doi:10.1016/S0926-9851(99)00052-X
Copyright © 2000 Elsevier Science B.V. All rights reserved.
Road evaluation with ground penetrating radar
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Timo Saarenketoa, * and Tom Scullion1, b
a Roadscanners Oy, P.O.Box 2219, FIN-96201 Rovaniemi, Finland
b Texas Transportation Institute, Texas A&M University System, College Station, TX, 77843-3135, USA
Received 9 March 1999;
revised 8 June 1999;
accepted 10 June 1999.
Available online 28 February 2000.
Abstract
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.
Author Keywords: Ground penetrating radar; Road structure; Subgrade; Dielectric value
Fig. 1. Finnish National Road Administration (Finnra) GPR survey van with GSSI 500 MHz ground-coupled antenna.
Fig. 2. Texas Transportation Institute (TTI) GPR survey van with Pulse Radar 1.0 GHz horn antenna.
Fig. 3. 400 MHz ground-coupled antenna survey result from TH 28, Burtrum, Minnesota presented with interpretation and reference drill data (Saarenketo, 1998b).
Fig. 4. 500 MHz ground-coupled data collected from Rd 17469, Kuortane, Western Finland. Measurements were performed in May 1998 when the subgrade was still partly frozen. GPR data is presented together with FWD data. Clear reflections in section 2140–2240 at depth of 1.4 and 2.0 m present upper and lower interface of the frost table.
Fig. 5. GPR data from HW 170 Östersundom near Helsinki, Finland. The section of settled road can be seen between 4440 and 4620 m, where the old concrete road constructed in 1930s lies at the depth of 1.5 m. The bridge presents the level where the road was originally constructed.
Fig. 6. 500 MHz ground-coupled data collected in March 1998 from HW322 Skalstugavägen, Sweden presented together with IRI (International Roughness Index) data. Clear reflection at the level of 1.4–2.0 m present frost line. The GPR data at the road section with severe damages between 5720 and 5820 m, shows strong reflection above frost line indicating the presence of segregation ice. Uneven section at 5875 m is caused by settlement in transition zone from till subgrade to peat subgrade.
Fig. 7. GPR trace from a new pavement measured with a 1.0 GHz horn antenna and after background removal. Peaks A1, A2, and A3 are reflections from road surface, base and subgrade.
Fig. 8. Basic processing of GPR data. The actual traces are shown in upper left box. The computed layer thickness and dielectrics are shown in other boxes.
Fig. 9. 1.5 GHz ground-coupled antenna data collected from TH71 Willmar, Minnesota presented with FWD data. The road section with severe stripping on the bottom of the asphalt between 900 and 990 m can be seen both with GPR and FWD data.
Fig. 10. Classification and interpretation of different subsurface reflections from asphalt layers containing a buried moisture barrier (chip seal or fabric).
Fig. 11. Road Analysis profile over section 2200–2600 m of HW930 in Ylitornio, Finnish Lapland.
Fig. 12. Results of the Finnra laboratory tests 1996, dielectric values versus void content.
Fig. 13. Asphalt void content measured with GPR in the field versus void content measured in the laboratory.
Fig. 14. Surface dielectrics from a longitudinal construction joint on IH20 near Pecos, Texas. The drop in dielectric value indicates density problems over the joint.
Table 1. Quality assessment of soils and unbound road materials according to their dielectric properties
Table 2. Quality criteria for unstabilized base material
*Corresponding author. E-mail: timo.saarenketo@roadscanners.com
1E-mail: t-scullion@tamu.edu.
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