Mechanism and control measures for floor heave in gob-side entry of weakly cemented soft rock

Weakly cemented soft rock goaf-side entry, as a typical extraction entry, faces the characteristics of low Surrounding Rock strength and water-induced softening. Under excavation and mining-induced disturbances, the entry experiences significant deformation dominated by floor heave, severely restricting safe and efficient working face extraction. Therefore, investigating the mechanism of floor heave in weakly cemented soft rock goaf-side entries and its control measures has become a critical issue for ensuring efficient production. This paper adopts a comprehensive research methodology integrating laboratory tests, theoretical analysis, field monitoring, and numerical simulation to systematically manuscript the water-softening behavior of weakly cemented soft rock and the evolution law of floor heave, establishing a mechanical model of floor heave throughout the mining process in goaf-side entries, revealing its disaster-causing mechanism, and proposing targeted prevention and control strategies. The main conclusions are as follows: (1) The cohesion of weakly cemented soft rock is relatively low, and its internal friction angle is significantly smaller than that of non-weakly cemented rocks. After water immersion, the weakly cemented soft rock exhibits a pronounced characteristic of reduced compressive strength.(2) Through field investigations, during the entry excavation period, the floor area near the solid coal side at the center of the entry is more prone to floor heave. During the extraction period, as the working face continuously advances, the heave magnitude on the pillar side gradually increases, and the heave peak dynamically shifts toward the pillar side.(3) By comparing the mechanical models of floor heave in the goaf-side entry during the excavation and extraction periods, it is evident that the stress levels on both sides of the entry remain asymmetric throughout both phases. This asymmetric stress on the entry sides is the primary cause of the resulting asymmetric floor heave.(4) The "floor corner bolt pile" technology is proposed to control floor heave during extraction. The 3DEC numerical simulation software was used to simulate the control effects of different floor bolt layout schemes on floor heave. When no floor support measures were implemented, the maximum floor heave in the entry was 780 mm. After installing floor bolts, the maximum reduction in heave magnitude reached 61.4%.(5) Based on simulation results, the "floor corner bolt pile" solution was field-tested. The entry's floor heave magnitude decreased by 74.3% compared to the unsupported condition, demonstrating that implementing floor bolt reinforcement combined with floor grouting effectively mitigates floor heave in weakly cemented soft rock goaf-side entries.