Early-age load resistance of fibre reinforced shotcrete linings

Widespread interest has developed into early-age strength development for fibre reinforced shotcrete (FRS) and its influence on the time to safe re-entry immediately after spraying. Cycle times for drive development within mines, and in civil tunnel construction, can strongly depend on the time to safe re-entry and this, in turn, affects excavation progress rates and overall project economy. The majority of research into safe re-entry times has focused on strength development in hardening shotcrete under the assumption that toughness, adhesion to the rock surface, and the ability of the FRS lining to support unstable ground are all related to the strength of the concrete matrix. Although anecdotal evidence supporting this assumption has been gathered through observations of satisfactory ground control at mines utilizing FRS for ground support, ad hoc evidence alone cannot be used as a basis for rational estimation of safe re-entry times. Instead, the present investigation has sought to quantify the parameters that influence early-age FRS lining capacity and develop an engineered approach to shotcrete lining design and estimation of safe early-age re-entry times through a rational assessment of load resistance.