Beam enhancement capacity of a thin fibre-reinforced polymer liner

This study investigates a glass-reinforced polymeric thin spray-on liner and its ability to reinforce substrate surface in underground excavations by the use of laboratory testing. Twenty-three hydrostone beams uncoated and coated with 5 mm thick fibre-reinforced polymer  (FRP) coating were subjected to four-point bending tests to study their strength. The hydrostone beams coated with FRP experienced 1·3 times increase in strength when compared to the plain uncoated beams. Experiments also showed that in addition to the increased strength, the beams failure modes were also altered where the uncoated beams failed in tension while the polymer-coated specimens failed predominantly in shear. To study the influence of the FRP on fractured and notched surfaces, several beams with artificially induced rectangular and V-shaped notches were also tested. The results indicated that a single notch located at the bottom centre of the uncoated specimens led to strength reduction by 86% while polymer-coated notched beams had 13-fold increase in strength compared to a notched but uncoated specimen. The specimen strength further increased when the notch was infilled with the polymer material. Substantial reinforcement of rock substrate in an underground tunnel is possible with the application of this polymeric liner.