Deflectograph surveys assess the structural condition of pavements by measuring the transient deflection of the road surface under the action of a rolling wheel at standard loading conditions.
The survey data is used together with a well-established design procedure to estimate structural residual lives and where necessary to design overlay thicknesses to extend the structural life.
The Deflectograph is an automated deflection measuring system based on the Deflection Beam principle and is ideal for regular network deflection surveys and has a daily survey capacity of 15 to 20 kilometres, with an operating speed of 2.5 km/hr
Deflection measurements are taken in both wheel paths using two deflection beams, mounted on a common reference frame resting on the road surface.
The deflection beams and reference frame are stationary during the deflection measurement cycle and remain stationary until the maximum deflection has been recorded. The reference frame is then pulled forward at twice the vehicle speed by a clutch and winch system to the initial position for the next measurement cycle. With the reference frame again at rest, the measurement cycle is repeated.
This method of operation gives measurements of deflection in both wheel paths at about 4 metre intervals. To travel between measurement sites, the Deflectograph measuring frame can be picked up hydraulically, to ease the burden on operator and driver.
The operator controls the survey and adds location reference markers to the data during the survey and also records pavement temperatures at regular intervals. The deflection data is stored on USB flash drives.
The Deflectograph is calibrated before each day’s testing and processing is undertaken using a suite of computer programmes. The deflection data recorded by the Deflectograph is temperature corrected and used, together with information defining pavement construction and commercial vehicle traffic flows, to estimate structural residual lives. It is also used to design overlays of different thickness to extend the structural life of a pavement.
W.D.M. Limited manufacture the British version of the Deflectograph, which is a fully self-contained, vehicle mounted system of standard configuration, consisting of a deflection measuring assembly and data recording electronics. Standard rear axle loading (6 – 10 tonne) is achieved using ballast fitted to the vehicle chassis.