An Efficient Method to Describe the Geometry and the Roughness of an Existing Unlined Hydro Power Tunnel

The waterway counts as a main and costly part of a hydro power project. Excavating tunnels for waterways by rock-blasting is a rapid method compared to utilizing tunnel boring machines (TBM). However the variation in cross-section geometry and surface roughness that arises in unlined rock-blasted tunnels results in a considerable increase in head loss due to friction. Several empirical formulas are available to calculate the total friction loss of an unlined hydro-power tunnel. However, the existing methods of documenting the final geometry, such as manual measuring, leveling and photographing, are time-consuming and introduce uncertainty.Recent development of terrestrial laser scanners (TLS) has increased the efficiency and accuracy of surface measurements. Improved documentation of the geometry of these hydraulic structures enables higher accuracy in hand-calculations, as well as in physical and numerical modeling.This paper investigates the application of TLS on existing rock-blasted hydro power tunnels. The measuring procedures and results from a test performed by a Topcon GLS-1500 scanner are presented. The result shows that three dimensional representations of the tunnel geometry can be derived in an efficient way with high accuracy. Hence, this method yields as an efficient method to document the geometry and estimate the roughness of an existing unlined hydro power tunnel. Parameters such as accuracy, resolution, time consume and costs are investigated in the current study.