Sensitivity analysis of key factors influencing compression-induced deformation of waste rocks for backfilling to reduce environmental pollution.

As solid wastes are generated during coal mining, waste rocks can be backfilled into goaf so as to reduce geological hazards and environmental damage caused by coal mining; however, under different stress regimes, the sensitivities of factors influencing compression-induced deformation (CID) of waste rocks for backfilling (WRBs) are different. In order to control the compression-induced deformation of waste rocks for backfilling more efficiently, compression characteristics of waste rocks for backfilling under four different stress levels were tested by using a homemade loading test system for granular materials based on an orthogonal experiment. The influences of lithology, particle size distribution (PSD), lateral stress, and number of lateral loading cycles on compression-induced deformation of waste rocks for backfilling and sensitivities ranks of the four factors were analysed. The test results showed that: (1) under an axial stress of less than 10 MPa, lateral stress was considered the main factor influencing compression-induced deformation of waste rocks for backfilling; when the axial stress ranged from 10 to 20 MPa, particle size distribution was the main influencing factor; (2) under four different axial stress levels, the optimal combination of influencing factors is sandstone, a particle size distribution from 0 to 10 mm, 3 MPa lateral stress, and 7 lateral loading cycles; (3) to control the compression-induced deformation of waste rocks for backfilling, it was necessary to optimise the lateral stress under an axial stress of less than 10 MPa; while the axial stress was between 10 and 20 MPa, it was essential to optimise the particle size distribution.

Recycling of crushed waste rock as backfilling material in coal mine: effects of particle size on compaction behaviours.

Crushed waste rocks can be used as materials for backfilling goafs, so as to achieve the simultaneous goals of processing solid waste and controlling surface subsidence; however, particle size distribution directly affects the compaction of crushed waste rocks. Therefore, by employing a self-designed bidirectional loading test system for granular materials, this study tested compaction characteristics of crushed waste rocks with four different particle size distributions. Moreover, this research tested the changes of parameters in lateral and axial loading of crushed waste rocks and analysed the influence of particle size distribution on lateral strain, axial strain, porosity, lateral stress, and lateral pressure coefficient during compaction. The test results show that (1) particle size distribution affects porosity, strain, and lateral pressure coefficient of crushed waste rocks under lateral and axial loading. (2) For the samples under particle size distribution ranging from 0 to 10 mm, the initial porosity is low and deformations are small under axial loading, so that particles can make contact and bear effective stress in grain-grain contact. Therefore, more stress is transferred to the lateral direction. (3) After compaction, the curves of the samples of crushed waste rocks under four particle size distributions all shift upwards in comparison with those before compaction, indicating that particles are crushed and the proportion of small particles constantly increases. (4) A reasonable particle size distribution can significantly improve stress characteristics, reduce crushing of particles in the samples, and increase the stiffness of the samples, so as to achieve better compaction effects.