United States Department of Transportation
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Abstract:The presence of swelling clay beneath roadway poses a significant problem to road rehabilitation design and construction. Roads constructed over areas of clay are generally subjected to potential differential settlement due to volume changes caused by swell/shrink and low shear strength of the clay resulting from high moisture content. If roadways with clay seams are not properly designed, a premature subgrade failure may occur and will also pose difficulties during construction resulting in higher construction costs. This report summarizes multi-phase geophysical demonstrations using various electromagnetic induction (EMI) methods on SR537 near Dulce, New Mexico. The road has had extensive surface rehabilitation due to the presence of swelling clay-rich zones in the road base. Using electromagnetic geophysical methods with rapid acquisition procedures provided a means of detecting the location of potential swelling clay-rich zones. This information was used to guide the soil boring program, thus greatly reducing the risk of missing a clay-rich zone during the site characterization planning stage and thus preventing or minimizing cost-overruns during the reconstruction phase. The results from the three-phase investigation prompted a production survey along Natchez Trace Parkway, Mississippi. The combined results from Dulce and Natchez have shown that the EMI method can provide qualitative correlations for evaluating the roadbase materials. A comparison between individual Atterberg Limits of soils obtained from the soil lab analysis and the EMI data suggests that no direct correlation can be established. However, the correlation between the bulk conductivity and the Casagrande Plasticity Classification may be used as a quick evaluation tool for predicting Casagrande soil type along the entire length of the roadway surveyed.
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Content Notes:COTR: Khamis Haramy, FHWA-CFLHD. Advisory Panel Members: Roger Surdahl and Linden Snyder, FHWA-CFLHD, and Khalid Mohamed, FHWA-EFLHD. This project was funded under the FHWA Federal Lands Highway Technology Deployment Initiatives and Partnership Program (TDIPP).
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