Understanding mechanisms of destressing mining-induced stresses using hydraulic fracturing

High mining-induced stresses can cause a series of problems related to the stability of entries and pillars including roof fall, rib failure, floor heave, and even coal bursts. In extreme cases, stress relief measures have to be carried out to help control those mining-induced stress-related problems. This article presents a field experiment of utilizing hydraulic fracturing as a preconditioning measure to relieve high abutment stresses caused by longwall coal mining. Field measurements and observations demonstrate that hydraulic fracturing in the main roof above the pillar can substantially destress abutment stresses. A numerical study is performed to study the related mechanism. The result suggests that abutment stress relief is achieved by shear sliding along generated hydraulic fractures and natural fractures stimulated by fluid injection. If designed appropriately, hydraulic fracturing operation in the main roof can substantially reduce abutment stresses, rather than transfer it to deeper rock mass. Factors controlling the effectiveness of destressing abutment stresses are also discussed.