Diagnosis of rock fracture structure in thick coal seam roadway and research on coordinated control of layered grouting

To address conventional support failure and roadway instability in thick coal seams induced by primary and mining-induced fractures, this study investigates roof fracture characteristics and the layered grouting support mechanism, taking the ZF3806 working face of Shuiliandong Coal Mine as the engineering background. Channel-wave CT, microseismic monitoring, borehole coring, and borehole imaging reveal a roof structure characterized by shallow fragmentation and deep micro-fracturing. The channel-wave attenuation anomalies are interpreted as potential fractured zones and are further checked against microseismic and borehole evidence. Based on this diagnosis, a layered grouting support method is proposed: shallow bolt grouting rapidly cements the fragmented top coal into a load-bearing shell, whereas deep anchor-cable grouting reinforces the deeper fractured zone and connects it with relatively stable strata, forming a superimposed beam load-bearing structure. Physical similarity simulation shows that, compared with the original support scheme, the maximum model roof subsidence decreases from 8.4 mm to 2.0 mm. Field monitoring further shows that the shallow and deep roof bed separations decrease from 184 mm to 254 mm to 45 mm and 55 mm, respectively, and the maximum overall roof displacement after treatment is about 0.12 m. The laboratory and field indices are different mechanical indicators, but together confirm the effectiveness of the layered grouting support in reconstructing the bearing structure of fractured roadway roofs.