PRIMAX FWD Measuring Trailer 531

Bearing Capacity Surveys (FWD)

Sweco participates in projects all over the world. This involves projects funded by local highway authorities and internationally funded contracts (World Bank, TACIS, EBRD, ICAO) to measure the bearing capacity of roads or airpot taxiways and runways. The final reports are used by design engineers as a basis for the preparation of feasibility or rehabilitation design studies.

What does the FWD do?
FWD PRIMAX3000The FWD measures the bearing capacity of road or airfield pavements. In this way data is acquired, which allows you to find out, whether your road or airfield pavements need reinforcement e.g. if the traffic load changes.

The FWD simulates the actual wheel loads in both magnitude and duration. For all tests the pulse time duration must be between 20-30 ms. The dynamic load for roads is normally 50 kN and for airfields up to 250 kN and in some cases up to 300 kN. Linear bearing capacity calculation is often impossible if a runway pavement is measured with a load lower than kN 250 - especially if an airfield should be capable of withstanding the load from a Boing 747 aircraft.

Prior to analysis of acquired data, several external and internal parameters are entered to the computer program. External parameters, which are all site-specific, consist of information on material, traffic forecasts, layer thicknesses, pavement temperature and data collected by the FWD. Internal parameters consist of information on distress relationship, design parameters, etc. Layers of different stiffness are transformed into a single homogeneous semi-infinite layer.

Equations used for back-calculation of the modulus of each layer (up to 4 layers) by comparison are those of the theoretically calculated deflections and the deflection bowl actually measured in the field. Then the critical stresses and strains in each layer are calculated for the design wheel load. Furthermore, a pavement overlay is calculated for each test point, if the actual residual life is shorter than the required design life.

Quality assurance with Prima 100
PRIMA100 300PRIMA 100 is primarily used for compaction control in connection with laying of asphalt, cobbles and flagstones, but is also ideal for measuring bearing capacity where geogrids are to be used or where pipeline trenches are to be reinstated. PRIMA 100 is also indispensable for compaction control prior to industrial flooring.

Sweco offers this service to customers, however customers may also rent equipment to make measurements.

Bookmark and Share
PRIMAX FWD Measuring Trailer 226


Hans Christian Korsgaard
Hans Christian Korsgaard
Technical Manager
+45 8228 1443


Jens Pedersen
Jens Pedersen
+45 8228 1490


Falling Weight Deflectometers

PRIMA 100 for construction QA