Influence of deep synclinal structures and residual coal pillars on roadway deformation behavior and control measures

To investigate the complex roadway stress environment arising from the coupled influence of deep synclinal structures and remnant coal pillars, we established a mechanical model to characterize the stress concentration zone induced by the pillars, with the 4301 working face of the Dongtan Coal Mine serving as the engineering background. Comparative numerical simulations under different pillar–roadway offsets were then performed, which elucidated the evolution of the stress field and the deformation behavior of the surrounding rock under the combined effects of synclinal structures and remnant pillars. The results indicate that the roof stress rises markedly as the roadway advances into the synclinal core, reaching 2.1 times that observed in non-synclinal regions. The superimposed influence of remnant coal pillars further amplifies the extent of roof stress concentration. Specifically, when the horizontal offset between the pillar and the roadway is 11.75 m, the roof stress peaks at 18.46 MPa—1.23 times the in-situ stress—thereby exacerbating the instability of the surrounding rock. Building on this work, field comparative tests of different support schemes were conducted. The results demonstrate that full-cable support effectively restrains surrounding rock deformation, reducing roof and rib displacements by factors of 4.03 and 1.77, respectively, and significantly outperforming conventional bolt–cable combined support. These findings furnish both a scientific basis and practical guidance for the stability control of roadway surrounding rock in closely spaced coal seams under complex structural conditions.