EVALUATING PAVEMENT STRUCTURES WITH FWD

This article describes the Falling Weight Deflectometer (FWD) and its applications to the maintenance and repair of road pavements. A dynamic impulse load is used, which generates surface deflections similar in size and duration to those of a moving wheel load. In the FWD mechanism, deflections are measured with velocity transducers situated at the load's centre and at various user-defined distances from the load. Deflection measurement accuracy is very important, and can be verified independently by very rigorous calibration tests. Since it was first produced in the 1970s, the FWD's use has increased rapidly, and over 160 FWDs now operate in the world. Recent FWD developments have mainly refined existing technology, for example by increasing the number of sensors. A Heavy Weight Deflectometer (HWD) has been developed to test airfield pavement deflection. The authors emphasise that: (1) the FWD has become recognised as the standard for measuring pavement surface deflections; (2) the FWD is relatively fast and accurate, and provides useful data at project and network levels; (3) FWD data are well suited to the trend to wider use of mechanistic pavement design evaluation; (4) FWD load and deflection data fairly closely simulate pavement response under actual traffic loading. For the covering abstract see IRRD 862464.