Laboratory evaluation of in-situ tests as potential quality control/quality assurance tools

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There are new in-situ test devices such as the Geogauge, Light Falling Weight Deflectometer (LFWD) and Dynamic Cone Penetrometer (DCP). Unlike the nuclear density gauge, the new methods provide measurements based on the engineering properties (strength/stiffness) of soil instead of physical properties like field density and moisture content. However the geogauge, LFWD and the DCP are not yet proven to be reliable and the correlations of these tests with standard tests are limited. An extensive laboratory investigation was carried out to evaluate the Geogauge, LFWD and DCP as potential tests to measure in-situ stiffness of highway materials and embankments. In this study, test layers were prepared in two boxes that measure 5 ft length x 3 ft width x 2 ft depth at Louisiana Transportation Research Center (LTRC) Geosynthetic Engineering Research Laboratory (GERL). The results from a series of laboratory tests on embankment soils and base course materials were used to correlate Geogauge, LFWD, Dynamic Cone Penetrometer (DCP) measurements with the Plate Load Test (PLT) and California Bearing Ratio (CBR). There is good correlation between the LFWD dynamic modulus and PLT elastic modulus. The LFWD is a better alternative for static PLT compared to the Geogauge. Although LFWD is a dynamic test, the similarity in depth of influence with the PLT and the quality of developed correlations suggests that the LFWD has better potential to replace the PLT. There is no significant correlation between the LFWD and the CBR test. The Geogauge and the DCP correlates better with the CBR and DCP is already proven to be an effective tool to estimate in-situ CBR. Based on the developed correlations and laboratory experience, it was found that the investigated devices have the potential to measure in-situ stiffness of highway materials and embankments.