Background and Objective
Many valuable results have been obtained from tests conducted on flexible pavements at the FAA’s NAPTF. These include:
(1) The elevation surface of each layer on the construction, subgrade properties including CBR, DCP, and material properties such as resilient modulus, shear strength, etc. from lab tests done on materials sampled from the field.
(2) The history of profiles from ‘0’ pass to failure indicates the pavement surface variation that can be observed;
(3) The trench cross sections at end of each test indicate all layer thickness change from the pass = 0 to the test end, including the observed material move during the complete load passes.
However, we do not know very well on the layer properties changes such as material and thickness, though they were significant in a few top layers. Therefore we have planned FWD tests along with the increase of traffic. The objective is to investigate the FWD data changes along with traffic increase number and find the correlation between the FWD data and observations from pavement surface as mentioned previously.
When to do the FWD
1) It is important to look everyday at the pavement cross section profiles and upheaval and rutting depths measured by profiler along with the traffic pass numbers. After reviewing these, if it looks that there is unusual change in the pavement structure, we need to stop the trafficking as soon as possible (at the 66 passes in a wander group) and run the FWD tests.
2) HWD tests should be done before we increase the load as well as after 5-6 wanders with increased load.
When to increase the load
1) If it is seen from profile curves that the pavement structure is not changing with the traffic passes, we increase the load from 58k to 65k.
2) Also if upheaval and rutting depths measured by profiler seems to indicate that the pavement structure is relatively stable, load should be increased to 65k.
FWD Test Locations
HWD tests will be done in all the 6 test items on the North Side. In each test item, these will be performed at the first profile line in each test item i.e. at station 10, 55, 105, 150, 200 and 250. The FWD drops will be made at 6 points on each profile line and these points are shown in the figure 1.
Offset 25N – Outside traffic area
Offset 23N, 9N, 1S- Top of upheaval
Offset 22N, 10N, 1N- Close to upheaval
Offset 16N & 12N – Offsets equal to MDD locations
In 10-wheel test items, offsets 1N & 1S are chosen to look at the upheaval due to 4-wheel gear. Upheaval due to 6-wheel gear will be looked from Offset 10N & 9N. And looking at the HWD Test data from Offset 23N & 22N, we would be able to look at the difference in the deflection values from few passes at increased load (there were 2 passes at offset 23N & 22N at 58K before HWD testing whereas offset 10N & 9N were still at 50K condition).