Major hazards associated with cave mining: are they manageable?

Abstract

Cave mining methods have become viable and preferred mass underground mining options where the objectives are low cost and high production rates. However, the cave mining industry has already entered into a less certain period or environment where some of the current cave mining options are already showing not to be fully suitable to achieving the envisaged low cost and high productivity objectives. This environment includes deeper and sometimes blind deposits (up to 1,400 m from surface), lower average grade deposits, harder and heterogeneous rock masses, higher stress and, in some cases, higher temperature environments. This is requiring design of greater caving block heights, demand for increased safety and productivity, and escalating mining costs (capital and operating). In addition, there is increasing shortage of technical skills, capital becoming more difficult to access, and communities desiring higher environmental standards. In this new cave mining environment, several hazards are identified that can have critical impact on safety, productivity and profitability. It is necessary, therefore, that these major hazards be acknowledged, and the likelihood of their occurrence be evaluated and minimised during the deposit investigation, mine design and planning, and operational stages of the caving process. These are not trivial issues and can have the most serious of consequences. They demand serious managerial and technical attention (Brown 2012). This paper focuses on the major hazards associated with the caving process which are rockbursts, air blast, subsidence and inrushes. These hazards are experienced during the cave establishment (development, drawbell opening, undercutting), cave propagation, cave breakthrough to surface, and steady state production stages. Measures to manage these risks aiming to reduce their consequences are also discussed.

Undercutting method selection at Cadia East PC2-3 extension

“…• Newcrest's design and operational caving rules for block and panel caving including seismic management planning, intensive preconditioning (combining hydrofracturing and confined blasting techniques) and dynamic ground support among others (Cuello & Newcombe 2018;Flores-Gonzalez 2019); and…”

SEG Newsletter 119 (October)

“…Moreover, caving is also subject to the range of risks usually associated with large-scale mining of hard rock masses at depth, under conditions of high rock stress. Among these risks is a group referred to as major operational hazards, which in caving include rock bursts, air blasts, subsidence, and inrushes (Flores et al, 2004;Flores-Gonzalez, 2019). If inadequately managed, each hazard has the potential to affect the safety and profitability of the mining operation or sterilize large sections of the deposit, i.e., prevent a portion of the deposit from being mined.…”

“…Destressing FIGURE 6. Rock-burst management strategy using de-stressing technique with remotely operated equipment (Flores-Gonzalez, 2019).…”

“…FIGURE 7. (a, b) Examples of rock-burst damage after opening a drawbell and undercutting(Flores-Gonzalez, 2019); open spaces are about 3 m high.…”

Application of empirical methods to estimate crown pillar failure in caving mines

“…As described by Flores (2019), breakthrough is an important stage in the cave establishment process for caving mines. Breakthrough corresponds to the connection between the growing cave and surface or upper level.…”