Falling Weight Deflectometer (FWD)

Falling Weight Deflectometer (FWD) is a system used for performing non-destructive testing on pavements and measure the vertical deflection response of a surface to an impulse load to simulate the weight of a passing wheel load.

FWD’s are commonly used on highways, local roads, car parks and airport runways, for a wide range of applications, such as pavement structural evaluation and design.

FWD Features:

  • Double Axle Trailer
  • Hydraulic Brakes
  • 2-cylinder 18-horsepower gasoline engine with 12 volt alternator permits 
high-speed and independent operation of the tow vehicle
  • DGPS enabled
  • 4 drop automated sequence in 30 seconds
  • Data capture from 1-35 drops at each location with up to 35 forces ​
  • Load Plate: 300mm
  • Geophones Accuracy: 2% +/- 1 micron and Range: 0 to 2032 microns
  • Force Measurement (Automatic Load Sensing) Accuracy: 1% +/- 0.07kN, Range 0 to 200 kN, Material: Stainless steel
  • Temperature Measurement (Pavement)
  • Accuracy: +/- 2% rdg, Range: -18 C to 400°C
  • Temperature Measurement (Ambient) Accuracy: +/- 2% rdg Range: -18 C to 400°C
  • Automatic Load Sensing, Computer automatically determines drop heights for varying loads up to 99 drops.
  • Data Output, Data is outputted into AASHTO recommended file format Pavement Data Deflection Exchange (PDDX) format
  • Data Acquisition: 1.25 Msamples/second Up to 32 Differential A/D channels 2 Analog Outputs, 8 Digital I/O +/- 10V Input Range​.

Benefits of FWD’s:

  • Non‐destructive economical pavement testing.
  • Imparts a dynamic load to a pavement structure similar to a moving wheel load.
  • Measures deflection of the pavement surface.
  • Determine pavement structural capacity and pavement performance and remaining life.
  • Load transfer efficiency of joints in concrete and identify voids under concrete slabs.
  • Project and network pavement structural evaluation.

As deflection data is increasingly used to accurately define pavement response to loading the need to develop robust back-calculation procedures has become greater. With the speed of computers increasing more mathematically intensive procedures can be used for developing solutions of large data sets. The back-calculation program enables the rapid calculation of layer stiffness modulus using a singular decomposition technique.

Oscorp Engineering uses back calculation programs to estimate the layer moduli with the help of accurate Back calculation program which offers the following:

  • Automatically iterates the layer module of an input pavement. configuration that best represents the existing pavement structure.
  • Consider stress-dependent module of granular materials and sub-grade.
  • Assigned values of Poisson’s ratio and degree of anisotropy are consistent with those adopted in Australia roads GMP overlay design.
  • Automatically access raw FWD data files and import FWD data from Excel Spread Sheets.
  • Automatically perform back-analyses of deflection data from FWD data files to produce solutions of elastic properties for layers.
  • Automatically prepare summary reports (in Excel format).