Page 174 - Failure Analysis Case Studies II

Failure Analysis Case Studies I1
D.R.H. Jones (Editor)
0 200 I Elsevier Science Ltd. All rights reserved IS9

CATASTROPHIC FAILURE OF A RAISE BORING
MACHINE DURING UNDERGROUND REAMING
OPERATIONS

ALAN JAMES
Metallurgical and Corrosion Services Programme, MATTEK, CSIR, Private Bag X28.
Auckland Park 2006. Republic of South Africa
(Received 29 August 1996)

Abstract-This paper describes the investigation of the catastrophic failure of a raise boring machine used for
underground reaming operations. The results of the investigation indicate that failure was due to the fracture
of the 32 drive head bolts, 30 of which had failed as a result of corrosion-induced fatigue. Metallurgical
examination confirmed that the bolts had been manufactured in accordance with the SAE 5429 Specification.
A number of recommendations have since been implemented by the mine, who have also introduced a quality
system specifically for the control of drive head bolt sets. The equipment has now operated without problems
for several years. Q 1997 Elsevier Science Ltd. All rights reserved.

I. INTRODUCTION
The process of raise boring (or back reaming) has been in use for over 30years, and has proved to
be a very successful technique in underground mining operations. Its primary use is in the production
of interconnecting vertical or near vertical channels (raises) between underground levels in mines.
However, this method of rock drilling can also be used for producing channels at any angle between
the vertical and the horizontal [l].
This technique of underground drilling was developed to overcome some of the problems of
personnel safety in the mining industry. Previously, the process of drilling and blasting was used,
which required people to enter dangerous areas of mine workings. The development of raise boring
techniques also gave the mining industry a new method to construct long ore passes and ventilation
raises which is economical in both time and cost.
Current raise boring operations are used to produce raises of up to 6.0m in diameter and up to
I000 m in length.

2. REAMING PRINCIPLES
2.1. Rock mechanics
The process of drilling and boring in rock differs from other similar engineering operations in
two respects [2]. Firstly, the diameters and lengths of holes and tunnels in rock are usually much
greater than those made in other materials, and the volume of material removed in making them is
especially large. Secondly, the mechanical properties of rock differ significantly from those of other
engineering materials. The latter usually deform in an elastic-plastic manner, whereas most rocks
deform in an elastic-brittle manner. Rock is also a very abrasive material.
Typical stress-strain curves for an elastic-plastic material and an elastic-brittle rock are shown
in Fig. 1. A consequence of the brittle or work-softening nature of rock deformation is that it tends
to be unstable, and results in the formation of chips when a rock surface is loaded by an indentor
of any kind. Virtually all mechanical devices for drilling or boring rock behave like indenters.
However, the precise form of these working tools varies considerably in accordance with the
strength, brittleness and hardness of the rock which they are designed to work. In general, they do
not cut the rock in the usual sense of the word, but cause it to spa11 away on cithcr side of the area

Reprinted from Engineering Failure Analysis 4 (l), 71 -80 (1997)