ABSTRACT:

In underground coal mines, rockbolts and cable bolts are two dominant forms of support elements to prevent instability of the surrounding rock mass. Using these steel anchoring elements with high strength and toughness provides better rock reinforcement in high stress environment, however failures identified of being caused by Stress Corrosion Cracking (SCC) have been observed. SCC is a substantial problem in a number of underground mines in Australia. It is difficult to detect and can result in catastrophic consequences without warning. Understanding and predicting this failure phenomenon plays a very important role in keeping the underground support system in good performance. This paper outlines the major developments of a study on SCC failure of the steel anchoring elements based on laboratory tests. SCC detecting technologies are discussed and, advantages and shortcomings related to each technology are provided. A SCC-Acoustic Emission (AE) testing system was set up in the Controlled Mine Environment (CME) laboratory at UNSW Australia that is aimed to provide a better understanding of this failure mode as well as to determine whether there is any relationship between AE signal activities and corrosive damage mechanisms. The test results showed the laboratory samples failed in a brittle manner and the cracking propagated in the transgranular mode. Evidences were found the cause of the failure is SCC.

1 INTRODUCTION

Rockbolts and cable bolts are two dominant forms of high capacity supports used in rock reinforcing system in underground coal mines inAustralia (Rajapakse 2011). Rockbolts are the primary form of ground support for roadway development with typically length up to 2.4 m. Cable bolts are widely used as auxiliary support materials with length up to 8 m. Typically, rock bolts and cable bolts are installed in predrilled holes at regular spacing in the roof (after (Hutchinson & Diederichs 1996) as shown in Figure 1.

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