There is great variation in the lithology and lamination thickness of composite roof in coal-measure strata; thus, the roof is prone to delamination and falling, and it is difficult to control the surrounding rock when developing roadway in such rock strata. In deep mining, the stress environment of surrounding rock is complex, and the mechanical response of the rock mass is different from that of the shallow rock mass. For composite-roof roadway excavated in deep rock mass, the key to safe and efficient production of the mine is ensuring the stability of the roadway. The present paper obtains typical failure characteristics and deformation and failure mechanisms of composite-roof roadway with a buried depth of 650 m at Zhaozhuang Coal Mine (Shanxi Province, China). On the basis of determining a reasonable cross-section shape of the roadway and according to the failure characteristics of the composite roof in different regions, the roof is divided into an unstable layer, metastable layer, and stable layer. The controlled unstable layer and metastable layer are regarded as a small structure while the stable layer is regarded as a large structure. A superimposed coupling support technology of large and small structures with a multi-level prestressed bearing arch formed by strong rock bolts and highly prestressed cable bolts is put forward. The support technology provides good application results in the field. The study thus provides theoretical support and technical guidance for ground control under similar geological conditions.

Complex pores and fissures are the main transportable channels of coal reservoir resources and key factors affecting the permeability of coal seams. Owing to different tectonic stresses, the development characteristics of pores and fissures in coal can differ significantly, which also results in differences in reservoir permeability. Therefore, analysing the influence of pore structure characteristics on coal-rock permeability is needed. In this study, four samples from the DaTong Coal Mine in the central and southern Qinshui Basin of Shanxi Province were selected for analysis. Combined computerised tomography (CT) scanning and digital image processing technology revealed the development characteristics, distribution rules, morphology, and structural differences of different coals. Based on the capillary seepage channel model and fractal geometry theory combined with the pore structure parameters obtained by CT scanning, the permeability was predicted. Furthermore, the control mechanism of the pore structure on coal permeability is discussed. The results showed that the coal porosity is positively correlated with pore diameter, pore volume, connectivity factor, and connectivity strength at the micrometer scale. Coal reservoir permeability is controlled by multiple factors, including pore size, pore volume, porosity, connectivity factor, connectivity strength, and fractal dimension, among which pore size has the most significant influence. After the complexity and connectivity of the micropore structure in coal rock were considered, the accuracy and applicability of the pore structure parameters obtained by CT scanning to predict the permeability were verified by comparing with the measured permeability.