1. FALLING WEIGHT DEFLECTOMETER TEST At KARACHI HYDERABAD (M9)
10-06-2015 ATIF RAFIQ GT & GE Div.
2. FALLING WEIGHT DEFLECTOMETER TEST OBJECTIVE: A falling
weight deflectometer (FWD) is a device designed to simulate
deflection of a pavement surface caused by a fast-moving truck. The
FWD generates a load pulse by dropping a weight. This load pulse is
transmitted to the pavement through a 300-millimeter (mm) diameter
circular load plate.
3. FALLING WEIGHT DEFLECTOMETER TEST SIGNIFICANCE: FWD is a
non-destructive test to determine a deflection basin caused by a
controlled load with accuracy and resolution superior to other
existing test methods. The FWD produces a dynamic impulse load that
simulates a moving wheel load, rather than a static, semi-static or
vibratory load. FWD generated data, combined with layer thickness,
can be confidently used to obtain the in-situ resilient E-moduli of
a pavement structure. This information can in turn be used in a
structural analysis to determine the bearing capacity, estimate
expected life, and calculate an overlay requirement, if applicable
(over a desired design life).
5. Before description of the whole test procedure, a quick
schematic animated video (1.30 min) of FWD field test is available
on next slide. The video demonstrates the whole procedure, impact
and mechanism of the test. FALLING WEIGHT DEFLECTOMETER TEST
6. FWD Schematic Video
7. FALLING WEIGHT DEFLECTOMETER TEST At KARACHI HYDERABAD
(M9)
8. Sensors/Geophones: used to measure deflection. It is
cylindrical, and about 25 mm (0.98 inch) in diameter and 50 mm
(1.97 inches) high. Geophones are mounted in spring loaded sensor
support brackets suspended along the sensor bar. Each geophone has
a unique serial number that is used to identify critical
calibration information in the FWD data collection software.
9. Load Plate : Directly contacts the pavement surface to
transmit the load. The type used by LTPP is solid, and it has a
300-mm (11.81-inch) diameter. It consists of three layers: the
topmost is steel, the middle is polyvinyl chloride (PVC), and the
bottommost is a ribbed rubber sheet.
10. Sensors/Geophones: Lateral distances of installed geophoes
from primary geophone present in load plate are 8, 12, 18, 24, 36,
48 and 60 inches respectively 8 12 18 24 36 48 60
11. Weight Package: The entire assembly that is raised and then
dropped to generate load. Removable steel weights mounted to the
weight package. Their mass is 20 kilograms (kg) (44.1 pounds (lb))
each.
12. Buffer : A rubber Cylinder attached to the underside of the
weight package to control the shape of the generated load pulse.
There are four mounted on the weight package.
13. Load Cell : Measures the force imparted to the pavement by
the FWD. The load cell is located directly above the load plate and
below the swivel. The load cell has a serial number, which is
visible from the rear.
14. Control Box : Contains connectors for the geophones, load
cell, temperature sensor, and other sensors mounted on the FWD.
Located on the FWD trailer, the control box sends these signals to
the signal processor located in the tow vehicle through the
multisignal cable. The control box also has buttons for manual
control of the FWD hydraulics.
15. Signal Processor : Signal ProcessorConnects the trailer
control box through a multisignal cable to the data collection
computer using an RS-232 serial cable.
16. Multisignal Cables: Carries electrical signals from the
control box to the signal processor. These signals include the
outputs from the transducers on the FWD and the command signals for
the FWD hydraulics.
17. Multisignal Cables : Carries electrical signals from the
control box . These signals include the outputs from the
transducers on the FWD and the command signals for the FWD
hydraulics.
18. Processing System: A computer laptop is used to process and
store the acquired data from the field test having Windows 7 or XP.
The data processing software used for FWD is ELMOD 6 or
FWDwin.
19. Load transfer in progress
20. FALLING WEIGHT DEFLECTOMETER TEST From RD 0+000 (at Leyari
Bypass) upto RD 135+470 (at Hyd N5 Toll Plaza). Test was carried
out throughout the reach (both ways) on both slow and fast lanes
individually with intervals of 250 m and 1km selectively. The load
was transferred in 3 drops of different load settings i.e. 7 , 9
and 14 kips respectively. Reportedly, results from load drops 7
& 14 kips will be used for comparison while load drop 9 kips
will be used for simulation purpose. Rehabilitated reaches e.g.
patched and milled were not tested because of the possibility of
erroneous information.
21. References: Falling weight Deflectometer.(2006,December
12). Long- Term Pavement Performance Program Manual for Falling
Weight Deflectometer Measurements,3,4-3,4.
https://www.youtube.com/watch?v=0KDplKQwOAQ
