Layered grouting reinforcement technology for coal–rock composite roof: A treatment system based on model experiments

Severe deformation and support failure of coal–rock composite roofs are widely encountered in deep mining roadways, posing significant challenges to long-term roadway stability. Taking the 3806 fully mechanized top-coal caving face mining roadway of the Shuiliandong Coal Mine in the Binchang mining area, China, as an engineering case, this study systematically investigates the reinforcement mechanism and control performance of layered roof grouting through laboratory rock mechanical tests, physical similarity modeling, and field-scale industrial application. Borehole coring and mechanical testing were conducted to characterize the stratified structure and mechanical heterogeneity of the fractured top coal, immediate mudstone roof, and overlying sandstone. Based on these results, a plane-stress physical similarity model was established to comparatively analyze roadway deformation, stress evolution, failure modes, and microseismic responses under the original support scheme and a layered grouting reinforcement scheme. A layered grouting technology centered on “shallow bolt grouting and deep cable grouting” is proposed to reconstruct a superimposed beam-bearing structure within the coal–rock composite roof through differentiated grouting parameters. The similarity model results indicate that layered grouting reduces the maximum roof subsidence from 8.4 mm to 2.0 mm, significantly optimizes the stress redistribution of the surrounding rock, suppresses crack propagation and roof fragmentation, and effectively mitigates microseismic activity. Field application demonstrates that the maximum deformation of roadway ribs and roof–floor convergence decreases from 0.42 m to 0.53 m to 0.20 m and 0.12 m, respectively, with markedly improved roof integrity and long-term stability. The proposed layered grouting strategy provides a practical and reliable solution for stability control of coal–rock composite roofs in underground roadways.