煤与瓦斯突出的微震前兆特性试验研究与预警案例分析

Experimental study on microseismic precursory characteristics of coal and gas outburst and case analysis of early-warning

为研究煤与瓦斯突出的微震前兆特征,对关键结构体模型进行优化,基于优化的突出物理模型,借助COMSOL Multiphysics构建出煤体力学性质空间渐变的三维模型,首先分析巷道掘进前后原岩应力和采动应力的分布及演化规律;然后分别分析地应力、瓦斯压力和煤体力学性质对煤体破裂过程声发射响应的影响规律;进而根据突出危险区域附近的煤体分布、瓦斯赋存和巷道掘进过程采动应力的演化特征,三方面综合分析煤与瓦斯突出之前微震信号的演化规律。研究结果表明:煤体力学性质剧烈变化部位伴随着局部的高应力区和低应力区以及较大梯度的应力分布,且原岩应力峰值和谷值分别位于硬煤和软煤的边界面处;在由硬煤区向软煤区边界方向掘进过程中,采动应力峰值演化经历了3个阶段,正常期、高值期和低值期。突出原煤和型煤常规三轴加载破坏过程中声发射参数与加载应力总体上均呈正相关关系,且在裂纹的非稳定发展阶段,声发射参数快速增大并达到最大值;另外,硬煤和构造软煤相比不仅具有较高的煤体强度,还伴随着较大的声发射强度。煤巷掘进遇区域构造煤突出之前微震信号演化经历3个阶段,安全期、前震期和平静期,且随着软煤渐变梯度的逐渐减小,前震峰值逐渐减小,平静期逐渐增大,煤与瓦斯突出的微震前兆特征逐渐变得模糊,突出的突发性增强;而石门揭煤突出之前没有平静期的出现,前震直接发展成主震。

The key structure model is optimized in order to study the microseismic precursory characteristics of coal and gas outburst. Based on the optimized physical model of coal and gas outburst,a three-dimensional model with the mechanical properties of coal changing gradually in space is constructed by COMSOL Multiphysics. Firstly,the distribution and development of the original rock stress and the mining stress before and after the tunnel excavation are analyzed. Then the effects of ground stress,gas pressure and mechanical properties of coal on the acoustic emission in fracturing process of coal are analyzed. Finally,the development of microseismic signals before coal and gas outburst is analyzed according to the coal distribution,gas storage and the variation of the mining stress in the excavation process of tunnel around the dangerous area of coal and gas outburst. The places with the mechanical properties of coal changing drastically have areas of local high-stress,low-stress and large stress gradient. The peak stress in the high-stress area is located in the boundary surface of hard coal,while the stress valley in low-stress area is located in boundary surface of soft coal. In the tunneling process from the hard coal area to the boundary of soft coal area,the peak mining stress has experienced three stages：a normal period,a high value period and a low value period. The acoustic emission parameters of raw coal and briquette for outburst coal generally have a positive correlation with the loading stress during the failure process in conventional triaxial loading. Especially in the unstable development stage of the crack,the AE parameters increase rapidly and reach the maximum value. Besides,compared with the soft coal,hard coal has higher strength and acoustic emission intensity. Before the coal roadway tunneling meets the regional tectonic coal,the microseismic signals experienced three stages,a safe period,a foreshock period and a quiet period. And with the gradient of soft coal decreases gradually,the peak in the foreshock period decreases gradually,the quiet period increases gradually,the microseismic precursor of coal and gas outburst gradually becomes fuzzy,and the suddenness of coal and gas outburst is enhanced. However,before the uncovering of cross-cut coal,there is no quiet period,and the foreshock directly develops into the main shock.