Pullout evaluation of steel slag fines and dredged material blends with geogrids
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Increasing quantities of dredged material (DM) from navigation waterways have led to a growing need to find alternative methods of disposal. Using this material in earthwork construction is a very attractive avenue, but poses concern of quality from a geotechnical standpoint. By blending DM with granular materials like industrial steel slag fines (SSF), studies have showed that the geotechnical properties of the mixture are greatly enhanced. If these materials can be proven to be competitive for use in earthwork construction, they would pose as an economically viable alternative, and would obviate the need for the relatively expensive conventional granular backfill. The scope of this project entailed the characterization of pullout interaction of SSF-DM blends in different proportions with Tensar uniaxial geogrids to determine an optimal combination for usage in earthwork construction. The media used for testing included the individual SSF and DM materials, and the 80/20, 50/50 and 20/80 blends mixed based on dry unit weights of the individual components. The SSF media comprised of particles smaller than 3/8 in. and classified as SW, while the DM was classified OH soil. Two Tensar uniaxial geogrids UX1400 and UX1700 were undertaken for the study. Pullout tests were conducted and performances of all the blends are compared with each geogrid at various normal pressures. Pullout loads and interaction coefficients give an idea of the quality of the interaction, and are studied in this thesis. Also, various variables that could potentially affect the pullout interaction are identified and investigated. Results show remarkably high pullout resistances for the 100% SSF and 80/20 SSF/DM media, and high interaction coefficients indicating excellent pullout interaction, even better than conventional sands. It was also clear that the dredged material exhibits very poor pullout interaction with geogrids. The 50/50 and the 20/80 SSF/DM media were significantly lower than the 80/20 SSF/DM blend in terms of quality of pullout interaction, but still higher than the 100% DM. The results observed with the 80/20 SSF/DM blend show that it is a suitable backfill material and also poses to be a very competitive and cost-effective alternative to be used in earthwork construction.