Ž .
Journal of Applied Geophysics 43 2000 119–138 www.elsevier.nlrlocaterjappgeo
Road evaluation with ground penetrating radar
Timo Saarenketo
a,
, Tom Scullion
b,1
a
Roadscanners Oy, P.O.Box 2219, FIN-96201 RoÕaniemi, Finland
b
Texas Transportation Institute, Texas A M UniÕersity System, College Station, TX, 77843-3135, USA Received 9 March 1999; received in revised form 8 June 1999; accepted 10 June 1999
Abstract
Ž .
This paper provides a status report of the Ground Penetrating Radar GPR highway applications based on studies conducted in both Scandinavia and the USA. After several years of research local transportation agencies are now beginning
to implement GPR technology for both network and project level surveys. This paper summarizes the principles of operation of both ground-coupled and air-launched GPR systems together with a discussion of both signal processing and data
interpretation techniques. In the area of subgrade soil evaluation GPR techniques have been used to nondestructively identify soil type, to estimate the thickness of overburden and to evaluate the compressibility and frost susceptibility of subgrade soil.
In road structure surveys, GPR has been used to measure layer thickness, to detect subsurface defects and to evaluate base course quality. In quality control surveys, GPR techniques have been used for thickness measurements, to estimate air void
content of asphalt surfaces and to detect mix segregation. Future developments are described where the technique has great potential in assisting pavement engineers with their new pavement designs and in determining the optimal repair strategies
for deteriorated roadways. q 2000 Elsevier Science B.V. All rights reserved.
Keywords: Ground penetrating radar; Road structure; Subgrade; Dielectric value
1. Introduction
In Scandinavia, the first Ground Penetrating Ž
. Radar GPR tests with ground-coupled anten-
nae were performed in early 1980s in Denmark Ž
. Ž
. Berg, 1984 and in Sweden Johansson, 1987 ,
but the method did not gain general acceptance at that time. In Finland the first tests were made
Ž .
in 1986 Saarenketo, 1992 and after the Road District of Lapland of the Finnish National Road
Ž .
Administration Finnra purchased its own unit
Corresponding author. E-mail: timo.saarenketoroadscanners.com
1
E-mail: t-sculliontamu.edu.
in 1988, the method has been used as routine survey tool in various road design and rehabili-
Ž tation projects in Finland
Saarenketo, 1992; Saarenketo and Maijala, 1994; Saarenketo and
. Scullion, 1994 . Most of the research and devel-
opment works in highway applications in Fin- land has been performed with low frequency
Ž .
100–500 MHz ground-coupled antenna in or- der to evaluate subgrade soils and their interlay-
ers, probe the depth of overburden and survey road structural layers. GPR technique was also
Ž applied in aggregate prospecting
Saarenketo .
and Maijala, 1994 . In early- and mid-1990s tests with high frequency 1.0–1.5 GHz air-cou-
pled and ground-coupled antennae were started
0926-9851r00r - see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž
. PII: S 0 9 2 6 - 9 8 5 1 9 9 0 0 0 5 2 - X
Ž in bridge deck surveys Saarenketo and Sode-
¨
. rqvist, 1993; Maijala et al., 1994 , and in pave-
Ž ment design and quality control Saarenketo and
Roimela, 1998; Scullion and Saarenketo, 1998; .
Saarenketo, 1999 . The history of GPR tests on road surveys in
the USA relates to the mid-1970s, when accord- Ž
. ing to Morey 1998 , Federal Highway Admin-
istration tested the feasibility of radar in tunnel applications and later on bridge decks. The first
vehicle mounted GPR system for highways was developed under a FHWA contract in 1985
Ž
. Morey, 1998 . Since then, most applications
have been focused on pavement thickness mea- Ž
. surements Maser, 1994 , detecting voids under
Ž .
concrete slabs Scullion et al., 1994 and detect- Ž
ing deteriorated areas in bridge decks Alongi et .
al., 1992 . These surveys have mainly been Ž
. performed with high frequency 1.0 GHz air-
Ž .
launched antennas see Scullion et al., 1992 . A good description of the current practices of
GPR applications in highway agencies in North Ž
. America is given by Morey 1998 . The result
of the questionnaire sent to 50 states, Puerto Rico, the District of Columbia and 11 Canadian
transportation agencies showed that 33 agencies of the 51 responses had experience with GPR.
The most common GPR applications reported
Ž .
were pavement layer thickness 24 agencies , Ž
. void detection 22 agencies and bridge delami-
Ž .
nation 16 agencies ; followed by delamination Ž
. Ž
detection 11 agencies , depth to steel dowels 8 .
Ž .
agencies , buried objects 8 agencies , depth to Ž
. Ž
bedrock 8 agencies , asphalt stripping 7 agen- .
Ž cies , and scour around bridge support 6 agen-
. cies . Of the various applications GPR seemed
to be the most successful for pavement layer thickness measurements, while agencies report
less satisfactory results with void detection and questionable results locating areas of asphalt
Ž .
stripping Morey, 1998 . This paper gives a state-of-the-art review of
GPR applications in road surveys in Scandi- navia and in the USA. The testing of bridges
with GPR will not be addressed in this review because this is a large area which needs a
separate article. In other parts of the world GPR techniques have been used for road monitoring
in more than 20 countries and according to the knowledge of the authors, GPR surveys on roads
are widely used in Canada, France, Italy, Switzerland and the UK.
2. GPR hardware and software for roads
