Hydraulic fracturing stress transfer methods to control the strong strata behaviours in gob-side gateroads of longwall mines

Abstract

With hard roof conditions and the influence of side and front abutment pressures, pressure bump and large deformations periodically occur in the advanced support area of longwall face gob-side gateroads. To control the strong strata behaviours in gob-side gateroads, “directional hydraulic fracturing, to cut off the roof hanging over the adjacent gob area, and pre-fracturing of the roof, located behind the working face being extracted,” are performed. The directional initiation of hydraulic fracturing is controlled by pre-slotting, and this action guides the propagation of hydraulic fractures in three-dimensional space. The oriented fractures meet engineering requirements by cooperating with both the in situ ground stresses and the mining-induced stresses, as well as the technology of hydraulic fracturing. In field applications, hydraulic fracturing has proven to be a viable option for weakening hard roofs, destressing the side and front abutment pressures at the mining face and also transferring in situ and mining-induced stresses. Successful field tests in the Tongxin coal mine, Datong district, as well as other coal mines, show that hydraulic fracturing in both a hanging roof over an adjacent gob area and in the gob area behind the advancing working face controls the behaviour of strong strata material on the gob-side of gateroads in longwall mining and also guarantees safe extraction at the working face.