Mechanism and Control Measures for Floor Heave in Gob-Side Entry of Weakly Cemented Soft Rock

Weakly cemented soft rock roadways exhibit large deformation dominated by floor heave due to their low strength and water-induced softening characteristics under excavation disturbances, significantly constraining mining face recovery efficiency. Therefore, effectively controlling floor heave in such roadways under mining-induced disturbances is critical. This study employs an integrated methodology combining laboratory experiments, theoretical analysis, field monitoring, and numerical simulation to systematically obtain mechanical parameters of weakly cemented soft rock and characterize floor heave evolution. A mechanical model of floor heave in goaf-side roadways throughout the mining process is established, revealing its failure mechanisms and proposing targeted control strategies. Key findings include: (1) Weakly cemented soft rocks exhibit low cohesion and internal friction angles significantly smaller than those of non-weakly cemented rocks, with a marked reduction in compressive strength after water immersion. (2) Field investigations demonstrate that floor heave predominantly initiates at the mid-floor near the solid coal side during roadway excavation, while during mining, heave magnitude at the coal pillar side progressively increases with advancing working faces, accompanied by dynamic migration of the heave peak toward the coal pillar side. (3) Comparative analysis of floor heave mechanical models during excavation and mining phases reveals persistently asymmetric stress distributions on both roadway sides, which fundamentally drive asymmetric floor heave.(4) A "floor bolts + floor grouting" combined support system is proposed for mitigating mining-induced floor heave. 3DEC numerical simulations evaluating different bolt layouts show maximum heave reduction of 61.4% (from 780 mm unsupported to 301 mm bolted), with optimal control achieved through bolt reinforcement.(5) Field trials of the "symmetrical floor bolts on both sides + floor grouting" scheme demonstrate 74.3% reduction in floor heave within a 100 m advance monitoring zone compared to baseline conditions, confirming the effectiveness of integrated bolt-grouting measures in controlling floor heave in weakly cemented soft rock goaf-side roadways.