近距离煤层群叠加开采采动应力-裂隙动态演化特征实验研究

Evolution of the superimposed mining induced stress-fissure field under extracting of close distance coal seam group

围岩应力、裂隙分布特征是影响突出危险煤层瓦斯抽采效果的重要因素,为优化突出危险煤层群瓦斯预抽方案,以沙曲煤矿近距离煤层群开采为背景,采用相似模拟实验研究了保护层与被保护层双重采动影响下围岩应力-裂隙分布与演化特征。结果表明：3＋4号煤初采时,叠加采动的影响下,顶底板卸压程度较一次采动影响时高,但高卸压程度阶段持续长度减少,约105 m,底板最大应力降低值可达12 MPa,是保护层开采时最大应力降低值的1.5倍;进入正常推进阶段,仅距采空区两侧煤壁一定范围L内仍保持较高裂隙发育和应力降低程度,且较保护层开采时L值减小,20～30 m,采空区中部覆岩裂隙再次闭合,围岩应力出现恢复现象;工作面推进距离一定条件下,双重采动影响下顶底板卸压程度及裂隙发育程度较一次采动影响下明显升高;被保护层开采时,3＋4号煤同2号煤之间岩层破碎程度最高,裂隙最为发育,覆岩裂隙发育程度随工作面推进距离增加而升高,由于形成稳定顶板结构的随机性,覆岩裂隙频数程台阶式增长。最后将研究结果应用于沙曲煤矿高瓦斯煤层群开采时瓦斯抽采钻孔的布置设计,取得较好的抽采效果。

As the superimposition mining of the short distance coal seam group,the strata between get repeatedly per-turbation and destruction. Therefore the evolution characteristics of the superimposed mining induced stress-fissurefield were different from the ones of the single coal seam. In order to obtain the evolution characteristics,the similarsimulation was adopted in this passage. The study show that：the high stress relief length of the No. 3＋4 coal was about105 m and it continued to decrease. However,Its stress extent was 12 MPa which was 1. 5 times of the No. 2 coal seamand reached much higher degree. The stress relief extent of the survey line in the floor of No. 3＋4 coal seam was stillhigher than the No. 2 coal seam,and the stress in the coal wall nearby the goaf dropped obviously,especially the No. 2coal seam was mined,which the extent reached 30-40 m. Meanwhile,the extent dropped to 20-30 m,when the No. 3＋4 coal was mined. The sum of the fissure increases apparently,and the frequency of the fissure character come to stepgrowth. This passage proposed a model for the differentiation based on the characters of the mining induced stress-fis-sure field in the coal seam floor and the passage also give a conclusion about the evolution characters under the keytime nodes,which provided experimental support for the judgement of the best gas drainage time.