松软突出煤层钻进钻孔堵塞力学特征

基于粉体力学理论,建立瓦斯抽采钻孔堵塞段力学模型,推导疏通压力p与堵塞段长度L关系方程。着重分析了侧压系数k、钻孔倾角θ对钻孔堵塞的影响规律。结果表明,侧压系数k增长致使钻孔堵塞段摩擦阻力增大,软煤层钻进钻屑颗粒硬度低、直径小,堵塞段内摩擦角小,其侧压系数较大,钻孔堵塞段疏通更为困难;施工仰孔,伴随倾角增大,疏通压力迅速降低,存在θU,对应疏通压力为0,当θ＞θU时,堵塞段在自重作用下疏通;施工俯孔,存在θD相应疏通压力达到极值,在θD～0区间,伴随钻孔倾角绝对值增大,所需疏通压力增大,在θD～-π/2区间,所需疏通压力略有降低。应用钻孔堵塞段力学模型,根据钻孔施工工艺参数,建立相应p-l特性曲线,可定性评估不同钻孔施工工艺方案优劣。

Mechanical characteristic of borehole clogging drilling in soft and outburst coal seam

Based on powder mechanic principles,a clogging segment mechanical model of gas drainage borehole was established,the relationship equation between the dredging pressure p and the clogging segment length L was derived.Borehole clogging law between the changes of lateral pressure coefficient k,drilling angle θ were analyzed.Result shows that,frictional resistance in clogging segment rapidly increases with the increase of lateral pressure coefficient k.During drilling in soft coal seams,the drilling cutting particles hardness is low,and the diameter is small,the internal friction angle of borehole clogging segment is also small,its lateral pressure coefficients k increases correspondingly,the clogging segment dredging is more difficult.In upward drilling operation,the drilling angle θ is in the range of 0-π/2,the dredging pressure decreases rapidly.There is a drilling angle θU,a pressure of 0 is needed (standard pressure to a reference pressure) for dredging the borehole clogging.When the drilling angle θ＞θU,clogging segment will be dredged as their own weight.In downward drilling operation the drilling angle θ is within the range of -π/2-0,there is a drilling angle θD and corresponding maximum dredging pressure.In the range of θD-0,the dredging pressure will increase with the absolute increase value of drilling angle,in the range of θD--π/2,with the drilling inclination absolute increase value,the blowing-through pressure is slightly lower.According to the parameters of drilling process,using the borehole clogging segment mechanical model,a corresponding p-l equation was established for evaluating the merits of the different parameters of drilling process.