Geosynthetics June/July 2019 - 29

the centerline of the 12-inch (30.5-cm)
load plate to measure permanent surface
deformation on the HMA surface layer.
One pressure cell was installed 1 inch
(2.5 cm) below the subbase surface. One
pressure cell was installed 1 inch (2.5
cm) below the subgrade surface, and one
pressure cell was installed 2 inches (5.1
cm) above the bottom of the subgrade.
The pressure cell used in the Phase I
and Phase II study were 9 inches (22.9
cm) diameter and 4 inches (10.2 cm)
diameter, respectively. The pressure cells
were reduced in size to limit the area of
influence considering the overall size
of the experiment. One pore pressure
transducer was installed 1 inch (2.5 cm)
below the subgrade surface. Figure 4 on
page 30 shows a cross section schematic
of the instrumentation plan.

Results
Cyclic plate load tests were conducted
on 10 representative flexible airport
pavement test items under a 254.6 psi
(1,755 kPa) simulated aircraft load. Five
different geosynthetic products placed
at two distinct locations were compared
to unreinforced control test items.
Pavement surface deformation was
monitored using a series of six LVDTs,
while maximum pressure was monitored at various pavement depths using a
series of three pressure cells for each test
item. The pavement response data for
each of the 10 test items were compared
to the control test item of its respective
phase. This is due to the significant difference in performance of Phase I and
Phase II control test items, which may
be attributed to noticeable differences in
the as-constructed material properties of
the HMA layer between the two phases,
as shown in Table 4 on page 27.
Tables 6 and 7 and Figure 5 (on
page 30) are used to evaluate pavement
behavior and quantify performance.

Test Item No.

Load Cycles
at 1" Surface
Deformation

Load Cycles
at 2" Surface
Deformation

TBR at 1"
Surface
Deformation

TBR at 2"
Surface
Deformation

Test Item 1 - Phase I Control

304

1,278

-

-

Test Item 2 - Phase I - GP1

1,000

4,304

3.3

3.4

Test Item 3 - Phase I - GP2

6,322

25,960

20.8

20.3

Test Item 4 - Phase I - GP3

9,024

34,901

29.7

27.3

Test Item 5 - Phase II Control

3,700

16,990

-

-

Test Item 6 - Phase II Control

3,000

14,000

-

-

Test Item 7 - Phase II - GP1

1,460

9,890

0.4

0.6

Test Item 8 - Phase II - GP2

9,720

44,960

2.6

2.6

Test Item 9 - Phase II - GP4

4,100

17,600

1.1

1

Test Item 10 - Phase II - GP5

2,575

20,830

0.7

1.2

TABLE 6 Calculated TBR values at 1-inch (25-mm) and 2-inch (51-mm) surface deformation

Test Item No.

Total
Cycles

Test Item 1 - Phase I Control

Individual Layer Deformation (inches)
Hot-Mix
Asphalt

P-209
Aggregate Base

P-154
Subbase

CH
Subgrade

2,000

4.3

4.4

4.8

3.7

Test Item 2 - Phase I - GP1

5,000

2.6

2.6

2.6

0.4

Test Item 3 - Phase I - GP2

30,000

2.6

2.6

2.8

0.6

Test Item 4 - Phase I - GP3

30,000

2.1

2.1

2.2

0.4

Test Item 5 - Phase II Control

20,000

2.5

2.6

2.5

0.8

Test Item 6 - Phase II Control

13,500

2.3

2

2.2

0.5

Test Item 7 - Phase II - GP1

13,500

2.6

2.5

2.4

1.3

Test Item 8 - Phase II - GP2

50,000

2.2

2.2

2.3

0.6

Test Item 9 - Phase II - GP4

18,800

2.2

2

2

0.7

Test Item 10 - Phase II - GP5

24,000

2.3

2.2

2.5

0.8

TABLE 7 Final individual pavement layer deformation

Permanent surface deformation data
collected directly from the LVDTs is
also shown in Figure 5. Total number
of cycles to achieve failure at 1 inch (2.5
cm) and 2 inches (5.1 cm) of surface
deformation and TBR values are shown
in Table 6.
The Phase I results shown in Figure
5 show a promising trend that a geogrid
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