废弃采空区裂隙带高度预测模型及应用

煤炭开采引起覆岩破断及地表下沉，覆岩及地表运移规律可反映裂隙带高度的动态演化过程。因地表下沉滞后于煤炭开采，对于废弃采空区，长期压实作用导致裂隙带高度较采动期间有所降低。基于地表点下沉速度的阶段特征将裂隙带高度的演化过程分为2个阶段，第1阶段裂隙带发育对应岩层破断逐步向上传递的过程，第2阶段裂隙带高度降低对应离层及裂隙闭合、断裂岩层受压后变形回弹及破碎岩体自然压实的过程。着眼于压实作用对裂隙带高度的影响，根据煤层采厚、垮落带和裂隙带岩层变形量及地表下沉值之间的定量关系，建立了第2阶段裂隙带高度预测模型，并结合太平煤矿实测结果进行验证，采用控制变量法分析了单一因素影响下废弃采空区裂隙带高度的演化特征。结果表明：废弃采空区裂隙带高度受控于垮落带块体强度、垮落带初始碎胀系数、采动期间裂隙带高度最大值及对应的垮落带高度、煤层埋深、地表最终下沉量等因素，太平煤矿采后15 a的裂隙带高度实测值11.36～13.00 m与理论预测值12.75 m吻合度较高，模型的可靠性得到验证。最后，应用此预测模型对武安煤矿（关停矿井）2002－2003年采空区裂隙带高度开展理论计算，结合地空瞬变电磁探测确定了地面瓦斯抽采钻孔理想的终孔位置并成功开展了地面钻孔瓦斯抽采试验。

Prediction model of the height of fractured zone in abandoned goaf and its application

Coal mining leads to overburden breakage and ground subsidence, and the dynamic evolution process of height of fractured zone could be revealed by the law of overburden and surface migration. Because the ground subsidence lags behind the coal mining, after the mined-out area is abandoned, the height of fractured zone is lower than mining process due to long-term compaction. Based on the characteristics of the subsidence velocity of surface point, the evolution process of the height of fractured zone is divided into two stages. The first stage corresponds to the process of rock layer breaking and gradually passing upward, then the second stage with subsidence of fractured zone corresponds to the process of separation of layers and closure of cracks, deformation and rebound of fractured rock layers after compression, and natural compaction of broken rock masses. This paper focused on the influence of compaction on the height of fractured zone. According to the quantitative relationship between the thickness of coal seam, the rock deformation in caved zone and fractured zone, and the ground subsidence, the prediction model of the height of fractured zone in the second stage was established, which was verified with the actual measurement results of Taiping coal mine. The control variable method is applied to further analyze the evolution characteristics of the height of fractured zone in the abandoned goaf under the influence of each single factor. The results show that the height of fractured zone is related to the uniaxial compressive strength of block in the caved zone, the initial bulking coefficient in the caved zone, the maximum height of fractured zone during mining process and the corresponding height of the caved zone, the depth of coal seam, and the amount of grounding subsidence. After 15 years of mining in Taiping coal mine, the measured value of the height of fractured zone is 11.36?13.00 m, which verifies the reliability of prediction model with predicted value of 12.75 m. Finally, the prediction model was used to carry out theoretical calculations on the height of fractured zone 2002?2003 in the abandoned goaf of Wu’an coal mine (closed mine), combined with ground-airborne transient electromagnetic system to determine the ideal location of ground gas drainage borehole, by which a ground borehole gas drainage test was successfully carried out.