Fibre reinforced shotcrete application in an underground tunnel
The South African mining industry has become a major user of fibre-reinforced shotcrete for underground support. This is according to CHRYSO Southern Africa technical sales consultant Willie Nel, who reports a growing uptake for the CHRYSO CSF 6000 high performance macro-synthetic fibres in this application.
Fall of ground (FOG) is recognised as one of the leading causes of injuries and fatalities in underground mines and fibre reinforced shotcrete is being used as an important tool in the quest to eliminate FOG incidents.
The industry traditionally used reinforced shotcrete with wire mesh or welded mesh before moving to the use of fibres. Initially steel fibres and then rigid polypropylene, so-called ‘broombrissel’ fibres were used but there has been an increased switch to the use of polypropylene homo-polymer fibres, which are described as soft tape fibres.
“The move to soft tape fibres gained traction from around 2012,” explains Nel. “During that period, we have experienced growing demand for our CHRYSO CSF 6000 high performance macro-synthetic fibres which are specifically designed to satisfy the demanding requirements for modern day shotcrete reinforcement technology. In our experience, the trend is largely being driven by new mining projects.”
A major advantage of the CHRYSO CSF 6000 is said to be its flat, flexible nature which leads to better tensile strength than, for example, the rigid ‘broombrissel’ counterparts. In addition, it is engineered to combat the formation of plastic shrinkage and plastic settlement cracking, while still providing high impact-, abrasion- and shatter-resistance. Nel emphasises that the technology boasts greater ductility, which allows it to deform under tensile stress, as well as enabling greater energy absorption.
“Traditional reinforcement practices such as wire mesh and welded mesh are not conducive to high productivity and are costly due to the labour-intensive process of mesh installation. In contrast, macro-synthetic fibre-reinforced shotcrete is a system capable of supporting rapid application and semi-automation,” concludes Nel.