Estimating propagating velocity through steel fibre reinforced concrete

Steel fibre reinforced concrete (SFRC) is the primary lining in many urban constructions including tunnels. The thickness of the tunnel segmental lining blocks is highly precise: within ±1 mm of the nominated thickness [1]. In tunnels, the deeper layers are backfill material and surrounding ground. For structural integrity it is important that the inner layer is correctly embedded. The integrity of the layers can be explored non-destructively using a ground penetrating radar (GPR). The images produced by a GPR device are called radargrams, and are typically interpreted manually. The goal of this research is to analyse radargrams automatically and provide confidence in integrity of these layers. For this purpose it is first required to accurately determine extrados of the first layer of the tunnel lining built using SFRC. We perform this analysis using three thicknesses of concrete segmental blocks.