Mapping of bridge pier scour with projection moire

During the construction works for an extension of an existing bridge pier s evere scouring occurred after the placement of a sheet pile cofferdam. A de tailed investigation of the situation was conducted at the Bundesanstalt fu r Wasserbau (Federal Hydraulic Research Institute) in Karlsruhe, Germany. F or the measurement of the scour development without protective layer, an op tical measurement method - out-of-plane projection Moire - was employed in order to investigate its suitability. This technique uses the Moire effect to map surface contours which are indicated by superposition lines or fring es. The Moire fringe patterns generated by the measurements were then digit ised for further analysis. The contour model revealed that, although the sc ouring depth did not increase significantly with time after the initial sco ur had formed, scour size did in fact do so. In addition, the contour model allows to map the scour extension and to determine the maximum deposition height. A 3D model of bridge pier and scour showed, in combination with pho tographs, the validity of the measurement technique and pointed towards the generation of a virtual environment for the representation of experimental results.