1. Jagadeesh D(EEC159)
Assistant Engineer
Presented By

2. CONTENTS
 Introduction
 Structural Evaluation of FWD
 Comparison of BBD & FWD
 Principle of FWD
 Specifications of FWD
 Calibration of the FWD
 Pavement evaluation survey and data
collection
 Analysis of field data
 Conclusion
 References

3. introduction
Falling Weight Deflectometer (FWD) is an impulse-loading
device in which a transient load is applied to the pavement
and the deflected shape of the pavement surface is
measured.

4. Structural Evaluation
structural evaluation of pavements involves application of
a standard load to the pavement and measuring its
response in terms of stress, strain or deflection.

5. Comparison of BBD & FWD
 Benkelman beam has been among the earliest
equipment used for measuring deflection.
 In this technique, a static load is applied to the pavement
surface and rebound deflections are measured.
 Measurement of deflection under a static load does not
simulate the loading conditions produced in pavements by
a moving vehicle. And this method is labour-intensive &
time consuming.

6. Principle of FWD
The working principle of the FWD is a mass of weights is
dropped from a pre-determined height onto a series of
springs placed on top of a loading plate. The corresponding
peak load and peak vertical surface deflections at different
radial locations are measured.

7. Figure 1: Working principle of falling weight deflectometer

8. Specification of FWD As per IRC:115-2014

10. Battery box Fuse box

11. Battery box Mother Board

14.  In FWD 6-9 geophones are generally adequate for
measuring surface deflections of flexible pavement and this
geophones have reading resolution of at least 1micron.
S.NO Number of
geophones
Radial Distance from center of load plate (mm)
1 2 3 4 5 6 7 8 9
1 9 sensors 0 200 300 450 600 900 1200 1500 1800
2 7 sensors 0 300 600 900 1200 1500 1800 - -
3 7 sensors 0 200 300 450 600 900 1500 - -
4 6 sensors 0 300 600 900 1200 1500 - - -
5 6 sensors 0 200 300 600 900 1200 - -
Table 1: Typical geophone position & Configuration

17. Calibration of the FWD
 The period of Static calibration is nearly 365 days
 The Standard deviation of the peak load in the load
repeatability test estimated from a minimum of 12
load drops should be less than 5% of the mean value of
peak load
 Absolute calibration of geophones are calibrated by the
Stack test. The deflections produced in this test should
be in the range of 250µm to 600µm.Difference
between maximum and minimum of the recorded
(normalized) deflections should be within 4µm

20. Pavement evaluation survey and
data collection
 Historical data about pavement
 Pavement condition survey
 Deflection measurements using FWD

21. Historical data about pavement
 Historical data on pavement can be useful in identifying
the reasons for different distresses and in establishing
whether the distresses were caused by deficiency in
design, poor material selection,improper construction
and other reasons such as high water table and poor
drainage.

22. Pavement condition survey
 Pavement condition survey shall precede the actual
deflection measurement and consists primarily of visual
observations supplemented by measurements for
estimation of cracking, rutting and other distresses in
the pavement.

23. Table 2: Criteria for classification of pavement section

24. NOTE: 90% confidence level and 10% margin of error (ME expressed as
percentage of mean) considered in the guidelines
Cv- coefficient of variation for
• Good – 15%
•Fair – 30%
•Poor – 45%
• Z value=1.285

26.  For Two lane/single carriage-way
Poor Fair Good

27. Steps involved in measuring the
deflection
 Mark the test point on the pavement.
 Raise the mass to a pre-determined height
required for producing a target load of 40 KN.
 Raise the mass and drop. Record load and deflection data
into the computer through data acquisition system.
 Record air & Pavement temperature at hourly interval.
 Measure pavement temperature by drilling holes of
40mm depth into the pavement surface layer.
 Deflection measurements should not be made when the
pavement temperature is more than 45 degree centigrade.

29.  Raw data extraction
 Normalization & Average
 Min & Max Ranges for BT, Granular, Sub grade layers
 Crust thickness
 KGP BACK Analysis (E values)
 Temperature corrections
 Seasonal corrections
 Dividing Sections
 15 percentile value
 Calculating strains by IIT PAV
 Calculating Fatigue & Rutting Life
 Calculating Remaining life
 Design over lay

34. Conclusion
 we concluded that the FWD is more better than the BBD
and we can handle easily. By using this FWD we can
determining the elastic moduli of pavement layers, and
using these moduli as inputs to a pavement design model
for overlay requirement. And we can also estimate the
residual life of an existing pavement and overlay
requirement.

35. References
 Guidelines for structural evaluation and strengthening of
flexible road pavements using falling weight deflectometer
(FWD) technique IRC:115-2014.
 www.eraymachinery.com

37. THANK YOU