Numerical Studies of the Floor Heave Control Method in Gob-Side Entry Retaining in Deep Coal Mines

In the case of pillarless coal mining, the floor uplift reaches 60–80% of the total vertical convergence in gob-side entry, while total convergence often exceeds 1.0 m. This is one of the key factors impedimental to pillarless mining in deep coal mines. Traditional methods of floor heave control in gob-side entry are not effective enough, so they need to be improved. This paper is devoted to the improvement of the anti-shear pile method in gob-side entry retaining. Finite element analysis was used as the main study method. The influence of pile diameter and its design on the stress–strain distribution in the surrounding rock and on the floor uplift magnitude was determined. It was found that the filled piles are the most efficient in reducing floor heave magnitude, asymmetry of floor uplift, and size of post-peak strain in the immediate floor. In filled piles, the steel tube prevents the concrete core from fracturing, while the concrete core prevents the steel tube from plastic yielding. Therefore, with the same diameter and elastic modulus, filled piles are 1.06–1.7 times more effective in floor heave control than comparable analogs.