Mechanism and control of floor heave in two entry retained roadways using dense boreholes

This study addresses severe floor heave in retained entries of two-entry longwall faces through a case analysis of Chahasu Coal Mine, China. Surrounding rock deformation and failure in the 31,317 tail entry were characterized through field monitoring and laboratory tests, followed by analysis of geological and mining impacts on floor heave. Stress evolution in the coal pillar between entries during mining was examined through 3DEC numerical simulations, revealing floor heave mechanisms. Support strengthening and stress improvement measures were comparatively evaluated. A dense borehole roof-cutting technology (CRDBDCS) was developed for floor heave control, with key borehole parameters optimized. When implemented in the 31,315 head entry and adjacent roadways, an over 87% reduction in floor heave volume was achieved, enabling entry reuse. The effectiveness of CRDBDCS was thereby demonstrated, providing technical support for the safe and efficient operation of coal mine roadways.