Physical modelling as a tool to improve our understanding of mechanisms of cave flow

Abstract

In block caving, gravity flow of broken ore has been studied using different tools, highlighting the application of scaled physical models, numerical modelling and field studies. These tools, with their advantages and disadvantages, have allowed different variables involved during ore draw to be studied. In this paper, we summarise years of physical experiments run in the Block Caving Laboratory to study different underground mining issues. In particular, experiments have been carried out to study fine material migration, induced stresses due to ore draw, secondary fragmentation, hang-ups formed on drawpoints, drawbell geometries, inrush of fines material, and ore extraction in mud conditions. The main significances, its impact and application, are discussed here. This work shows that physical modelling continues to be a powerful and useful tool to study gravity flow in block cave mines, allowing to understand diverse mine engineering problems and to be a practical input to calibrate complex numerical models.

Procedure for estimating broken ore density distribution within a draw column during block caving

“…These represent very uniform gradations from Cu = 2– 2.5 and BOD between 1.4 and 1.7 t/m 3 . This data compilation is in agreement with a cave mining benchmarking study carried out by Castro (2007) who reported a uniformity index Cu of 2.9 for an average block size range from 0.5 to 0.9 m. Data was also compiled for broken ore size distributions measured at the drawpoints for several different caving operations reported in the literature (Figure 9). These represent draw column heights ranging between 60 and 180 m, and also incorporate secondary fragmentation and fines migration processes (which are discussed in the next section).…”

“…These cases involve fragmented rock that share similar characteristics with broken ore in terms of particle size distributions and shapes, and have likewise been used as an analogue to broken ore to support other empirical and numerical cave mining studies (e.g. Castro 2007, Pierce 2009). Although fragmented rock in a draw column is affected by gravitational flow under confinement, this movement is in practice slow enough that inertial forces can be assumed to be negligible, and therefore, the laws of continuum mechanics apply (Verdugo and Ubilla 2004).…”

“…In cases where there is a significant amount of fines close to the drawpoint, large blocks may be found floating in a fine matrix of sand and gravel. Although the fines migration process has been investigated in several empirical (Castro 2007; Cheng et al 2009; Hashim and Sharrock 2012) and numerical (Leonardi et al 2008; Pierce 2009) studies, there is no standard methodology or procedure to evaluate fines migration through a draw column.…”