The FWD (Falling Weight Deflectometer, Figure 1) is currently the most widely used device for assessing the bearing capacity of road pavements. It allows to measure the canopy of pavement deflections under a given load (Figure 2). Once the device is positioned at a given measuring point, a pressure plate (Figure 3) is automatically lowered onto the pavement, along with a central sensor and sensors located on the measuring beam of fixed distances. A load drop of a predetermined weight (maximum pressure of 120 kN) is performed from a certain height. As a result of the load impact, the pavement structure and the subsoil undergo elastic deformation over a certain area, the magnitude of which depends on the magnitude of the defined test load and the stiffness of the structure under test. The magnitudes of pavement deflections are usually measured using 7 - 9 sensors set at well-defined distances from the axis of the loading force (e.g. 200, 300, 450, 600, 900, 1200, 1500 and 1800 mm). The waveforms of the loading and deformation processes of the structure are recorded simultaneously. The results of the deflection canopy measurement are used to determine, usually by back-calculation analysis, elasticity (or stiffness) moduli of pavement construction layers. The elasticity modulus is a fundamental parameter in mechanistic analyses of the durability (load-bearing capacity) of road pavement structures.


FWD rys 1

Fig. 1 Falling Weight Deflectometer (property of IBDiM)

Sterowanie tym urządzeniem jest automatyczne. Kierowca będący jednocześnie operatorem przy pomocy dodatkowych urządzeń (dystansomierz, kamera) dokonuje wyboru miejsca badania oraz kontroluje przebieg procesu pomiarowego. Aparat FWD jest sterowany przez procesor pokładowy, a poprawność wyników uzyskiwanych w trakcie pomiarów kontrolowana jest na bieżąco przez komputer pokładowy.

FWD rys 2


Fig. 2 FWD operation diagram


FWD rys 3

Fig. 3 View of the pressure plate and two geophones

Testing with FWD and HWD is falls within the scope of accreditation of the Testing Laboratory No. AB 426, issued by the Polish Accreditation Centre.