中厚煤层软硬复合顶板切顶卸压沿空留巷关键参数优化研究

Optimization on Key Parameters of Roof Cutting and Gob-Side Entry Retaining at the Soft and Hard Composite Roof in Medium Thick Coal Seams

中厚煤层软硬复合顶板地质条件复杂,切顶留巷后极易出现采空区顶板分层垮落、二次垮落以及留巷变形严重等问题。为解决这一难题,以新驿煤矿1706工作面为工程背景,从切顶留巷关键参数选取方面展开系统研究。从煤层厚度和顶板岩层分布入手,分析判断影响切顶留巷效果的因素主要为切顶高度和炮孔封堵长度与封堵方式;基于岩石碎胀自承特性原理,初步设计切顶高度,再建立含裂缝复合顶板岩梁断裂力学模型,理论分析切顶高度与复合顶板断裂间的关系;基于炮孔封堵作用机理和爆破破岩机理,针对软硬复合顶板岩层提出分段封堵炮孔的思想,推导出软岩段和硬岩段封堵长度计算方法。现场试验和监测数据表明:切顶关键参数为切顶高度8.5 m,硬岩段封堵0.5 m,软岩段封堵1.5 m,按这些参数实施切顶后,孔内裂缝连续,裂缝率达到了92%;切顶后锚索受力稳定在172 kN,顶板最终离层量为35 mm,相较于未切顶段分别降低了23%和55%,复合顶板顺利一次垮落,留巷效果良好。

The geological conditions of soft and hard composite roof in medium thick coal seam are complex. After cutting the roof and retaining entry, it is very easy to cause problems such as layered collapse of goaf roof, secondary collapse and serious deformation of retaining entry. In order to solve this problem, taking 1706 working face of Xinyi Coal Mine as the engineering background, a systematic study on the selection of key parameters of roof cutting and gob-side entry retaining were carried out. Starting from the coal seam thickness and rock stratum distribution of roof, the parameters affecting the effect of roof cutting and gob-side entry retaining were mainly roof cutting height and blast hole plugging. Based on the principle of self bearing characteristics of rock fragmentation and expansion, the cutting height was preliminarily designed, and then the fracture mechanics model of rock beam with crack composite roof was established to theoretically analyze the relationship between cutting height and fracture of composite roof. Based on the mechanism of blast hole plugging and blasting rock breaking, the idea of segmented plugging was proposed for the soft and hard composite roof rock, and the calculation method of plugging length of soft rock section and hard rock section was deduced. The field tests and monitoring data show that when the key parameters of roof cutting are 8.5 m of cutting height, 0.5 m plugging of hard rock section and 1.5 m plugging of soft rock section, the cracks in the hole are continuous and the crack rate reaches 92%;after roof cutting, the stress of the anchor cable is stable at 172 kN, and the final separation of the roof is 35 mm, which is reduced by 23% and 55% respectively compared with the non roof cutting section. The composite roof collapses smoothly at one time, and the entry retaining effect is good.