Effects of particle size of crushed gangue backfill materials on surface subsidence and its application under buildings

In recent years, solid waste backfill mining has developed rapidly and widely used to control surface subsidence and reduce accumulation of solid waste. As crushed materials are used to backfill goafs, the particle size of backfill materials becomes a key factor influencing the control of surface subsidence. To analyse the influences of particle size of backfill materials on surface subsidence, the compaction properties of crushed gangue backfill materials (CGBM) with different particle sizes were tested by using the YAS5000 testing machine and a self-made compacting device. Moreover, based on the strain hardening behaviour of CGBM in the process of compaction, a method of simulating CGBM using double-yield model was put forward. By employing this method in simulation, the influence of particle size of CGBM on surface subsidence was studied. The research results are demonstrated as follows: with the increase in particle size of the backfill materials, these maximum values such as the maximum surface subsidence, horizontal movement, inclination, curvature, and horizontal deformation increased gradually. Little difference was found in the surface subsidence and movement while using CGBM with particle sizes in the ranges of 2.5–16 and 2.5–50 mm with uniform gradation. However, both values were obviously smaller than those using CGBM with particle sizes of 20–31.5 and 31.5–50 mm. In terms of samples with particle sizes of 2.5–50 mm, the gradation of particles was uniform. By using large particles to form frame structures and small particles to fill fractures, such structures with strong anti-deformation abilities produced a small amount of deformation under the load from overlying strata. Therefore, this structure exerted a good controlling effect on surface deformation.