**Abstract**

The primary objective of this research is to provide practical mine ventilation engineering tools (i.e., cave resistances and pollutant emission rates) to model and predict adequate airflows and pressure drops across the cave with respect to cave propagation in underground block or panel cave mines. We used several research methods to investigate the phenomenon of cave ventilation and pollutant gas emissions in block or panel cave mines. The research methods include computational fluid dynamics (CFD)—continuum and discrete approaches in conjunction with advanced geo-mechanical analysis through numerical modeling, scale model studies, mathematical modeling, field observations, discrete fracture network (DFN), flow through porous media, particle flow code (PFC), Ventsim, MATLAB, and Python programming. The study investigated the several research questions related to block or panel cave mines: immature and mature cave properties, radon and airflow behavior, radon control measures, cave characteristics, ventilation on demand, blasting fumes, prediction of porosity, and permeability of different cave zones, the effect of undercut ventilation, forcing, exhaust and the push-pull system, the effect of airgap, and broken rock porosity and permeability on the cave ventilation system. The findings from this study provide useful information for optimizing the block or panel cave mine ventilation systems.

**Keywords:** block cave ventilation, panel cave characteristics, discrete fracture network (DFN), radon control measures, flow through porous media, computational fluid dynamics (CFD)

### **1. Introduction**

In the panel caving method, the caving process begins with the ore blasting, then drawing the broken ore from the draw points located at the production level. The extraction of broken ore creates a void volume inside the cave. This void (known as an airgap) and gravity do the rest of the work in breaking the ore in the cave. This rock-breaking process continues as the broken ore is withdrawn from the draw points (**Figure 1**).

### **Figure 1.** *Panel caving schematic [1].*

The cave initiation is when the caving activity begins, and the hydraulic radius starts to form. As a result of stress increment after the blasting, a stable arch forms in the rock mass. However, the arch cannot resist gravitational stresses indefinitely, and as the cave propagates and the hydraulic radius continues to increase, rock failure will re-initiate. The hydraulic radius at which propagation is achieved can be interpreted as the limit of cavability. However, caving can only actualize when the cave draw starts, and an airgap is created by removing the support provided by the caved rock mass [2].

At the study site (panel cave mine), the panel arches over with a maximum height of 550 m. The ore body rock mass rating (RMR) ranges from 27 to 60, with uniaxial compressive strengths typically ranging from 100 to 275 MPa. Although this is at the high range for caving, there have been minimal problems initiating and advancing the cave because of the lubricating property of the mineral and fillings on the geologic structures [3].

It is already known that gravity and the stress induced in the crown or back of the undercut or cave are the two major factors that trigger the caving event. Caving occurs in two distinct situations—a low-stress environment, where gravity falls due to the lack of confinement is the dominant mechanism; the other extreme, in which the induced tangential stresses are high compared with the compressive and shear strength of the rock mass. This form of caving is often referred to as stress caving [2].

In the caving mining methods, assessing the initiation and growth of caving in rock masses is important to determine the higher-production, lower-cost method. Currently, experience and empirical methods based on the rock mass characterization, such as rock quality designation (RQD), Norwegian Geotechnical Institute's Q system, and rock mass rating system (RMR), are integrated to predict the hydraulic radius for sustained cave growth and the resulting "break" angles and propagation rates of the cave as it grows to the ground surface.

Although this mining method seems most straightforward, it has to be designed carefully; otherwise, the rock will not break properly; hang-ups will develop in the cave. This will result in the development of a large airgap, which can create dangerous conditions in the form of air blasts.

### **1.1 The sequence of operations in a panel cave mining**

The sequence of the caving operation starts by advancing the undercut level. A set of parallel and horizontal tunnels is created to develop the upper cavern of

*Block Cave Mine Ventilation: Research Findings DOI: http://dx.doi.org/10.5772/intechopen.104856*

broken rock. In the second phase of the production, parallel to the undercut level, the production level is advanced. To collect ore beneath the rock mass, vertical holes are drilled to form funnel-shaped structures called drawbells, which are created above the production level, and extend to the undercut level. The broken ore is extracted from draw points and loaded into the equipment to deliver to the ore passes or an underground crusher.
