Abstract
<title>Abstract</title> <p> In deep coal seam groups, pressure relief induced by lower protective seam mining does not necessarily lead to synchronous gas-drainage enhancement, making it difficult to define effective protection ranges and drainage timing. This study investigates the mechanical–hydraulic mismatch in the III1022 working face of Luling Coal Mine by integrating FLAC <sup>3D</sup> numerical simulation, field verification of pressure-relief boundaries, roof–floor deformation monitoring, and surface-borehole drainage data within a unified advance-distance framework. An initial compaction compensation ratio, <italic>C</italic> <sub> <italic>n</italic> </sub> ( <italic>x</italic> ), is proposed to normalize the formation criterion of strong pressure relief by comparing mining-induced expansion release with the initial normal compaction strain of the protected seam. The onset of drainage enhancement is further identified using a continuous piecewise-growth model of the total drainage rate <italic>Q</italic> ( <italic>x</italic> ). Results show that the protected seam exhibits staged and zoned responses. Once established, the strong pressure-relief zone evolves within a finite stable range rather than expanding indefinitely. The criterion <italic>C</italic> <sub> <italic>n</italic> </sub> ( <italic>x</italic> ) = 1 identifies the onset of strong pressure relief at 128.8 m, with a continuous strong pressure-relief interval of 128.8–1216.6 m. In contrast, working-face-scale drainage enhancement begins at 280.4 m, indicating a spatial lag of 151.6 m. Lag-corrected local conversion intensity reveals that drainage conversion is highly nonuniform and concentrated in preferential windows. These findings demonstrate that strong pressure relief is necessary but insufficient for effective drainage; hydraulic effectiveness depends on fracture connectivity, pressure-field reorganization, gas-source mobilization, and borehole interception. </p>