Crack propagation law at the interface of FRP wrapped coal-backfilling composite structure

Abstract

The coal-backfilling (CB) composite structure jointly bears the excessive stress. The interface between the coal pillar and backfilling is the weakest area. The instability of the interface can induce the splitting failure of the composite structure, and fibre-reinforced polymer (FRP) could be applied to solve this problem. The Brazilian splitting laboratory tests were carried out on the CB composite specimens and FRP wrapped CB composite specimens (WCB) with different interface angles (α = 0°, 15°, 30°, 45°, 60°, 75°, 90°). The failure modes of the above specimens were monitored by using the digital image correlation (DIC) technology. The stress intensity factors (SIFs) and the energy release rates (ERRs) at the interface centre of the composite specimens were calculated. The result shows that three types of failures, namely interfacial crack, tensile crack, and concentrated failure zone, appeared on the composite specimen. The interface angle was an important factor affecting the failure modes of the composite specimens. Interfacial stability of composite specimens could be enhanced by FRP wrapping. The SIFs KI and KII increased, and the expansion of the interface cracks was hindered by FRP wrapping. The critical load in the stable stage and the ERR of specimens were improved by FRP wrapping.