In this paper, gangue backfilling mining in an environment of alluvium soil with different thicknesses was simulated using FLAC3D software and taking into account the actual geological conditions of a coal mine in eastern China. Furthermore, the effects of gangue backfilling mining on the surface subsidence in this environment were analyzed. The results show that with an increase in the thickness of the alluvium soil, the surface subsidence basin range significantly increases, whereas the surface subsidence, surface horizontal movement value and final compression ratio of the backfilling body decrease linearly. Moreover, the effect of the alluvium soil’s thickness on the surface subsidence coefficient, surface horizontal movement coefficient and final compression ratio of the backfilling body is larger than that of the bedrock thickness; whereas the effect of the bedrock thickness on the surface subsidence is greater that of the alluvium soil’s thickness. Additionally, with an increase in the proportion of the alluvium soil’s thickness at a certain mining depth, the surface subsidence coefficient increases exponentially and the surface horizontal movement coefficient decreases in a quadratic polynomial. Meanwhile, backfilling mining can significantly limit the failure caused by overburdening and surface deformation, and lead to the key strata supporting the overlying strata and soil mass effectively. Therefore, the soil mass in a thick alluvium soil environment only causes a small deformation, if any, and reduces the rheological behavior of the thick alluvium soil, which is better for the protection of the surface buildings. These findings have great significance with regard to understanding the surface movement rules of gangue backfilling mining in an environment of alluvium soil with different thicknesses, and could lead to better guidance in this area.
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