,扰动煤体塑性区、破碎区呈椭圆形分布,随着侧压系数的增大,扰动煤体塑性区、破碎区的上、下两翼的长度也越来越大,较小应力方向的塑性区、破碎区半径大于较大应力方向两区的半径;煤体塑性区、破碎区的半径均随着垂向载荷的增大而增大,随着初始黏聚力、残余黏聚力的增大而减小,垂向载荷对其形状产生的影响可以忽略不计;当钻孔直径由0.1 m扩孔为0.5 m时,距钻孔中心0~1.0 m的煤体产生强扰动作用,1.0~4.6 m的煤体产生弱扰动作用,4.6 m之后的煤体几乎无影响;通过古汉山煤矿16032底抽巷水力扩孔现场实例,观察到扩孔段扰动煤体的破坏程度较高,基于出煤量反推出扩孔直径为1.5 m,进而分别通过理论计算与数值模拟获得钻−扩孔煤体变形破坏特征,2者吻合度较高,从而验证理论模型的可靠性。

The deformation and failure characteristics of coal around gas drainage boreholes in deep soft and low permeability coal seams affect coal seam gas pre-drainage.Based on the condition of non-uniform stress field,the mechanical model of borehole disturbed coal mass was developed,the analytical solutions of stress,strain and displacement in the damaged zone,plastic zone and elastic zone of borehole disturbed coal mass were deduced,the influence law of factors such as lateral pressure coefficient,load condition,cohesion and hole expanding behavior on the“three zone”distribution of disturbed coal mass were analyzed,and the reliability of the theoretical model was verified through engineering ex-amples.The results show that under the condition of non-uniform stress field,the plastic zone and damaged zone of dis-turbed coal mass are elliptical distribution.With the increase of lateral pressure coefficient,the length of the upper and lower wings of the plastic zone and damaged zone of disturbed coal mass becomes larger and larger,and the radius of the plastic zone and damaged zone in the direction of smaller stress is greater than the radius of the two zones in the direction of large stress.The radius of plastic zone and damaged zone of coal mass increases with the increase of vertical load,and decreases with the increase of initial cohesion and residual cohesion.The influence of vertical load on its shape can be ig-nored.When the borehole diameter is expanded from 0.1 m to 0.5 m,the coal mass 0−1.0 m away from the borehole cen-ter produces a strong disturbance,the coal mass 1.0−4.6 m produces a weak disturbance,and the coal mass after 4.6 m has almost no influence.Through the field example of No.16032 bottom pumping roadway hydraulic reaming in the Guhan-shan coal mine,it is observed that the disturbed coal mass in the reaming section has a high degree of damage.Based on the coal output,the reaming diameter is deduced to be 1.5 m,and then the deformation and damage characteristics of drilling reaming coal mass are obtained through theoretical calculation and numerical simulation respectively.The two are in good agreement,so as to verify the reliability of the theoretical model.