Evaluation of deformation characteristics and bearing capacity assessment of crushed-rock backfill with various grain size distributions

This study addresses issues related to deformation processes in crushed rock backfills, which are used to control the condition of surrounding rocks in the extraction areas of coal mines. The task under consideration is to maintain mine roadway stability by preventing roof collapses in the gob area by ensuring the bearing capacity of backfills. Deformation processes were studied on model materials made of crushed rock of various grain-size distributions and bulk densities. The material was subjected to compression testing, which simulated the complete backfilling of the gob area. It was shown that the energy characteristics of deformation and compaction of crushed rock determine the bearing capacity of backfills. The deformation energy density was determined by the grain-size distribution of the crushed rock with a polyfractional composition. The maximum values of the specific potential deformation energy were recorded during compression of crushed rock with a coefficient of uniformity Сu = 5.99, which has a stiffness 7–13% higher than that of polyfractional materials with Сu < 4, which ensures the bearing capacity of the backfill mass. It was established that with an increase in the compaction coefficient of the backfill material, the relative volume change per unit of convergence, ΔVK (m⁻1), occurs according to a hyperbolic relationship, allowing the prediction of the ultimate compaction of the backfill material. The stability of gob-side retained entries can be ensured by complete gob backfilling. The expected settlement of the backfill material determines the nature of the limitation of lateral rock movements in the gob area, the bearing capacity of the artificial massif, and depends on the grain-size distribution of the crushed rock