ABSTRACT:
Doe Run’s Southeast Missouri Mining and Milling Division (SEMO) currently operates six underground room and pillar mines which produce approximately 5.1 million tonnes per year of lead, zinc and copper ore. Pillar extraction represents approximately 34% of this tonnage and 44% of the total lead, 43% of the total zinc and 18% of the total copper metal produced. Estimating a pillar’s strength has long been a goal of both mining researchers and mining practitioners. This paper presents the successful application of an established computer code and a novel strength prediction method for estimating pillar stability and will show how numerical modeling can play a significant role in day-to-day mining operations. Since 1986, Golder Associates has been successfully using Displacement Discontinuity models to predict pillar stability for the Doe Run Company at their SEMO operation. Traditionally, the pillar height to width ratio, along with the intact rock strength and empirical constants, were used to estimate pillar strength. More recently, the Confinement Method combining the traditional pillar strength ideas with the observation that the inside of a pillar is stronger than the outside has been applied. The outcome of using this method in the extensive modeling of the SEMO operation and the use of AutoCAD scripting for processing and analyzing results is a robust model that can be calibrated accurately to observed pillar conditions.
1 INTRODUCTION
The Doe Run Company is the largest integrated lead producer in the US and the third largest in the world, supplying approximately 60% of the total lead used in the U.S. Doe Run’s domestic operations own and operate two primary lead smelters, the world’s largest single site recycling factory, two lead fabricating sites, four mills and six undergrounds mines (Fletcher, Brushy Creek, Casteel, Sweetwater, No 29 and the Buick Mine) in southeastern Missouri.
