ABSTRACT:

The highwall mining method was introduced in Australia in early 1991. Since then, at least 13 mines have used this method to mine coal. Abundant experience has been accumulated during the past 8 years, through some failures as well as successes. This paper presents a brief review of highwall mining experience at four Australian mines, with focus on geotechnical issues affecting mining performance. The paper also summarizes one case study, which involved major pillar/roof instabilities. The aim of the review and the case study is to assist the highwall mining industry to learn from past experience and to avoid similar instabilities in the future.

INTRODUCTION

Highwall mining is a remotely controlled mining method which extracts coal from the base of an exposed highwall, typically via a series of parallel entries driven to a significant depth within the seam horizon. The method allows recovery of coal from surface pits that have reached final highwall position due to uneconomic stripping ratios, or in areas where coal has become sterilized in, for example, service corridors. The current highwall mining technologies originated in the USA in the mid-1970's. Two types of highwall mining systems have been commonly used: the Auger System which creates separate or twin circular holes of various diameters, and the Continuous Highwall Mining System (CHM) which mines rectangular entries, usually 3.5m wide. These technologies were first utilized in Australia in early 1991 when Callide Mine used an Auger System to mine coal. Since then, at least 13 coal mines in Australia have applied the highwall mining technologies over more than 30 pits. The CHM has been more widely used than Augers because of its advantage in productivity and recovery rate. A typical CHM operation is illustrated in Figure 1.

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