Validation of DEFSTRA Water Film Prediction Model

Water film thickness is one of the main variables influencing the friction values available in the tyre-pavement contact area. Water film depth is influenced by rainfall intensity, grades and cross slopes, length of draining path and pavement texture. During the EU funded VERT and VERTEC research projects an empirical model allowing to evaluate water film depth on constant slope surfaces, having different textures, was developed. The model was afterwards theoretically extended to consider variable slope surfaces and was included in the VERT MBS vehicle model for driving simulations on varying road surfaces in dangerous conditions. The experimental validation of the variable slope water flow model has been implemented by means of a full scale physical road model constructed in the Road Laboratory at the University of Florence. The 3,5 m wide per 24 m long model has a longitudinal grade of 2% and a cross slope varying between +1,5% and – 1,5%. The model is equipped with an artificial rainwater simulation system allowing to simulate rain intensities between 20 and 100 mm/h. The paper will describe the setting up of the road physical model, its calibration and the experimental program performed to validate the water flow model. The results of the experimental study are presented and discussed.