Small FWD System

Small FWD - Portable Falling Weight Deflectometer is a dynamic loading test apparatus for measuring rigidity of earth structures such as embankments, cuttings, and subgrades non-destructively and in a short amount of time.
Small FWD System “FWD-Light®” allows measurement of modulus of subgrade reaction (K) necessary for evaluating rigidness of the ground and modulus of deformation (E) that can be converted to CBR or uniaxial compressive strength.
The rigidity of the ground can be measured speedily, reducing inspection costs as well as enabling multifaceted construction and quality management.

In addition to the conventional Small FWD System, Wireless Small FWD System has also been added to the product lineup, so that even faster measurement without the need for cabling is possible.

Outline of the system

A FWD (Falling Weight Deflectometer) is used for estimating the construction of pavement or the rigidity of subgrade. A plate loading test is also used for estimating the characteristics of subgrade. However, these methods require much time and works for their preparation, data acquisition and analysis. TML small FWD System "FWD-Light" features excellent portability and enables simple and quick measurement of a coefficient of subgrade reaction which is called K value and a modulus of subgrade elasticity which is called E value. The FWD-Light consists of a main body KFD-100A and an indicator TC-351F. The main body includes a load cell and an acceleration transducer whose measuring ranges are 20kN of load and 2.5mm of displacement at the maximum. Values of the maximum load and displacement, and the analysis results of K value and E value are indicated on the indicator. Each analysis result can be stored in a memory card and printed by an exclusive printer. Data stored in the memory card can be transferred to a personal computer by directly connecting the card or via the indicator. The measurement and processing software TC-7100 is available as an optional item for indicating waveforms of load, acceleration, velocity and displacement, O-P time and time integration using a personal computer.




  • Display automatic measurement load and displacement waveforms in real time for ground rigidity, as well as modulus of subgrade reaction and modulus of deformation
  • Compact and lightweight — very portable
  • Abundant data recording in a short time
  • 2-wire system digital transmission line
  • Battery-powered, measure anywhere
  • CF memory card recording
  • Data recording software (TC-7351) standard installed

System Diagrams



Operation outline

The weight in Small FWD is made to fall freely, and the resulting impact load and displacement are measured with the load cell and acceleration transducer. The displacement is obtained by integrating the value measured by the acceleration transducer twice. Using External Displacement Sensor KFDS-1B allows up to 4 points of external displacement to be measured at the same time. By processing the integral of acceleration data with a unique patented method, a highly accurate displacement result with little scattering can be obtained.

Modulus of subgrade reaction: KTML formula

KTML Coefficient of subgrade reaction obtained by TML Small FWD system (MN/m3)
P Maximum Load (N)
D Maximum displacement (m)
r Radius of loading plate (m)
R Diameter of loading plate R=2r (m)
R300 Diameter of standard loading plate (Φ300mm)

Modulus of deformation: ETML formulas

ETML Modulus of subgrade elasticity obtained by TML small FWD System (MN/m3)
P Maximum load (N)
D Maximum displacement (m)
r Radius of loading plate (m)
ν Poisson's ratio (0.30 changeable)

Factory settings are set to Boussinesq.