Abstract

Flowability is defined as the flow capability of a given granular material to flow under a given drawbell geometry and vertical stress condition. Gravity flow interferences of the broken material at a drawpoint (hang ups) highly influence the efficiency and production rate in block/panel caving mines. Despite its importance in underground block/panel, there is a lack of methods to estimate the flow-ability and hang up frequency for a given set of geotechnical conditions (vertical stress, particle size, fine content, drawbell geometry). The main objective of this article is to describe research conducted at the University of Chile, Block Caving Laboratory aimed to quantify the influence of the fine material, humidity and vertical load on the gravitational flow of caved rock. Experiments were conducted using a 1:75 scaled physical model to evaluate the flowability of caved rock under high vertical loads and with various percentages of fine material and humidity. The results show that vertical pressure fine contents and humidity highly influence flowability and hang up frequency.

1. INTRODUCTION

Block/panel caving mining methods are adequate for exploiting massive, low-grade ore bodies because of their low productions costs, compared to other underground mining methods. High productivity and low operational cost, in addition to automation potential, make these methods a key factor in future massive deposits mining (Brown 2007).

In block/panel caving, ore production is affected by interferences associated with the caving process, especially those related to the gravity flow (Chitombo 2010). Hang ups and oversize rocks are the most common phenomena, which affect the mine design, draw strategies, mine recovery and, consequently, production rate.

Ore flow depends on ore properties, infrastructure geometry, and stress conditions. The flow condition or ability of a granular material to flow is defined as flowability. The flowability can be qualitatively classified into free flow, intermittent flow, assisted flow, and no-flow (Castro 2014). This classification depends on the ratio of particle size to opening size of the drawpoint (Laubscher 2000). Kvapil (2008) indicated that flowability depends on many parameters including particle size, extraction rate, particles´ shape, surface roughness between particles, friction between particles, moisture content, compressibility, compaction, particle resistance as well as magnitude, distribution and direction of external loads and forces. However, to-date, the flow characteristics have not been well defined quantitatively (Gómez et al 2014). Studies using gravel show that the flowability of granular material is influenced by the vertical load (Fuenzalida 2012). Castro et al (2014) proposed a chart to present flowability of coarse and dry material in terms of vertical stress and drawpoint width/d50 (Figure 1). These charts were derived based on the experiments carried out using dry material and without the presence of fines.

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