Experimental study of gravity flow under confined conditions

• Gravity flow experiments were conducted for the first time under vertical load.
• Secondary breakage for coarse rock due to compaction was quantified.
• A flow-ability graph was built for designing underground mines.
• Hang up frequency was quantified as a function of vertical load.

Caving methods rely on gravity to break up and transport large amounts of ore and waste. Massive underground mining is becoming even more prevalent due to the depletion of surface mining reserves. It is thus relevant to study the gravity flow mechanisms that will occur at deeper levels. Despite the importance of gravity flow, there is a lack of quantification of the influence that confinement (the weight of the ore column) has on the secondary fragmentation and the caved rock ability to flow. This paper presents the design and results of an experimental setup used to investigate the flow mechanisms of cohesionless material when drawing from a single drawpoint under confinement. Experimental results showed that the flowability of the material is influenced by the rock fragment size, dimension or diameter of the opening and the vertical load applied. Secondary fragmentation is mainly influenced by the vertical load applied and the size distribution of the fragmented rock. Finally, flowability mechanisms are presented in terms of a state graph and a hang-up frequency graph, both of which could be used for the design of openings in mining.