Improving the Foundation Layers for Pavements: Pavement Foundation Layer Construction – Wisconsin US 10 Field Study - TPF-5(183)

(2015) Improving the Foundation Layers for Pavements: Pavement Foundation Layer Construction – Wisconsin US 10 Field Study - TPF-5(183). Transportation, Department of

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Abstract

This technical project report is one of the field project technical reports developed as part of the TPF-5(183) and FHWA DTFH 61-06- H-00011:WO18 studies. This report presents results and analysis of field and laboratory tests from a field study conducted on US Highway 10 just north of Junction City, Wisconsin. This project involved new construction on US Highway 10 with portland cement concrete pavement underlain by dense aggregate base, granular subbase, and compacted subgrade. The Iowa State University research team was present on site during construction to conduct field testing on the new pavement and foundation layers. Field and laboratory testing was conducted to determine modulus of subgrade reaction (k), elastic modulus (E), California bearing ratio (CBR), resilient modulus (Mr), moisture content, dry unit weight, soil index properties, and frost-heave and thaw-weakening durability of the subgrade and subbase layers. k values determined from falling weight deflectometer (FWD) and static plate load tests (PLT) were close to the design assumed value. Use of empirical relationships to estimate k from CBR and Mr resulted in values that are 3 to 5 times higher than the design value. Field testing conducted in a dense grid pattern showed spatially non-uniform modulus and strength properties on subgrade and subbase layers, while the density measurements were relatively uniform. The high variability in the stiffness/strength properties is attributed to variations in the moisture content and underlying layer properties, which are not reflected in the density measurements. Laboratory Mr testing on a layered composite sample (i.e., with both subbase and subgrade) showed about 1.4 times lower modulus than a single subbase layer with similar density. The reason for this reduction is attributed to the weaker subgrade layer. Frost-heave test results on subgrade samples indicated that the heave rate was greater for the second freezing cycle than for the first freezing cycle, which indicates that the material is susceptible to increased heave as the number of freeze-thaw (F/T) cycles increases.