基于声发射特征的含水煤体钻屑法临界指标优化试验研究

Experimental study on critical index optimization of drilling cuttings method of water-bearing coal based on acoustic emission features

蒙陕部分冲击地压矿井由于受到洛河组砂岩含水层的影响,煤层含水率过高钻屑煤粉泥化成团导致钻屑量始终不超标,钻屑法结果存在误差甚至失效,影响现场冲击地压危险的监测预警。基于此,以不同含水率煤体为研究对象,开展不同应力加载水平下的三轴加卸载钻进试验,探究含水率0、1.7%、3.7%和5.6%煤体钻进过程中声发射(AE)及其损伤空间特征,获取计算理论钻屑量数值的方法,通过理论与试验称量钻屑质量比确定煤体在不同含水条件下钻屑法临界指标。结果表明:(1)随应力水平和含水率增高,声发射事件呈现钻孔中心向周围扩散的现象,破坏趋势由剪切部分破坏向剪切整体破坏转变;(2)载荷水平和含水率对由声发射事件空间分布确立的损伤椭球体(DE)体积影响较大,损伤椭球体与声发射事件空间分布特征具有一致性,计算得出的损伤椭球体质量为含水煤体受到应力及钻杆切削作用的主要损伤空间质量M;(3)通过分析理论与试验称量钻屑质量整体变化趋势,发现含水煤体受到水的弱化作用后理论钻屑量有所增加,但相较于水的弱化作用,水的黏结占主导作用,导致现场收集的钻屑量偏小;(4)依据理论与试验称量钻屑质量比值得出不同含水率煤体的钻屑法修正系数H,当含水率为0~1.7%、1.7%~3.7%和3.7%~5.6%时,H分别取值1.00、2.32和4.05,当含水率大于5.6%时,钻屑法失效。

Due to the influence of the Luohe Formation sandstone aquifer in some rock-burst coal mines of Shaanxi Province and Inner Mongolia Region,the moisture content of coal seam is too high and the amount of drilling cuttings cannot reach the standard.The results of drilling cuttings method have errors or failures,which affects the monitoring and pre-warning of rock burst risk.Based on this,the coal mass with different water contents is taken as the research object for carrying out the triaxial loading and unloading drilling tests at different stress loading levels,exploring the acoustic emission(AE) and damage spatial characteristics of coal with 0,1.7%,3.7% and 5.6% water content during drilling.And the method of calculating theoretical drilling cuttings is obtained.The cuttings critical index of coal mass under different water conditions is determined by the cuttings mass ratio of theory and test.The results show that(1) with the increase of stress level and water content,the AE events show that the borehole center diffuses to the surrounding area,and the failure trend changes from shear partial failure mode to shear integral failure mode.(2) Load level and water content have great influence on the volume of damage ellipsoid(DE) established by the spatial distribution of AE events.The DE is consistent with the spatial distribution characteristics of AE events.The calculated mass of DE is the main damage space mass M of water-bearing coal subjected to stress and drilling pipe cutting.(3) Through the analysis of the overall change trend of cuttings quality in theory and test,it is found that the theoretical cuttings amount increases after the weakening effect of water on the water-bearing coal body.Compared to the weakening effect of water,water bonding plays a dominant role,which leads to a small amount of cuttings collected on site.(4) The cuttings correction coefficient H of water-bearing coal body is obtained according to the ratio of cuttings mass between the theory and test of coal specimens with different water contents.When the water content is 0-1.7%,1.7%-3.7% and 3.7%-5.6%,H is 1.00,2.32 and 4.05,respectively.If the water content is greater than 5.6%,the drilling cuttings method fails.The critical index of drilling cuttings for waterbearing coal based on the test can provide reference for drilling cuttings monitoring in the water-rich rock-burst coal mines.