"Observations of Shotcrete Performance in Dynamic Loading Conditions"

Christopher C Langille

Shotcrete has become an increasingly important ground support system in the mining industry to cope with continual rock mass deformation associated with changes in stress conditions brought on by mining. Shotcrete is now considered a viable and valuable ground support option. Most mining engineers or operations personnel would describe the benefits of shotcrete as ground support in very general terms (ie: shotcrete is used to provide support, reduce reconditioning cost, improve safety and/or acts as a protective cover and protection to the primary support), with little actual understanding about how shotcrete functions in an underground tunnel or mine opening.

As a form of ground support, steel mesh reinforced shotcrete can act to reinforce and/or to retain the rock mass. The required support function will govern which of the different attributes or properties of shotcrete will be important in a particular application. These attributes include:

· the adhesion of the shotcrete to the rock (both mechanical and effective adhesion),

· unconfined compressive and tensile strength of the shotcrete,

• integrity and continuity of the shotcrete lining and of the mesh/fibre steel reinforcement embedded within the shotcrete,
• rock mass quality behind the shotcrete
• corrosion protection of the mesh
• connection to the holding elements (bolts/plates),

· stiffness and toughness of the shotcrete and mesh system, and

· ductility of the shotcrete and mesh system.

It is not well understood which of these attributes govern the reinforcement and retaining support functions in bursting conditions. However, it is proper to conclude that not one, but a combination of these attributes contribute collectively to the ability of a thin mesh reinforced shotcrete liner to provide substantial support capacity in dynamic loading conditions. This paper presents examples of a record and interpretation of observations of mesh reinforced shotcrete performance in direct response to mining and is based on the author’s observations of the performance of shotcrete in response to high stress, dynamic loading conditions in the Sudbury Basin, Ontario, Canada and with reference to experience in Western Australian mines.