Research Reports

Enhancements and Verification Tests for Portable Deflectometers

Principal Investigator:

Olivier Hoffmann, Bojan Guzina, Andrew Drescher

February 2002

Report no. MnDOT 2003-10

Projects: Enhanced Portable Device for Subgrade and Granular Base Characterization

Topics: Pavement design for cold climates

In this study, the accuracy of the stiffness estimate from portable deflectometer devices is investigated, based upon the example of a particular device, the Portable Falling Weight Deflectometer PRIMA 100. A laboratory calibration setup, assembly comporting a simply supported steel beam of variable span, is designed to verify the calibration of the device (sensors and data interpretation method). Associated with the tester apparatus, an enhanced setup for the portable device is examined. From verification of the stiffness estimated from the portable device against the known stiffness of the beam the inconsistency of the data interpretation method using peak values of load and displacement time histories is pointed out. An alternative method using Frequency Response Functions, spectral average, Single Degree of Freedom System analog, zero frequency estimates and curve fitting is proposed to extract the static stiffness from PRIMA measurements. Test results show the good agreement between estimates stemming from the modified analysis and true beam stiffness. Baseline for the application of both the alternative method and the enhanced device setup to quality control field measurements is proposed.

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