The state technology in shotcrete has evolved steadily throughout the world and particularly in North America during the last 20 years. The use of supplementary cementing materials such as silica fume, fly ash and slag, the new generations of chemical admixtures and the development of various types of fibres (steel and synthetic) significantly enhance the performance of shotcrete for a variety of applications.

These technological advancements have lead the international mining industry to become a
major user of shotcrete for underground support. Since the potential for instability in
underground rock openings is an existing threat to the safety of miners, the support of
permanent openings in underground mining is a critical and important area of shotcrete
application. For over 20 years, mining companies have recognized the value of steel fibre
reinforcement in shotcrete. It has been proven that steel fibre reinforced shotcrete compares
favourably with steel welded wire mesh reinforced shotcrete in various ground support
applications. At INCO’s Stobie Mine in Sudbury (Canada) in 1996, a study was also
conducted on field pull testing of shotcrete to evaluate possible replacement of mesh by
shotcrete which indicated steel fibre reinforced shotcrete could replace #6 gauge welded wire
mesh where only minor displacements were expected (0-10 mm) after the application of
shotcrete. Where large ground movements are expected plain and steel fibre reinforced
shotcrete as a replacement for mesh may be inappropriate.

It has been established that the introduction of steel fibres in shotcrete increases the energy
absorption or “toughness”, increases impact resistance and provides increased ductility.
Ductility is defined as the ability to continue to carry load after the shotcrete microstructure
has cracked. These mechanical properties are considered extremely important parameters with
respect to support linings designed for the underground environment. (The effects of
addition rate, geometry and property of fibres are beyond the scope of this paper.)

Although the ability of steel fibre reinforced shotcrete to carry loads in flexure beyond the
flexural capacity can be assessed in laboratories using a variety of beam and panel test
methods developed by Europeans, North Americans, Japanese, and recently by Australians,
the understanding of how to relate it to ground support design guidelines for underground
mine development is limited and subjective.

To read the full article, click on the PDF buttons below.