National Geoscience Conference 2011 - Department Of Geology ...

NATIONAL GEOSCIENCE CONFERENCE 2011
11 – 12 June 2011 • The Puteri Pacific Johor Bahru, Johor, Malaysia
Paper B6
Application of electrical resistivity method in road subsurface profiling
Azmila Mohd Kamil*, Haryati Awang & Fredrickson Anthony Idi
Institute for Infrastrure Engineering and Sustainable Management
Faculty of Civil Engineering, Universiti Teknologi MARA, Shah Alam, Malaysia
*Email address: azmilakamil@gmail.com
In highway engineering projects such as design, rehabilitation and maintenance of existing pavement, a
geotechnical assessment at the proposed site is required. Recently, the most commonly method to obtain subsurface
profile is by using borehole drilling, which takes a long period to complete and costly. Even though borehole drilling
provides the subsurface depth, but it is only at the sampling location. The data in between the boreholes need to
be interpolated and the result was in an assumption data. In road engineering study, the conventional approach
to evaluate the properties of asphalts and subgrade soils involves a core sampling procedure and a complicated
laboratory testing such as resilient modulus, Marshall Test and Dynamic Cone Penetration test (Livneh et al., 1994).
In order to improve the method of road subsurface profiling, the use of electrical resistivity as an alternative method
was proposed. This paper presents the findings of a study on the application of electrical resistivity method in road
subsurface profiling. The purpose of this study is to obtain the road subsurface profile including the thickness of
the sub layers. In this study two field tests were carried out, electrical resistivity and Dynamic Cone Penetration
test (DCP). The electrical resistivity measurement was conducted at the parking vicinity using ABEM Terrameter
SAS4000 LUND Imaging System. Direct current was applied into the ground through two current electrodes and
measuring the resulting voltage differences at two potential electrodes. A multi-electrode resistivity data acquisition
system proposed by Dahlin (1996) was used. Forty-one electrodes were connected with two multi-cored cables
along 20 m road within 0.5 m spacing. By using a computer program RES2DINV, a 2-D image of road subsurface
was produced. By inversion analysis, the appropriate resistivity value was determined. The DCP test was conducted
to determine the thickness of the surface course, base course, sub-base course and the sub-grade course. Surface
course is the upper layer of the pavement while base course is the main pavement structural layer. The sub-base
course is the secondary load spreading layer underlying the base meanwhile subgrade course is an embankment on
natural earth. The pavement was cored to measure the actual thickness of the structural layer. Then, the DCP test was
carried out by dropped the hammer and the data which is the number of blow was recorded. The tip on cone was laid
to the testing surface as the first step in DCP test. The lower shaft containing the cone moves independently from
the reading rod sitting on the testing surface throughout the test. This process is continued until a desired penetration
depth is reached. The resistivity result is produced in the image form. From the resistivity image, the thickness of
each road sub surface layers was determined. DCP test resulted the blow counts versus penetration depth which
was plotted as a graph as shown in Figure 1. A curve line with four different degrees of gradient was displayed in
the graph, which can be interpreted as four straight lines. From the graph, it was interpreted that the different in
gradient indicated the subsurface which is consists of four layers. Both results of resistivity image and DCPT graph
were compared. It was found that the thickness of each layer in the resistivity image was matched to the layers
determined by DCP test. From this study, it can be concluded that the electrical resistivity method can be used to
obtain the subsurface information and the thickness of the sub-grades and sub layers. So that the coring method that
can damage and defect the road pavement can be avoided.
References
Awang H., 2010. Geophysical Characterization of Meta-
Sedimentary Interbeded Rock for Geotechnical Work.
Unpublished Thesis, UiTM
Edwin, R.S & Coruh C., 1988. Basic Exploration Geophysics,
Virginia Polymeric Institute and State University, pp. 445-
478.
Livneh, M, Ishai, I. & Livneh, N. A., 1994. Effect of
Vertical Confinement on Dynamic Cone Penetrometer
Strength Values in Pavement and Subgrade Evaluation,
Transportation Research Record, pp. 1-8.
Withlow R., 2004. Basic Soil Mechanics, Prentice Hall,
Singapore. Edition 4.
Salgado R. & Yoon S., 2003. Dynaminc Cone Penetration Test
(DCPT) for Subgrade Assessment.
Figure 1: Interpretation of dynamic cone penetration test
result.
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