The FWD - Falling Weight Deflectometer is a device that gives reliable measurements of the bearing capacity of the pavement. In addition the remaining life of the pavement as well as the needed reinforcement can be calculated.

The basic principal of the FWD function is as follows: a specifi weight drops from a predetrmined height producing a force on the pavement, which through a specific plate is translated into pressure. A series of accelerometers, called geophones, record the vibration of the pavement up to two (2) meters from the point that the wight was dropped. The geophones close to the dropped weight give information for the upper layer while as the distance increases, geophones give information about the lower layers. Special software is utilised for the back-calculation in order for the elastic layer modulus to be calculated; this is the RoSy Design software. With this the elastic layer modulus is calculated for each layer seperately. Taking into account pavement design data, the remaining life of the pavement can also be calculated. When this is calculated below the specified one, the needed reinforcement in mm can be calculated so that the remaining life meets the design's specifications.

For the above rsults to be calculated some data need to be know in advance. These are: thickness of each layer and material it's build from as well as traffic loads. Depending on variation of the pavement profile, FWD measurements can be taken every 500 m distances for homogenous profiles until even every 50 m for significally varying pavement profiles.

Geophones in touch with the pavement

Diagramms of measurements - results