Pillars have a central role in an active stress management approach, which has been proposed for the extraction of thick tabular and massive hard-rock mineral deposits. A mining method making use of this approach, is the novel raise caving mining method. Initially, the pillars have width-to-height ratios of 5 to 10. In the course of stope extraction, the dimensions of the pillars are altered, namely the height of pillars is increased and the width of pillars may be decreased. Consequently, the pillar strength is reduced and pillar crushing is triggered. A stable crushing process must be ensured. Knowledge on the complete stress-strain behavior of massive hard-rock pillars is paramount for the design of these pillars. However, a review shows that there is insufficient knowledge available. An in-situ pillar test is found to be best suited to improve the knowledge. The need for, objective of and design of such a full-scale in-situ pillar test are discussed. An in-situ pillar test is planned in one of LKAB's underground operations in connection with the development of the raise caving mining method. The layout and sequence of the test and the current progress of design and open points in the design are outlined.
Pillars are used in underground mining for several, different purposes. The tasks for pillars comprise regional support of the overburden strata (panel pillars), local support of the immediate roof strata (crush pillars), the separation of adjacent extraction areas (inter-panel pillars), the control of regional convergence and the associated limit of mining-induced seismicity and abutment stresses (stabilizing pillars) and the protection of critical infrastructure, such as shaft systems (protection pillars). This paper addresses massive hard-rock pillars, which take over a central function in an active stress management strategy in massive deposits or in thick tabular deposits. Due to the shape and dimensions of the deposits and the considered purpose, the pillars are massive and they have a width and height in the range of several tens of meters and a length of up to and more than hundred meters.
