Ground Control in Hard Rock Using Fibre Reinforced Shotcrete

Dr. E. Stefan Bernard, TSE P/L, Australia.

Introduction

Fibre Reinforced Shotcrete (FRS) linings have been used for ground support in tunnels and mines for many years. Several guides exist on the use of shotcrete in general construction [1-3] and these provide advice on issues ranging from mix design to spraying technique. However, load determination and resistance design for ground support in underground applications have seldom been addressed in a comprehensive manner. FRS linings for civil tunnels are commonly designed using methods such as that provided by the DBV [4], but ground control using FRS linings in mines is more commonly based on simple methods developed from basic engineering principles [5, 6]. This paper provides a review of methods of design for FRS linings based on the limited number of available papers and guides together with experience gained in the Australian mining industry.

The reasons why FRS linings are used for ground support include the demonstrated ability of shotcrete linings and rockbolts to effectively stabilize a wide range of ground conditions with little more that a variation in strength, toughness, or geometry necessary to accommodation different levels of stability. This makes FRS linings possibly the most adaptable method of ground control available. However, there are limits to its effectiveness and economy that mean it is not suitable for all circumstances. Another motivation for the use of shotcrete is that it conforms to the profile of the ground and does not require formwork. This increases its effectiveness for immediate support of ground and greatly reduces construction costs. Indeed, once the initial hurdle of establishing a capacity for delivery and spraying is overcome, shotcrete has been found to be economical when compared to alternatives in most ground conditions, especially when varying conditions or geometry are encountered. In addition, the durability of shotcrete is good compared to alternatives, although problems of corrosion remain a concern for steel fibres and conventional reinforcement, especially at cracks.

NBM&CW April 2011