Author(s): Jochen Aberle; Ralph Eikenberg; Till Branss; Christy Ushanth Navaratnam; Pierre-Yves Henry; Nils Reidar Olsen
Keywords: Scale model; Unlined rock blasted tunnel; Roughness; Hydraulic resistance
Abstract: This paper presents results from hydraulic laboratory tests carried out with four scale models of unlined rock blasted tunnels. High-resolution laser scanning data acquired with a terrestrial laser scanner in about 180 m long sections of the emptied conduits provided input for the construction of milled miniature tunnels in a geometric scale of 1:15. Head losses and friction factors were determined experimentally for a range of discharges, and the geometrical roughness of the tunnels was assessed based on statistical analyses of the digital elevation models used as input for the milling of the tunnel-models. The high spatial resolution of the scale models enabled the detailed quantification of the geometrical roughness pattern associated with variations in cross-sectional area resulting from the blasting such as sudden and gradual expansions as well as sudden and gradual contractions. The experimental data allowed linking hydraulic losses with these topographical features. Based on specific experiments with one tunnel, it is shown that the friction factors were smaller when the flow direction in the tunnels corresponded to their driving direction. The data were finally used to derive a new formula for the determination of the friction factor based on geometrical parameters of unlined rock blasted tunnels that can be obtained from the analyses of high-resolution laser scanning data.