ABSTRACT
Behaviour of fragmented ore and waste rock can affect the rock mass behaviour. Fragmented rock mass usually compacts and that may not only provide confinement to the surrounding rock mass but can allow for transfer of stresses. Such transfer may result in ground deterioration around drawpoints and crosscuts on the extraction level.
Movement of fragmented ore and waste rock by draw affects rock mass response in caving zones, open stopes and orepasses. Draw enhances caving and prevents broken ore compaction. Slow draw rate or its suspension can prohibit caving, cause structural damage to drawpoints, and result in water accumulation (that can cause mud rushes). Controlled and consistent draw is used to control wall deterioration/collapse in the stopes (e.g. shrinkage stoping) or orepasses. In orepasses, it is a common practice to keep orepasses full, and limited draw is used to prevent wall deterioration by wall sloughing and formation of breakouts. There is a direct relationship between rock mass response and fragmented material movement.
The behaviour of fragmented ore (ore flow) in the cave zone in response to drawing is governed by ore fragmentation, rock size distribution and drawing practices. It can also be indicative of damage to the surrounding rock mass.
Two case studies of ore flow in caving mines and the behaviour of broken material in orepasses are presented, namely a case study from a block caving mine and a case study from a sublevel caving mine. Mining and draw parameters such as height of the draw zone, tonnage drawn, and diameter of the draw zone are compared.
Behaviour of fragmented ore in orepasses and factors contributing to hang-ups in the passes are discussed.
