基于煤层应力的水力致裂防冲机理与试验研究

Mechanism and Experiment of Hydraulic Fracture in Rockburst Prevention Based on Stress of Coal Seam

为了从煤层应力角度研究水力致裂的防冲机理,首先进行了理论分析并提出了空间应力梯度概念来表征冲击地压危险性,随后进行了煤层顶板水力致裂现场试验,利用应力在线监测系统,监测得到了致裂前后及工作面推进过程中煤层应力的变化。水力致裂前后,煤层应力变小。采动影响下,煤层应力不断增加,直至达到应力峰值,随后迅速减小。水力致裂后,煤层应力峰值位置向深部移动,峰值处煤层应力增值下降,开采过程中煤层应力的空间应力梯度最大值也得到降低。结果表明:煤层顶板水力致裂可以降低煤层应力,达到卸压效果;可以减小开采过程中煤层应力的局部集中,降低煤层应力的空间应力梯度。

In order to study the mechanism of hydraulic fracture in rockburst prevention from the aspect of stress in coal seam,the theoretical analysis was carried out and the concept of spatial stress gradient was proposed to characterize the risk of rockburst.Then the field test on hydraulic fracture in the roof of coal seam was carried out.The on-line stress monitoring system was adopted for monitoring the stress change of coal seam before and after hydraulic fracture as well as during working face advancing.The stress of coal seam decreased after hydraulic fracture.Owing to the mining activities,the stress of coal seam gradually increased until reaching the peak,then decreased sharply.After hydraulic fracture,the stress peak position moved to deep place,the increment of stress in coal seam decreased at the stress peak position,and the maximum spatial stress gradient in coal seam was also reduced in mining process.The results show that hydraulic fracture in the roof of coal seam not only can reduce the stress in coal seam and achieve pressure relief effect,but also can reduce the local stress concentration and the spatial stress gradient in coal seam during mining.