Abstract
Crushed waste rock (CWR) can be used as backfill for goafs allowing disposal of solid waste and control of surface subsidence. Waste rocks for backfilling (WRBs) have a certain density before use if cyclic lateral loads are applied to CWRs, therefore, by employing a self-designed bidirectional loading test system for granular materials, the influence of the number of lateral loading cycles on the compaction characteristics of WRBs was explored. Through testing, changes in mechanical parameters of WRBs during lateral and axial loading were attained to analyse the influence of lateral loading on lateral strain, axial strain, porosity, and lateral pressure coefficient during their compaction. The test results showed that: (1) the lateral loading exerted a significant influence on the porosity, strain, and lateral pressure coefficient of crushed WRBs during lateral and axial loading; (2) under lateral load, the more cycles of lateral loading applied, the greater the lateral strain and the reduction in lateral porosity of samples; (3) during axial loading, for samples subjected to multiple cycles of lateral loading, owing to the porosity of WRBs having been decreased in advance to improve their density, the final axial strain was low; (4) after compaction, the particle size distributions of CWR samples after different numbers of cycles (1, 3, 5 and 7) of lateral loading all shifted upwards compared with those obtained before compaction, implying that rock particles were crushed. However, the number of cycles of lateral load did not affect crushing of particles before, and after, compaction.
Highlights
The mining of coal resources results in the generation of waste rock from washing and mining operations
We investigated the influence of lateral loading cycles on compaction characteristics of WRBs
Based on the experimental data from samples recorded during lateral loading and results calculated by use of Formulae (1) to (3), the changes in strain and porosity of WRB samples after different numbers of cycles of lateral loading can be acquired (Figure 9)
Summary
The mining of coal resources results in the generation of waste rock from washing and mining operations. The presence of waste rock dumps occupies land, and leads to serious environmental pollution [4,5,6]. 5.5 × 109 t, forming more than 1600 waste rock dumps, which occupy a land area of 15,000 ha [7,8]. The discharge increases at the rate of 4 × 108 to 8 × 108 t annually If this waste rock fails to be appropriately disposed of, severe environmental issues arise [9,10,11,12], To solve the problems caused by discharge of waste rocks, we proposed direct backfilling of goaf with waste rock: waste rock is crushed and transported to the underground coal face and filled into goaf [13,14,15]. The method can dispose of solid waste rocks and can control stratum movement and surface subsidence
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