ISSN 2086-5953 of backcalculation concept in order to determine the
elastic modulus of pavement which can be used to assess the quality of pavement structure.
2 LITERATURE REVIEW
2.1 Falling Weight Deflectometer
FWD
The FWD was first introduced in France about 30 years ago to test the flexible road networks
[10] and it was developed by many researchers around the world to assess the material under
pavement, such as in USA [1, 4, 14, 22, 7, 20], China [9], Japan [3], Canada [18] Turkey [5, 17],
Indonesia [11, 16], Denmark [19], among others.
The following advantages of using FWD in road management system noted at [15]:
1. The FWD test can present the structural
condition of existing road pavement by determining the elastic modulus of every layer
2. The FWD can be operated easily and producing
the result accurately 3.
The weight and the drop height can clearly be measured hence the load intensity represented
as the traffic load can be adjusted to the traffic load condition in Indonesian 8.16 ton
2.2 Backcalculation Concept
Generally, there are two approaches which can be used in the backcalculation procedure, first is
database approach and second is iterative approach. Database approach is done by comparing the
measured and the theoretical deflections recorded on the database with different values of modulus
which are conducted before. Essentially, although the database method is efficient, it does not consider
the variation of in-situ structural condition of pavement. On the other hand, iterative approach is
done to calculate the pavement modulus by iterative method according to the in-situ structural condition
of pavement until it is appropriate with the convergence criterion [11].
The pavement is modeled as two, three or four- layer system in order to analyze the structural
pavement condition. Ideally, to get the best result, the modelling system must be the same to the in-
situ number of pavement layer. The utilization of these modelling systems is the most influenced
factor to the result analysis. In addition, the environmental
factors, such
as pavement
temperature is considered to calculate the elastic modulus and the season number in every year is
used to determine the elastic modulus of subgrade.
2.3 BAKFAAV and MICHBACK
Program
BAKFAAV is the backcalculation program
requiring windows 9598. BAKFAAV is made by the Federal Aviation Administration FAA USA
used to analyze the structural pavement or runway. MICHBACK is the backcalculation computer
program developed by the Michigan University. This program uses the Newton Method to analyze
both the flexible and the composite pavement. The calculation of elastic modulus is done iteratively by
matching the theoretical to the measured deflection basin from field measurements.
3 RESEARCH METHODOLOGY
3.1 Location
The FWD testing has conducted in three different locations i.e. a Soekarno-Hatta Road,
Bandung b Subang Road and c West Ring-Road, Yogyakarta, Indonesia.
3.2 The Equipment
The equipments used in FWD testing are the loading plate, the geophone in order to measure the
deflection and the computer which is used to collect the data and to control the FWD instruments.
3.3 The Pevement Structural Modeling
The backcalculation
process used
to calculate the theoretical deflection will be
producing the best result if the structural pavement can be modeled accurately. In this research, the
structural pavement is modeled in four-layer systems as shown in Figure 1. Different pavement
layers in this modeling system can be joined in one layer if those layers have the same characteristics
[21]. In addition, the thickness of the bottom layer is assumed infinite [11].
Previously, the constant poisson µ must be determined before the calculation process is begun.
For four layer system. 0.35 is used as the poisson ratio of surface layer whereas 0.4 is the poisson
ratio of both base course and sub-base course however 0.45 is the possion value of subgrade
layer. These poisson values are taken from the manual using of MICHBACK.
ISSN 2086-5953
Figure 1. Pavement structural modeling in Soekarno-Hatta Road using 4 layer system
3.4 The Mechanism of FWD Testing
