FWD measuring

We use a Falling Weight Deflectometer (FWD) Dynatest 8002 for determining the load bearing capacity of the road structure. This device is suitable for flexible, composite as well as rigid pavements. Dynamic deflectometers, including Dynatest FWD 8002, are widely used in the whole world and it is one of the few devices that enables to study the pavement structure without breaking it. The FWD simulates a load created by a moving wheel by letting a load with certain weight to fall from a certain height on a loading plate of 300 mm in diameter.

The road deformation caused by the load (so-called deflection basin) is measured with seven load cells, out of which one is placed in the centre of the loading plate, and the rest to the distances 300, 600, 750, 900, 1200 and 1500 mm from the centre of the loading plate. The deflection data measured by the load cells is registered and saved on a computer.

Pavement equivalent E-modulus is deducted from the FWD device’s measurement data based on dr A. Aavik’s study „Methodical Basis for the Evaluation of Pavement Structural Strength in Estonian Pavement Management System“ (2003).
FWD device can be used for:

  • the comparison of deflection values and deflection basin shapes;
  • the determination of load bearing capacity (pavement’s equivalent elastic modulus);
  • the determination of elastic modulus of separate layers of the pavement.

If a precise data is needed, the input data needs to be precise. For example, in order to determine the elastic modulus of separate layers of the pavement their thickness needs to be measured using drilling or ground penetrating radar.

Dynatest FWD-8002 has regularly been tested at pan-European FWD-device comparative testing in the Netherlands; the last testing was organized in October 2011. The test results show that measurement results obtained with this device are comparable with those obtained with other similar devices.