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Abstract
Knowledge of particle percolation impacts on both the economics and safety of cave mining operations. Nevertheless, very little research has focused on particle percolation in block or sub-level caving mines. The aim of this thesis is to study the percolation of fine particles in highly angular particle assemblies similar to caved rock, using physical and discrete element numerical models.
In the first stage the magnitude and distribution of shear strain resulting from isolated draw was measured using scaled physical models (1:100) on 13.20 mm crushed basalt aggregate. Digital images of marker particles were taken after each draw cycle and the changes in shear strain were calculated.
In the second stage, a Shear Cell for Percolation of Geomaterials (SCPG) was designed for angular rock particles. Percolation tests were carried out for ideal media consisting of steel spheres (4.00 mm), glass spheres (4.00, 5.00, 6.00, 15.75 mm) and plastic spheres (4.00 mm) and highly angular crushed basalt aggregate (2.86, 4.05, 5.21, 6.18, 13.20 mm). Key combinations of fine and bed-matrix particles were tested to quantify the effect of strain rate, particle diameter ratio, density and shape. Of the parameters tested, percolation was most influenced by particle diameter ratio, shape and strain rate, while density had the least effect. To explore the mechanisms controlling percolation across the range of tested particle shapes and sizes, a dimensionless percolation rate (DPR) relation was derived using the method of Bridgwater et al. (1978).
In the third stage selected SCPG experiments were numerically simulated using PFC3D. Due to the limitations of PFC, particle shapes and sizes were simplified and all other parameters were kept as similar to the measured parameters as possible. Results from the physical SCPG experiments on angular particles were simulated using clump logic. The results were compared to corresponding numerical and physical experiments on mono-spherical particles with the same equivalent spherical diameter as the angular particles. The PFC results had broad agreement with the SCPG physical experiments showing that percolation is predominantly affected by particle shape and the ratio of fine and bed-matrix particle sizes.