Assessment of the Danish High Speed Deflectograph in France

Abstract

The High Speed Deflectograph (HSD), developed by the Danish Road Institute and Greenwood Engineering A/S, measures the speed of vertical deformation of the road surface under the action of a load by means of two laser sensors with Doppler effect. During autumn 2003, LCPC assessed this prototype in the north of France. To make the tests, three different routes (motorway, trunk road and secondary road) were selected. Each route comprised a 2 km test section on which the HSD carried out several runs. The FWD took measurements on the same sections. Measurements of the HSD comprise the slope of the tangent to the basin of deflection at the point of measurement of the Doppler sensor. This parameter relates to the bearing capacity of the roadway and is the object of the analysis, which comprises the calculation of the repeatability on measurements of the test sections and the comparison of the values of the HSD with those of the FWD. Comparisons with the Flash deflectograph were also made. The conclusions of the study underline that HSD measurements are repeatable and could detect clear differences in levels of deflection. Following this assessment, a new HSD prototype has been designed.