Montana DOT Looks to GPR for Pavement Rehab Design

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Infrasense recently completed a study for the Montana DOT showing how its ground penetrating radar highway system can be used to provide more accurate pavement structure data and how, in conjunction with its falling weight deflectometer program, the DOT can develop more appropriate and cost-effective rehabilitation designs.

GPR Testing in Montana

Infrasense, Inc. recently completed a study to evaluate the feasibility and value of expanding the Montana Department of Transportation's (MDT) Ground Penetrating Radar (GPR) program to pavement design and rehabilitation, and to network level evaluation. The study included a field evaluation project designed and implemented to evaluate the accuracy of GPR pavement thickness data on Montana pavements, and to correlate these findings with the accuracy requirements of the individual applications. This field evaluation began with identifying 26 pavement test sections of different composition and structure located throughout the diverse climatic regions of Montana. At each site, Falling Weight Deflectometer (FWD) and GPR data was collected, followed by coring and augering to determine the thickness of the pavement layer structure and base moisture content.

This testing was carried out both in the spring and fall to capture seasonal variations. The GPR data was analyzed for thickness, and the GPR thickness data was evaluated for seasonal changes, and compared to core and plan data to investigate thickness accuracy and the effectiveness of calibration methods. Compared to cores, the average GPR bound layer thickness error was 10.3% vs. 15.2% using plan data. A GPR data-checking method was developed using FWD and plan data to identify potential layer analysis inconsistencies and suggest alternative interpretation. Implementation of this method reduced the GPR error to 7.6%. A sensitivity study was carried out to investigate the impact of having the more accurate GPR data. This study showed that, on average, the use of GPR reduced the pavement life prediction error by 62% when compared to using as-built plan data. The complete project report can be found at: http://www.mdt.mt.gov/research/projects/pave/gpr.shtml .

Pavement strength evaluations using a Falling Weight Deflectometer provide useful data to pavement engineers for estimating remaining life and planning rehabilitation. Accurate pavement layer thickness data, as provided by GPR, enhances FWD pavement strength evaluations, since thickness data is required for calculation of the pavement moduli. The Montana study therefore illustrates that the availability of GPR data provides a better estimate of the remaining life of a particular pavement and can lead to more appropriate design and planning decisions.

Infrasense has played a key role in the development and implementation of GPR for pavement assessments over the past 25 years. Currently, the most common application of this state-of-the-art technology is the determination of pavement layer thickness because, unlike traditional coring, GPR requires no lane closures and provides a timely and cost-effective means of collecting continuous thickness data. This data may be used for network-level pavement management, project-level rehabilitation design, or quality assurance of newly constructed pavements. Infrasense has conducted GPR thickness surveys on over 10,000 lane miles of pavement.

About Infrasense, Inc.

Since 1987, Infrasense, Inc. has applied the most current technologies to the most difficult challenges in subsurface scanning. Infrasense’s engineers are able to nondestructively extract critical information from a diverse range of structures. The firm has conducted research to advance the field of subsurface detection, while also providing valuable information to clients across the country. Learn more about Infrasense, Inc. and its services at http://www.infrasense.com.

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Ken Maser
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