Impact of Multilayered Fibre Reinforced Shotcrete on Structural Integrity: A Study in Underground Mining

Fibre reinforced shotcrete (FRS) is commonly used in underground mining, tunnelling, and many other applications to support the stability of the substrate structure. Thick shotcrete must be sprayed in multiple layers due to either the constructional need of the composite structure or operational need of preventing shotcrete fall or wet decohesion. The purpose of this study is twofold. The first one is to conduct a systematic review of shotcrete, fibre reinforced shotcrete, typical tests and strength values, and failure modes of shotcrete. The second one aims to investigate the effect of multilayered FRS on the uniaxial compressive strength and flexural toughness. The study was conducted in an underground mine in Australia and the test results were compared with the data of quality control and quality assurance (QCQA) in the mine. Rectangular and round panels were sprayed with a pause of 12 h between layers. The rectangular panel was used to core samples for compressive tests and round panels were for flexural toughness tests at 28 days age. It is found that it is impossible to distinguish the layer boundaries on the crosscut of the rectangular panel, or no cold joint on the interface of multilayered fibre reinforced shotcrete. Furthermore, both the compressive strength and flexural toughness meet the QCQA criteria applied in the underground mine, and there is no reduction in the compressive strength of multilayered fibre reinforced shotcrete and an insignificant difference in the flexural toughness.